8 3/4 back brace

Posted By: 8urvette

8 3/4 back brace - 08/29/11 10:18 PM

I know this has been beaten to death about what power will a 8 3/4 take, but i have a question about how much strength a back brace will add to it.
i have a 68 cuda rb stroker 543 with a 4 speed, 8 3/4 with 3.23 and a 3.91 center chunk. If i back brace my housing and don't launch hard will this rear end live for any amount of time? I have small street licks so i don't imagine ill have much traction, but i ran out of funds so my dana will have to wait till taxes.... does anyone know if a homemade back brace will add enough strength to the lil guy to make it last a few months??? no power shifting, easy launches, and my throttle cable only gets me about 60% throttle, so that should help too!!!

Is it realistic to expect it to live? mainly street driving.

Posted By: DemonDust

Re: 8 3/4 back brace - 08/29/11 10:31 PM

IMO, if you are just street driving and not beating on the car. You don't even need the back brace. If you are taking it to the track Then I'd think about beefing it up. Start with billet caps (this is the weakest point), then move on to back bracing the rear. The back brace will add much needed strength so the housing doesn't twist now that the caps won't break

Posted By: dOc !

Re: 8 3/4 back brace - 08/29/11 10:40 PM

I am an 8 3/4 fan .. but I say NO to any 4 speed car with a decent hook.

PLUS ...if you try adding a brace now .. it could move-around the housing so the bearing races could jam-up.

I say save your $$$ for the Dana.

Posted By: Moparnut426

Re: 8 3/4 back brace - 08/29/11 11:18 PM

Pluss you might have clearance issues with the brace in the way of the fuel tank. I know a Dana is close, and most guys have to "clearance" the tank

.

I think an 8.75 will hold up for a while, are you an auto or stick cause IMHO thik that makes a difference also.

Sorry just read its a 4 gear, so I guess ya better brace or upgrade.

Kasey

Posted By: Blusmbl

Re: 8 3/4 back brace - 08/29/11 11:27 PM

Depends how grabby your clutch is. If you have something like a centerforce, you'll be driving over your driveshaft at some point. If you do baby the car on the street, it will be okay until you upgrade, but don't dump the clutch (feather it out only), no burnouts, and no powershifting. Or, just put junk street tires on it that won't hook, you'll be fine on them.

The brace won't help you any, either. It's not worth the effort.

Posted By: Guitar Jones

Re: 8 3/4 back brace - 08/29/11 11:43 PM

Quote:

Depends how grabby your clutch is. If you have something like a centerforce, you'll be driving over your driveshaft at some point. If you do baby the car on the street, it will be okay until you upgrade, but don't dump the clutch (feather it out only), no burnouts, and no powershifting. Or, just put junk street tires on it that won't hook, you'll be fine on them.

The brace won't help you any, either. It's not worth the effort.

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/29/11 11:47 PM

As for the back brace it helps ALOT... the ends of the
housing are trying to bend forwards if it has any bite
at all... I've seen and fixed many with bent axle tubes...
I would also invest in the caps... 4 speeds are hard
on the 8 3/4 but there were PLENTY of cars that came
with the 8 3/4, including 4 speeds but with the brace
and caps it will help alot... can you still break it...
sure you can(and you can break a dana also)... everything
has a breaking point.... now days if I narrow a 8 3/4
for a customer I always suggest the back brace

Posted By: Blusmbl

Re: 8 3/4 back brace - 08/30/11 12:57 AM

I probably should've clarified. I agree, the back brace does help, especially for the axle shafts themselves. However, I don't think they'd help at all in this situation, with the common shock loading failure that a 4 speed adds to the equation- I'd guess it is more likely to break the pinion or ring gear than the axles.

They lived behind 383 4 speed B bodies on street tires. It certainly is not going to live behind a 543" RB 4 speed with a street friendly clutch and cheater slicks. The money spent on a backbrace and axle caps should be saved and applied to a Dana or 9".

If you can make one on your own for little/no investment, it's not going to hurt anything, but I wouldn't put any faith in it either.

I tried to make my 8 3/4 live in my Charger, as soon as I put decent tires on the car it spit out a ton of rearend parts. U joints, a pinion (in half- not missing teeth), axle (on a drag radial, cutting stellar 2.0 60's at Milan), etc. I never broke a ring gear, but I'd imagine with any more power it would've been next.

