I have a '91 Firebird with T-5 and 3.42 posi that I am upgrading to 3.73 ratio.

I've read the tech article about speedo/VSS driven/drive gears but my brain isn't working tonight and I can't figure it out. Has anyone done this swap before and knows what the gear combos are to keep the speedo accurate ?

thx in advance,
RP.

 

IIRC the correct 3.73 combo is 7 tooth drive (you probably already have that) and 19 tooth driven. I think the 3.42 combo is 7 & 20 but I could be wrong.

 

you have to change your gear speedo driving but you dont have to change gear speedo( on the output shaft) or speedo adapter

 

Sorry I don't get it yet. Could you please try again more detail maybe ?

thx in advance,
RP.

 

well I'll take mine off and and send you a pic about speedo parts and whitch one you have to change and hopfully will explane it better
i'll send it on this sunday

 

Try this link:
http://www.bgsoflex.com/speedo1.html

 

well I had bad time with my camra did not work at all (stupid windows xp)
so what i can do on monday I'll call chevy dealer and get you
the part #

 

I'm switching to 3.42 from 3.08, so if you can, could your please verify the 3.42 speedo tooth counts also?

Thanks
Dan

 

palric your part# 3987921
alloy your 3.42 has 21 theeth your part #39687921

 

Excellent AYMAN thank-you VERY much for your time and effort I am grateful.

RP.

 

no problem whenever you need help with your transmission just let me know ayman1982@msn.com

 

Ok, think I got everything I need now for the posi/3.42 gear swap over. I picked up a complete 3.42 rear drum to drum, with sway bar, lower control arms, panhard bar, torque arm, driveshaft, and the speedo gear setup for $75. I really don't need all the extra parts, but who knows. I might break something and need them.

Wonder if anyone would buy an 18mm sway bar and mounts?

Dan

 

palric I THINK I GAVE YOU PART# FOR 411 REAREND JUST LET ME MAKE SURE AND I'LL GET YOU THE RIGHT #

 

Humm, well, shoot. A while back, I did some searching and thought I'd found the answers to my questions about 3.42s and 3.73s. According to what I found, the 3.42s had a 7-tooth purple (or perhaps) blue drive and a 19-tooth white driven gear (14071731 and 14090592). The 3.73s had a 7-tooth purple drive and a 21-tooth orange driven (14071731 and 14090594). Is anyone positive?

JamesC

 

The car I pulled my 3.42 rear out of car that had a complete drive train, and the speedo driven gear is blue, and has 20 teeth.

 

WELL I DID SOME SEARCHING BUT I HAD VARY PARTS# EVERY DEALER GAVE ME DIFFREANT PART# SO I WAS AND WHEN I GAVE palric THE PART # FOR 373 WAS WRONG BECAUSE I BOUGHT ONE FROM DEARER 2 WEEKS AGO AND I FOUND OUT IT WAS THE WRONG ONE BECAUSE MY SPEEDO WAS 90MILES@2100RPM
MANY DEALERS WERE ME BUT TODAY I CALLED CHEVY AND THEY WILL LET ME KNOW IN COUPLE DAYS

 

HERE THE REPLY FROM CHEVY

Dear Mr. Ayman,

Thank you for contacting the Chevrolet Customer Assistance Center. We
appreciate the opportunity to be of assistance to you and have documented your
request in file numberXXXXXXX

Unfortunately, we at the Customer Assistance Center do not have access to parts
information. Your best resource for parts will be your local Chevrolet dealer
Parts Department which has established as a comprehensive resource for all parts
pricing, availability and compatibility information.

We have also reviewed your previous file number XXXXXXXand see that a restoration packet is being sent to you. When you receive this packet, it
should provide you with contact information for suppliers which may be able to
help you locate past model parts for your vehicle.

You may also want to contact GM Restoration Parts at 1-888-245-5800. You may
also visit their Website at:

http://www.gm-restorationparts.com/e...ITES/entry.asp

If you should need to contact us in the future, please e-mail us again or call
the Chevrolet Customer Assistance Center at 800-222-1020. Customer Relationship
Managers are available Monday through Friday from 8:00 a.m. to 11:00 p.m.,
Eastern Time.

