Moparts Tech Archive
Drag Racing Tips
Back Brace 8-3/4 rearend
Bracing the 8-3/4
Most of the time when we add a back brace we are going to shorten the housing anyway, But we always check the housing ends with an alignment bar if we don't shorten it to make sure the ends are still strait. If they need to be fixed we will cut them off and reweld them back on right.
But when we weld the brace on we will install a pig or case to the housing and bolt it down, Then we take a come-a-long and run it from bearing end to bearing end over top of the end of the case.We will usaully use an old pig that still has a pinion gear with the yoke on it so we have something there to hold the come-a-long in place over the end of the case.Then apply enough tension on the come-a-long to help keep it from warping. Then after all the brackets and brace are welded on we cut the ends off and straiten or shorten the housing to the length we want and reweld it back.
You might be susprized to find the the housing is bent in it's stock form. After 30+ years of use and not knowing what kind of treatment it's seen or how many potholes it's hit and what it's pulled, It's a good thing to check before you invest alot of $$$ just to find out it's bent.They are fairly easy to straiten but it's always best to know where you're at before you start.So you know what has to be done during your build up.
Heres some pics of the way we fit the brace to the housing before we weld it.-------------------------------------------
We use alot of clamps.
We are trying to fit and form the brace to the housing.
The better the fit the smaller the gaps and less welding.
The more that the brace conforms to the back of the housing will help suport the housing.
We put alot of time and effert into this step as it will help ensure a strong unit once it is finished.
The back brace has been welded on.
The brace was made from 2"x 3" box tubing.
A plate has been added between the 2 ladder bar brackets on all sides.
Drain plug is added to the housing.
Fill bung is also added.
The cap is alum and has an O-ring to seal it.==========================================
Any Time you weld a back brace or brackets on the rear end housing esp the 'thin' type housing of the 8-3/4 you need to have the ends checked with an alginment bar. And in 'most cases it will have drawn out of alignment and will need to have the ends cut off and re-welded onto the housing.
We've done a few of these over the years. and all of them need to be cut and redone. Some are 'close' after the welding, but not worth the cost of building a new rear end because of a few bucks the first time it's built.