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 01:28 AM

Quote:

I probably should've clarified. I agree, the back brace does help, especially for the axle shafts themselves. However, I don't think they'd help at all in this situation, with the common shock loading failure that a 4 speed adds to the equation- I'd guess it is more likely to break the pinion or ring gear than the axles.

They lived behind 383 4 speed B bodies on street tires. It certainly is not going to live behind a 543" RB 4 speed with a street friendly clutch and cheater slicks. The money spent on a backbrace and axle caps should be saved and applied to a Dana or 9". If you can make one on your own for little/no investment, it's not going to hurt anything, but I wouldn't put any faith in it either.

I tried to make my 8 3/4 live in my Charger, as soon as I put decent tires on the car it spit out a ton of rearend parts. U joints, a pinion (in half- not missing teeth), axle (on a drag radial, cutting stellar 2.0 60's at Milan), etc. I never broke a ring gear, but I'd imagine with any more power it would've been next.

Based on the info he gave it wont have a problem

Posted By: 8urvette

Re: 8 3/4 back brace - 08/30/11 01:29 AM

does anybody have pics of a well made home made brace? I have access to just about everything i could ever need to do this. I am a ok welder at best, but my friend owns a welding fabrication business. He offered me the use of his shop, equipment and expertise... so i figured for the cost of the steel I could make my own. And be well ahead of a stock housing. If any pics are out there i would live to see them!

thank for all the input guys.
The rear end was originally bought and narrowed when i went to a from a stock smogged down 360 to a semi built 383 727 combo.

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 01:37 AM

I have one on my 8 3/4 but its sorta hard to see and
I have one on my 9" thats easier to see.... same thing
basically 2" X 3" rectangular tubing
this first one is my 8 3/4

Posted By: fishy340

Re: 8 3/4 back brace - 08/30/11 01:38 AM

Im an advocate of 8 3/4 but with a 4 speed...no way thats why all hemi 4 speeds had a dana

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 01:40 AM

This is the 9"

Posted By: CrAzYMoPaRGuY

Re: 8 3/4 back brace - 08/30/11 01:59 AM

1968 340 4 speed Barracuda, 4.56 gears, beaten to death street racing over a 10 year span.... 8 3/4 rear with stock caps and NO back brace. Never had any rear end problems whatsoever.

This is what I did for my Coupe, after destroying a half dozen ferd 9" rear centers in my Demon... with a HYDRAULIC CAMMED 440... I swore never again a 9".
I backbraced my housing with load bolt provisions and MW caps. I'm 650hp with 2900 pounds. If it breaks it breaks, but I'm confident it won't, and have no problem trying other solutions if it does.

I had a 500ish hp 440 in the same car for YEARS and YEARS with a non-braced 8 3/4, never had any trouble with it either. Beat the car on a daily basis.

New setup...

Posted By: Guitar Jones

Re: 8 3/4 back brace - 08/30/11 02:01 AM

Quote:

I probably should've clarified. I agree, the back brace does help, especially for the axle shafts themselves. However, I don't think they'd help at all in this situation, with the common shock loading failure that a 4 speed adds to the equation- I'd guess it is more likely to break the pinion or ring gear than the axles.

They lived behind 383 4 speed B bodies on street tires. It certainly is not going to live behind a 543" RB 4 speed with a street friendly clutch and cheater slicks. The money spent on a backbrace and axle caps should be saved and applied to a Dana or 9". If you can make one on your own for little/no investment, it's not going to hurt anything, but I wouldn't put any faith in it either.

I tried to make my 8 3/4 live in my Charger, as soon as I put decent tires on the car it spit out a ton of rearend parts. U joints, a pinion (in half- not missing teeth), axle (on a drag radial, cutting stellar 2.0 60's at Milan), etc. I never broke a ring gear, but I'd imagine with any more power it would've been next.

I still agree, I personally wouldn't expend the effort to back brace the 8.75 in your application. I don't think it's going to help anything. If you get the tires to hook you are going to have way more problems than a backbrace can solve. So why bother? Just baby it and save your money for a Dana.

Posted By: 8urvette

Re: 8 3/4 back brace - 08/30/11 02:05 AM

crazymoparguy- what are the load bolt provisions?

