Carrera Sway Bar Mount Repair and Mod

MotoSook · 11:14 PM

I've been putting off repairing the "Fat Bastard" for nearly a year. It's been needing a top end rebuild and suspension work. I got tired of not having a running 911 (both "Bastard" and "Fat Bastard" are out of commission!) and wanted to get back to the track....

I was hoping to get it all done in a week and make a DE....nope..didn't happen...one thing led to another and here is part of the repair.

I completely tore off the driver's side sway bar mount and the passenger side was about to go. The PO had the passenger side repair at some point, but it too was starting to tear again. So I made a more permanent fix.

Driver's side:

Passenger side:

I left the opening on the mounts so I can shoot some sealer or coating on the inside. The mounta seem to tear from the outside in starting at the welded on M8 nut. And as long as I added metal to the outside so forces couldn't pull the nuts off the mount, I'm not worried about the opening. I can weld it shut later. You might see a little of the tear at the nut on the passenger side before I welded it up. Bits were missing from the driver's side.

Anyhow, with some 1/8" steel. my grinder, wire wheel on my drill and the welder I got to work....

I cold galvanized the metal after these pictures were taken, and I still need to grind down some of the welds before I put final dressing on the metal. Hopefully I won't get stuck at the office and get home to late to finish it tomorrow...I'll post the finished product them...

MotoSook · 07-25-2006, 10:33 PM

Too much of this was the reason

MotoSook · 11:07 PM

And the reason why it all had to come apart.....which led to all the "while you're in there stuff!"

Jeff Alton · 07-25-2006, 10:52 PM

Souk, those heads all from the same motor??

Cheers

MotoSook · 07-25-2006, 10:58 PM

Yep...I was running on 4 cylinders in the mornings. It was loppy until the #2 and #5 cylinders got hot and expanded enough to hold compression for combustion. I was probably running with some horses asleep in the engine

Alusil jugs...and bad valve guides don't make for a happy horse farm

sjanes · 07-26-2006, 05:27 AM

Souk,

I've torn off 4 of those rear sway bar mounts on my 87. The combination of a stiff rear sway bar (TRG adjust) plus 255 R compound tires is more than they can handle. I broke the factory one, broke the reinforced factory one, broke aother reinforced factory one that we added extra reinforcements to, and finally, we came up with one that wouldn't break and it started to crack the pinch weld on the frame that it was welded to.

I now use a mount that bolts around the torsion tube that I got from my mechanic (who tried to convince me to buy it two broken mounts ago). It's designed to add a rear sway bar to the early cars that didn't have one.

MotoSook · 07:36 AM

sjanes:

I suspect I'll be under there again in the future

As you found out, all the welding did was transfer the load to another weak point. WEVO makes a nice mount that's casted and looks to be the strongest solution out there as far as replacement mounts go, but as in your case...something else will tear. I guess we should go slower...NAHHHH

I've seen the Weltmester sway bar mounts for non-sway cars. It's probably something I'll try later...or I'll build something similar .... but better

I was running 265 R compounds....so I had plenty of stick. I will come up with something better when I'm bored, but I needed to get the car running and back on the road again w/o the EPA coming after me. So the engine is waiting to go back into the car...and I got to practice my welding a little more

Now when I tear the mounts off...I know I'm not alone

Guavanecta · 07-26-2006, 07:28 AM

After three torn stock mounts, I went the way of WEVO.

MotoSook · 07-26-2006, 07:37 AM

Nice Ted. Is that POR-15...the gray stuff?

89911 · 07-26-2006, 08:00 AM

Quote:

Originally posted by sjanes
Souk,

I've torn off 4 of those rear sway bar mounts on my 87. The combination of a stiff rear sway bar (TRG adjust) plus 255 R compound tires is more than they can handle. I broke the factory one, broke the reinforced factory one, broke aother reinforced factory one that we added extra reinforcements to, and finally, we came up with one that wouldn't break and it started to crack the pinch weld on the frame that it was welded to.

I now use a mount that bolts around the torsion tube that I got from my mechanic (who tried to convince me to buy it two broken mounts ago). It's designed to add a rear sway bar to the early cars that didn't have one.

I broke and repaired mine before those nice WEVO replacements were available. The shop added a nice bracket to trianglulate the mounts. I also run 255 r compound with 31mm SRB's and broke them several times before this was done 3 years ago. Since then, no problems.

Guavanecta · 07-26-2006, 08:08 AM

Yep...three coats of POR-15. Lovely overkill.

sjanes · 07-26-2006, 08:29 AM

Quote:

Originally posted by 89911
I broke and repaired mine before those nice WEVO replacements were available. The shop added a nice bracket to trianglulate the mounts. I also run 255 r compound with 31mm SRB's and broke them several times before this was done 3 years ago. Since then, no problems.

Looks like a nice solution. Wish I thought of that with my last set. The second set I broke (factory reinforced ones), I pulled the welded nuts (that the sway bar mount bolts to) through the mount. Mount was 2 months old

mb911 · mb911's Garage

Souk,

that looks great.

