Any quick reliable solution for rear end ring and pinion issue?

[darrenr]

I just purchased this 1971 GMC Jimmy (Grandfather Medicine Cougar) with a sarcastic notion that it may be a driver. It may have a busted ring and pinion and who knows what else in the rear end.

My initial question (answered here before) is “Should I retain the ½ ton 10 bolt with 6 lug” or upgrade to a “3/4 ton 12 or 14 bolt with 8 lug”? My concerns are a lack of experience and lack of extra-$ and I don’t want to change the wheels/tires now.

In reverse, especially while turning, there is a pop, pop, pop in the rear end and there are small bumps on the exterior chrome rear axel cover like a demonic metal fly is trying to break out. Ring and pinion issue? If I replace the relatively small ring and pinion I may as well put in new bearings, etc (Parts and Labor $500 to $1000).

Someday, I want to upgrade axels, brakes, wheels, tires, etc (Parts and Labor $3,000+) to make Grandfather near bullet proof when I have more funds and if we are wheeling more often. Right now I need to get him on the road daily with a quick, cheap, clean bill of health.

Does anybody have any quick reliable solution for a rear 1/2 ton 10 bolt ring and pinion issue? Or rather than spend the money on repair of the 1/2 ton, should I just park it and wait a few months until I can upgrade to 3/4 ton front and rear?

[jcfoote60]

Well I guess one issue is how are you going to rotate your tires front to rear to prevent cupping and wear if your front and rear diffs are 6 vs 8 lug? Tire wear is gonna suck if you don't rotate bud. You either need to go 1/2 ton front and rear or 3/4......mix and match don't work real well.

My suggestion is to get a whole new rear differential rather than invest in a rebuild of your current diff.. they are readily available for the most part from guys here or I am sure locally in wrecking yards close to you for just a song compared to what you would face with a whole rebuild of what you got. That corporate diff was used across a wide range of years so you don't have to worry about looking for a 1971 model. also you need to know what gear ratio you have. there is a metal tag (or hopefully so) on your rear backing cover that tells you that because you need to match your rear ratio with your front. If you don't have that there is a way to tell and there are threads here that tell you how to do that. The other thing is to look for the tag on your front diff, that should tell you what you need for the rear.

Cheaper solution to go 1/2 ton diff replacement now...then figure out your long term plans as you get cash. hope this helps

JC

[krue]

Welcome to the board. I would buy a good used rearend until you are ready to do the 3/4 ton swap front and back.

[jamie72]

i`m with krue, you should be able to find a rear for like 100-150 i would think, i sell them for that here.

[MNorby]

Maybe I am too off-road related but I have never had any luck with a 10/12 bolt rear. If you are gonna replace it I would upgrade now. 14FF rears are dime-a-dozen. I have hauled them off for people for free even. If the new rear is the same gear ratio as your current setup just use the spindles out on the front and you wouldn't even have to swap out the main axle. If not same ratio and axle swap is way easy. IMO might as well upgrade if we are throwing money at it.

[Jimmy72custom]

I think I would pop the diff cover, before I make my decision. It may be a small problem

[LUV2XCLR8]

From West TN

[MNorby]

Originally Posted by Jimmy72custom

I think I would pop the diff cover, before I make my decision. It may be a small problem

true, if it is just spider gears or worn center pic could replace easily/ cheap or go for a locker or lunchbox locker on the cheap. IMO though if $$$ is involved to fix pony up now for the 14FF and be done.... forever.

[IGOR]

I would also go 14 bolt. 10/12 bolts are junk - especially with larger tires. A 14 bolt if properly set up will last forever.

[70rs/ss]

Open the diff, how can you realistically decide what to do if you don't know what's wrong? I have 12 bolts in mine (all trucks had 12's in out vintage (1/2 ton that is) that being said, I have not broken one yet. I have two sets of 3/4 tons, but if I don't break the 12 bolt, then why swap? Randy's ring and pinion has gears for $150, kits for about that, but a good used one from SoCal U-pull it lots would be the way, just pop the rear cover to ensure that you don't buy another heart-ache for you mystical beast, err Blazer?

[onetonk5]

It shouldnt be much of a problem to find a usable 12 or 10 bolt in a decent junk yard....just pull the cover make sure you have the correct ratio and that nothing looks like it could be a problem.
GMC=Great Mountain Climber

[darrenr]

Thank you all for the great feedback! Gradfather is running strong! Problem solved. It was the rear end positraction and Henrik at GM Truck Center in Burbank, California had a replacement in his shop last Friday so I was on the road for Labor Day weekend. He too says I should definitely upgrade the axels now, but we agreed to keep its current configuration with the intent to upgrade when I can afford to do it right.

Therefore all your recommendations will be very useful.

KC you were on it with suggested ½ ton diff replacement now, upgrade later when more cash is available.

Krue and Jamie, thanks for the wise recommendation, given my financial constraints, to fix it with used rear end parts. Your advise will be useful time and time again…

MNorby, I will be saving up funds to do upgrade of everything that goes with the 14 FF when the time is right, “and be done…forever”. I liked hearing, “If the new rear is the same gear ratio as your current setup just use the spindles out on the front and you wouldn't even have to swap out the main axle. If not same ratio and axle swap is way easy.” I may just do that if funds remain tight. Thanks.

Jimmy72Custom, the diff cap was removed just as you advised and problem quickly solved. I’d like to see more pictures of your 72 Custom. Thanks.

LUV2XCLR8, thanks for the kind welcome.

IGOR and MNorby, I look forward to someday setting it up right with 14FF.

70rs/sf and onetonK5, I appreciate both your recommendations to stick with 10 or 12 bolt if well inspected within the diff cover and I will check out SoCal U-pull it lots.

Thank you all for the excellent recommendations!

[MNorby]

Glad to hear you got it going! Now since there isn't any time crunch to get it running find screamin deals on 3/4 or 1-ton stuff and start colelcting parts slowly/ cheaply.

[WORNBRAKES]

I had a similar situation. Finally got an engine in the Blaz, changing all fluids and find more water in the rear than oil. Not to mention there is a hang nail on every tooth on the ring.
I am looking for a good 3/4 t donor truck. Untill then, I put some new oil in it just to make it mobile. No plans for pereminate driving though.