1955 Pontiac - Restoration Project
 

Hi everyone, another newbie here - this time from Europe :cool:

I'm not new to car restorations, but so far I was in the Volkswagen scene and I own and drive a Rabbit convertible MK1. This is my first US oldtimer.

I came across this forum on my search for good Pontiac knowledge, since I recently bought one from 1955 as a good restoration base. The recommendation for this forum was on www.pontiacsafari.com :D

Since a few weeks I was already reading a lot here, and also this thread was very helpful and came just at the right time for me:
https://forums.maxperformanceinc.com...d.php?t=882633

This is the good piece of automobile art what it's all about:

https://golf1wiki.de/downloads/pontiac/ponti06.jpg
https://golf1wiki.de/downloads/pontiac/ponti04.jpg
https://golf1wiki.de/downloads/pontiac/ponti02.jpg

Originally I was looking for a Chevy Bal Air, but there are just too many around in here, and I really fell in love with the beautiful dashboard of this Pontiac:

https://golf1wiki.de/downloads/pontiac/ponti11.jpg
https://golf1wiki.de/downloads/pontiac/ponti05.jpg

Since these a very rare in Europe, I hadn't much offers to chose from. I was looking for about 3 years now to find one at a reasonable price, almost complete and with a body in good condition. This one met all my criteria, and it drives, steers and brakes ;) I already know that the previous owner added emblems from later models, like the Star Chief lettering on the dashboard.

This is going to be a longer restoration project, since there is a lot of work to do until it will be in a nice state.

What's roughly planned:

• Medium engine overhaul. Its running nicely, but way too fat and the engine is leaking everywhere ;) Also the carburetor needs to be checked, and the ignition will be upgraded to contactless, I already bought a Pertronix kit and a matching coil
• The Hydramatic transmission only shifts two gears instead of four. It was overhauled by the previous owner, and this is the result :mad:
• The interior will be completely renewed
• A new professional painting and chrome renewal is planned, since the painting wasn't done professionally and the chrome is very spotty
• More or less complete renewal of the electrics, since its really (!) botched :confused:

And a hundred other little things of course :)
I already own the shop manual and was reading a lot on pontiacsafari.com.

Parts are really a problem here, but rockauto and pontiacparts.net will be my friends I guess.

I'll keep this updated and I hope for some good tips and hints of the experienced members here.

Welcome Onestone.

HydraMatic transmissions of this era are very sensitive to proper throttle linkage adjustment. Maybe that is all that is wrong with yours. When you say "only shifts two gears instead of four" do you mean it only shifts once (for instance from 2nd to 3rd gear) or does it shift two times (2nd to 3rd and then 3rd to 4th)?

Can you tell which gears it is using?

At the moment it only shifts once, but I'm not sure which two gears its using. It must be either the 2nd and 3rd or 1st to 3rd (...is that even possible?) I guess, since I can start driving without any problems and then it only shifts once at a higher speed.
If I decrease speed it also shifts back from the higher to the lower gear, so its working both ways.

Reverse an neutral are working fine too by the way.

Cool color combination!

Welcome!
Where in Germany? I ask because I spent three years stationed very near Luxembourg, and drove a Pontiac-powered Chevy. Back then ('64-'67) Luxembourg and Belgium were sources of American car used parts.

Ah very nice! I'm from the "heart of Germany", next to Frankfurt :D I saw a few old Bel Airs for sale from Belgium the last years, but not a single old Pontiac

Any hints where to start? I will check the Hydramatic shop manual tonight too.


While renewing electrics, I got stuck on the horn button yesterday. Under the engine hood everything is working fine after the renewal, relay switches as it should and horns are blowing very loud :)

Inside I removed the steering wheel because the horn button relay contact had permanent ground. After steering wheel removal the problem was gone. It looks like this, the horn blows if I connect the brass contact with the center nut. So far so good, so thats what the botton should do:

https://golf1wiki.de/downloads/ponti...adaufnahme.jpg

How is the button supposed to work? The horn should sound if I tip the inner wheel to the left or right, right? Is there an isolation missing maybe? This is how my steering wheel and button looks from front and back:

https://golf1wiki.de/downloads/ponti...krad-front.jpghttps://golf1wiki.de/downloads/pontiac/lenkrad-back.jpghttps://golf1wiki.de/downloads/pontiac/hupenknopf.jpg

Assuming that ..........
1. the engine starts with the shift lever in "N" as it is supposed to and will not start with the shift lever in any other position
2. the transmission provides "park" as it is supposed to by locking the output shaft when the shift lever is in "R" with the engine turned off as it is supposed to and will not lock the output with the shift lever in any other position
.......... then the shift linkage is probably adjusted close enough that it isn't a problem.

