[unruhjonny]

Originally Posted by 455hota

My 70 TA with M20 4 speed and 3:55 gears does have that same speedometer adapter. I was wondering if it was correct as well. I guess the answer is yes!

now that is weird.
I had understood that the adapter was used for cars with lower gear sets;
My car (not bought stock) has the correct plastic gear for the (standard) 3.55:1 gearing;
I found an adapter that would be perfect for retaining the original speedo gear, and the adapter would correct for my desired 3.90:1 gearing.

I would have presumed that "standard" gear set cars would not have needed any adapter.

[unruhjonny]

Originally Posted by TA455HO

The speedometer heads were calibrated for a specific tire size, transmission and rear end ratio. If parameters start to fall outside of the values used for the calibration then an adpater is commonly used if the speedo driven gear can't be changed enough to get an accurate final reading.

In 1970 there were 4 combinations that used an adapter and 12 combinations that did not.

In 1971 speedo cable routing was carryover. The number of cables was reduced by one due to the elimination of the adapters on automatic transmissions. The only adapter used was the Right Angle Adapter 6477964 used on the R.H. side of the manual transmissions, but not with a 455 engine.

.

What is your source?

I may have it, but may have overlooked it;

I am wondering what is correct in which given application.

[Norwood]

1970 July T/A. RAIII. 4sp original 3:55 rear gears has adapter and cable is routed over top of the trans

[dadsformula]

I have a 73 4 speed formula, and both the Assembly Manual as well as the
Car show the Speedo Cable going over the Trans-Tunnel with clips on the
upper Bell Housing Mount as well as a lower Clamp that I can't remember the
location. Reason for chiming in hear, is another clamp I don't see mentioned.
There is a welded flap (or Tang or clamp) under the Trans Tunnel (Drivers Side)
that keeps the Speedo Cable from Contacting the Shift linkage. Often I see these
gone with just the small Square Welded mount left over. The Cable seems
unnatural as it leaves the Firewall, and make a hard turn. The natural routing the
Cable want's to take is down under the Tranny, so easy to see how this can be
confused. The Welded Clamp under the Trans Tunnel, keeps the Cable stationary
after it leaves the firewall, and the others are to allow movement with the Drive
train. These are the ones on the Trans Tunnel and the lower clamp I cant remember.
Also the TH400 Cable is about 60 inches and connects on the Drivers side of the
Trans. All these clamps are needed for the 4 speed as the Cable inters the Trans on
the passenger side. The 4 Speed Cable is 59 or 60 inches.

The Mounting of this cable is much the same as Wiring under the Hood. A clamp is
used to stabilized after exiting the Firewall at a fixed point, and additional Clamps on the Drive train allow movement without effecting the Cables function or connection.

[superdutybob]

Originally Posted by dadsformula

I have a 73 4 speed formula, and both the Assembly Manual as well as the
Car show the Speedo Cable going over the Trans-Tunnel with clips on the
upper Bell Housing Mount as well as a lower Clamp that I can't remember the
location. Reason for chiming in hear, is another clamp I don't see mentioned.
There is a welded flap (or Tang or clamp) under the Trans Tunnel (Drivers Side)
that keeps the Speedo Cable from Contacting the Shift linkage. Often I see these
gone with just the small Square Welded mount left over. The Cable seems
unnatural as it leaves the Firewall, and make a hard turn. The natural routing the
Cable want's to take is down under the Tranny, so easy to see how this can be
confused. The Welded Clamp under the Trans Tunnel, keeps the Cable stationary
after it leaves the firewall, and the others are to allow movement with the Drive
train. These are the ones on the Trans Tunnel and the lower clamp I cant remember.
Also the TH400 Cable is about 60 inches and connects on the Drivers side of the
Trans. All these clamps are needed for the 4 speed as the Cable inters the Trans on
the passenger side. The 4 Speed Cable is 59 or 60 inches.

The Mounting of this cable is much the same as Wiring under the Hood. A clamp is
used to stabilized after exiting the Firewall at a fixed point, and additional Clamps on the Drive train allow movement without effecting the Cables function or connection.

This is the way my 74 was routed and retained. I had forgotten about the metal tab in the tunnel.

[TA455HO]

Originally Posted by unruhjonny

What is your source?

1970 and 1971 Assembly Manuals.

.

[FunctionalShaker]

Since this thread is hitting on cables and adapters, here is a chart showing the use of the adapter for 70 manual trans.

[unruhjonny]

@ FunctionalShaker - Can you please send me a larger (easier to read) copy of that application chart?

There's a link in my profile to directly email me.

