Rear End Ratio Change

[Joel T.]

I think I know the answer to this one but wanted to run the question past you guys just in case... This relates to the 1978 PCR which I have been working on for a while now.

I have the original rear out of the car which has 3.70 gears (this was one of the L82 4 speed cars) and I would like to bump this up to 4.11's. Can I do this with the carrier in there and just swap out the ring and pinion??

Thanks,

Joel

[Gary R.]

Re: Rear End Ratio Change

Yes you can still use the 3 series case by using Tom's Differentials (US Gear) 411's. I would add ARP RG bolts and solid steel clutches in place of what you have in there at a minimum.

[Jim T.]

Re: Rear End Ratio Change

Joel Corvette rear ends with 3:08, 3:36, 3:70, and 4:11 have the same tooth combination of 37 for the ring gear. For your 3:70 the pinion gear is a 10 tooth. For a 4:11 the pinion gear is a 9 tooth.

This information taken from AMA Specifications for my 1970 Corvette.

[Joe L.]

Re: Rear End Ratio Change

Joel Corvette rear ends with 3:08, 3:36, 3:70, and 4:11 have the same tooth combination of 37 for the ring gear. For your 3:70 the pinion gear is a 10 tooth. For a 4:11 the pinion gear is a 9 tooth.

This information taken from AMA Specifications for my 1970 Corvette.

Jim------


Yes, but the 37 tooth ring gears are not interchangeable among the various axle ratios. A specific 37 tooth gear is used for each ratio using a 37 tooth ring gear.

[Jim T.]

Re: Rear End Ratio Change

Joe do you know what the differences would be with the different 37 tooth ring gears required for different pinions?

[Duke W.]

Re: Rear End Ratio Change

...gear tooth geometry. Each of the 37T ring gears has different detail tooth geometry to allow them to mesh with specific tooth design/tooth count pinions. Hypoid gear sets have to be very precisely manufactured to achieve long life and low noise, which is why they are only sold as matched sets, and the auto manufacturers have been dealing with the issues for about 75 years.

In production ring and pinion sets are set up very precisely in a fixture, run with a load, and lubricated with an oil that contains fine abrasives. This "seats" the gears together. and they must be installed in the axle in precisely the same alignment. This is why pinion depth and backlash have to be carefully set using shims to provide the same alignment as when the gears were "run in".

Hypoid gears have highly loaded tooth contact areas- much higher than typical helical or bevel gears, which is why they require GL-5 oil that has an EP additive, and it's the additive that gives GL-5 its pungent odor.

Duke