stumpshot

I marked the driveshaft and one of the tires. Jacked the rearend up---both tires off the ground and tranny in neutral---rotated the tire one full revolution. The driveshaft turned 1 full revolution and part of another. Had my helper rotate the tire till the mark on the shaft lined up i its original spot---looked at the tire and the mark was almost exactly an extra 1/4 revolution of the tire. I expected at least 3 revs of the driveshaft. Where am I screwing this up???
1975 350 w/ th400 trans. tires are 245/60 15's.
Thanks. Stump

tpfarm

I may be wrong but I think that only works on manual transmissions, maybe someone will chime in with info on Auto's.

tpfarm

After further thought I'm not sure if the transmission would make a difference, I'm sure someone will chime in with a correct response.

Gale Banks 80'

You did the right way of determining the Gear Ratio but got the wrong answer. So this means there is something slipping, and that would be the Limited Slip, Posi Traction or what ever is in there. Try Turning the other Wheel and see what happens. If that doesn't work do it the other way around, turn the driveshaft x amount of times to get the wheels to turn one revolution.

REELAV8R

This may be a dumb question, but are you looking at the drive shaft and not the half shaft?

stumpshot

I didn't check the other tire to see if it was turning, forward,backward or static. I was not marking the 1/2 shaft but the driveshaft behind the front u joint. Thanks for all the replies. I'll try the other side tomorrow and see what happens.
Stump

doorgunner

This chart should get you close to the answer (even if a P.O. swapped "chunks" in the diff.)

72-75

Positraction 3:36 Ratio

AX


72-75

Positraction 3:36 Ratio

LR


72-75

Positraction 4:11 Ratio

AC


72-75

Positraction 3:70 Ratio

AB


72-75

Positraction 3:55 Ratio

AA


72-75

Positraction 3:08 Ratio

AW

jim-81

I think the better way would be to rotate the drive shaft one turn and see how many times the tire(s) turn. This will give you the 'number' you are looking for. So if you turn the drive shaft EXACTLY one turn and the tire turns about 3.3 times then you are at 3.36:1. Best thing to do is scribe a small chalk line on each and maybe line it up with a jack stand or something then start. I don't think the limited slip would 'slip' just rotating by hand. This should give you exactly the correct ratio.
Jim

313hitman

its actually the other way. count how many turns on the driveshaft it takes to turn the TIRE 1 time. 3.3 times on the driveshaft to 1 turn on the tire would equal to around 3.36:1 ratio.

jim-81

ahh! thanks and sorry

thegazman

Good luck doing that by hand.

thegazman

Easy way to do this is mark your driveshaft and tire with white chalk. Count the driveshaft revolutions white someone rotates your tire one turn.

stumpshot

Exactly what I did but being lazy I went under once, marked the driveshaft and then slipped my iPad, on record, under the car and rotated the tire one revolution. Retrieved the ipadband watched the video.

C3Hawk

After marking, it might be easier to get an accurate count if you rotate the rear wheel 10 times while counting the driveshaft revolutions. Then divide that count by ten.

thegazman

You are just too hi-tech for me. LOL I'm just an old farm kid from the central valley. We never had a TV until I was in high school.