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Welding a back brace on a 8 ¾, advice please??

Posted By: FlyFish

Welding a back brace on a 8 ¾, advice please?? - 05/25/12 05:50 PM

I’m about to try welding a back brace on my 8 ¾ and I need some advice. I’ve done some reading, and most folks agree that the right way to do it is to use a jig to keep it from warping the housing. Well….I’m a backyard mechanic, so I don’t have a jig…but this was my thought.

What if I tack weld a piece of angle iron on the opposite side of the housing from the back brace, and leave my axles and spool installed…would this be enough to keep the housing fairly strait if I space my welds (to not build too much heat) and work my way slowly around welding the brace?

Also, dose the brace need to be fully welded all the way around?

Any and all advice is appreciated,
Thanks in advance
Posted By: 340B5

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 05:57 PM

You could stitch weld it. 1-1/2 in on one side, the go to the other side. If the gears and axles are out, you could use an air compressor and blow air through it to keep it from getting too hot.
Posted By: BradH

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 06:16 PM

Quote:

You could stitch weld it...


x2 - That's how mine was done by a friend and it turned out OK.
Posted By: MR_P_BODY

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 06:34 PM

All I do is stitch weld... no more than 1" at a point
and jump all around so 1 area is cooling while your
in another area... take a couple of long straight edges
and clamp them on the flanges to measure between to
make sure the ends stay square
Posted By: FlyFish

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 06:56 PM

So, with stitch welding, are you talking like...weld an inch...move down 6 inches...weld another inch...etc? Also, how long do I need to let it cool before coming back to an area...like 10 minutes?
Posted By: Polarapete

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 08:10 PM

Make sure that your ground path does not pass through the bearings when you weld. In other words don't hook your ground clamp to anything other than the housing or a bracket already welded to the housing
Posted By: MR_P_BODY

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 09:49 PM

Quote:

So, with stitch welding, are you talking like...weld an inch...move down 6 inches...weld another inch...etc? Also, how long do I need to let it cool before coming back to an area...like 10 minutes?



I jump side to side... let it cool till you can put your
hand on it
Posted By: MrSixpack

Re: Welding a back brace on a 8 ¾, advice please?? - 05/25/12 09:59 PM

Do it like you torque a head, start in the center and move slow outwards.
Like they said and inch at a time, shift sides and let it cool.
Easy but it takes time, and it's worth it

Good luck
Posted By: STEFF

Re: Welding a back brace on a 8 ¾, advice please?? - 05/26/12 05:21 PM

The problem you have is all of the welding is being done to one side of the tubes. It's not the heat that causes the warpage. It's when the weld cools, it shrinks, pulling the metal. Hense the reason to use a jig to pull the tubes in the opposite direction.

The correct way to back brace a housing is to mount it to a jig to preload (pull) the tubes towards the mtg. face of the housing. About 3/16" is good. Ideally, you would want to weld the backbrace on then cut and reweld the bearing flanges to make sure they are on center after all the welding, using an axle jig (centerless ground shaft and sleeves that go thru the carrier, in the diff bearing bores and sleeves that go in the housing end bores).

Just because you're a backyard mechanic doesn't doesn't mean you can't doing things right. Take your chances and what ever happens, happens.

Here's a pic of my back brace jig I made when I back braced my Ford 9" housing, for my Road Runner.





Posted By: 8urvette

Re: Welding a back brace on a 8 ¾, advice please?? - 05/26/12 06:24 PM

^^^^^^^ i like it!
Posted By: jcc

Re: Welding a back brace on a 8 ¾, advice please?? - 05/26/12 08:29 PM

Quote:

The problem you have is all of the welding is being done to one side of the tubes. It's not the heat that causes the warpage. It's when the weld cools, it shrinks, pulling the metal. Hense the reason to use a jig to pull the tubes in the opposite direction.

The correct way to back brace a housing is to mount it to a jig to preload (pull) the tubes towards the mtg. face of the housing. About 3/16" is good. Ideally, you would want to weld the backbrace on then cut and reweld the bearing flanges to make sure they are on center after all the welding, using an axle jig (centerless ground shaft and sleeves that go thru the carrier, in the diff bearing bores and sleeves that go in the housing end bores).