Mine is torn as well And I have been thinking of what to do for a while as it has not been high on my to do list but needs to be. Question for those of you in the know. Does the wevo mount really solve the problem? Or is it just a strong mount making a problem somewhere else?

Anyhow looks great

sjanes · 07-26-2006, 10:28 AM

My last mount (not a wevo) was strong enough to move the problem to the pinch weld on the frame and cracked it. The guy that welded it back together said the metal on the frame was good and it just cracked from fatigue.

MotoSook · 07-26-2006, 07:24 PM

I don't know what size t-bars you all are running, but I suspect that we are relying too much on the sway bars and its mounts to handle the track forces. I'm running stock suspension on the Fat Bastard, but if it were to be my main track car, I would go up a few sizes on the t-bars. That should help (along with tighter shocks) a lot with the body roll...without relying on the sway bar so much.

My problem after this fix will probably be the nuts pulling out. A problem the Wevo mount should prevent from the looks of it. Coupled with bigger t-bars and tighter shocks the Wevo mount should prevent problems....except for some extreme cases.

Anyhow, here are some better pix of the mount after tonight's work. I'll put one more coat of paint on them then put some sealer along the seams before I am done.

Driver's side:

Passenger side:

Cory M · 07-26-2006, 09:36 PM

I went with the Wevo mount. The one that failed was a reinforced factory mount, as you can see in the pictures the reinforcement didn't help much at all and the bracket tore off some of the body sheetmetal when it broke. I had to repair the sheetmetal before I could weld on the new one. I thought it was going to be hard to fix but it was actually pretty easy. I was glad to do the work on a lift, it really would have sucked to do it laying on my back with hot sparks and slag falling down on me.

Jeff Alton · 07-26-2006, 10:46 PM

There are two different failures of the mounts, both seen here. Some tear the mount right off the sheet metal and other tear the mounting nuts out of the mount. I did the latter twice. I think 89911's cure should work as it will reduce flex in both areas.... Of course if you have to replace them, the WEVO ones make sesnse!

Cheers

MotoSook · 08:19 AM

After reading all the posts and looking at the pictures, I think the big problem with the mounts is flex. On the track there are lateral components of the force on the mounts that over time weakens the metal and welds as the mounts move (flexes) . So even if I added more material to my modified mount, it is a matter of time before the thing rips away from the chassis as Ted and Cory found out. I like the brace that "89911" has on his car. That will help with the lateral force (components).

Cory's last picture has me wondering if the Wevo mount won't one day rip away from the chassis (with the mount intact!). With the spacer on there, it increases the magnitude of the lateral force (or the lateral component of the force) on the mounts.

My post about t-bars is still valid. But I will be adding some material under the welded in nuts and adding a brace that's welded to the mounts and the t-bar tubes...like "89911" has. Hopefully the only problem I'll have after that will be the threads on the nuts and bolts...the next weaker component(s).

Cory M · 10:31 AM

That lateral brace could help prevent the mount from deflecting and could strengthen the area if your welds are good enough. I would probably use a piece of metal with a C or V shaped cross section so it would be stiffer and less likely to deflect or buckle.

I also considered the Wevo mount being too stiff and tearing off at the chassis sheetmetal. I thought about it a lot and looked at several failed mounts before I decided to go with the Wevo one. The vast majority of the failed mounts I saw failed by pulling the nuts out or cracking at the bend like yours- the Wevo bracket does a good job of reinforcing this area. I believe it is possible that the Wevo bracket could fail by ripping the sheetmetal off- but I think it will take a really long time for this to happen and I could probably spot the cracks and do something about it before it ultimately failed. If it did fail again I would patch the entire area with a thicker gauge sheetmetal and probably use a stiffening plate with a bunch of plug welds like the 914 chassis stiffening kits.

Those spacers were put on by the prvious owner to give a little more trans clearance and to allow the bar to rotate freely- they hung too low and I removed them when I put the bar back on the car.

I was running my bar at almost full STIFF* and my torsion bars are pretty stiff, but putting wide 315 Hoosiers and pushing the limits on banked turns, over kerbs, etc will put much higher loading on the brackets then the factory ever anticipated and stuff will break.

I was really impressed with the Wevo bracket, I think it is an
excellent product.

*edit

sjanes · 07-27-2006, 10:26 AM

Souk,

I completely agree with the statement that we are using too much bar, not enough spring. I run a 30 in the rear, and I should increase it. FWIW, here's a pic of a mount sans nuts:

Cory,

My last failure was the chassis sheet metal cracking itself (starting at the pinch weld). We (my mechanic and I) checked the sway bar mount before the event, and didn't see anything (although there was probably cracking starting under the rustproofing stuff). After the event, the crack was about 4" long and open enough that I could stick a popsicle stick into it. Once it started, it cracked pretty quick.