differential problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rcfatcat · 10-18-2009, 03:03 PM

i am having a hard time getting my rear diff to hold together. the the first time the rear went the ring and pinion and spider gears all launched and i forked out 800 dollars for another but once that was installed it lasted about 2 months and then blew again. this time the ring and pinion and the pinion bearing. so because of lack of money i temporarly threw in a 10 bolt axle instead of a 12 bolt to just be able to drive the truck and now i feel the 10 bolt goin because it is vibrating all over the place. i have been running 35 in tires with a 4.11 rrear end ration in both the 12 and 10 bolt axles and the 12 bolt had a posi unit in it. i need suggestions on how to build it up so this thing stops blowin up i am runnin out of money just tryin to keep the truck on the road. it is an 85 k5 with a sm465 manual. any ideas would be very helpfull

Lonnies Performance · 10-18-2009, 09:22 PM

Look into putting the 12 bolt car gears in the truck axle. It takes special pinion bearings, but is stronger because the pinion stem is larger for the car gears.

It sounds backwards, but the car gears are stronger. I broke a set of 4.56's in my 12 bolt approx. every year, until did this swap.

The bearings are readily available. I'll see if I can find the part numbers.

**special-K** · 10-19-2009, 06:10 AM

I never heard that and would like more ino.Always good to learn an old trick.
It sounds to me like the pinion bearing was bad which could cause the ring and pinion to fail.The pinion bearing was overlooked the first time and that`s on the mechanic who did your rear.The 12-bolt isn`t that weak that it would blow in two months after a new r&p.It`s the carrier and pinion bearings that fail and cause r&p failure from poor alignment.Either the pinion bearing was shot or it got ruined from the first r&p failure.Both are due to lack of inspection by mechanic.

LONGHAIR · 10-19-2009, 06:55 PM

I am with Tim on this one. I would be looking to the installer if it only lasted 2 months.
They may try to blow you off by saying "we can't control how you drive it" ....but if it was a bearing issue, that really shouldn't have anything to do with driving style, or even driver abuse.

Do you have the pinion angled up for the u-joint angles?

One thing above all others.....SYNTHETIC LUBE

Lonnies Performance · 10-19-2009, 07:56 PM

Bad parts are a definite source for failure, but my recommendation is for a higher strength part, for only a minimal increase in price.... since you have to replace the gears anyway.

The truck pinion stem is 1.438", whereas the car is 1.625", a substantial strength increase. I believe the 10 bolt even has a larger pinion than the truck 12 bolt.

My failures were due to deflection of the pinion leading to gear tooth failure. The larger pinion shaft can help in high power situations.

Mine was a built 427 turning 35" tires. The steeper gears have less tooth contact due to the smaller pinion (I ran 4.56's which has a 9 tooth pinion) & result in higher gear loading. 4.10's are not that much bigger (10 tooth).

Do it right & be done with it.

duallyjams · 10-19-2009, 08:00 PM

The first time you launched the rear did you start with a completely different housing or use the same one that blew up. If you use the same housing that blew up you could have stretch the caps that would cause it not to last.Been there done that.
Sounds like it is time to up grade to a 14b rear.

rcfatcat · 10-20-2009, 09:52 PM

the first time i launched the rear was my own fault. dumping the clutch at light with 35s will only last soo long. when the rear was rebuilt the same axle housing was used and absolutly everything was replaced (bearings, seals, carrier, etc.) then it launched again and the tech said that i was apparently downshifting too hard? which launched the pinion bearing and inturn shredded 7 teeth on my ring gear. i have started looking into a fourteen bolt but i would also appreciate more info on the car vs truck 12 bolt set up? i dont really understand what is being changed? what do you mean by the pinion stem?

OLDCHEV4X4 · 10-22-2009, 08:20 PM

The pinion stem is the diameter where the pinion bearings are pressed on. It would be the inside diameter of the big pinion bearing.

rcfatcat · 10-26-2009, 10:22 PM

ok that explains it thanks for the info so any ideas on the best way to proceed for the rebuild?

