Big block swap C1500

[97c1500ext]

Your truck weighs a thousand pounds more.

I'm well aware, that wasnt my question. Im looking for the weakest link. Is it the exact same axel or not? I want to know what part of the rear actually fails.

 

[b454rat]

I'd just run it and look for a better axle meantime. Not like its gonna break by just putting it in gear. I had people tell me the 7.5" axle in a G-body wouldn't hold up to a big block. My 79 Malibu with 4-speed and healthy 454 did just fine. I didn't drag race it, but may on occasion did some clutch dumps in 1st n 2nd....

 

[L31MaxExpress]

I'm well aware, that wasnt my question. Im looking for the weakest link. Is it the exact same axel or not? I want to know what part of the rear actually fails.

Wheel hop is what is going to destory it. The heavier the vehicle and the more torque it makes the easier it is to break something when it wheel hops. My 8.5 actually overchrushed the pinon crush sleeve and then ate the ring and pinon because the gears were no longer in the correct mesh. A good build will use a crush sleeve eliminator to make certain the pinon gear stays where it belongs.

 

[97c1500ext]

Wheel hop is what is going to destory it. The heavier the vehicle and the more torque it makes the easier it is to break something when it wheel hops. My 8.5 actually overchrushed the pinon crush sleeve and then ate the ring and pinon because the gears were no longer in the correct mesh. A good build will use a crush sleeve eliminator to make certain the pinon gear stays where it belongs.

Thank you, all of your responses have been greatly appreciated

 

[Schurkey]

Plenty of racers do 8.5 swaps over an 8.2, is it really as pathetic as people say?

The 8.5" is an improvement over the 8.2"; which was used beginning in the early-to-mid 1960s primarily behind small-blocks.

The 8.5 was designed for compact and intermediate vehicles, mostly with small-block engines, not for full-size pickups. Far as I know, GM never put the 8.5 into a full-size car until '77 when "full size" cars were downsized to the intermediate platform. GM didn't put an 8.5 in with a "Big Block" engine until after the big-blocks were emasculated by emissions controls and low compression.

Is there a difference between the 8.5 in these trucks and the 8.5 in camaros or other chevys?

Some 8.5s have bolt-in axle shafts. Most have C-clips. I won't make any promises on the actual differential cases, but I suspect they were changed--perhaps multiple times. Of course the Gov-Bomb case was never used in a Camaro or non-truck Chevy. The open case MIGHT be a carry-over from The Good Old Days, but I won't put money on it.

i already have a newly rebuilt 8.5 with a trutrac in the truck. Its not a stock G80 grenade. I also intend on adding TA Girdle and potentially having the tubes welded.

Most of the problems with the 8.5" axle are differential case failures. Gov-Bomb differential cases of 8.5" and smaller are prone to shattering. The 9.5" and bigger seem fairly robust.

Even the "open" differential cases in the 8.5" are weak and will explode.

So adding an aftermarket differential case is probably the single-best thing you can do to improve reliability of an 8.5" axle. Welding tubes-IF DONE CORRECTLY--is another reasonable plan. Problem is, it's really easy to warp the axle housing. I'm not opposed to adding a "girdle", although I gotta say that it seems to me that girdles are an excellent way to lighten your wallet.

You'd be WAY better off to get decent rear brakes (11.x Duo-Servo drums, for example) than to dump a bunch of dough into welding tubes and installing a girdle. But that assumes you have the horrible 254mm Leading/Trailing drums now.

My 8.5 actually overchrushed the pinon crush sleeve and then ate the ring and pinon because the gears were no longer in the correct mesh. A good build will use a crush sleeve eliminator to make certain the pinon gear stays where it belongs.

I don't know how the crush sleeve can be over-crushed in service. The rear bearing cannot move on the pinion gear, it's seated against the pinion head, the race is seated against the housing. The front bearing outer race is seated against the axle housing. Neither one should be able to move tighter onto the crush sleeve unless one or both of the bearings fail first.

But I have lots to learn about axles and gear-mesh, so maybe I'm wrong.

 

[L31MaxExpress]

The 8.5" is an improvement over the 8.2"; which was used beginning in the early-to-mid 1960s primarily behind small-blocks.

The 8.5 was designed for compact and intermediate vehicles, mostly with small-block engines, not for full-size pickups. Far as I know, GM never put the 8.5 into a full-size car until '77 when "full size" cars were downsized to the intermediate platform. GM didn't put an 8.5 in with a "Big Block" engine until after the big-blocks were emasculated by emissions controls and low compression.


Some 8.5s have bolt-in axle shafts. Most have C-clips. I won't make any promises on the actual differential cases, but I suspect they were changed--perhaps multiple times. Of course the Gov-Bomb case was never used in a Camaro or non-truck Chevy. The open case MIGHT be a carry-over from The Good Old Days, but I won't put money on it.


Most of the problems with the 8.5" axle are differential case failures. Gov-Bomb differential cases of 8.5" and smaller are prone to shattering. The 9.5" and bigger seem fairly robust.

