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Old 04-22-2021, 08:57 AM
Mwieczorek Mwieczorek is offline
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Default Soooo... How hard is it to do a 4 speed swap on a '66?

Like the title says, I'm considering a 4 speed swap. I know the buckets and center console are likely unobtanium, and I'm fine with keeping the bench seat and running a simple floor shifter. with that said...

It appears that there was a longer version of the Muncie for large Pontiacs with a tailshaft P/N of 9779246. It looks like I need to find that specific transmission, but wanted to double check with the experts. Is that correct?

Also, is there anything different functionally about an earlier or later version of the Muncie? Does it make a difference if the transmission is from a 64, 66, or even a 68? I know there were improvements made to the transmission over its life and a later one is likely better, but if I find an earlier one will it still fit?

Also, what about pedals and linkage? Is there B body specific stuff that is unobtanium, or is it the same stuff as an A body? Can I use parts marketed for the GTO?

What about the shifter? Is there anything special about it, or should a shifter marketed for a bench seat Impala do the job?

I'm hoping to get an idea of how tough the parts will be to source before I buy anything. If its going to be difficult to impossible to find the parts I'll just deal with the TH400 for now.

I did try the search function before asking, but I didn't find the answers I was after.

Thanks!

  #2  
Old 04-22-2021, 04:56 PM
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I have been gathering parts to convert my '66 GP for several years , and now have all of those hard to find. Just haven't got my lazy a$$ going yet, as I've been playing with a few things on my wagon.

Not really any cross over from A body, maybe a few smaller items. I have a '65 Muncie longtail M20 as a trans which will work for me. Consoles are sometimes seen but can cost ya...alot. Pedals are 65/66 only and can either be for manual or power brakes. I have a set of both but will use the power setup for mine.

I am by no means an expert and will rely on some friends who have done conversions before. It should be a fun project but I'm glad I have another car to drive while I'm doing this swap. I can try to answer questions as I go along myself

Ken

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  #3  
Old 04-24-2021, 03:26 PM
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Several years ago I bought a 1965 WF code 389 tri-power Catalina 4 spd car. I owned and drove it a few months without any problems. It had a “short tailshaft” Muncie out of later model Chevelle which apparently someone had used to replace the original 4 spd (or 3 spd?).

I think the mid-60’s Pontiac big cars had “long tailshaft” Muncies and the GTO’s had short tailshaft Muncies. The 63-65 had slightly different ratios than the 66-74 and the ratios were the same for long and short in the same model years.

I don’t know what all you contemplate doing to your car but if it is just swapping from automatic to manual tranny, BEFORE YOU DECIDE, you should make sure your engine’s crankshaft is drilled with the larger register size to accommodate the pilot shaft bearing/bushing that a manual tranny requires.

It appears that from the factory your car likely is a 389ci-290hp (with 2bbl and 092hds) and has a rear axle ratio of 2.41or 2.56. If the car was a 4spd from the factory, it would have had a 3.42 ratio axle. You likely will need a rear axle ratio change if you go with a 4spd.

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Old 04-25-2021, 09:40 PM
Mwieczorek Mwieczorek is offline
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Quote:
Originally Posted by Doug View Post

It appears that from the factory your car likely is a 389ci-290hp (with 2bbl and 092hds) and has a rear axle ratio of 2.41or 2.56. If the car was a 4spd from the factory, it would have had a 3.42 ratio axle. You likely will need a rear axle ratio change if you go with a 4spd.
Thanks for the tip on the crankshaft. I'm still very much in the planning stages and right now the job is to get it running and driving reliably. A 4 speed swap is some time away, but I may start looking for parts...

Regarding the car, It's a little better than you thought... It' actually a 389/4bbl/325hp YE code, and it looks to be original to the car. You're right about the rear end, it is open, I just haven't been able to determine the ratio yet. I'll figure that out when I jack the rear end up to get into the rear brakes. I just rebuilt the Carter AFB, and it appears to be original to the car (complete with 55 years of sludge). It's crazy, all the factory hard line vacuum fittings are still there and correct, not like most cars this age that have been hacked up.

  #5  
Old 04-25-2021, 09:44 PM
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I have long shaft Muncie transmissions. They were made from 1965-1968. The 1965 transmission has the small counter gear shaft than the 66-68. You probably have a 2.56 or A 2.73 rear. You would want a 3.23 or 3.42 rear.
There is a bunch of stuff that you need.
I did this swap to my 67 GP convertible 30 years ago.

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Old 07-15-2021, 10:31 AM
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I converted my '65 to a 4-speed bench seat, manual brakes.

The M-20 gearbox is interchangeable, as long as you have the long output shaft and tail housing. The pedals are hard to find, I had 2 extra sets, but sold one to a local guy that never paid me in full. I asked for $375 for a power brake set, he paid me $300...I'll pay the rest later. Right. I think they going for nearly double that last I saw one for sale. Factory shifters were Hurst Competition Plus. 2 different handles were offered. One for bucket, the other for bench...the bench handles are tough to find and were only offered in '66, not '65. Shifter porch and other small parts like the z-bar, springs and brackets are only used. The outboard z-bar bracket is welded to the chassis, so that's a challenge.

3.42 rear is the highest gear ratio you should use. Pontiac didn't go any higher than that with a 4 speed.

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  #7  
Old 07-15-2021, 11:18 AM
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Should be starting the conversion this fall on my '66 GP. Wanted to get the AC working in my '63 Safari first, which is now done!

Having my trans guy rebuild the long tail M20 I have and I've collected all the hard to get parts. Have a sweet console and shifter. I should be able to update as I progress.

1963 Catalina Safari
1966 Grand Prix

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  #8  
Old 07-15-2021, 11:38 AM
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Just be sure you get a large shaft Muncie (later). Most small shafts wound up scattered all over drag strips.