[Pepi]

Originally Posted by dadsformula

I have a 73 4 speed formula, and both the Assembly Manual as well as the
Car show the Speedo Cable going over the Trans-Tunnel with clips on the
upper Bell Housing Mount as well as a lower Clamp that I can't remember the
location. Reason for chiming in hear, is another clamp I don't see mentioned.
There is a welded flap (or Tang or clamp) under the Trans Tunnel (Drivers Side)
that keeps the Speedo Cable from Contacting the Shift linkage. Often I see these
gone with just the small Square Welded mount left over. The Cable seems
unnatural as it leaves the Firewall, and make a hard turn. The natural routing the
Cable want's to take is down under the Tranny, so easy to see how this can be
confused. The Welded Clamp under the Trans Tunnel, keeps the Cable stationary
after it leaves the firewall, and the others are to allow movement with the Drive
train. These are the ones on the Trans Tunnel and the lower clamp I cant remember.
Also the TH400 Cable is about 60 inches and connects on the Drivers side of the
Trans. All these clamps are needed for the 4 speed as the Cable inters the Trans on
the passenger side. The 4 Speed Cable is 59 or 60 inches.

The Mounting of this cable is much the same as Wiring under the Hood. A clamp is
used to stabilized after exiting the Firewall at a fixed point, and additional Clamps on the Drive train allow movement without effecting the Cables function or connection.

What assembly manual are you looking at? As HFR and johnta1 references, it is hard to tell but looks like underneath. Does the manual you reference show a better picture?

[dadsformula]

I have the Photo copied GM Assembly Manual for 73 Birds. Was a very nice gift
from a member. Check when I get home, but I am sure of this Cables routing as
my Car was missing it's Cable, so I did a lot of research when Installing it.
I cannot say how this effects other years, as I have not compared them.
I think I may have steered in the wrong Direction A little, aka the Clamps on the Trans.
now that I think a little Harder, this Clamp was on a trans to bell housing bolt
not the Bellhousing to engine. That location is for the Wire Harnees Clamp.
So this Cable exits the firewall and takes an unnatural turn to that welded Clamp
then over the trans and down to the Speedo input. If the Clamps are all in the
correct locations, and the Cable is the right length (59 or 60 Inches) this provides
nice smooth curves on all the bends, and prevents Cable binding.

In General GM or any Manufacture would never (except possible E-Brake lines) allow
any Cable to track under the Drive line. Way to easy for it to get snagged. Even
Front break lines although under the Engine are always shielded by the Frame, and
any junction exposed will have some type of protective cover. This Speedo Cable is
one of those parts that is Pontiac specific in that it enters the Pass side, not the Drivers
like others. Pontiac did this to keep it clear of the shift linkage. I am much more sure of the existence and use of the welded tab clamp under the Tunnel, than I am the
exact location of the other Clamps. I actually did not use the factory clamp at the
lowest point (and last before the cable enters the trans.) The aftermarket Cable I used
was slightly longer than the Original, so I used an extra PCV clamp from a 67 A-Body
in that location as it extended further from the Trans and allowed a larger loop to
help eliminate binding. It worked perfect, but is one of the few non original parts on
my car. All of this is for the single piece Cable, and should not be assumed for the
split cable (cruse control) as I am not familiar with that setup. Anyway I will confirm
with the Manual when I get home tonight.

[455hota]

Does anyone know of a source that reproduces speedo cables?

My original "CH" 4 speed cable (approx. 63" long), is in very rough shape. The outer sheath is melted and worn through in a few places. It still has the "CH" visible though.

I see Ames lists some cables, but has anyone ordered one? What about fitment?

[dpoltzer]

You can get a cable from NAPA and they are around $20. As I recall, the cables they sell are about 7-8 inches too long so you have to make a bigger loop when you route it up and over the transmission to the passenger side.

[racerboy]

I know this is an old thread, but I was putting the M21 back into my ‘70 TA today (I have another thread about running a 428 until my RA III build is done) and I had a question about the speedometer routing. I have only owned this car since 2021, so I have no way of knowing if the cable had ever been changed before, but my transmission had no adapter, but has factory 3.73 gears. I also had a clip for the speedometer, but unlike HFR’ clips, my clip was attached to one bolt on the side case of the transmission. I have no way of knowing if it was original. My cable also did not go over the top, but sort of ran alongside and looped over the tail. I didn’t pay a lot of attention to the routing when I removed it, because I assumed it would be easy to find out the correct mounting when it went back together. Silly boy that I am. I think my cable is an aftermarket NAPA version, because it seems to be longer than necessary.

Was there ever a final answer in the routing for a ‘70) and should my car have the adapter?

Here’s a picture of the clip I removed. I’m not saying it’s factory, but it would strike me a bit odd that someone would add this to the car.



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[Formulabruce]

Yes, goes on top.
Yes adapter for a 373 car.
Why on top? Simple.. speedo cable is part of the body assembly, and the drive train assembly ( on frame) was slid under it and connected .
Any 355 and taller gears had an adapter. 14 or 15 inch due to being off by more that 5 mph UNDER. or more.

[racerboy]

Ok thanks. Is the adapter available?


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[racerboy]

In FunctionalShakers pics above, it doesn’t show an adapter for 3.73 gears and F60-15 tires. Am I reading that incorrectly?


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[Formulabruce]

The chart could be missing rare info, which was penciled in many times, like the floor version of the assy manual

[Trevor78]

Inline tube sell that cable bracket too.