This manual https://www.pontiacsafari.com/L1Gara...ic_1946-55.pdf is about as good as you'll find for understanding HM operating theory and making adjustments to the HM transmission. It may help with your troubleshooting efforts. Unfortunately, it depends on special tools and gauges for the adjustments. I had a set of the tools that I used to loan out, but I sold it along with a bunch of HM manuals when I totaled my HM equipped truck in 2012.

One of the HM parts suppliers used to loan out a tool set. If I can find his name I'll post it here.

Found it. Dave Edwards at https://www.autotran.us/

If you are not all ready a member join POCI (Pontiac Oakland Club International) they have an international chapter whose director lives in Sweden. They have technical advisors for everything. Your car is beautiful. Your horn wiring is correct as far as the wheel. Something in the chrome horn ring is grounding out.

Hi Bill,
my transmission behaves exactly as you describe. Everything is fine, just it uses only two gears :( But I will take a closer look into that at a later time. I also got the original Hydramatic shop manual meanwhile. Als thank you very much for the link to Autotrans for the required tools.


Thank you for that hint! Gettings parts from Sweden would be much easier for me.


Meanwhile I fixed the hornbutton completely. This is how I started...:

State of the pulled parts:

https://golf1wiki.de/downloads/pontiac/hupenknopf-0.jpghttps://golf1wiki.de/downloads/pontiac/hupenknopf-1.jpg


Cleaned from corrosion etc.:

https://golf1wiki.de/downloads/pontiac/hupenknopf-2.jpghttps://golf1wiki.de/downloads/pontiac/hupenknopf-3.jpg


Then I saw that the isolation of the contact point was missing. So I designed an exactliy fitting one and 3D printed it with TPU material:

https://golf1wiki.de/downloads/pontiac/hupenknopf-4.jpg


I also understood that the pushback of the inner steeringwheel with the hornbutton is originally done with a foam part underneath. This foam part was also shrunk over the years so it couldn't push the contact back anymore. That also was obviously the reason for the permanent ground contact :gag:
So I desigend a new one and also 3D printed it with TPU. After three or four tries I found the perfect size and filling for the required flexibility ;)

Old part and new part (with some adhessive strips as mounting help):

https://golf1wiki.de/downloads/pontiac/hupenknopf-5.jpg

All parts assembled. Fits nice and the horn now works again as it should:

https://golf1wiki.de/downloads/pontiac/hupenknopf-6.jpg


If anyone is interested in the 3D-prinfiles let me know, maybe it can help other people too.


Next questions I have while reworking electrics:

- I need to remove the rest of the steering wheel (the part under the horn button), because I need to fix the direction lights lever. How is this done?
- How do I remove the knob from the light switch? This might sound stupid, but there is no screw and I already tried to turn and pull it. I just don't want to destroy anything...

More updates to come shortly :cool:

I'm not sure about '55 Pontiacs, but on most old GM cars the knob along with the shaft it mounts on is removed by pushing a small metal "button" on the side of the light switch. I think the knob has to be in the "off" position when you push and hold the button. Then pull the knob.

It would help if you could tell which 2 gears. Can you change gears by moving the shift lever while driving?

Great work on the horn switch!;)

Hi Bill, I will take a deeper look into that later. Right now temps are below 0°C here and snow / rain, no driving weather :(

Thank you so much for that hint! There is in fact a release button on top of the switch body, it worked!


