Different diff, tried to fix speedo?

[tomjan87]

Ok, so I have an 87 Supra Turbo 5 speed
When i bought it, it had a 4.30 diff non lsd.
I wanted a little better mileage, without loosing too much, so i swapped in a diff that was a 3.91. The speedo was off about 7 mph around 50 or so.

I heard that you have to change the speedo gear in the tranny from one that is off a 87 or 88 turbo for the speedo to be right again. i hav ea parts car that is an 87 turbo 5 speed. I swapped the gear out and its the same.

What do I ahve to do to get the speedo right again. I dont drive it much, so its not hat big of a deal, but when i do, i like to know when im speeding, not just guessing at a general area.

thanks for any help
Joe

 

[CTsupra]

a 87' turbo with no lsd and a 4.30? wtf?!

are you sure it's off? it's probably not the gear per se, but it could be the cable coming off of the gear going into the speedo.

 

[1TuffSupra]

Did the previous owner alter the car to compensate for the speedo when installing the 4.3 diff? If not your car is probably spot on, and was off prior to your swap

 

[tomjan87]

ok i forgot i posted, sorry school had me beat up right now.
The speedo was dead on when i got the car. it is a 87 turbo, not messed with too much. I guess it could be the cable. does any one else have a big square thing 2inx2in in the speedo cable about 6 inch from where it goes into the tranny?

ct surpa, what gear are you talking about,, where exactly is it.
thanks bunch
Joe

 

[7M-GTE]

you can actually go to your local toyota dealership and order the tranny/speedo gear... it's located where the speedo cable goes into the tranny... there are three different gears... one for the 4.30 gears, one for the 3.91 and I forgot what the other one is... but the 4.30 is basically an na gear... just swap those out and it should fix your problem...

 

[tomjan87]

I tried that already, it didnt work. I got a speed gear off another 87 turbo car. it was the same. I dont want to spend money that i dont have to. What are the chances that 2 cars have both the same thing done to them. and one was bone stock.
any other idea's
joe

 

[mkIIIman089]

I don't think you have a 3.91 diff. If my math is right you almost certainly have a 3.73 from an 89+ turbo. And somehow you wound up with 2 4.30 speedo drive gears. Since there is a 14% difference from 3.73 to 4.30 making it 14mph off at 100mph; or 7mph at 50mph.

So if you are indeed 7mph off and not 5 then you have a 4.30 drive gear and a 3.73 diff. If you were 5mph off then you would have a 3.91 diff with 4.30 speedo drive gear.

 

[tomjan87]

hmm,
Ill have to check that.
ill swap the diff from the other car into mine maybe and see if that does the job.
thanks for your help,
joe

 

[Jason T]

The speedo was dead on when i got the car. it is a 87 turbo, not messed with too much. I guess it could be the cable. does any one else have a big square thing 2inx2in in the speedo cable about 6 inch from where it goes into the tranny?

Yes i have a box like that in my speedo cable juntion to calibrate my speedo cost $225 to get my speedo correct


Remove it see if speedo is correct its prob there to compensate for the old diff