Sincerely,

Michael Highlands
Customer Relationship Manager
Chevrolet Customer Assistance Center

 

Sheesh....

The gears for a 3.42, T5 trans car are:

Driven Gear-- WHITE w/19 Teeth
Drive Gear-- PURPLE w/7 Teeth

Keep in mind that the purple gear gets confused with dark blue.

 

How about 3.73 in a T-5 ?

 

I think the 3.73/ T5 combo was in the 2.5L thirdgens. The oldest F-Body manual I have access to is an 1987 which doesn't have 2.5L info. Sorry, can't help you with that one.

 

DUDE I HAVE AN 84 5.0 HO HAS T5 AND373 POSI DISK BREAK

 

Dude, are your "Caps Lock" and "Period" keys broken?????

 

Just got the new rear end installed with the 3.42's and zexel about 30 minutes ago. I can definately notice the difference in the 3.42's verses the 3.08's. Haven't noticed any difference with the zexel yet, but when I was swapping the rear, I found I have a blown rear Formula GP shock, so I'm not going to get on it until the shock is replaced.

Anyway, I put the 20 tooth blue driven gear in out of the car that I got the 3.42 rear out of without changing the drive gear just to see where I was at. The stock gear for the 3.08's was 22 teeth. I would guess I'm a about 10 mph fast on the speedo. I can't be positive, but later I'll have my wife pace me in our mini van with the digital speedo and see where I'm at. Just seems to read real high.

I also found out something interesting about the zexel. When you turn one wheel, the other goes the opposite direction. So you can't go to a wrecking yard and test for a posi in the traditional way by making sure both wheels turn the same way. Just doesn't work with a zexel.

 

for t-5 the gears are

drive gears
9 tooth red #14053347
7 tooth purple #14071731

driven gears
19 tooth white #1409592
20 tooth blue #14090593
22 tooth gray #14090595

 

Dude Sorry
if you please send me a new keyboard:hail: :lala:

 

and I noticed you guys are going backwords when you put steeper gears in you car the drive shaft turns faster to maintan the same speed the higher gears would have done, so your "driven gear" needs more teeth not less. or less on your drive gear.

the drive gear is on your output shaft, and the driven is on your sensor.

 

88 350 tpi-

I had the 22 tooth that was in my 87 when we bought it new with 3.08 gears. I pulled a 3.42 rear out of a 85 v6 5spd. car and also got the driven gear from that car. The gear from the 85 with 3.42's is 20 teeth. I don't know what my drive gear is, or what the drive gear is in the 85 I pulled the rear out of.

So my line of thinking is to go with the driven gear out of the complete 85 that had the 3.42's from the factory. But not knowing what my drive gear is, that may be my problem. I have yet to pace my car and check to see how far I'm off.

So, a 9 tooth drive gear would make the driven turn faster. So in your thinking the 22 tooth driven gear will slow the speedo down, where as the 20 tooth I put in wil lspeed it up. Ok, so in reading another post from someone else that did a 3.08 to a 3.42 swap he said his speedo was off 10 mph too fast. If I already have the largest driven gear available, and more than likely I have the 7 tooth drive gear, how did the factory adjust for a 3.42 or 3.73 gear?? I just need to figure this out. It seems like I've got the biggest drive gear available.

Hmmm, this is confusing.

 

I had the 3.73 delema before as well, I had to change the drive gear to the smaller 7 tooth and if I remember it called for a 21 tooth driven which may or may not be made but, I used the 22 tooth one I think. I know I have the 7 tooth because I had to change it.

 

I'm thinking I will have to change the drive gear also. I don't like doing that, but I've got no choice I guess. I'll go next weekend and grab the drive gear off the car I got the 3.42 rear out of.

 

I just talked to a local speedo shop and they have a 25 tooth driven gear for $10. He's not sure if it will fit, but if it does that saves me from tearing apart the tail housing on my T5. I'll keep you guys posted as to whether or not the 25 tooth gear works.