While working a little bit further on the electrics, I am replacing ugly extra switches installed by the preowner. Two of the switches were for the electric wiper motor and the washer pump. Luckily I got the original wiper switch of the original vacuum wipermotor along with the car. I really want to keep the original look, so I thought of how to use the original vaccum switch for the electric wipers. So I constructed and 3D printed a holder for two small electric switches which fit plug&play to the original switch. After a few tries and few wasted prints it works now as a charm:

These are the parts, the 3d printed holder and the two electric switches. The small pin extends the washer button, the black cap on the original switch I also printed is just for dirt protection:

https://golf1wiki.de/downloads/ponti...schalter-0.jpghttps://golf1wiki.de/downloads/ponti...schalter-1.jpg

Installed switch, original look:

https://golf1wiki.de/downloads/ponti...schalter-2.jpg

I also printed some switch plates as you can see, dunno if I keep them, just a small look&feel experiment :)

I also made a small video where you can see how it works. The holder fits to the original screw holes on the switch:

-->>> Original wiper switch for use with electric wiper motor <<<--

If anyone is interested I can provide the 3d printfiles and also a link to the switches on Amzn.


Under the hood I also got new battery cables, reworked the groundcontacts and installed an extra fusebox on the battery:
https://golf1wiki.de/downloads/pontiac/battfuse-0.jpghttps://golf1wiki.de/downloads/pontiac/battfuse-1.jpg

Lights are brighter and the car starts also better already, I can now measure 0 ohms of resistance from the battery minus to the engine and car body :)

Two more questions I have right now:

• I got the small red light which comes next to the parking brake lever. How is this connected? Is there an extra switch somewhere? Its sadly not in the electric diagram of the shop manual.
• I still need to remove the complete steering wheel to fix the direction lights lever. How do I get the steering wheel off completely?

I got a step further on the steering wheel, I will need two 5/16 screws and a puller. Time to order some more inch screws ;)

Any info on the wiring of the parking brake light? See pic attached what I mean, maybe it's named differently.

My 1955 did not have the parking brake light but on my other cars that did have one there was a switch at the base of the parking brake assembly. Keep posting your pictures. They may help someone here.

Ah great Info, thank you @Goatracer1 ! This is what I found under the carpet, is this the place where the switch belongs to?

Wiring would be easy I guess, the switch works against ground and the other wire connects to +12V on ignition, correct?

Does anyone have a pic how the original switch looks like and how it is attached to the base?

Another small update here: I could nowhere find how the original switch at the base of the parking brake looks, so I designed another replica to make it work again:

These are the parts, its a 2-part holder, a micro switch and a little cylinder to push the microswitch:
https://golf1wiki.de/downloads/pontiac/parkbrake1.jpg

Everything assembled together:
https://golf1wiki.de/downloads/pontiac/parkbrake2.jpg

And installed:
https://golf1wiki.de/downloads/pontiac/parkbrake3.jpg

Works like a charm. If anyone wants to have the 3D-Print files to make one yourself, just send me a message.

At the moment I replace every cable which is botched. Usually such an evening ends like this:

https://golf1wiki.de/downloads/pontiac/electrics2.jpg

I can't count how many of these insulting tapes, rubber caps and electricity thieves I've thrown away :D

Last night I checked the dome light which isn't working too, and one more time I just thought "WHYYYYY :confused:" :gag:

https://golf1wiki.de/downloads/pontiac/electrics1.jpg

To be continued...

Hey Onestone! I just saw your comment on the windshield washer switch over on my post, and I'd love you to forward the 3d printfiles/send me the links. I've got another idea I want to test out first, but if that doesn't work, your solution looks quite elegant. My switch is different than yours, though, since it's the combination wiper/washer switch, so it might need some tweaking. See photo below.

Attachment 663599

My Pontiac also has a bunch of the same options that yours does, if you want photographs of how something specific looks (like the parking brake light wiring) just let me know.

Hi Parkman,

just send me a private message with your email, I will send you the 3D-print files.

Or maybe Safari Larry can put the files on his great webpage ;) ?

My switch is the same as yours, I also have the combined wiper/washer switch as you can see in the video. It just looks different on the pictures, because I have already removed the backside of the switch. If you loosen the two small screws on the backside and remove the vacuum part it will look exactly as on my pictures, see attachment what I mean.

