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Re: Building a strong 8 3/4 rearend. [Re: MR_P_BODY] #2799403
07/21/20 02:07 PM
07/21/20 02:07 PM
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jcc Offline
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Who here with a Dana has passed a 8.75" at willow Springs with similar hp/driver?


Discovering "good trouble" everyday
Re: Building a strong 8 3/4 rearend. [Re: MR_P_BODY] #2799407
07/21/20 02:13 PM
07/21/20 02:13 PM
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Posts: 13,240
north of coder
moparx Offline
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thank you mr. P. bow
i have narrowed several rears over the years, using an 1 3/4" or 2" bar, plus machined pucks for the ends and differential case.
some for leafs, some coil springs, and some coil overs.
these were followed by straightening the housings using a 12" piece of very heavy I beam to clamp the housing to, [it's what i had laying around] plus heat and a jack or press as needed. also to make sure the bearing ends were parallel with each other in both the vertical and horizontal planes, approximately 18-20" out from center line.
i just never back braced a housing before.

thanks again mr. P.
beer

Re: Building a strong 8 3/4 rearend. [Re: moparx] #2799408
07/21/20 02:18 PM
07/21/20 02:18 PM
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Originally Posted by moparx
a stoopid question, [i'm sure] but those that have back-braced an 8 3/4 and moved the springs while running the brace to the very ends of the tubes, have you inserted tubes into the brace for the U bolts to pass through ?
if so, how did that work out ?
beer


I didn't feel running the brace to the ends was really necessary. However the shock interference issue is real, and you can see in the link the slight "kink I put in my brace to miss the angled shocks. The rear end housing outside the springs is being thrust forward, the housing inside the springs is being bent backwards, and all torsion/twist is only acted on the housing between the springs, We are excluding any braking forces as, they are much less and "softer" IMO. I don't feel a typical back brace is very efficient at resisting torsional loads.

https://board.moparts.org/ubbthread...ay-protour-practice-car.html#Post1553866


Discovering "good trouble" everyday
Re: Building a strong 8 3/4 rearend. [Re: MR_P_BODY] #2799411
07/21/20 02:30 PM
07/21/20 02:30 PM
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Tulsa, Ok
WadeMetzinger Offline
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Here is the 8 3/4 I had in my wife's 1968 Barracuda, it has Mark Williams caps on both sides (dad told them to put it on the wrong side the first time..lol), 35 splined alxes, spool, 4.30 gears, back braced and notched for shocks, boxed in spring perches, 5/8 suds, Strange billet 1350 yoke and then dual caliper Strange disc brakes.

Never broke on me running at 3,600lbs with 700hp motor running 1.43 sixty foots but I knew I was on borrowed time and called up Doc Diff and ordered a Strange S-60 that bolted right in, so now this sits on the shelf for the next project.

8.75b.jpg8.75.jpg

Wade Metzinger 918-809-0987
71 Cuda 9.28@145 -1s, Pglide
68 Cuda 10.64@124 1.45 60's 318->390 eddys
Moparts discount code on WIX - moparts www.Filter1.com
Re: Building a strong 8 3/4 rearend. [Re: WadeMetzinger] #2799476
07/21/20 05:07 PM
07/21/20 05:07 PM
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fredericksburg,va
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Probably shouldn’t throw this out there but..
I was told this long ago by a racer-engineer that this will make the 8-3/4 street gear last longer. He said they were hard and brittle to last a long time in a regular car but not good for racing, this process (in oven) will soften them up so I wrote it down. Never tried it but?..

7A481BDC-22A9-475B-8984-CE548933C718.jpeg
Last edited by cudaman1969; 07/21/20 05:08 PM.
Re: Building a strong 8 3/4 rearend. [Re: cudaman1969] #2799549
07/21/20 09:00 PM
07/21/20 09:00 PM
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I believe the concept is valid, but not sure if the numbers are spot on.


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Re: Building a strong 8 3/4 rearend. [Re: migsBIG] #2799575
07/21/20 10:04 PM
07/21/20 10:04 PM
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Milwaukee WI
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I think I have taken the 8 3/4 as far as you can. I cured all the issues with durability up to the point where I started shearing off pinion shafts. Everyone beefs up the wrong parts in my opinion. A stock case needs support mainly in the caps. The housing must be reinforced to support the caps not only from the rear, but also (and mainly) from the sides. The biggest problem with high power going through the 8 3/4 is that the case spreads. I doesn’t take much at all to flex the caps away from each other. You can easily confirm this by measuring the caps from outside to outside before pre-loading the spool bearings, and then after.
Putting supports in the case in both directions eliminates the gear chipping problems, even with stock caps. My car was 3700lbs, trans brake, mid 1.3x 60ft. Sub 9.50 times with stock case and gears. Started feeding it power and it began shearing pinions. At that point there is nothing that can be done to make it live. Went to a 35 spline pinion 9” ultracase from strange. Never had to worry about it again.


