Olds front hub driving speedometer

[carbking]

Need some information, and some parts.

Have an other GM vehicle that I need to drive the speedometer from other than the conventional transmission. Have been told some Olds used left front wheel. So questions:

(1) Which Olds used the front wheel to drive the speedometer?

(2) Is the drive mechanism cable?

(3) Which Olds would be the easiest to adapt to a 1974 Pontiac GTO?

(4) Hopefully, where would I locate the parts?

About the only sources I have are carburetor related, and this isn't.

Jon.

[joe_padavano]

(1) Which Olds used the front wheel to drive the speedometer?

Early to mid-1960s full size (Eighty Eights and Ninety Eights)

(2) Is the drive mechanism cable?

Yes

(3) Which Olds would be the easiest to adapt to a 1974 Pontiac GTO?

None of them.

(4) Hopefully, where would I locate the parts?

HAHAHAHAHAHA....

The wheel-driven speedo will not be easy to adapt to your X-body. The cable runs through a hole in the center of the left front spindle and attaches to the dust cap on the hub, which is what drives the cable. The spindles and dust caps are unique to those cars and are difficult to find. The 65-70 B-body spindles do NOT interchange with the 68-74 X-body spindles. Finally, the speedo calibration is a function of tire diameter. If you use a different diameter than what the system was designed for, your speedo calibration is off and there is no easy way to fix it short of a ratio adapter box in the speedo cable.

Care to elaborate on why you can't use a conventional trans-driven speedo cable?

[carbking]

Early to mid-1960s full size (Eighty Eights and Ninety Eights)

Care to elaborate on why you can't use a conventional trans-driven speedo cable?

Sure, the transmission I am using originally had a top loaded shifter. When I installed the side loaded shifter, the shifter covers the hole for the speedometer drive. Since I am using an aluminum flywheel, I wanted a tall ratio first gear, and equally spaced ratios, which this transmission has. There is insufficient room above the transmission in the X-body to use the top loaded shifter.

And before someone suggests it: I am aware of the 90 degree adapter. There is insufficient space to use it.

If the Olds unit cannot be made to fit (I am pretty good at modifications, if I have something to modify), might someone have another idea USING THE ORIGINAL SPEEDOMETER. I will NOT use an aftermarket electronic gizmo. I have a tachometer, and can use the tach for speed. But others would like to drive the car.

Have been working on this project now for many years, and finally (this year) have the car licensed and enjoyable. Car has a weight to power ratio of approximately 6:1 (runs pretty good), but still gets way better than 20 MPG (measuring miles driven and measuring fuel).

Jon.

Edited November 1, 2010 by carbking (see edit history)

[joe_padavano]

Jon,

The Olds parts aren't really necessary, nor are they particularly useful to your application. You could simply drill your stock spindle to accommodate the drive cable and modify a dust cap to allow the cable to be attached to it, the way the Olds hardware was connected. Then all you need to do is get the appropriate calibration box to go in the speedo cable to correct for tire diameter.

You've piqued my interest, however. What trans converts from top to side shift? A T5 or T56? I'd be interested in seeing how this side shifter works. I still have to believe that there's an easier way to accommodate a stock cable. At a minimum, couldn't you weld a bung on the opposite side of the tailhousing and run the cable out the RH side like the factory 4spd transmisisons did?

[carbking]

Joe - the transmission is one of the oddball B/W Super T-10 4-speeds.

I made a bracket to attach the side shifter (normal holes were present); but unfortunately, the shifter covers the speedometer takeoff (completely). The location of the takeoff was moved on the top shifter transmission cases. We tried the 90 degree adapter, but there simply is not room. We cannot easily move the shifter due to the location in the car plus the length of the rods.

The gear ratios in the transmission are also weird (the reason I wanted the transmission). Low gear is much lower than either the 2.2 or 2.52 conventional gearsets. I am using an aluminum flywheel, plus I am using a 3.08:1 final drive ratio. I lighted the car by some 800 pounds, and literally "have my cake (weight:power) and eat it too (fuel economy)".

This car was started before the five speeds became popular. And if I hadn't already special ordered a custom clutch (different spline count) and custom cut the driveshaft, I would probably just install a 5 speed with a lower final drive.

I had two local transmission builders look at changing the speedometer takeoff to the other side. Both said it couldn't be done economically with this transmission.

Does the cable affix to the hub? Might you have an exploded diagram?

And I apologize to the moderators, as this is a modified vehicle, but so far Joe is the only one to respond with good information after I have asked the question on several other forums.

Jon.

[joe_padavano]

Is there a reason why you can't use the GM Super T-10 tailhousing like this one? It has the RH speedo drive for exactly the reason you need.

Super T10 Tail Housing / Extension Housing

[carbking]

Joe - I honestly don't know. Carburetors are my thing, transmissions are not. But a close friend, who has been rebuilding transmissions for 50 years says no.

Jon.

[joe_padavano]

Joe - I honestly don't know. Carburetors are my thing, transmissions are not. But a close friend, who has been rebuilding transmissions for 50 years says no.

Jon.

Might be worth asking the question with this photo in hand. While it's not a T-10, the tailhousings of the T-5 are routinely swapped to get the shifter in the correct location. I don't know if there's an output shaft difference on the T-10, but that might increase cost. Bottom line is that it IS possible to swap the tailhousing, since the BW factory built T-10s with these different tailhousings. The issue is what other parts need to be swapped. As an engineer and motorhead, I cannot believe that it is impossible to swap the tailhousing and frankly even with some machining I believe that the swap will be much more cost effective than building a wheel-driven speedo cable.