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  #9  
Old 07-15-2021, 11:42 AM
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I have a 7/8” ‘65 M-20 in my car. Fully rebuilt but the countershaft leaks. Not a priority to upgrade at this point.


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Old 07-15-2021, 11:53 AM
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Muncies are great for power shifting. Pull back on shifter as hard as you could (why larger rods were available for Hurst shifters) and bat either clutch or gas, not both. Friends said it sounded like an automagic.

Would not recommend with a small shaft.

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  #11  
Old 07-15-2021, 12:21 PM
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Right. I won’t be power shifting this setup. Still not on the road after 20 years apart. But close. It moves on its own.


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Old 07-15-2021, 01:49 PM
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Learned the hard way to never take a driving car apart unless all of the parts and materials to put back together were on hand.

This time of the year best working hours are midnight to 6am.

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  #13  
Old 07-15-2021, 02:31 PM
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I'm pretty I know a guy in So. Ca. that still has what your searching for? He will be asking top $$$ for the parts he has! Let me know if you want me to contact him. Scott

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Old 07-16-2021, 11:00 AM
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Quote:
Originally Posted by Mwieczorek View Post
Like the title says, I'm considering a 4 speed swap. I know the buckets and center console are likely unobtanium, and I'm fine with keeping the bench seat and running a simple floor shifter. with that said...

It appears that there was a longer version of the Muncie for large Pontiacs with a tailshaft P/N of 9779246. It looks like I need to find that specific transmission, but wanted to double check with the experts. Is that correct?

Also, is there anything different functionally about an earlier or later version of the Muncie? Does it make a difference if the transmission is from a 64, 66, or even a 68? I know there were improvements made to the transmission over its life and a later one is likely better, but if I find an earlier one will it still fit?

Also, what about pedals and linkage? Is there B body specific stuff that is unobtanium, or is it the same stuff as an A body? Can I use parts marketed for the GTO?

What about the shifter? Is there anything special about it, or should a shifter marketed for a bench seat Impala do the job?

I'm hoping to get an idea of how tough the parts will be to source before I buy anything. If its going to be difficult to impossible to find the parts I'll just deal with the TH400 for now.

I did try the search function before asking, but I didn't find the answers I was after.

Thanks!
Also don't forget a 3 something gear ratio needed for 4 speed since most common 66 auto cars have 2.56 (Catalina 2v) 3.08 3.23 minimum. Also I would consider a much newer 5 speed to see viability of swapping in and gain OD and maybe a deeper first gear. Aftermarket universal hyd clutch (hyd throwout bearing) set up can save you messing with unobtanium dinosaur stuff. If you find a deep gear 5 spd you may only need a 2.93 posi or something milder to get a good stop light drive away gearing in 1st.

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Old 07-16-2021, 01:00 PM
Mwieczorek Mwieczorek is offline
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Quote:
Originally Posted by PONTIAC LARRY View Post
Also don't forget a 3 something gear ratio needed for 4 speed since most common 66 auto cars have 2.56 (Catalina 2v) 3.08 3.23 minimum. Also I would consider a much newer 5 speed to see viability of swapping in and gain OD and maybe a deeper first gear. Aftermarket universal hyd clutch (hyd throwout bearing) set up can save you messing with unobtanium dinosaur stuff. If you find a deep gear 5 spd you may only need a 2.93 posi or something milder to get a good stop light drive away gearing in 1st.
Yeah, so now that I've done more research I'm leaning towards what you list above!

First order of business is to source a rear end with respectable gears and limited slip. I'm going to start a new thread to solicit information about suspension geometry...

Thanks!

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Old 07-16-2021, 02:00 PM
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Quote:
Originally Posted by Mwieczorek View Post
Yeah, so now that I've done more research I'm leaning towards what you list above!

First order of business is to source a rear end with respectable gears and limited slip. I'm going to start a new thread to solicit information about suspension geometry...

Thanks!
your 66 gear interchange is between 65-70 full-size Pontiacs B body big 10 bolt cover that has a 12 bolt ring gear 8.875" 31 spline bolt in axles.

Great donor cars are Bonnevilles or Grand Prixs or Catalina 2+2 cars or any factory manual trans equipped car ... these will have a lower ratio than the average
automatic 389-2v Catalina or Star Chief.

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70 Olds Cutlass Cruiser Red Wagon 350 101k miles 15 sec 1/4 12 sec w 455
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Old 07-16-2021, 02:57 PM
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I don't know about 1966, but in 1961 there were two four speed transmissions for big cars - one for the Catalinas and Venturas, and another one with a longer tail shaft for Bonnevilles. They used different transmission mounts as well. Was that the case for 1966 as well? I don't know but it may be something to consider.

As for the shifter, I'll bet you can call Summit or Jegs and they'll have the correct Hurst Competition Plus for a 1966 Pontiac with a bench seat - I replaced the OEM shifter in my '61 with a Hurst, and when I called Summit they had it in stock, no problem.

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Old 07-16-2021, 10:01 PM
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1965-1968 B Body Pontiacs used basically the same long shaft Muncie

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Old 07-19-2021, 05:20 PM
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Default trans swap

My 61 Bonneville came with a heavy duty T-85 three speed, when I replaced it with a long tail shaft Munci I measured the total case length both are exactly 27 1nches long. The result was the drive shaft worked with no changes. just to let you know.

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Old 07-19-2021, 06:47 PM
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Quote:
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My 61 Bonneville came with a heavy duty T-85 three speed, when I replaced it with a long tail shaft Munci I measured the total case length both are exactly 27 1nches long. The result was the drive shaft worked with no changes. just to let you know.
65-68 is totally different

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