"use it 'till it breaks, replace as needed"
Re: Building a strong 8 3/4 rearend. [Re: TRENDZ] #2799662
07/22/20 09:11 AM
07/22/20 09:11 AM
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Yes, I would agree, once pinions start to shear, that is the end of the line in upgrades. But curious, which pinion, 742 or 489's?


Discovering "good trouble" everyday
Re: Building a strong 8 3/4 rearend. [Re: cudaman1969] #2799699
07/22/20 10:51 AM
07/22/20 10:51 AM
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East Coast
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Originally Posted by cudaman1969
Probably shouldn’t throw this out there but..
I was told this long ago by a racer-engineer that this will make the 8-3/4 street gear last longer. He said they were hard and brittle to last a long time in a regular car but not good for racing, this process (in oven) will soften them up so I wrote it down. Never tried it but?..


Its been a while since I performed this heat task. Only worked for a specific gear series by Richmond, if I remember correctly. Did 3 sets for a 426 wedge car that I had making 500+ HP @ 3600 lbs. 3 years with many passe with a J converter and 4.88 gears. Sold the chunk and did another with same amount of time with lots of street racing too. I would not try this today. That formula was for a specific steel and treatment of the time. Most 8 3/4 gear are either softer ar brittle.

Re: Building a strong 8 3/4 rearend. [Re: migsBIG] #2799766
07/22/20 01:06 PM
07/22/20 01:06 PM
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Canada
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all tese stories have me nervous taking my 8.75 to the track not running that much power only 520 hp 560 torque at the crank in a 3150 lb car people tell me if my tires hook the dif will break , guess the Dana is the only way to go for reliability . like you say py me now or pay more later . maybe i'll sell my 2 8.75 A body difs and have enough for the Dana .
interesting thread

Re: Building a strong 8 3/4 rearend. [Re: jerry9] #2799774
07/22/20 01:19 PM
07/22/20 01:19 PM
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Kirkland, Washington
Pacnorthcuda Online boogie
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I don’t think this thread has addressed traction enough and it’s affect on 8.75 strength. On a street car that may see some track time, but still shod with DOT rubber, the 8.75 has proven capable over the years.

With a 4 speed and slicks, and a decent amount of torque, things change.

Has the OP even stated if the car is an auto or stick?

Last edited by Pacnorthcuda; 07/22/20 01:22 PM.
Re: Building a strong 8 3/4 rearend. [Re: jerry9] #2799777
07/22/20 01:22 PM
07/22/20 01:22 PM
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Originally Posted by jerry9
all tese stories have me nervous taking my 8.75 to the track not running that much power only 520 hp 560 torque at the crank in a 3150 lb car people tell me if my tires hook the dif will break , guess the Dana is the only way to go for reliability . like you say py me now or pay more later . maybe i'll sell my 2 8.75 A body difs and have enough for the Dana .
interesting thread


Probably the best bang for the buck out there is the ford explorer (2000- 2006?) 8.8 rear. You can usually buy one from a junkyard for 100.00 to 300.00 . They usually have 4.10 gears with a somewhat decent posi unit, and factory disc brakes. My son bought one from a junkyard for 150.00. We put new perches on it, bolted it in and ran it......Stock axles and all, even left the junkyard fluid in it ! ! ! It literally has hundreds of passes on it , 11.50's to 10.90s in a 3200lb duster. Cant get much better than that. THen when you upgrade your power its not that big a deal to upgrade the 8.8 and there are a ton of aftermarket good parts for it, and its light and strong enough to handle 7 second HP.


....BAD A$$ STREET CAR.....
Re: Building a strong 8 3/4 rearend. [Re: n20mstr] #2799809
07/22/20 02:08 PM
07/22/20 02:08 PM
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IL
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Dart451 Offline
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I completely agree a dana 60 or 9" when starting from scratch is a better option. I wouldn't be so nervous on 8 3/4 for occasional runs
8 3/4 in wife's car normally 60' in the 1.40 zone would be little better if we took the small wheelie out of it. Car weights #3200 with her #3300 with me. Probably 120+ runs now and a dragweek trip.
Typical run is 10.1 @ 133 best is high 9's one 9.8 with small shot of spray
Ladder bar car with back brace, gears installed by me, only third set of gears i installed so not much experience.
I do know i'm on borrowed time and agreed the dana or 9" is better..

