VCCA Home Forums TECHNICAL - GENERAL Trucks and Vans Ring and Pinion for a 56

If I am ordering a new ring and pinion from someone like a Summit, what is the size of the ring and pinion in my 56-3100? I know it is 10 bolt. Is it 8.2 or 8.5? 1.438 or 1.625? 17, 25, or 27 spline? It is the original. Thanx ahead of time.

I have looked through everthing I have and thats quite extensive. I see no ring gear size listed, the only thing I can find is that the axles had 17 splines.
We never refered to the various ring gears back then by size. That began in 1965 when some cars had 10" and some 12" ring gears.

Thanx Gene, that is a little more info. 17 spline is offered at Summit. It may end up that I take it out and measure and count, but I would love for someone who has done the conversion to smaller ratio (for freeway) to tell me what they purchased. I just pulled my 56 into the garage today to block up and disassemble.

Rob,
A quick look at my parts catalogs indicate that 1/2 ton rear end parts are generally interchangeable from 55-62.
I would not assume that those gear sets advertised by their diameters and 10/12 bolt cover distinction will fit in your truck, even if the dimensions seem to match up.
I will be happy to do some more research for you if you like. There is probably someone out there who has been down this road. Maybe they will chime in.
Mike

Mike there are a lot of people that want to go 70, but not whine out at 3600rpm. I would appreciate all the info I can get. Thanx.

I own a '55 1st series. The rear end in this is the same as 55 2nd and the '56. I changed out the rear end for the same reason. (see my previous posts) I have a 10-bolt cover - that should help some.

The splines on the rear end of the pinion shouldn't matter because you should count on getting a new yoke too. As long as the yoke will mount up to your u-joints, it shouldn't be a problem.

There were 3.90, 3.70, and 3.38 gears available from 55-62. The more desirable ones may have been in Powerglide or hydramatic equipped trucks. This would make them scarce. I think one of these would fit in your truck as a complete unit (drop-out), if you could find one.

Mike

The "automatic" trucks used the same ratio as a stick 3.90, This was a very common ratio. The 4.11 was used with overdrive. The 3.70 was very rare. The 1960-62 had an economy option of 3.38. Also rare. The best of all would be to install an overdrive unit.

I measured the original ring and pinion from my truck last night, so I'll try to answer your questions. I measured it with a tape measure, so I could be off by an eighth or two.

"what is the size of the ring and pinion in my 56-3100?"
Ring gear:
OD is 9.5"
ID to gear teeth is 8"
ID to inner ring is 5-3/8"
There are 12 bolts that hold it to the carrier
There are 39 teeth in this ring
For trivia buffs, stamped on the back is:
3697702 GM 10 39 10 54 2
Pinion:
17 splines in the pinion shaft.
overall length: 9"
10 teeth
pinion diameter varies.
stamp on end: 54 3707341-10-39-GM GC

Differential gear ratio: 39/10 = 3.9:1

"I know it is 10 bolt."
Yes, the outer differential cover and the differential (dropout) bolt to the axle with 10 bolts.

"Is it 8.2 or 8.5?"
Not sure what these numbers refer to.

"1.438 or 1.625?"
Not sure what these numbers refer to either.

"17, 25, or 27 spline?"
There are 17 splines in the pinion shaft.

Wow Lyn, thank you so much for all that info and time spent. Same to everyone else as well. I am so impressed with all the commitment to assist fellow Chevs.

Now I see why many folks drop in an entire different rear end.