z11375ss

Does anyone know the color or part number for a speedo gear inside an M-20 for a 3.73 rear end? I have converted to a banger and now I want the speedo to work correctly. Any ideas?

J-(Chicago)

I too need to figure out my speedo situation.
There was a company nearby that had all that stuff a few years ago called Allservice

I have yet to call them up however. It's worth a shot. Hopefully there's still some old timers that know exactly what you need there.
(630)257 7719

z11375ss

Thanks Jeremy.

joe_padavano

The correct speedo gear depends not only on the axle ratio but also the tire diameter. The Chassis Service Manual has a list of the possible combinations.

74 Omega

I too have been fighting this since I swapped gears. I was told it not only depends on the gear at the speedo cable, but the gear on the tail shaft of the trany. The trany shop told me the only real way tho know is to look at the gear in there. If I went from say 3.08 to 3.73 it would usually take just the gear next under the cable, I went from 2.73 to 3.73 they told me I would also need the gear around the tail shaft. I hope I explainded that well. (not good at writing my expanations).
The funny thing is from 0 to about 30 miles per hour it is off by about 10 miles per hour. At 50 to 80 miles per hour it is off by over 20 miles per hour (had my wife follow on the highway)

I just pull the GPS out of the truck...works for now.

z11375ss

I haven't contacted anyone yet as today was quite busy at work. I will find the answer to this and when I do I will let you guys know. Joe, thanks for the info. The tire dia would certainly play a huge part in the equation. As we all know putting big or little tires on our cars affects trap speed etc. Jim

joe_padavano

I assume you have a TH350? There are two speedo gears, a drive gear that is mounted on the output shaft of the trans under the tailhousing and a driven gear that goes in the side of the trans. Depending on the tire size and gear ratio, you may need to change one or both. Try this website:

http://www.transmissioncenter.net/sp...____va.htm#350

Olds64

Aren't these gears color coded? You should be able to see the color of the drive gear on the output shaft of the transmission with the driven gear out. I know they were color coded for my 90 Buick Estate Wagon with a 200 4R.

mugzilla

You should have a shop somewhere that calibrates the Highway Patrol vehicles. Call the Hoghway Patrol and ask them ...

z11375ss

I believe these gears are color coded. They were when I switched from a 3.08 to a 4.11. That was in 1985 though. I need to find a trans shop here that knows what it's doing.

74 Omega

Yep, that is what I was trying to say, but you said it much better and clearer than I...I have yet to get under the car as of my last post, when I get under there again, I will do the speedo gears and try the trick BILL told me to help with the shifter issues