Another update here. I'm not posting pictures of every wire I replace, but the renewal of the electrics inside is almost done, while the weather here is still bad, no oldtimer driving weather :(

One of the tasks I did was restoring the fuse holder, because ist looked like this:

https://golf1wiki.de/downloads/pontiac/fuseholder-0.jpghttps://golf1wiki.de/downloads/pontiac/fuseholder-1.jpg

Very rusty, bad contacts, some non fitting fuses violently pressed in by the preowner :mad: I had very strange electric effects because of contact resistances and loose connections - like direction lights failing from time to time, contacts getting hot when I turned on the lights etc.

I also had much trouble while I was trying to retrofit hazard warning lights (legally required here, I'll post this story later), because I needed 12V for the relay. My multimeter proofed there were 12V on the line, but the relay strangely didn't work. After some troubleshooting I found out that the reason was another contact resistance :cry: As soon as the line had some electrical load, the voltage dropped down to almost zero :smash:

So I removed the fuseholder, removed the fuses and began cleaning all the contacts and all of the small metal plates. First mechanically...:
https://golf1wiki.de/downloads/pontiac/fuseholder-2.jpg

...and last chemically by using Pelox RE:
https://golf1wiki.de/downloads/pontiac/fuseholder-3.jpg

Pelox RE is just phosphoric acid, it etches all the remaining rust particles away and passivizes all metal surfaces.

After cleaning it again and drying I replaced all the old fuses by new ones and also all the screws were replaced by new ones of stainless steel:

https://golf1wiki.de/downloads/pontiac/fuseholder-4.jpg

...I know its 10A fuses and not 7,5 like original, but these are the closest ones you can get here in Germany with this mechanical size.

Back in business...:
https://golf1wiki.de/downloads/pontiac/fuseholder-5.jpg

Direction lights now worked 10 times in a row without failing, and no contact is getting hot anymore, wow :D:D

More stuff will follow shortly :cool:

Great job cleaning up the fuse block!

Are all the fuses supposed to be 10 amp or did you just install them for the picture? The spare fuse holder at the bottom is marked for a 7.5 amp fuse.

But the blue plastic covered crimp connector in the STOP-DOME-COUR fuse position of the "before" picture takes the prize.

Absolutely Bill, I really don't know why the previous owner didn't spent a few bucks for new fuses and other small things. Seems to me like he just used stuff he already had there, regardless if it fits or not. There are also a lot of other things on this car, like using sanitary silicone on the engine instead of spending a few bucks for the right gaskets and so on :mad:

According to the shop manual they should all be 7,5A, (except the rheostat one which ist 4A), but 10A (or bigger) is the only size of this old fuse format which is available in shops here in Germany.


I try to keep everything in the original state and look, but I really wanted to have a few additional instruments, like a rev counter and a voltage indicator. Oilpressure too, but luckily my Pontiac has one originally. I'm the type of person who needs to know if my engine is healthy, to keep my heartbeat in a healthy state too :D

So while doing electrics I also designed and 3D-printed an additional instrument holder. I did it two-part with a cover painted in the original metallic dashboard color. It took me three tries until everything was perfectly primed, filled, polished and painted, including clear coat with no inclusions etc. :cool:
Its screwed on the holes which are already in the dashboard, so no drilling necessary. I also spent a lot of time to adapt the rev counter (which is originally for a V12 marine engine) and find LEDs with the exact same light color of the original instruments. After a long search I found some beautiful instruments with chrome rings which had almost the same look as the original instruments. This is how it looked in the end:

https://golf1wiki.de/downloads/ponti...truments-2.jpg
https://golf1wiki.de/downloads/ponti...truments-4.jpg
https://golf1wiki.de/downloads/ponti...truments-3.jpg
https://golf1wiki.de/downloads/ponti...truments-1.jpg

If some wants to have the 3D-print files of this instrument holder for his Pontiac, just let me know. It fits any 52mm instruments.

More updates incoming shortly, I got the original radio meanwhile and also the original clock is on its way to me, really looking forward to that package :bounce:

PM me your name and address and I'll send you some 7.5 amp glass fuses.

Hi Jack, that is very kind of you! I'll send you a PM.

