Part 14 – Rear axle Bracing

[RJacobsen]

After building the reinforcement plate for the rear lower control arm brackets, I decided to make some changes to the way the rear axle was held in place. The standard arrangement is that the center section is attached to the frame with 4 bolts at the top and stabilized with a brace from the rear main frame that attaches to the lower control arm pivot shafts. The original brace is in the next picture.

http://www.uniquecobra.com/gallery/files/1/5/0/5/originalrearendbrace.JPG

I redesigned the rear brace so that it attaches primarily to the new reinforcement plate and also to the control arm pivots.

http://www.uniquecobra.com/gallery/files/1/5/0/5/newrearbrace.JPG

Here’s how it looks installed.

http://www.uniquecobra.com/gallery/files/1/5/0/5/newrearbraceinstalled.JPG

I then made a similar, but shorter brace to go in front of the center section.

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlefrontbrace.JPG

This picture shows the bracket mounts that are welded to the frame, they are tapped for the mounting bolts and located low enough to clear the rear stabilizer bar.

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlefrontbracemounts.JPG

Here are a couple pictures of the front brace installed.

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlefrontbraceinstalled.JPG

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlefrontbraceinstalled2.JPG

[RJacobsen]

Both braces installed.

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlebracing.JPG

After I thought I was done I realized that some hard cornering could produce a lateral load on everything, so to help with that I added some webbing to the front brace.

http://www.uniquecobra.com/gallery/files/1/5/0/5/rearaxlefrontbracewebbing.JPG

I’m pretty sure this will hold everything in place, and maybe it’s a little over-engineered, but I did come across a thread from a forum member that had broken all but one of the upper mounting bolts so I can’t see that this won’t help.

To be continued….

[Slither]

maybe it’s a little over-engineered...



What do you mean... over-engineered? Is that possible:cool:;)?

This will certainly remove the potential of the original to flex[thumb]! (Not that it would.)

I like it Rod, nice work.

[weaver]

Who was the member that broke all but one of the bolts, I have never heard of that happening.

Alan

[eliminator]

I am like Alan, I can't beleive 3 of the 4 upper mounting bolts broke....

I can't beleive you could break 1 of the 4 upper mounting bolts, I don't think were talking about the same think here. I think it was the four bolts , 2 on each side that go into the side of the differential that are normally safety wired. The originals were grade 5 and tapered, the upgrades are grade 8 with a tapered sleeve. And the reason these original bolts broke was because the lower plate that most people have to tie both sides to the differential was not in place.

[RJacobsen]

Who was the member that broke all but one of the bolts, I have never heard of that happening.

Alan

Here's the thread http://www.uniquecobra.com/forums/showthread.php?t=6066&highlight=broken+bolts
Look at the photo in post # 18

Alan, in post #20 he indicates that this was not an installation done by you guys and it is apparent that the wrong bolts were used, but it does indicate that alot of stress can be applied to that area.

[eliminator]

Rod,

The guy used the wrong bolts, with that taper I can see how they broke. The taper is what caused them to loosen up. Plus that bolt is no more than a common Grade 5 if that. And the differntial to the frame was loose and all the load positive and negative created under aceleration and deceleration caused the bolt failure. So "alot of stress" can be easily handled with the proper bolts, hex head, grade 8's with a hardned flat washer, and the proper torque.:)

[Brent]

Another thought may be that the "installer" was a little happy with an impact wrench and the bolts were 1/2 broken when they were installed. To some people "torque" means "tight as can be."

Don't get me wrong, the work RJacobson did looks nice and sure as heck will strengthen things.

[brfutbrian]

the bolts look to me like the ones used by jaguar to bolt the top of the diff to the cage subframe. the scary thing is that the control arm bracket bolts to the diff. with the same looking bolts but in a smaller diameter. enjoy, later, brian

[RJacobsen]

This whole modification evolved from the fact that I didn’t like the way the rear brace was attached to the pivot shafts of the lower control arms. It made sense to me to utilize the reinforcing plate (a part that should be on everyone of these cars) as a solid place to attach to. The front brace just completes the “locking in” of the center section and eliminates any possibility of the frame flexing (not that I think it can). The broken bolts in the other thread are not a common problem with our cars but are a result of improper assembly.:( The Jag rear end, when still in a Jag, has a cage around the entire assembly that holds everything together and the bolts that they use are adequate for that use. When we use that same rear end in our cars, the cage is removed (and the strength that it supplied), we increase the horse power by 2, 3 and 4 times, put larger, stickier tires on and drive them quite differently than we would a XJ6, the least thing we should do is replace the standard Jag bolts with stronger versions. I’m pretty sure that the standard setup from Unique is quite adequate and none of you should feel like you need to change it.:) But for me, I have a welder and a pile of scrap steel and a frame that hasn’t gone to the powder coater yet.:D I would find it interesting if some of the more educated ones out there could calculate the load on 4 half inch bolts in a rather tight pattern with about 12 inches of leverage (the distance from the top of the rear end to the lower control arms) and whatever force can be created by a 2400 pound car with lots of HP.

[weaver]

Your rear bracing probably put you over the 2400 lb mark.

[Jeff 427]

Hey Rod,
Your mod's look really stout and heavy duty.

Are you planning on some serious track time?

[Naumoff]

Great mod Rod.
I have been thinking about something like that for a while. I know the center section moves around in hard cornering as I have had the yoke hit the driveshaft loop. I hope you don't mind if I use your design.

[RJacobsen]

I know the center section moves around in hard cornering as I have had the yoke hit the driveshaft loop. I hope you don't mind if I use your design.

I Don't mind at all Tony, thanks for confirming my suspicions.

[RJacobsen]

Your rear bracing probably put you over the 2400 lb mark.
I might have to put myself on a diet to make up for it.[thumb]

Jeff, I definitely will be on the track with the car. I did a driving school in Vegas last year that really got me hooked

[Jeff 427]

Rod,

I did 30 laps at Las Vegas Motor Speedway last year in a "Mario Andretti" rear engine car. It was a blast!!!! Got up to 157 MPH and the car stuck like glue!!! I followed my instructor and all he kept saying was lets go faster!!! Those banked turn are steep!!!

It should be lots of fun in the Cobra. Take some video for us to see.

[RJacobsen]

very cool Jeff, The class I took was at a road course in Pahrump (just outside Vegas) they used FFR spec racers and Corvettes.

[davebetts]

I've got Grade 9's in with the tapered sleeves. So far so good. I also firmly believe it was the slapping on and off the throttle that created the shearing. Those Hoozier Street TD tires can sure hook up the 560 lbs of torque. Wonder what's the next leakest link in the chain? No more Pocono for me. Done that, been there and I have the pictures for the memories.

[RJacobsen]

Dave, which bolts did you break, the ones that hold the lower control arm brackets to the rear end or the ones that hold the rear end to the frame?