Sorry in advance

Just bought a 1988 Formula lb9/t5 w/ the 9bolt and 3.45 rear gears. The previous owner told me he had to replace the old T5.

Problem is that the speedometer is WAY off, I mean like 15-20 MPH at street or highway speeds (60-65mph). My understanding is that the poncho's used a VSS, but is there a gear that drives that VSS inside the extension housing? If so, what gear would I need for the previously mentioned combination, and is this an off-the-shelf dealership peice - or where might I get one?

Thanks in advance.

 

Yes it is off the shelf at the GM stealership. Not their shelf though, but rather, the "zone warhouse" or whatever they call it. It'll almost certainly be a special order item.

You need a 7-tooth blue/purple drive gear, and a 21-tooth driven gear for your VSS. The 2 parts should cost around $12-15 total.

 

Wow, thanks.... did you have some kind of reference material for that ... you seemed to have the answer right at your finger tips...

(Also, how big of a pain is it to do both gears?)

 

Some of us here have some gear combo printouts from GM. They tell us what VSS gears one need for what tranny and rear end. Or you can calculate it yourself, there are many gear calculators online.

It is very easy to replace the driven gear (on the sensor shaft) but a bit harder to replace the drive gear (on the tranny tailshaft), you have to pull the tailhousing for that.

If you need more info, just ask.

Lou

 

RB83L69, I'm not sure if I'm looking at it wrong but my GM gearing sheet tells me that for 3.42's (with stock tire size) one would need the 7/19 gear combo. The 7/21 gears are indicated for the 3.73 gears.
I don't mean to argue or anything, I'm just not sure why my sheet says something different.

Respectfully
Lou

 

Could be.... I don't usually mess with those highway gears like that, so I could be wrong.

Just seems to me, the last junk trnasmission I had that came out of a 3.42 car, had that combo in it. But my memory could be failing. If somebody has better info than me, please put it up for everybody to see.

The GM "book" on their computers has all that stuff. It's all right there. The hardest thing is, finding a parts counter guy that will futz around with a retail customer for a half hour of doing actual real work like looking stuff up and thinking and all that, for a $12 ticket. It helps if you walk in there prepared; like, have the axle codes from the vehicle SPID label, the tire size or codes, etc., so that the info you can give him is in the format that the computer has it listed in.

 

Yeah, I'll just collect as much info as possible and hope the monkey behind the desk can guess'timate te right gears for me.

 

do speedo gears from a 700r4 fit a th350? if not, would it still be the same ratio? I have 3.42's and a th350.

 

I believe the driven gears are the same but the drive gear differs in thickness.
The ratio is the same though, that's a given.

Hope this helps.
Lou

 

immensely. if the ratio is the same, than i can at least order them from somebody. thanx guys!

 

hey, I have a t-10, 3.73 in the rear, and 245/50R16 tires. What adapter do I need to get in order for my speedometer to work right? thanks

 

The smart GM printout says you need the 7/21 gears (7-tooth drive gear #14071731 and 21-tooth driven gear #14090594). But if you can't locate the 21-tooth driven gear, try the 20-tooth (#14090593) because both would give you the same deviation (you're right in the middle betwee these two).

Hope this helps.
Lou

 

I called them and they said it would be about $30 for both of the gears, does that sound right? Also, I dont think I quite know everything about this yet, does the 7-tooth go into my tranny and the 21-tooth go into my cable? If I'm right how hard is it to change these two?

Thanks

 

You might already have the 7-tooth gear on the tranny tailshaft. I'd check before you buy another one, restocking fees at dealers are not exactly low.
Replacing the driven gear (20 or 21-tooth) is pretty easy, just remove the cable, remove the gear housing, catch tranny fluid in a pan or something, replace gear, install gear housing, attach speedometer cable and refill tranny.
The drive gear is a little bit more involved (gotta remove the tailshaft and unbolt tailhousing) but not much harder.

Hope this helps.
Lou

 

Just thought I'd stop in on the thread I started to say hi...

 

I dont think I have a hole to put the driven gear into. I looked and looked underneath my tranny and I could not find a place to hook it up. I started a new thread on the Transmissions and Drivetrain board. I didnt want to upset GOY for taking over his thread. It is just talking about my tranny and what is wrong with it. thanx for your help so far BigBabyLou!