Just because you're a backyard mechanic doesn't doesn't mean you can't doing things right. Take your chances and what ever happens, happens.

Here's a pic of my back brace jig I made when I back braced my Ford 9" housing, for my Road Runner.









You have touched on many valid seldom mentioned points, but, using a jig to try and restrict warpage seldom works, and when it does, the finished item has many and huge welded in place streeses, making an item ready to fail before any racing loads are added, not good. Short of heat stress relieving after welding, which will surely result in warpage, best option imo is good design, no welded gaps (tight fit), go slow, skip around when welding, use a jig to "check" for straightness, and add housing ends on last.
Posted By: FlyFish

Re: Welding a back brace on a 8 ¾, advice please?? - 05/26/12 09:07 PM

Quote:

The problem you have is all of the welding is being done to one side of the tubes. It's not the heat that causes the warpage. It's when the weld cools, it shrinks, pulling the metal. Hense the reason to use a jig to pull the tubes in the opposite direction.

The correct way to back brace a housing is to mount it to a jig to preload (pull) the tubes towards the mtg. face of the housing. About 3/16" is good. Ideally, you would want to weld the backbrace on then cut and reweld the bearing flanges to make sure they are on center after all the welding, using an axle jig (centerless ground shaft and sleeves that go thru the carrier, in the diff bearing bores and sleeves that go in the housing end bores).

Just because you're a backyard mechanic doesn't doesn't mean you can't doing things right. Take your chances and what ever happens, happens.

Here's a pic of my back brace jig I made when I back braced my Ford 9" housing, for my Road Runner.









Very nice setup ....unfortunatly, I've been doing most of my work at night (or at least that is what I would like to blame this on) and after removing the perches and grinding things smooth I realized that the housing is indeed bent. I have no clue how I missed this the first 2 days of working on this thing .

Does anyone know if a MO875 housing with a back brace will clear a stock gas tank on a Barracuda? I think that is the route I'm heading....looks like no racing for me this Memorial day weekend.
Posted By: DemonDust

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 07:26 AM

Quote:



You have touched on many valid seldom mentioned points, but, using a jig to try and restrict warpage seldom works, and when it does, the finished item has many and huge welded in place streeses, making an item ready to fail before any racing loads are added, not good. Short of heat stress relieving after welding, which will surely result in warpage, best option imo is good design, no welded gaps (tight fit), go slow, skip around when welding, use a jig to "check" for straightness, and add housing ends on last.





I just recently did a rear for someone, before I did anything I checked the housing and it was off by 3/16 and this rear was in a driving car. So this just goes to show that just cause the rear works doesn't mean its right. I cut the ends off, do your welding all at once, straighten the tubes after you're done and weld the ends back on with an alignment bar and bearing pucks. This will net you a straight rear and take the least amount of time. Any other method you use will get you close but you are just guessing if it's straight. Like I said just cause it works doesn't mean it's right.
Posted By: EDDIEB

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 02:02 PM

How much does it cost to have a 8 3/4 back braced?
THANKS EDDIE B
Posted By: tboomer

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 02:08 PM

How far are ya from mr.peabody? Raff is a good egg and knows his stuff!!
Posted By: MR_P_BODY

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 02:15 PM

Quote:

How much does it cost to have a 8 3/4 back braced?
THANKS EDDIE B



I get between $200-$225
Posted By: STEFF

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 02:36 PM

Quote:

Quote:

How much does it cost to have a 8 3/4 back braced?
THANKS EDDIE B



I get between $200-$225




I'll beat that price......Just kidding Raff. LOL!!
Posted By: MR_P_BODY

Re: Welding a back brace on a 8 ¾, advice please?? - 05/27/12 02:51 PM

Quote:

Quote:

Quote:

How much does it cost to have a 8 3/4 back braced?
THANKS EDDIE B



I get between $200-$225




I'll beat that price......Just kidding Raff. LOL!!



Thats cutting the end flanges off (IF NEEDED) to true
the housing... using a 1.250 hardened truing bar
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