Next task I want to do is the installation of the Pertronix Ignitor II electronic ignition. Since I have to adjust the ignition timing afterards, I am wondering how to do it correctly... This is why I am confused a bit:

The shop manual shows the marks on the flywheel and the pointer on the harmonic balancer:

https://golf1wiki.de/downloads/ponti...ne timing2.jpg

This is how it looks on my engine. The middle mark is missing, but that's not a problem I guess, I think the upper mark is the 5° BTDC mark I need:

https://golf1wiki.de/downloads/ponti...ine timing.jpg

So far so good, but now comes the confusing part. This is what the shop manual says about how to adjust the timing:

https://golf1wiki.de/downloads/ponti...ne timing3.jpg

I did many times engine timing on other cars, but I am missing several details here:

- at which engine condition the timing should be made? I guess on a warm engine with around 70-80°C oil temperature, as usual, right?

- at which revolutions should the 5° BTDC be met? The shop manual doesn't say anything about this, but this is important since the distributor has centrifugal and vacuum advance too. Is this meant like this: 5° BTDC should to be met at idle revs, so at around 450-500 rpm?
I saw the mentioned table at 12-46 in the shop manual, where the centrifugal advance of the ditributor is shown. There is no centrifugal advance at idle revs according to this table.

- and most important: what about the vacuum advance? From other old cars I know that the vacuum hose from the carburetor needs to be removed while doing the timing. Here the shop manual doesn't say anything about it. We also dont have a rubber hose here, but a stiff steel hose coming from the carb. Is the vacuum meant to stay connected while doing the timing?

All my questions are regarding the original 1955 Pontiac 287 cui V8 engine. Any hints are appreciated ;)

Base timing is usually set at idle and with vacuum advance disconnected. There should be no mechanical advance when setting the base timing. Unless they did things differently in 1955?

Standard transmission the timing is set at 460 RPM in neutral. Auto trans is set at 400 RPM in drive. 1955 only has 2 timing marks. The one farthest clockwise is 5 degrees before top dead center. The one counter clockwise is top dead center.

Are you sure timing is done in drive with auto trans, not neutral?? Where do you have that info from?

Also, any info about the vacuum part?

Could probably be done in neutral or drive, RPMs just need to be low enough so that no centrifugal advance is in place.

Right from service manual.

Do you have a link for me to this service manual? I just have the workshop manual, which just contains the small description I posted below. Is there any information about the vacuum while doing the engine timing?

...I found something the craftsman updates from November 1955 :D

So vacuum officially needs to be disconnected, and the port on the carb must be taped during timing.

Next update here:

My original fuelpump was leaking fuel and oil. I replaced it with an electric Hardi pump, but I think this type of pump is maybe called different in the US (?). ... Its maybe also known as "Mitsuba fuelpump", used in many other old cars.

Technically its a diaphragm pump like the original one, but electric driven and it has an internal pressure sensor which makes the pump stop when the fuelpressure against the carburetor gets high (above ~0,35 bar). This way the pump always pumps exactly to the need of the carb - so when the float chamber is full it stops automaticly, and starts again as soon as more fuel is needed.

Another advantage is it fills the float chamber before cranking, which makes starting much easier after not moving the car for a longer time. These pumps are used on many oldtimer restorations to greatly increase reliability.

This is how this pump looks:
https://golf1wiki.de/downloads/pontiac/fuelpump2.jpg

Preparation of the mounting location, also the integrated holder and mountplate I welded:
https://golf1wiki.de/downloads/pontiac/fuelpump3.jpghttps://golf1wiki.de/downloads/pontiac/fuelpump4.jpg

Ready mounted and wired:
https://golf1wiki.de/downloads/pontiac/fuelpump1.jpg

Wiring of this pump is very easy, it just needs ground and +12V ignition. Everything I touch at this car I use new accessories, so here of cource also new hoses, new screws, new filter etc. came in too. The filter is will not stay fo very long, I used this transparent one to check if too much dirt is coming from the tank. After some driving later I will replace it with a metal one.

Also a litte optical beautification came in - I replaced these tail lights (I think they weren't original Pontiac ones...?):
https://golf1wiki.de/downloads/pontiac/taillights3.jpg

...with new ones I got from a dealer in IL :
https://golf1wiki.de/downloads/pontiac/taillights2.jpghttps://golf1wiki.de/downloads/pontiac/taillights1.jpg



Coming up next: new crank case ventilation and pertronix ignition :)

For us undereducated folk, 0.35 bar = just over 5 psi.

