I've already put a back brace on my 8.75,but I feel there could be more done to prevent the housing from flexing and cracking the caps.

I'm wondering what everyone is doing, besides "putting a Dana in it" or a "9 inch"

I stumbled upon this 8.8 brace setup on my buddies car,and I'm thinking of doing something similar that attaches to where the pinion snubber plate bolts to, and attaching it to the axle housing similar to this.


Has anyone ever done something similar or different.

I've had no problems with a full back brace.. not
stopping short at the leaf springs... this is a 9"
but the same style brace

I have yet to hear a good explanation for how a back brace makes an 8.75 CENTER live longer, and I have heard a lot of them. Regardless, you may want to review this thread for some ideas, there are about 5? pertinent pics starting at pic #44?.

https://board.moparts.org/ubbthreads/ubbt...actice-car.html

Proving these are related has yet to be achieved IMO:
" to prevent the housing from flexing and cracking the caps"
if that is your real intended meaning.

I've got the full back brace already installed.


I'm just kinda thinking out loud, but i feel directly connecting the actual center section via an old pinion snubber mount to the housing would help as well. I could be wrong, but it's just a thought.

You can put them on... sure wont hurt but I never
seen the need... JMO

If you plan on making enough HP to need the back brace on any rear end with stock cast iron caps please replace the stock drivers side cap with a billet steel cap and better fasteners
I bent the crap out of my original 8 3/4 housing wuith no back brace with steel caps and 35 spline axles and spools with ladder bars in my old pump gas street Duster

Id weld square tubing vs several things and bolted.

Your pick looks neat but I think it would allow too many ways for things to flex.

i've been hammering my 8 3/4 for years behind a big block. the trans brake when it was fitted did the most damage twisting the housing & eventually breaking a cap. i have a good strong brace on the housing now & i made caps for my caps to prevent another failure there. i did this mod before Williams made their fancy cap upgrade.

I will tell my age, but I attended a direct connection seminar years ago with Ronnie sox and they said the bracing was for cars that had the leaf springs moved in for tire clearance, since the housing had less support out at the ends the tube would flex and the axle would lever the side bearing and then pop the cap.

I don't see how something like in the picture will help what plagues the 8.75 by design. It's done that way on an 8.8 b/c you can't really put a backbrace on it. That just keeps the housing from flexing, not the centersection.
To "fix" the 8.75, you need to somehow keep the pinion gear from moving away from the ring gear under load.
Instead of spending money trying to make my 8.75 live just a little longer, I replaced it w/ something stronger.

Not my strong subject (is there one?) but it seems to me that to relieve its load the pinion gear tries to move backward (toward the D/shaft).
This pulls the tubes with it, so a back brace working in tension (stretched) would be useful.
I can't see what force the front-mount turnbuckles would counteract, since they work in tension and are nearly useless to resist bending forward.

An aside: unless there's space/package problem, the farther behind the axle the rear brace extends (like a "V") the stronger it is, which may allow less wall thickness or skeletonizing the walls to save weight.

....and lived happily ever after. THE END


We went S60 when we noted things twisting/breaking when we reached transbrake level. Being I like things "easy", I wish we would have gone a derivative of the 9". It's so much easier to set up gears on a bench and throw them in at will, but to be honest, with the S60 and it's side adjusters over the side shims of a "stock" passenger car/truck D60, now that I have two sets of gears and the accompanying pinion shims, I can swap gears just as quickly and at less cost than having to buy a whole pig.

They don't make the gear ratio I need with a dana, so that's out of the question.

You can get any ratio imaginable for a 9".

[quote=polyspheric]Not my strong subject (is there one?) but it seems to me that to relieve its load the pinion gear tries to move backward (toward the D/shaft).[quote]

But its reactionary force is against the Ring, so the ds sees nothing of this force battle. The ring is forced to the drivers side, and towards the rear, as the hypoid gears push away from each other, or try to. This rearward force of the ring from an overhead view is counterclockwise in direction, which is why the Drivers side cap is loaded in tension, and I believe always the first to fail. The pass side cap mainly is just for positioning and stabilization.

As it has been mentioned, the greater the spring/control rod inset on the housing, the more leverage there is from a dead weight, and any acceleration forces to act on the housing from the bearing ends towards the center section by increased leverage. The back brace helps slightly with the dead weight angle, and will be much more helpful with the acceleration bending forces. However I think those forces might be over rated, when at the power levels for an 8.75.

I also doubt a spline fit 20"+ axle can add that much load to a bearing cap from housing flex. So how much is this housing really flexing? It would also be odd that this housing flex transmitted thru the spline axle normally only breaks the Driver side center section cap. Now that could be because its a combination of the way the cap is loaded with the housing flex, but..... None of my reasoning here applies to tire shake conditions when the forces are chaotic and off the chart.

Now with the rotational twisting of the housing under acceleration, two things stand out to me, a back brace is a rather poor choice to resist torsional twist of the housing, but it does improve matters, and in the situation where the springs are relocated, and moved in towards the center, the housing by design is now much stiffer, in a rotational standpoint, as the dimensions are all shortened on the center section side, and not sure any twisting is taking place outside of the springs, in the first place.

I like it. I've thought about this very design in my mind many times. Will it make your 8-3/4 stronger than a 9"?... no, but it certainly can't hurt.

My 8-3/4" has a moser backbrace, Williams main cap, Dr.Diff spool & 35-spline axles. To the OP: If you build this, let me know with a PM. I'd like to see how it comes together and may be interested in one.

IMO and you can do whatever you want, you can brace EVERYTHING on that rear and have nothing move.
Your weakest link will be the teeth breaking.
I'm in the same boat and not going to mess with the 8 3/4 . It's hard do to the fact I have everything I need for it.
In the long run i will be getting a 9 inch. Dana or 9 for me is a tossup but the 9 gets the nod because of availability.
Matt

I braced mine in several ways. In the end I ended up with a strange ultracase 9".
I took the 8 3/4 as far as it would go. It was back braced, load bolt supported, and the most important(in my opinion) was the internal bracing that went right up to the caps so they could not spread. After the internal supports, the teeth didn't break anymore. got me through a season of racing. low 9s at 3700 pounds with a trans brake. Started working on the 60' and started shearing pinion shafts. No patch for that!
Went with a 35 spline pinion ultracase and put the whole rear end doubt right out of my mind.
That said, with a lighter car, I probably wouldn't have needed to switch. It was a lot of work though.
I don't have any pics of the internal bracing.

My thoughts exactly with the bolts. I would do a brace inside like a can with no top or bottom that spaced from front flange to the back one, then holes drilled for axels. If there where some bearing with less taper to replace the back pinion bearing, or even bronze bushings like a metal lathe, would help on pinion deflection.

I think I'm going to shorten a Dana over winter and go with a 3.54 ratio.I order ends from Dr diff today, and ill reuse my 35 spline axles in the cut down dana.and reuse my aerospace brakes. I currently run a 3.23 and really really didn't want to stray away from it. It might pick up some with the 3.54 anyways, who knows.

I figured bottom 9s at 3600lbs, it won't live much longer even with my slow 60', but for 2 years it's going strong lol