Figuring out which Speedo gear I need for my vehicle. help!

[Brentdavis13]

I recently purchased a 1976 Chevrolet Wayne Busette which sits on a 1967-1972 Chevy van g30 chassis. its got a engine and transmission swap with a 700r4. the previous owners rebuilt the rear end and the speedometer gear isnt working now. Ive looked up videos for this but am thinking this is different because its a different type of vehicle than a regular g30. any help on figuring out which gear I need would be greatly appreciated

 

[Keith Seymore]

A few comments:

a) Pics?

b) I don't think the fact that it is a busette makes any difference. A 700R4 is the same regardless of what chassis it is sitting in.

c) Need to know rear axle ratio and tire size to choose the correct gear

d) If the speedo works but the reading is off incrementally you can always add an external adapter to fine tune it in.

Google Search

e) All of this assumes the speedo/odo is working presently.

K

 

[Brentdavis13]

A few comments:

a) Pics?

b) I don't think the fact that it is a busette makes any difference. A 700R4 is the same regardless of what chassis it is sitting in.

c) Need to know rear axle ratio and tire size to choose the correct gear

d) If the speedo works but the reading is off incrementally you can always add an external adapter to fine tune it in.

Google Search

e) All of this assumes the speedo/odo is working presently.

K

1. I'll attach pictures at the bottom.

2. I don't have an owners manual so I'm not sure how to get the axle ratio. i think thats what my biggest issue is.

3.the speedometer does not work currently but I believe that its because the owners put a new rear end on it and put the new transmission in it. I took the speedo cable off the speedometer itself and twisted the little ring counter clockwise and it does work if i do it manually like that.

(I'm still pretty green to working on cars which im sure you can tell so if you have any more questions im happy to answer them if i can

 

[Keith Seymore]

That is quite a machine.

To get the rear axle ratio:

a) For open rear diff - mark the tire and drive shaft. Jack up one tire and rotate the tire twice and count how many times the shaft goes around. Ie, if the shaft goes 3.5 times then maybe 3.42 (or 3.40, depending on axle type). If it goes around more than four times, then 4.11 or worse.

b) For locking diff - same as above but jack up both rear wheels and rotate the tire once.

Or - best method - pull the cover and count the teeth on the ring and pinion. Divide ring gear by pinion (that is, 41 teeth on the ring divided by 10 on the pinon = 4.10) Replace with fresh gear lube. It probably needs it anyway.

K

 

[Keith Seymore]

As far as the speedo not working - you can pull that little housing and slip the gear out. You would be able to buy that same gear, like if it's green you can buy a replacement green gear.

Google Search

I would make sure the square drive in the gear is not wallowed out and that it is able to drive the square portion of the cable. I would also rotate the trans and make sure the internal gear is driving the speedo gear.

K

 

[Snoots]

TCI Auto Speedometer Gear Calculator - TCI® Auto

Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!

www.tciauto.com