back brace for 9 inch rear

[Jim Comet]

HI all, I have a 66 Comet with a 600hp FE and a C6 trans that I foot brake. The car runs 10.7's and 60 foots are 1.45's. The car was a factory 390 car with the banjo 9 inch rear. I have 35 spline axles and Cal tracs. At what point should I consider adding a back brace to the rear? If I did, can I assume I would need a fixture to hold the axle from warping while welding on the brace? All is working well now but the rear end is out right now and I was wondering if I should just do it. Thanks Jim

[6667fan]

Strange Engineering calls out a brace out for 800 hp plus applications on their housings. This does not mean a brace for your situation is unwarranted. The factory housing metal thickness on the tubes might be .187? The Strange stuff is probably .250 and their welds of the tubes to the center section are more involved than a factory housing.
Can’t tell you anything about the welding concerns other than there will be smoke if you don’t drain the housing down.
If you pull it apart for the job you will have the opportunity to inspect the axles.

Alternatively you could upgrade the housing but it won’t be cheap and you might have to wait for it.

[Blueoval77]

Whats the old Comet weigh Jim ? Does the car see a ton of action ? Ive done my share over the years some on a fixture and some not . Ive not had one go wonky because it wasnt on the rod when I welded it up . I do however treat them a bit different when I weld them up.

[jayb]

The braces I use weld in the center of the axle housing, then out on the ends of the tubes.  The odds of warpage in the center when welding there are pretty small, I think.  Out on the ends, what I've done is weld in small areas where the back brace meets the axle tube, then duplicate that same weld on the opposite side of the axle tube.  Do a little at a time, back and forth.  This seems to even out any warpage.  I don't recall ever having one go out of alignment doing that, and I've done several...

[gt350hr]

  Jim with repeated launches , the housing does  bend causing a "toe in" situation and potential "tire scrub". I would add one in your case. To do it right , the brace is fit an welded before the housing is straightened so that the welding removes some ( or all) of the toe in. It is then checked and corrected as needed. I've seen .003-.005 improvements in the 60' times and nearly a mph on the big end.

[Jim Comet]

My car weighs 3500 with driver. Does anyone have a recommendation  or one to stay away from.

[pbf777]

     Yes, I would agree that a back-brace particularly on an O.E. housing is recommended for your application at that 60' and weight and if you intend repeated use.

     And, welding a brace (or much of any thing) is going to bend the housing; but think, if it's already bent forward from use and now welding on the backside, maybe you'll just be making it strait again!     And this effect has worked for me many times in the past when I have done such.   

     But these days, if regularly racing the car, I would recommend to just order a new housing (with it's heavier materials in construction) with all fabrication done as received.   

     Scott.

[frnkeore]

A continuous weld, joining two materials, will shrink the metal .005 - .015, depending on the heat generated.

But, if you do as Jay recommends, welding small areas (.50") on opposite sides, it will not move enough, if any, to cause a problem. I'd recommend bending some 1/4" square stock to weld to on the opposite side.

If your not a welder, have it done at a competent shop.

[Jim Comet]

Thanks for the input. I think I may install one or have one installed. I see  SW racecars makes one the the small banjo housing like I have. Thanks, Jim

[manofmerc]

Jim I have a comet runs 6.70s in the 1/8 460 powered I also have been welding for over 40 years . Yes you need a back brace I prefer the one Moser sells .It isn't a difficult job like Jay says I would remove the complete assembly from your car just so you can grind the paint off and to make welding easier .Tack it down in several places weld 1"-1 1/2" beads let them cool 5-10 minutes weld some more you will be fine .Where the axle tubes are welded into the housing those factory weld always look like doo doo to me a back brace strengthens all that .With a little patience (time ) it is an easy job.If you were in Ga I would help you out .Doug

[fekbmax]

+1 on the SW back brace for the banjo housing.  I have used many of those and they fit well although any of them (brand) will likely need a bit of grinding for fitment. 

[TomP]

Any welding on the housing will warp it.  Needs to be done in a jig , a piece of tube or bar stock with collars in the bearing locations. Stock housing is prone to warping, it's thin wall and wide.

[pbf777]

Any welding on the housing will warp it.

    +1 

     Yes, better technique will reduce the possible sum of deformation, but in the end, it's perhaps just a matter of how closely your going to scrutinize the end result.   

     Oh, and just the use of a "jig", though certainly of benefit, doesn't guarantee the housing will be perfectly straight, as generally when dismounting the "jig" a certain sum of resistance in the separation is experienced and the housing obviously relaxes to something other than "perfect", at least that as signified by the jig.   

     Scott.

[Jim Comet]

I found a shop that has a jig and experience adding back braces. Here is a photo of my prepped rear with the back brace set in place. The SW piece fits pretty nice out of the box with minimal trimming. I'll post a photo when it is done. Jim

[wowens]

Strap tied to Jack stand holding housing in place is slick.
Today is not wasted, I learned something new today.