Gears

[railroad]

Have the T up on the lift addressing different issues and decided to pull the rear axle cover to see the gears. Surprise 2.73's. I knew they were high ratio, but did not imagine. I turned the driveshaft and got about 1.4 turns x 2 = 2.8. I am shooting for something in the very low 2000 rpm range at 50 mph. I have found an on line calculator. The rear axle is a GM with 7.5" gears. It looks like 3.70 gears with my tires. I have a stock 302 Ford GT motor, C-4 trans and like mentioned a 7.5" gm rear axle. Rear tires are 315/70/15's, 32" tall. I do not do any road trips, Can you put 3.70s in a 2.73 rear with the right shim? I am open to any other advise you guys might want to offer.

thanks,
joe

 

[benT]

Railroad: the GM 10 Bolt 7.5/7.625" can be upgraded with different gears easily, but the carrier cases are different from the 3.08 down and the 3.23 up. This means you can't just use a factory 3.73 gear setup on your existing 2.73 carrier. You can buy aftermarket gears that do work on the lower carriers from Yukon Gear and other places.

If you want to do it cheap, best thing to do would be to find an axle with a 3.73 already and take the full guts. You can then set it up in your axle using your existing and the shims you take from the new axle. These are super plentiful in the junkyards and I have a cheat sheet for the axle codes for these. I did something similar as I took the 3.73 gears from one s10 axle and put them on a factory take-off posi unit and stuffed it into a different S10 Blazer axle. I do like the 3.73 gears in my 302/C4!

 

[railroad]

thanks for the useful information. We have a local pull a part in B'ham. I need to make a run and see what is available.
I think you are talking about getting the carrier with the ring gear, bearings, races and shims, plus the pinion and the same. For their prices I can probably get the whole axle.
Not up on chebbie stuff, but I do have the codes for the diff ratios.
good idea, thanks,

 

[benT]

Yeah, pulling the whole axle will probably be as cheap---bad thing is once you take it apart and start switching gears, you are into at least a crush spacer and pinion nut as well as bearings if you feel strong enough about switching them out. I think the local pull-a-part/pic-a-parts here have the whole axle for under $100. Bad part is you have to pay them to remove it , or figure out how to get it cut out without a torch and jack...

 

[Screaming Metal]

thanks for the useful information. We have a local pull a part in B'ham. I need to make a run and see what is available. I think you are talking about getting the carrier with the ring gear, bearings, races and shims, plus the pinion and the same. For their prices I can probably get the whole axle. Not up on chebbie stuff, but I do have the codes for the diff ratios. good idea, thanks,

Hey RR, theres a yard over there on the other side of Century Plaza, going toward Pelham, he's got a bunch of S10's. Was over there a month ago helping a friend there in Pelham getting a rod going there in his shop. We had to make a parts run.....guy had good prices.....all you need is a SawzAll! and assortment of blades.

 

[railroad]

More good advise. Thanks Screaming Metal. Good idea on the Sawz All. I have a Dewalt. I can grab a couple of batteries and handful of blades. I like it.

 

[railroad]

I found a salvage yard that said they had one or could get anything I needed. They have the parts already pulled for about $50 more.
Sounds reasonable to me, since it was 99* today. Anyway, he told me to get the letters off the top of the passenger side axle tube.
BP 01 05 CW I think, I read them to him over the C phone while looking at them. He said, he needed this because there are 2 types of rear axles. I explained to him my intentions of swapping the guts to get the 373 gears. He nodded, like he had heard it before.
Anyway, he said there should be some letters, but I have not found them and he has not called back with what the numbers interpret to. I'll do some more phone work tomorrow, before fighting that heat.

 

[Screaming Metal]

Yea RR, that heat will hurt you! I was walking up behind a tree at one of the meets a few months ago, IT WAS HOT! No traction compound was needed!!!!!! Well over 100. Everyone started laughing when I pulled my cap off, I had a folded up rag on top of my head, I took it down and wiped my face, folded it back up and put it under my cap again.
The cars were rolling forward to heat up the tires and everyone was laughing.....I get a damp rag and put it in the fridge for about 10 minutes and on top of my head it goes......

 

[railroad]

Well, I got a good buy on a 94 axle with the right gears. Watched the guy pull it from an S10, pulled the cover and everything looked good. Long story short, the pinions are different. For future use the newer pinions have a 1 1/4" nut and the old one like I have is 1 1/8". I'll probably just buy a ring, pinion and spacer unless I get some leads on an older model axle. The new axle is complete, I would not let him burn the brake cables and the drums and shoes looked new. Drums still had the speed nuts on to hold them on.
Maybe I can find a local rodder needing an axle.

 

[railroad]

I am getting a real education on this GM stuff. It seems I have an 8.2 inch ring and pinion. With the 2.73 gears I will need to step up to a series 3 carrier or use a spacer. I am not afraid of the spacer, not that much hp, but it just gets deeper and deeper trying to swap these gears. The rear axle is fairly old stuff. I think it may have been made up until 72, but most applications were in the 60's.
The 25 spline pinion was the key to identifying it. My brother does the rear ends and transmissions for an off road shop, maybe I can get a break on the price.

 

[railroad]

Good news guys. The gears are installed. Reeallly fun to drive. Forgot to compare rpm and speed. I am sure I will have to recal the speedo. Had a slight hesitation off idle, never noticed it with the other gears. Adjusted the pump are a little and all seems well. Ended up with 8.2 gm 3.73 gears with a spacer on the carrier. My brother was breaking up a green field in front of the shop and I talked him into pulling the pinion bearing and setting up the gears. I just dug through the shims, mic ed them and handed them to him as he set it up. Maybe 30 minutes, he's good.