Even the "open" differential cases in the 8.5" are weak and will explode.

So adding an aftermarket differential case is probably the single-best thing you can do to improve reliability of an 8.5" axle. Welding tubes-IF DONE CORRECTLY--is another reasonable plan. Problem is, it's really easy to warp the axle housing. I'm not opposed to adding a "girdle", although I gotta say that it seems to me that girdles are an excellent way to lighten your wallet.

You'd be WAY better off to get decent rear brakes (11.x Duo-Servo drums, for example) than to dump a bunch of dough into welding tubes and installing a girdle. But that assumes you have the horrible 254mm Leading/Trailing drums now.


I don't know how the crush sleeve can be over-crushed in service. The rear bearing cannot move on the pinion gear, it's seated against the pinion head, the race is seated against the housing. The front bearing outer race is seated against the axle housing. Neither one should be able to move tighter onto the crush sleeve unless one or both of the bearings fail first.

But I have lots to learn about axles and gear-mesh, so maybe I'm wrong.

I do not pretend to know the whole sequence, but both bearings and the crush sleeve as well as the ring and pinon were trashed. When the ring gear was removed, the pinon had 1/4" of play front to back and the pinon nut had not backed off. Always just assume it was a crush sleeve failure that started it all. I found the 9.5 SF 14 bolt for $300. Far cheaper than rebuilding the trashed 8.5. IIRC it cost me $75 per axle to get the bolt pattern redrilled and new studs pressed in. On the Express/Savanna 9.5 housing atleast it used the same backing plates as the 8.5. I replaced the mangled, bent up ones on the wrecking yard 9.5 plates with the still like new ones from my 8.5. With the axle bolt pattern redrilled my stock drums went right on. The 7,100 and 7,300 lbs vans had the same rear drum setup minus 5 vs 6 lug drums. The front brakes were the same too, just different rotors for the wheel bolt pattern change.

 

[Schurkey]

I am thinking--perhaps I'm wrong--that the only real purpose of the crush sleeve is to give the pinion nut something to press against (via the front bearing inner race/rollers.) With the crush sleeve in place to press against, the pinion nut has some thread friction that keeps it from backing off. IF (big IF) you could lock the pinion nut so it couldn't turn on the pinion threads by itself, you wouldn't need a crush sleeve at all.

But like I said...I've been wrong before.

I'm moderately certain you had a bearing failure that damaged the crush-sleeve, not the other way around. Or--who knows--maybe the sequence started with metal chips between ring and pinion that applied excess side-thrust on the bearings. Hard to say.

 

[L31MaxExpress]

I am thinking--perhaps I'm wrong--that the only real purpose of the crush sleeve is to give the pinion nut something to press against (via the front bearing inner race/rollers.) With the crush sleeve in place to press against, the pinion nut has some thread friction that keeps it from backing off. IF (big IF) you could lock the pinion nut so it couldn't turn on the pinion threads by itself, you wouldn't need a crush sleeve at all.

But like I said...I've been wrong before.

I'm moderately certain you had a bearing failure that damaged the crush-sleeve, not the other way around. Or--who knows--maybe the sequence started with metal chips between ring and pinion that applied excess side-thrust on the bearings. Hard to say.

All I can tell is I know what started the failure and it was my size 11 right foot on the skinny pedal. Banging the WOT upshifts so hard with torque management disabled that it would break the right rear tire loose and wheel hop shifting into 2nd at 50 mph. Also wheel hop from spinning the right rear tire on a hard take-off with the open differential. The 4L85E has somehow managed to live through that abuse, knock on wood.

 

[Erik the Awful]

I don't know how the crush sleeve can be over-crushed in service.

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[Road Trip]

That was 12 1/2 minutes well spent. Normally I don't hesitate to skip like a flat rock through
tech videos like this looking to improve the time spent/knowledge gleaned ratio, but after seeing
where he was going I relaxed and let this run without interruption.

I really like the fact that he explained exactly *why* these are used in production, how they can
loosen up in service, the benefits of a shim eliminator kit (if available) ...and especially shimming
the existing crush sleeve in order to extract another use out of what you got if you find yourself
at the mercy of a supply chain hiccup.

Took 100% of the mystery out of this production line time saver. (I've done enough
differential work to be able to get the good pattern & long term quiet operation after a gear ratio
change. But it takes me many iterations to get the right results, so if I did this for a living I'd
certainly starve to death. :0)

Color me a hobbyist who goes there only because I used to pay $$$+ for quiet running, but could
never predict what I would end up with after the vehicle came off the mechanic's lift. (!) So while
I'd be following the FSM careful cookbook style, I'd be wondering what benefits these fussy bits bring
to the table. Turns out it's not my table the mfg process engineers were worried about. :0)

Bottom line, the more I understand the underlying theory the more I enjoy the repair process.
And Uncle Tony answered every question I ever had about crush sleeves and why they were
part of the differential drill. And of course a shout out for red loktite at the very end.

@Erik the Awful, thanks for sharing!