Sorry Bill for tormenting with European units :( It's just I'm so used to it ;)


Next part done:

Removed the distributor, because oil leaking everywhere around it and I wanted to change from points to electronic ignition anyway. This is how my poor distibutor was looking before:

https://golf1wiki.de/downloads/ponti...tion_vent7.jpg https://golf1wiki.de/downloads/ponti...tion_vent6.jpg

I hate this red color the preowner used on the engine :mad: Why didn't he just kept the engine in the original nice color... :confused:
After removal I saw that no gasket was there, so oil came from the distributor hole and also from the ventilation hole too where the old rubber was hardened and didn't seal anything anymore.

Next I cleaned the distributor, removed the point and condenser, also cleaned the outside carefully and painted it with black satin finish engine paint. Installed the Pertronix electronic ignition set, and of course new rotor, new cap, new screws and new spark plugs came in too:

https://golf1wiki.de/downloads/ponti...tion_vent5.jpg https://golf1wiki.de/downloads/ponti...tion_vent4.jpg

Put the distributor back in its place with a new gasket, and for the ventilation I used a new 90° silicon hose. I also removed the ballast resistor and changed to the matching Pertronix ignition coil. I hope this part of the engine won't leak any oil anymore.... And as always new screws, reconditioned holder and vacuum line etc.:

https://golf1wiki.de/downloads/ponti...tion_vent2.jpg https://golf1wiki.de/downloads/ponti...tion_vent1.jpg

This is how I finshed the crank case ventilation, I extended the silicone hose back into the air filter housing. The preowner had already drilled a hole into it, and I just 3D-printed a small TPU-gasket so the hose won't get cut on the metal edges:

https://golf1wiki.de/downloads/ponti...tion_vent3.jpg

The advantage is at least no more oily smoke coming out, and later engines hat it this way too.

Question here: Is this how the experienced Pontiac owners do it too? Good idea with this engine or not? :confused:

Afterwards I timed the engine, with the information I gathered before:

• 5° BTDC at idle speed, about 400 RPM (info from shop manual)
• warm engine
• vacuum hose disconnected and sealed (info from craftsman updates Nov. 1955)

I used this timing light btw (no affiliate link :gag:):
https://www.amazon.com/Innova-5568-a.../dp/B000EVU8J8

Innova 5568, made in USA :) It's the best timing light I ever owned, I can really recommend it.
I also measured how the timing changed after reconnecting the vacuum line again. It changed to about 20° BTDC at idle speed, so its really a big difference if its done with or without the vacuum line connected.
According to the shop manual the vacuum advance is at max. 15° with the throttle fully closed (which it is at idle speed), so 5°+15° = 20° absolutely makes sense to me.

The engine runs very nice with these new components, also starts up like a charm ;)

The next step for me will be taking a closer look to the carburetor. It has a very old sticker on it that says "rebuilt", but I think the engine runs way too rich, and the carb has been tormented by the preowner too, who "converted" the automatic choke to a manual one, like this:

https://golf1wiki.de/downloads/pontiac/carb1.jpg

No clue why he did this, or if this is a good idea??? :confused:

Any hints how to deal with this are :welcome:

For the carb overhaul I opened a separate thread here:
https://forums.maxperformanceinc.com...d.php?t=884764

Still have the question which kind of choke would be the nest solution?


I was driving yesterday a little bit, engine is running really nice so far. Now is the time to take a deeper look into may transmission problem - it only uses two gears. Bill already asked me this...:

After driving I think its using the 1st gear, and then is only shifts once. The other gear I'm not suchre which one it is - but I can tell I'm at 2500rpm at 35mph with that gear :) Does that info help to guess which gear it is?

To determine which gears are in use try using the "OPERATING IN LO RANGE" section of the Owner's Guide as shown here: https://www.pontiacsafari.com/55/Owners%20Guide.pdf

The car should start rolling in 2nd gear and downshift to 1st if the pedal is floored. It shouldn't upshift beyond 2nd unless you get to ~ 40 MPH. Compare what happens to when you take off in the LEFT DR position which should start in 1st gear.

Once we get more information I'll break out the HydraMatic troubleshooting guide.