Re: Building a strong 8 3/4 rearend. [Re: jcc] #2799826
07/22/20 02:30 PM
07/22/20 02:30 PM
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north of coder
moparx Offline
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Originally Posted by jcc
Originally Posted by moparx
a stoopid question, [i'm sure] but those that have back-braced an 8 3/4 and moved the springs while running the brace to the very ends of the tubes, have you inserted tubes into the brace for the U bolts to pass through ?
if so, how did that work out ?
beer


I didn't feel running the brace to the ends was really necessary. However the shock interference issue is real, and you can see in the link the slight "kink I put in my brace to miss the angled shocks. The rear end housing outside the springs is being thrust forward, the housing inside the springs is being bent backwards, and all torsion/twist is only acted on the housing between the springs, We are excluding any braking forces as, they are much less and "softer" IMO. I don't feel a typical back brace is very efficient at resisting torsional loads.

https://board.moparts.org/ubbthread...ay-protour-practice-car.html#Post1553866



i completely forgot about the shocks ! [CRS and "oldtimers" i guess. laugh2]
i also have a sacrificial center section cut like yours, although it is a 489 case.
i have checked several rears before shortening, and have found some to be off almost 1/4" from straight. these were rears i know for sure weren't beat on. i did a pontiac rear one time that was off a tad more than 3/8" ! this was going in my buddy's 55 chevy, and needed to be cut 1 7/8" per side. we cut it at the spring mounting pad, then boxed it in around the tubes. a little heat and the bottle jack straightened it right out so the pucks would glide into the bearing bores with just a flick of the finger.
the reason for the 1 7/8" per side cut allowed stock oldsmobile axles from the "short" side to be used. i forget the application, however.
beer

Re: Building a strong 8 3/4 rearend. [Re: migsBIG] #2799923
07/22/20 05:59 PM
07/22/20 05:59 PM
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Mo.
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Anyone ever tried the Moser fab housing 8.75?

Re: Building a strong 8 3/4 rearend. [Re: racerx] #2800153
07/23/20 10:58 AM
07/23/20 10:58 AM
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Romeo MI
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I never found the need for them.. where a failure accures is the carrier.. thats why I went to
the alum MP carrier its much stronger with thu bolt for the caps that carrier dosent let the ring
and pinion separate like the stock one
wave

Re: Building a strong 8 3/4 rearend. [Re: MR_P_BODY] #2800184
07/23/20 12:07 PM
07/23/20 12:07 PM
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Eagle, Idaho
Neil Offline
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I think if I were doing a back brace I would dimple die it too. Those do make metal quite a bit stiffer.

Re: Building a strong 8 3/4 rearend. [Re: n20mstr] #2800302
07/23/20 04:31 PM
07/23/20 04:31 PM
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Thanks , I'll lok around for an old Explorer diff , does it make a difference 4x4 or 2 wheel drive ? I had an old explorer i think the carrier was offset if I remember correctly

Re: Building a strong 8 3/4 rearend. [Re: jerry9] #2800306
07/23/20 04:36 PM
07/23/20 04:36 PM
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Originally Posted by jerry9
Thanks , I'll lok around for an old Explorer diff , does it make a difference 4x4 or 2 wheel drive ? I had an old explorer i think the carrier was offset if I remember correctly


I don't think it matters 2 or 4wd, yes one Axle is longer than the other. On my sons we just cut the old mounts off, centered it under the car and welded on new perches.

This has to be the best junkyard rear ever...4 series gearing, posi trac and disc brakes


....BAD A$$ STREET CAR.....
Re: Building a strong 8 3/4 rearend. [Re: Dart451] #2800314
07/23/20 05:19 PM
07/23/20 05:19 PM
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Originally Posted by Dart451
I completely agree a dana 60 or 9" when starting from scratch is a better option. I wouldn't be so nervous on 8 3/4 for occasional runs
8 3/4 in wife's car normally 60' in the 1.40 zone would be little better if we took the small wheelie out of it. Car weights #3200 with her #3300 with me. Probably 120+ runs now and a dragweek trip.
Typical run is 10.1 @ 133 best is high 9's one 9.8 with small shot of spray
Ladder bar car with back brace, gears installed by me, only third set of gears i installed so not much experience.
I do know i'm on borrowed time and agreed the dana or 9" is better..



I will never run anywhere close to 10 sec , I'll be lucky to be in the 12's so guess I'm safe besides under 11 sec I would need a full roll cage that is not going to happen, daily driver in summer . plus insurance is hard to get and expensive once you put in a full cage . feel better about the 8.75 now . thanks

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