10-18-2009, 03:03 PM	#1
rcfatcat Registered User Join Date: Nov 2008 Location: pennington, newjersey Posts: 129	differential problems i am having a hard time getting my rear diff to hold together. the the first time the rear went the ring and pinion and spider gears all launched and i forked out 800 dollars for another but once that was installed it lasted about 2 months and then blew again. this time the ring and pinion and the pinion bearing. so because of lack of money i temporarly threw in a 10 bolt axle instead of a 12 bolt to just be able to drive the truck and now i feel the 10 bolt goin because it is vibrating all over the place. i have been running 35 in tires with a 4.11 rrear end ration in both the 12 and 10 bolt axles and the 12 bolt had a posi unit in it. i need suggestions on how to build it up so this thing stops blowin up i am runnin out of money just tryin to keep the truck on the road. it is an 85 k5 with a sm465 manual. any ideas would be very helpfull __________________ 78 k5 offroad project 350 sm465 60/14 np205 boatside, dovenose

10-18-2009, 09:22 PM	#2
Lonnies Performance Registered User Join Date: Oct 2009 Location: Pittsburgh, PA Posts: 63	Re: differential problems Look into putting the 12 bolt car gears in the truck axle. It takes special pinion bearings, but is stronger because the pinion stem is larger for the car gears. It sounds backwards, but the car gears are stronger. I broke a set of 4.56's in my 12 bolt approx. every year, until did this swap. The bearings are readily available. I'll see if I can find the part numbers. __________________ Lonnie Pavtis '82 Duramax Conversion in progress

10-19-2009, 06:10 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: differential problems I never heard that and would like more ino.Always good to learn an old trick. It sounds to me like the pinion bearing was bad which could cause the ring and pinion to fail.The pinion bearing was overlooked the first time and that`s on the mechanic who did your rear.The 12-bolt isn`t that weak that it would blow in two months after a new r&p.It`s the carrier and pinion bearings that fail and cause r&p failure from poor alignment.Either the pinion bearing was shot or it got ruined from the first r&p failure.Both are due to lack of inspection by mechanic. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

10-19-2009, 07:56 PM	#5
Lonnies Performance Registered User Join Date: Oct 2009 Location: Pittsburgh, PA Posts: 63	Re: differential problems Bad parts are a definite source for failure, but my recommendation is for a higher strength part, for only a minimal increase in price.... since you have to replace the gears anyway. The truck pinion stem is 1.438", whereas the car is 1.625", a substantial strength increase. I believe the 10 bolt even has a larger pinion than the truck 12 bolt. My failures were due to deflection of the pinion leading to gear tooth failure. The larger pinion shaft can help in high power situations. Mine was a built 427 turning 35" tires. The steeper gears have less tooth contact due to the smaller pinion (I ran 4.56's which has a 9 tooth pinion) & result in higher gear loading. 4.10's are not that much bigger (10 tooth). Do it right & be done with it. __________________ Lonnie Pavtis '82 Duramax Conversion in progress

10-19-2009, 08:00 PM	#6
duallyjams Registered User Join Date: May 2007 Location: Deale Md Posts: 4,663	Re: differential problems The first time you launched the rear did you start with a completely different housing or use the same one that blew up. If you use the same housing that blew up you could have stretch the caps that would cause it not to last.Been there done that. Sounds like it is time to up grade to a 14b rear. __________________ James 63 GMC V6 4speed carryall 65 chevy swb bbw V8 auto 68 K20 327/4 speed, buddy buckets 2002 GMC CC Dually Duramax 64 GMC lwb 3/4 V6 4speed SOLD 66 GMC swb bbw buddy buckets SOLD IG duallyjams The only thing that stays the same is constant change!

10-20-2009, 09:52 PM	#7
rcfatcat Registered User Join Date: Nov 2008 Location: pennington, newjersey Posts: 129	Re: differential problems the first time i launched the rear was my own fault. dumping the clutch at light with 35s will only last soo long. when the rear was rebuilt the same axle housing was used and absolutly everything was replaced (bearings, seals, carrier, etc.) then it launched again and the tech said that i was apparently downshifting too hard? which launched the pinion bearing and inturn shredded 7 teeth on my ring gear. i have started looking into a fourteen bolt but i would also appreciate more info on the car vs truck 12 bolt set up? i dont really understand what is being changed? what do you mean by the pinion stem? __________________ 78 k5 offroad project 350 sm465 60/14 np205 boatside, dovenose Last edited by rcfatcat; 10-20-2009 at 09:54 PM.

10-22-2009, 08:20 PM	#8
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: differential problems The pinion stem is the diameter where the pinion bearings are pressed on. It would be the inside diameter of the big pinion bearing. __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

10-26-2009, 10:22 PM	#9
rcfatcat Registered User Join Date: Nov 2008 Location: pennington, newjersey Posts: 129	Re: differential problems ok that explains it thanks for the info so any ideas on the best way to proceed for the rebuild? __________________ 78 k5 offroad project 350 sm465 60/14 np205 boatside, dovenose



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