Posted By: Guitar Jones

Re: 8 3/4 back brace - 08/30/11 02:05 AM

Quote:

1968 340 4 speed Barracuda, 4.56 gears, beaten to death street racing over a 10 year span.... 8 3/4 rear with stock caps and NO back brace. Never had any rear end problems whatsoever.

This is what I did for my Coupe, after destroying a half dozen ferd 9" rear centers in my Demon... with a HYDRAULIC CAMMED 440... I swore never again a 9".
I backbraced my housing with load bolt provisions and MW caps. I'm 650hp with 2900 pounds. If it breaks it breaks, but I'm confident it won't, and have no problem trying other solutions if it does.

I had a 500ish hp 440 in the same car for YEARS and YEARS with a non-braced 8 3/4, never had any trouble with it either. Beat the car on a daily basis.

Funny my 4 speed 340 Duster never made a full pass with the 8.75. It was either swap to a Dana or an automatic, I chose the automatic. I have the aluminum center section in mine with a pro gear and have been good to this point but before with a street gear I would plan on a ring and pinion every 2 seasons or so.

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 02:14 AM

I'm on my 5th year on my street gears... still perfect

To the OP... those load bolt just slightly load the
back of the caps (inside) so they are less likely to break

Posted By: Guitar Jones

Re: 8 3/4 back brace - 08/30/11 02:18 AM

Quote:

Funny my 4 speed 340 Duster never made a full pass with the 8.75. It was either swap to a Dana or an automatic, I chose the automatic. I have the aluminum center section in mine with a pro gear and have been good to this point but before with a street gear I would plan on a ring and pinion every 2 seasons or so.

I'm on my 5th year on my street gears... still perfect

To the OP... those load bolt just slightly load the
back of the caps (inside) so they are less likely to break

Yeah, your car is probably lighter than mine was but good luck to you.

Posted By: CrAzYMoPaRGuY

Re: 8 3/4 back brace - 08/30/11 03:50 AM

Quote:

crazymoparguy- what are the load bolt provisions?

Threaded tubes which allow a load bolt to be theaded up to the back of the caps.
I think a few companies make rear end covers for Dana 60s that do the same thing.

Posted By: CrAzYMoPaRGuY

Re: 8 3/4 back brace - 08/30/11 03:54 AM

Quote:

Quote:

Funny my 4 speed 340 Duster never made a full pass with the 8.75. It was either swap to a Dana or an automatic, I chose the automatic. I have the aluminum center section in mine with a pro gear and have been good to this point but before with a street gear I would plan on a ring and pinion every 2 seasons or so.

I'm on my 5th year on my street gears... still perfect

To the OP... those load bolt just slightly load the
back of the caps (inside) so they are less likely to break

Yeah, your car is probably lighter than mine was but good luck to you.

His car is a heckuva lot faster than yours too !!! My 340 was a second and a half slower than your 340!!
I have had ONE 8 3/4 rear break after 25+ years of very abusive street racing with dozens and dozens of cars.
My Cuda was beaten severely for years and years with the same 4.56 8 3/4 rear. It also had the same A833 tranny. Never had problems with either.

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 04:12 AM

Yeah, your car is probably lighter than mine was but good luck to you.

Probably is lighter... heck I got over 600 passes with
a stock pig with a set of 4.88 street gears before
it blew the caps off of it... at that time I changed
over to the alum center with 4.56 street gears running
1.19 - 1.21 60'(depending on how many passes on the slicks)

Posted By: lucky13

Re: 8 3/4 back brace - 08/30/11 04:51 AM

Any chance of getting some more info on the jack bolts? Are they just some regular bolts or are they like a jacking screw?

Posted By: 8urvette

Re: 8 3/4 back brace - 08/30/11 06:09 AM

and are the tubes sealed? i have access to a fantastic fabricator and his shop, he is willing to do whatever i want. he will be installing my cage, wants to build me some super crazy headers... etc... i just need the ideas and how to's to get it going!

Posted By: Slingshot383

Re: 8 3/4 back brace - 08/30/11 05:13 PM

It's just a threaded spud, you can use a long allen screw or cap bolt, use a jam nut to lock it down just past finger tight. It should hit the center of the caps, prevents them from moving rearward and getting broken or spit out.

Posted By: larry890

Re: 8 3/4 back brace - 08/30/11 06:41 PM

when you install the back brace, make sure you leave room for the shocks. I forgot and the first time the axle rotated up it dented both shocks.

