Tranny/Rear end ID

[Wes Price]

I am a fairly new owner of a 66' Roadster and am trying to ID the tranny and rear end to make sure that my speedo is reading correct (I believe it is way off, or that car is REALLY fast). Just need some help in ID'ing the rear end and tranny....where do I look to find the codes? Thanks

Wes Price

[Joe L.]

Re: Tranny/Rear end ID

Wes-----

The transmission will not make any difference as far as speedo calibration is concerned as long as you are checking it in 4th gear (assuming that you have a 4 speed). Both M-20 and M-21 use a 1:1 4th gear ratio. With the transmission installed in the car, there is no way to discern the difference between a 1966 M-20 and M-21 unless you have the transmission part number tag still attached to the side cover bolt or unless you remove the side cover and count input shaft gear teeth.

The differential code will be found stamped on the bottom of the carrier case, just forward of the cover attaching surface. There will be a date code followed by a 2 alpha character code. This code denotes the ratio ORIGINALLY installed in the case. Whether those gears are still in the case is anyone's guess, but you can confirm by jacking up the rear of the car and counting revolutions of the driveshaft while someone turns the rear wheel by hand.

If you determine the rear ratio and assuming that your tires are of near-stock diameter, I can tell you which speedo gears that you should have for proper speedo calibration. At least, I can if you find this out and post before tomorrow morning. After that, I'll be heading out-of-town for 2-1/2 weeks and I'll be "off line".

[Mike M.]

Re: Tranny/Rear end ID

joe, gonna miss your knowledgable posts next 2 1/2 week. going to nashville? mike

[Joe L.]

Re: Tranny/Rear end ID

Mike-----

Yes, I'll be in Nashville about next Wednesday afternoon. Then, a week from next Tuesday (July 1), I fly on to Boston for about a week.

[Larry S.]

Re: Tranny/Rear end ID

Wes
It good luck with your new car and most important remember to enjoy it,
When I first got my car I was unsure of the rear ends ratio,Allthought I had the numbers off the rear and they stated I had a 411 I wanted to confirm.First I had my wife drive behind me in a car with a cell phone.I called her at an excact speed reading on my speedo and we went thru the different speeds and I found my car was almost excact to her car in speeds give or take a mph or 2.Now I knew my spedo was close to correct.I then put up a post on this site or another (it was years ago) and posted my rpms at a crusing speed of 60 mph and asked what other guys had with there cars and what there gears were,What I had found out that at 3250 or so rpms the guys with 411 and stock tires were running the same rpms as me.So from this survey of other vette owners I had confirmed what my case said of 411's and from my wife following me I confirmed my speedo was correct.

I just aquired a set of 336's for my car for more pleasent rides 411's are fun for planting you in your seat but not fun for me on a long drive.

And dont be suprized if in fact your car is just fast