I recently swapped a different rear axle into my car that has 3.42 gears. I would like to have an accurate speedometer again. So my question to those of you with the same setup (TH700R4, electric speedo, 3.42 gears) is which gears did you use to get the speedo to read correctly? My car previously had 2.77 gears. I have done some research on this and I think I need to get the grey (15 tooth) drive gear for the output shaft of the trans and the yellow (41 tooth) driven gear for the VSS. I am not sure if this is a direct swap on my application.... I appreciate any help with this. Thanks in advance.........

Matt

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

 

I can't remember what my tranny had. I would recommend that you go to a dealer and have them look up what a V6 with a 700R4 had for speedo gears because they all had 3.42s in them.

Dale

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1986 FireBird
2.8L MPFI
1/2 CAI
Gutted Cat, No muffler
Was 700-R4 --> Now T5

Great cars aren't bought, they are built

 

What size tires?

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1989 IROC-Z 5.7L
NOS 5151 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Right now they are the stock rims and tires which I believe are 26" tall (16x8 GTA wheels with 245/50/VR16 tires). If (more like when) I do upgrade rims and tires, I will go to a 17" set of rims with tires that would be a direct swap for a fourth gen (I have to get spacers for the front to get them to fit but with the fourth gen rear already installed, that is all I will need to run fourth gen rims on my car). So they will be virtually the same height as my current rims and tires.

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

ttt

 

15T Gray Drive (8642620)
41T Yellow Driven (25513048)

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1989 IROC-Z 5.7L
NOS 5151 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Good deal. Those are the ones I ordered yesterday. I checked out T-****'s website and they had a conversion chart and GM part number chart. I think that this will be just a very slight bit off though since these are the gears that would go in a 3.45:1 car by their chart. Definately not enough to worry about, however.

On a side note; I did some more looking around and found that an '87 two-wheel-drive S10 that had a TH700R4 and 3.42:1 rear axle used an 18 tooth drive gear, a 36 tooth driven gear, and a .73333 conversion module which equates to an overall ratio for the VSS of .36665.

By using the gears I ordered (the ones you recommended as well); a 15 tooth drive gear (Grey one), and a 41 tooth driven gear (Yellow one) with no conversion module, the overall ratio for the VSS equates to .36586.

So, by comparing those overall VSS ratios, we can see the very slight amount that the output might be off.

The only difference would be in tire height but that S10 listing was for one with 215/60/R15 which, I believe, are the same height as 245/50/R16 - 26 inches.

So anyways, I should have my VSS gears in another day or two. Thanks for your help Omar.

Matt

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club