Posted By: 8urvette

Re: 8 3/4 back brace - 08/30/11 06:44 PM

sweet thanks guys, since all i have to pay for is the steel, (and my friend has tons of scrap, literally) it should only be a few bucks, and he will teach me how to do it, so it'll be a good learning experience too!

Posted By: MR_P_BODY

Re: 8 3/4 back brace - 08/30/11 07:09 PM

Quote:

It's just a threaded spud, you can use a long allen screw or cap bolt, use a jam nut to lock it down just past finger tight. It should hit the center of the caps, prevents them from moving rearward and getting broken or spit out.

Its simple to make... I lay it on the back with the
same gap at each end then set my dividers to the gap
then scribe the tubing keep your dividers square to
the axle housing ..... DONT WELD IT ALL AT ONCE
weld 1" sections and jump around so you dont bow the
axle tubes

Posted By: kilroy

Re: 8 3/4 back brace - 08/30/11 09:18 PM

Quote:

..... DONT WELD IT ALL AT ONCE
weld 1" sections and jump around so you dont bow the
axle tubes

THIS!

Be a builder listen to the guys that know! It will be better than doing nothing!!!

Posted By: 8urvette

Re: 8 3/4 back brace - 08/30/11 10:03 PM

o i know, i have learned this once or twice just welding little stupid things.
and like i said, my friend has been doing welding and fabricating for at least 10 years, owing his own shop, so 12-16 hours a day 7 days a week. you guys know how it is.

the main cap bolt tubes, do they leak then? what size should i use? what grade bolt? and does the threaded pitch matter?

Posted By: Labratt

Re: 8 3/4 back brace - 08/30/11 10:06 PM

I have to get Mike(P-Body)to put a back brace on my 8.750 in my GTX!...probably next spring,when I get rid of the stock,factory axles!

Attached picture 6802584-GTX@MILANDRAGWAY.jpg

Posted By: dragram440

Re: 8 3/4 back brace - 08/30/11 10:12 PM

Quote:

I have to get Mike(P-Body)to put a back brace on my 8.750 in my GTX!...probably next spring,when I get rid of the stock,factory axles!

I dont know why I worry about my 8 3/4 so much if you are running stock axles to low 11's. I like to see that. These 8 3/4's arent as bad as everyone on here says!

Posted By: CrAzYMoPaRGuY

Re: 8 3/4 back brace - 08/30/11 11:36 PM

Quote:

the main cap bolt tubes, do they leak then? what size should i use? what grade bolt? and does the threaded pitch matter?

I bought load bolts from TA who make covers, then modified them to fit my rear. (The car rear people....)
The tubes are welded inside the housing and outside the housing. They shouldn't leak, I don't think the gear oil is filled above their level and I anti-seize the bolts and use a lock nut...

Posted By: GOREO

Re: 8 3/4 back brace - 02/23/15 05:23 AM

Mike,
Could you IM me, questions about back bracing for my 8 3/4.
Thanks...

Posted By: TRENDZ

Re: 8 3/4 back brace - 02/23/15 06:04 AM

here's a pic of mine. was in a trans brake turbo car. 3600 lbs. started shearing pinion gear stems when the car was going hi 9s. Never had failures except for shearing pinion gears.

Attached picture 8438133-e-mailsizedpics014.jpg

Attached picture 8438133-e-mailsizedpics014.jpg

Posted By: 68roadrunner

Re: 8 3/4 back brace - 02/23/15 07:24 AM

Attached picture 8438202-141228_005(1).jpg

Posted By: jcc

Re: 8 3/4 back brace - 02/26/15 05:30 AM

Quote:

does anybody have pics of a well made home made brace? I have access to just about everything i could ever need to do this. I am a ok welder at best, but my friend owns a welding fabrication business. He offered me the use of his shop, equipment and expertise... so i figured for the cost of the steel I could make my own. And be well ahead of a stock housing. If any pics are out there i would live to see them!

thank for all the input guys.

A back brace IMO mainly pevents bending of the Housing under extreme acceleration, good traction and High HP applications, and some twisting of same. Does little to help the R&P tooth interface, also IMo the weakest point after
the already mentioned Driver side cap.

Not worth it for OP IMO, and fpllow my suggestion, not what I do.

See pic #43 https://board.moparts.org/ubbthreads/show...part=1&vc=1