lonzoo

I recently changed my 4.11 gears to 3.36 on my 63. I bought the correct speedo gear for the 3.36 with the BW T-10 factory trans. Now the speedo will not read correctly.It goes to 20 MPH and after 4th gear stays about 40 MPH. If I tach at about 3000 RPM (which feels like 75 MPH) it might get about 50MPH. The speedo worked fine before but was off about 10 MPH according to my GPS after the change out. The cable connection is finger tight. What did I do wrong ? I hate to change out the gear again cause it is a PITA and my fingers just now healed up after the first gear change.Any ideas or helpful hints would be greatly appreciated.

Jackfit

Hi, you may have to change the drive gear that is on the output shaft of tranny. Means taking out transmission. See some of the other posts, for same problem. Changing the just plastic gear will not cure problem, as both gears need to match
Jack

66jack

What color gear did you remove, and replace it with

For a 3.36 it should be small 8 tooth circle gear and use a "20 tooth BLUE gear"

For the 4.11 should be small 8 tooth circle gear and use a "24 tooth YELLOW Large gear"...

Both were based on 27" diameter tire...

The above calcs were from this site...

ww.stl-vettes.com/65Vette/GearCalc.htm

lonzoo

I removed a yellow one and installed a blue one. What has me puzzled is the yellow one was operating fine when a took it out..

Jackfit

I removed a silver from my 3:70 which was perfect. Do I put in a blue now that I will have a 3:36?

Jack

I have the wide drive gear.

JohnZ

Your car was "born" with a small-diameter (1.77") DRIVE gear pressed on the mainshaft, which only meshes with the family of "large" (0.87" dia.) DRIVEN gears that work with 3.70, 4.11, and 4.56; yours had the yellow 24-tooth gear for a 4.11.

Changing to a 3.36 rear puts you in the other "family" of both DRIVE and DRIVEN gears. You need to pull the transmission, remove the tailhousing, remove the existing pressed-on DRIVE gear, and install a large-diameter (1.85") replacement, which will mesh with the "small" DRIVEN gear family that covers 3.08 to 3.70 rears - you need the 20-tooth blue (#3987920) gear.

The alternative to pulling the transmission is to have a speedometer shop make up a ratio adapter gearbox that will work with your existing "small" DRIVE gear.

DZAUTO

FOLKS,
This is the exact correct answer!!!!!!!!!!!!!!

lonzoo

Thanks for your help. I might look into the adaptor vs. pulling the trans.

VITIV Coupe

I just replaced the speedo driven gear in my 3.36 because I was going about 10 mph under actual. I replaced it with the 20 tooth blue. Before I did, I read up on this forum about people dropping the old driven gear in the tail while they attempted to extract it, so I was ready for it. Guess what? Mine dropped in. I fished for an hour with my trusty long flexible claw and never did find it. Finally gave up, buttoned everything back up, took it for a ride, no sounds or grinding and my speed is dead on according to my gps.

lonzoo

What year do you have? Mine is an early 63 with original BW T-10 aluminum trans. I think after reading the previous posts that mine came with small diameter drive gear installed.

wilcar

Manchester Muncies in Manchester, Iowa sells the adapter.

VITIV Coupe

I have a 64 coupe, M-21 Muncie 4 speed with 3.36 rearend.

GEM '62

I bought my ratio adapter from these guys, they have everything you need in gears also. An adapter is much easier than trying to change the drive gear.

Performance Transmissions and Parts

www.TransmissionCenter.net
Parts Toll Free 1-888-2012066
Transmissions Toll Free 1-888-2012066
Speedometer Gears 1-888-8771008, 6:30 to 5:00 CST, M to F

PATC Speedometer World

4speeds

There is a speedo gear calculator at this link:

http://goo.gl/hK2jbU

You can now get 7 and 8 tooth drive gears for the Muncie in the 1.84 diameter. They are all over Ebay.

lonzoo

John..I screwed up. The gear I took out was not yellow. It was an 18 tooth brown gear. The gear was in perfect shape and read correctly. Now I am totally confused again

66BlkBB

From this post it appears that the 3.70 ratio came in both the large and small drive gear configuration? Is that true or did you mean 3.08 to 3.55 had the small drive gear?

JohnZ

The 18-tooth brown gear ("small" family) is for a 3.08 axle - it will NOT work with a 4.11 axle. You need to verify a) What axle ratio you really have, and b) What DRIVE and DRIVEN gears you need for your application.

The document below has all the info you'll ever need about DRIVE and DRIVEN gears, what works with what, how to identify them, etc.

JohnZ

Yes, it did, but not during midyear production - the 22-tooth #3987922 silver "small" family DRIVEN gear for 3.70 usage came along a few years later.

Jackfit

Here are some pictures of the small and large drive gears and driven gears. My tranny had a dented drive gear that ate plastic gears for 40 years. When I did my tranny over 5 years ago, we found the dent in the gear as you can see. My car came with a 3:36 and I put in a 3:70 44 years ago, and the speedo never worked.

I took out the narrow gear that was damaged and put in a wide gear with the 3:70 and that was a silver gear. Was dead on speed with GPS

Now that I have a 3:36 , I hope the blue gear will work for me.

Here are the pictures

See the dent in the gear



See that damage to driven gear



Narrow Gear and Wide Gear





Damaged Gear, hit with spike tool when installed years ago

lonzoo

John, i removed correct number 4.11 housing and gears and replaced with 3.36 housing and gears. My bw t-10 is factory for my early 63. However if someone replaced the original small 8 tooth gear that could be my problem. Is there a way too tell without taking trans out what gear is in there? My problem is now that I need to get a functional driven gear in order to go with a speed adaptor. The driven gear i pulled out caused the speedo to bounce all over the place.