Speedo Question

[87gnguy]

My stock 200r4 transmission blew up on the dyno destroying the case and some other parts. So I had a new one built with much better internals and a new case. When driving it home, I noticed my speedo was about 10 mile per hour off. I was following my buddy and he was going 70 to 75mph while my speedo was reading 60-65. Since I had to get a new transmission case (also a 200r4), could the gears left in the new case be from a different car and I can just swap gears to make my speedo accurate again?
Thanks,
Casey

 

[czimpel]

Do you know what gears are in the case? Should be an orange governor gear with a blue speedo bullet gear.

 

[87gnguy]

I don't know what gears are in it. I was told that the Monte Carlos and Camaros from that time frame also used this transmission and had different speedo gears than the GN. I know very little about transmissions but was told the gears are pretty easy to change.

 

[czimpel]

You need to drop the pan in order to change the governor gear, but the speedo gear gear is as easy as pulling the bullet out.

I also don't think that the monte trans has the right governor in it for the Turbo motor. I have a governor and orange gear for sale if you decide you need one.

 

[87gnguy]

Well, Jason White built the transmission for me and I just remembered that the bell housing on the passenger side was notched for a large downpipe so it would've had to come out of a turbo regal. I'm gonna say that the governor would be right. Plus I'm 100% sure that Jason knows that wouldn't work. I'm going to check it after work one day this week and make sure that it has the orange gear in it then I'll get back to you on that... Thanks for your help

 

[INEEDAGN]

Pull the driven gear out of the side of the transmission and shine a flashlight in to look at the color of the drive gear. Driven gear is easy to remove, unscrew the speedo cable, take out the 10mm bolt, pull the speedo bullet out and the gear will come with it. If it has an orange or green governor (drive) gear inside the trans, it's an easy fix. if its a neutral color or red, you will need to pull the pan to access the governor gear OR calculate the ratio and use a screw on ratio adapter. If it's an orange drive gear you need a blue 30 tooth driven gear. If it's green, you need a black 27 tooth driven gear. The proper driven gears that would allow use of a red or neutral colored drive gear do not exist.

This is all based on the assumption that you have stock 26" tall tires and 3.42 gears.

Only f body to get the 200-4r was the TTA.

 

[INEEDAGN]

Turbo regals did not have a specific case, odds are really good that a non performance 200-4r was gutted to donate the case.

 

[87gnguy]

I do have 342 gears and I'm running 275/60/15 drag radials. I'll pull the speedo gear after work tomorrow and check what you mentioned and let you know what's in it. I know the tire size does mess with your speedo, I just didn't think it would make the speedo that much slower. It's not really that much of an inconvenience, although it would be nice for it to be a bit more accurate. Thanks for your help.

 

[INEEDAGN]

Those are 28" tall tires. If you run that size all the time, we can get it calibrated to be correct for them. Give me the drive gear color when you get a chance and we will see if it's doable without yanking the pan.

 

[earlbrown]

Your speedo is reading about 13% off...

The circumference if your 275/60's are mathematically 1161 cm .... mathematical circumference of stock 205/70's 1026 cm for an error ratio of 13.157%


Damn those numbers came out good!!! I would guess you have the correct orange gear. I think gnttype.org has the % differences with the red and green on there.

 

[bison]

Chances are your transmission failed because the brakes were applied at speed. In reference to the gearing if your tires are MT's use 27.3" as the height during calculations.