rear dif gearing

[Chris Henige (17196)]

A while back I asked how to determine the gearing on my un tagged rear end. I want to make sure I did it correctly.

Raised the rear axle and turned the wheel 1 turn. The other side tuned by itself in the same direction and rate. I counted the turns of the driveshaft at 3.5.

I have a 3.55 axle, correct? '62 340 hp

Another question. Should the Passenger side have turned with the driver side I was rotating? When I turned the Passenger side the driver side did not turn. Perhaps my brakes were dragging?

Chris

[Verle Randolph (14764)]

Re: rear dif gearing

Chris,

Your second paragraph suggested a positraction differential.
Your fourth paragraph suggest you do not have positraction.
Internal friction or dragging brakes could contribute to one not turning.

Back to checking gear ratio. If it is an open differential you must be sure that both wheels turn the same amount or the driveshaft turns will be off.

You can also block one wheel so it does not turn then count drive shaft turns for one turn of the wheel. Multiply driveshaft turns times two to get the gear ratio.

Verle

[Terry Deusterman (11486)]

Times 2? *NM*

[Harold #36939]

Re: rear dif gearing

A more certain way to determine the differential ratio is to mark the input to the differential such as on the input yoke or the driveshaft; also mark the output such as on the tire. Each mark should be referenced to a starting datum. With the rear wheels off the ground rotate the input a "ridiculous" amount of turns such as 15 or 20 past a common reference and have a helper do a count on the output. Next divide the input by the output & this will be your ratio. The reason for doing so many turns is to reduce the error factor that too few turns will produce; additionally, visually noting the starting datum is a source of errors when too few spins are used.

[Verle Randolph (14764)]

Re: Times 2?

Terry,

Yes, times two.

In an open differential (non-positrac), if you hold one tire, the spider gears will "change" the aparent ratio so you must multiply the driveshaft turns by two.

I agree with the suggestion to make "many" turns to get a more accurate result.

Verle