So we are getting ready to start bolting Kirby's Trans Am together, but we were concerned about the rear axle. I had an 85 Camaro years ago that was a 12 second car and luckily the 7.5 rear held up. Kirby's Trans Am will be at a completely different build up level.

Kirby's Trans Am is a 91 Trans Am that he found with a full cage, nice interior and flawless, straight body, will need paint eventually, but has NO RUST whatsoever. It had been drag raced with a fuel injected Vortech blown motor prior, so there were some cool things in the car already, gauges, bottle mount on cage etc.

He will be running a carbureted blower on a 383 and a T56 so we thought that before dropping that in, we need to do the rear. The car will also have 250hp of juice if and when he wants to finally send the crankshaft into Route 93

As quite a few people have posted about rear end swaps, especially 12 bolts we wanted to document the build here so others will know what needs to be done.

Here is the car as found, was in Rhode Island and the guy brought it up to Kirby after a deal was struck.



ugly seat covers over perfect seats






383 - Dart Iron Eagle 2.05 valve heads

 

Here is the 12 bolt that someone began to start building as a swap for a 3rd generation, we will still need to add panhard rod mount and fab the torque arm mount but it is already pretty close. We may also change the spring mounts as we are not sure if the person fabbed them up 100 percent right.

The rear is from a 69 Chevelle, which is about 1/2 inch narrower, what makes this a nice candidate for a swap is the factory upper control arm mounts that are cast into the center section of the housing. This will make it easier in fabbing the torque arm mount, we will use one or two of these upper mounts as part of the anchors. A new bolt in would cost $2400 and though is worth it, where is the fun in that? and it is a lot of money

My dad and I came across the rear, then coupled with some other stuff we had laying around Kirby is starting with the following.

12 bolt housing with caliper mounts in place
4:11 gears
3rd gen rotors, recently turned
Extra set of backing plates
Single track center, that had a spool and 6:14's!
3rd gen calipers
$225 so far

 

 

 

I have to admit that I HATE the idea of a Chevelle 12-bolt being chopped for use in one of our cars...........but hey, if you bought it already modded I can't give you too much **** for it!

I've been interested in TA mounts using the upper 4-link mount for a while now. I'd say the lower part of the TA mount should wrap around and use 3 or 4 bolts of the diff cover and or extend some tubing out the side so you can weld it to the axle tubes.

 

yeah, Chevelle rears are desirable, but they are not as rare as say a 12 bolt for a 67 Camaro with single traction bar...plus this one was already modified, though needs more work. We will post pics so that people can follow the build.

 

We will likely use the upper control arm bolts along with anchor brackets from the tube and with holes drilled through the case.

 

Worked on the rear axle for awhile today, went in a different direction than originally anticipated, i built a girdle that will bolt through the cast iron ribs and also will have some serious brackets to go from the girdle up to the Chevelle control arm mounts. I feel that a girdle that is tied to each other and the housing in various places will work best.

I didnt fab up the torque arm bracket yet, but jut for some steel over to the general ballpark to work off of.

I also had some problems with my regulator and tip on the welder, so didnt have the best welds, which is usually my strong point.

I used scrap angle iron and left over center loop from a drive shaft loop.

Once all done, it will be smoothed out, welds will be hidden and will be sprayed gold to match the other rear components.

Panhard rod coming out of donor housing


12 bolt housing going to car wash for a bath...we are going to cut off all the brackets the guy welded on and start from scratch

 

Stock rear






Clearancing loop to fit housing

 

Clamped each piece to housing during welding

 

Notched ends at angle to allow to get at nuts easier, this is one of the points where the girdle will bolt through the cast iron ribs. believe it or not, would have still had pretty easy access to the nuts but notching it will make it even easier.

 

One u bend cooling down after holding ends over


I only use extra strong clamps haha

 

The existing bolt holes in the driveshaft loop will be one of the mounting points through the case.

 

All the edges are now rounded on the ends of the angle iron

 

Fit very tight, took a couple hits with the hammer to knock it off

 

I thought you were going to tie into the upper 4-link mount?

 

I am....I mentioned that above, it will have additional brackets welded to the girdle, that will then bolt on to the top control arm mounts....

 

Sweet

 

Here are the upper braces that will bolt through the control arm mounts, tonight I am going to build a cross brace from one of off the upper brace to the other

 

Some of the inside welds

 

Kirby has the day off, so he is in his garage spraying up the control arms, definitely going for a little bit of a different look, rather than red and black like everyone else, this will have some styling cues classic Trans Ams...all accessories will be a Trans Am type Gold such as control arms, panhard rod, calipers, backing plates.....the rear axle will be Tyrol Blue!

 

Here is a shot of a control arm

 

I'm all for DIY modifications but when it comes to steering and suspension, some of the stuff I see really scares me. I wish your mounting bracket was made with minimum 1/4" thick steel. Drilling holes and bolting it to the cast flanges of the case will be bad enough.

 

yeah, I am not too worried, I have seen a lot of people who have drilled cases with no problem for various reasons including similar swaps on the LS1 Tech forum..basically the girdle itself encapsulates the case, the bolts will merely be tie downs and the top control arm bolts should carry a lot of the load. This will also be getting a lot more reinforcements before it is done, this is basically a mock up to work off of - may add supports from axle tubes as well.