Thank you Bill, I will try that on the weekend and report the results here.

Hi Bill, I just drove a little round, since it's carfriday :) I just tested what you recommended:

Gear lever in LO:

• It starts rolling with the same gear as in LEFT DR
• Then I pressed the pedal completely to the floor - It never shifts down, just accelerates in that gear

Additional Info, maybe helps too:

• In LEFT DR it shifts up after a getting some speed, but only once (already wrote that), but almost never shifts down until I stop completely
• If I switch to RIGHT DR between 0 to ~40 mph, it always shifts down once if has shifted up before (in LEFT DR)

So atm it really only uses these two gears...


Thank you very much for that offer, but I need the carb kit from Mike's, nothing at Ames at the moment I need...

From a stop, with the gas pedal pressed down 3/4 of the way or so in left drive approximately what speed are you going when the upshift takes place? (RPM reading from a tach would be even better).

What speed will the car run at in the highest working gear at half throttle?

Don't go to stupid speeds to find out!

Just trying to figure out if your 2 gears are:
... a. 1 and 2
... b. 1 and 3 (not likely)
... c. 1 and 4 (really not likely)
... d. 2 and 3 (really, really not likely)
... e. 2 and 4 (really not likely)
... f . 3 and 4

Can you choose from one (or more) of these problems?

Wouldn't this be likely with front clutch failure?

I have a tach, so that's no problem. The gear it shifts up to is 2500rpm at 35mph - which gear is that?

Don't know the rear gear ratio or what the tranny gear ratios are, but think it is 1.86, possibly 2nd gear?


:confused:

I can't find '55 Pontiac HydraMatic ratios right now, so I'm going to use the ratios from my '57 GMC truck. They may not be exactly right, but they should be close. I'm going to use a rear end ratio of 3.23:1 and a 27" tall tire.

Maybe Larry can find the ratios for a '55 Pontiac tranny and the most likely rear end ratio.

Using the chart shown below I'm trying to answer Onestone's question of "The gear it shifts up to is 2500rpm at 35mph - which gear is that?"

Assuming his 2500 rpm is AFTER the shift completes and his speedometer is near-correct at 35 MPH I'm guessing that the shift that just occurred was INTO 3rd gear. I know the numbers don't line up, so if Onestone could give me the tire diameter and Larry can find a most likely rear end ratio I should be able to come closer.

Onestone: Please measure tire diameter and answer .....

1. What is engine rpm just before the shift at 35 mph?
2. What is engine rpm just after the shift at 35 mph?
3. What is actual speed (use the GPS function on a cell phone) at 35 MPH indicated?

Jack is much more the Dual-Range HydraMatic expert than I am, but ....

A. If the front clutch failed "engaged" and the front band was operating normally the front unit would be trying to be in direct drive and reduction mode at the same time. Assuming normal operation of the rear unit I would think the transmission would either lock up or the front unit would disintegrate once you left idle and the torus started to work.

B. If the front clutch failed "disengaged" and the front band was operating normally the front unit would work normally in 1st gear. When 2nd gear should engage the front unit band would release, but because the front unit clutch is off no power would be transmitted through the front unit, resulting in no power transmitted to the rear wheels.

Onestone:

If you are so inclined you could measure the rear end ratio by ...

1. Block the right front tire to prevent movement of the car.
2. Put the left rear wheel off the ground on a jack-stand. Be safe doing this.
3. Put a chalk mark at the 6 o'clock position on the left rear tire.
4. Put a chalk mark running linear on the driveshaft where you can see it.
5. Put the transmission in neutral.
6. Have an assistant rotate the tire forward exactly 1 turn while you count driveshaft rotations.
7. Estimate the last partial rotation. 1/4, 1/2 or 3/4 is probably close enough. Add that to the number of driveshaft rotations.
8. Divide the number of rotations by 2 giving rear end ratio.

By the way, this won't work if you have a positraction rear end (doubtful).

Attachment from 1955 Pontiac Shop Manual. Shows size of 7.10x15 and 7.60x15 tires as well as four "likely" rear end ratios.

I have updated the chart's HydraMatic ratios and tire size based on info found here:
https://over-drive-magazine.com/2023...urtesy%20lamps.