I have built a lot of cars, worked at a speed shop for many years, but thanks for the feedback

 

Still need to make up torque arm mount and will do some other reinforcements

 

That is one hard core mount. I made my rear also and it is no where near like what you made. I thought also to tie into the arm loops, but really could not come up with something I liked, but I do like what you are doing. I may just take it out one day and modify mine over to something like what you are doing. PS, if you find a good deal on LS1 rear brakes, they bolt right up to that rear with a little shimming, that's what I also did and they actually work properly unlike my old factory ones.

 

Thanks for feedback, did you swap a 12 bolt into your car? do you have pictures of what you did?

Would be good to see pics, as for the brake parts, this rear is going into mt91ta's car, he may be interested? we do have third gen brake stuff, that will also bolt on with a washer width of shimming, did this same swap when putting third gen brakes in my 67 Camaro.

 

I wish I had pics of what I did, but for whatever reason I did not take any. I'll try to explain what I did the best I can. I started off knowing my umi torque arm separated, so I could use the mount as part of the overall mount on the rear in the finished product. Measured everything out on the donor rear I had out of my parts car using the stock arm so I knew where to drill two holes in the webbing of the 12 bolt. After that, I used some round hollow stock my dad had laying around to use as spacers between the mount and each side of the webbing. Measured and cut those down and the back bolt was done. For the front, I used two pieces of 1/4 angle iron to go across the pinion (top and bottom) and end roughly about where the center of the webbing is towards the back of the rear.(if that makes sense) I had to trim down one end of the angle at the mount side and drill holes so I could slide them under the mount on both sides and again use the round stock to shim in between the pieces so it could be bolted up. The back round stock did not get welded, but after assembled, I welded the round stock to the 1/4 plates to finish that. On the other side, I used two pieces of 1/4" angle iron again to go from the end of the other pieces back to the webbing, sort of like the mount side. I drilled holes in the webbing roughly where the angle iron ended up and in the angle iron. Then using the round stock, I cut and put them in as sleeves for the bolts and bolted it up. Where the pieces come together on the opposite side of the mount, there are two 1/2" grade 8 bolts tying them together with some more of the round stock between the two pieces. I hope I described it well enough what I did. It held without any probs or noise with my old slicks and crappy 1.7 60' times after around 15-20 passes.

 

thanks for the information...when you can, be great to see some pics as I am sure it could help out a lot of people who want to do this type of swap, let me know, thanks, Tim

 

I will post some pics next time I have it in the air.

 

thanks, I am going to make a brace that will bolt to the axle tube via a flange and will be welded to the girdle. Should help pick up some strain, just want to over do it, rather than under do it....will see a lot more reinforcements before it is finished.

 

At the suggestion of others here, I thought it wise to beef up the girdle a bit more, added a brace that mounts to the axle tube, started out with a Moroso Solid Engine Mount. This should provide ample strength and allow it to unbolt easily.

 

Steel tube to be inside into the box tubing being fitted

 

The box tube is welded to the main part of the girldle, the plate it is welded to is 1/4 inch, the rest of the girdle in the area of the torque arm will also be reinforced before it is finished

 

Looking at it further, did you make sure you have enough room for the torque arm in the tunnel? That side piece seems to stick out further that the stock one would have and I know there is not a whole lot of side to side play with the arm and clearance in the tunnel.

 

Oh yeah, will be fine and if needed we will clearance the floor a little...the angle iron rests on the case, so is not any further out really - may also change some things about the torque arm, recently I have been looking at a lot of rear swap pics and often people have their torque arm out much further than stock in regards to where the pinion is, we are going to make this one as close to stock as possible, the whole tail section in the torque arm area is likely going to be snipped up and reworked in order to make it in the closest possible, to stock

 

Just found this post, similar set up as it is a cast iron case 8.8 - check this out

https://www.thirdgen.org/forums/tran...arm-mount.html

 

Kirby cut off all the Chevelle brackets and was about to cut the others off the old housing, then he thought to call Hawks....turns out they sell all the mounts, heavy duty ones made by Moser as replacements, so they got all the mounts, spring seats, panhard mount etc, sending it all to us for like $100 bucks!

A lot less work, heavier duty mounts and are also made to fit a larger diameter tube like that of a 12 bolt or 9 inch.

Here is a shot of it after Kirby cut the mounts off, we are going to use 85 style backing plates, which will bolt on to the 12 bolt, so he still has to remove the caliper mounts that the people who owned the rear before hack welded on there.

 

Start to finish all parts, materials, including argon, welding wire, PPG Tyrol Blue paint, posi, 4;11s and new Alloy American Made axles, wiill be into the rear for $1000, more than originally thought but still a great price for a complete rear with all new bearings, tubular control arms, new bearings etc.

 

Cut off the hacked up caliper mounts, going to use bolt on Iroc/Trans Am backing plates

 

Welded both tubes at the case

 

New mounts just came in through Hawks, from Moser

 

Panhard rod that Kirby bought and did up to match control arms

 

Another shot of the mounts...need to add shock mounting tabs

 

In keeping with the throw back, old school look, Kirby picked this up today, brand new but has been sitting around. Off Craigslist for $20.

 

Starting to strip housing

 

 

Panhard rod moutn kit by Moser, Kirby got it from Hawks

 

We found the center of the Chevelle axle and worked off the centerline, making sure to check the width of the spring seats and all angles, left and right side are actually different, easy to mock up with degree gauge.


The straight adge was clamped in place, acted as our guide, this spring seat will get a brace below it to beef it up

 

Kirby with panhard rod mount