So as some of you know, i have a 71 Skylark, and a freind of mine owns a 69 cutlass. Both cars are slowly headed into the pro-touring realm. He has the Hotchkis TVS system on his car, and i (just yesterday) installed some summit sway bars on my car. He had a shop do his installation, and i did mine myself. The sway bars went on beautifully, EXCEPT for the front sway bar "U-Clamp" that mounts to the frame and encompasses a D shaped bushing via 2 bolts. Hotchkis provides new bolts, and summit tells you to reuse you current ones. When i took my bolts out, i knew immediately they were unuseable (Ontario car...). I had a hard time replacing them, because they were so corroded it was almost impossible to tell the TPI. The threads were pretty well gone. No biggie, bolts are easy to replace. The threads in the frame were partly stripped as well. I had to jack up the car on each U clamp to compress the bushing, and to alleviate the tension on the threads so i could screw them in. I DO NOT TRUST THIS INSTALLATION although it is holding through normal street driving. Forward to today. The 69 Cutlass went to a light autocross event. All hair pin turns, and maybe 20 meter straight runs, so a max speed of about 50 km/h. After three runs, one of the Front U clamps let go. When he pulled into the pits the bolt was in excellent shape, but it litteraly PULLED the threads out of the frame. Ofcourse the U clamp was destroyed. SO ONTO MY QUESTION THEN: Whats the fix? Is there a threaded sleeve inside the frame, or is it just some threads on the outer cross section of the frame? If it is a sleeve, does it have enough material to be bored out and retapped? I beleive its a 3/8 x 16 thread pattern at the moment. Is it possible to go to 1/2? Somebody must have run into this issue before since big sway bars are so popular.
Incase my description was unclear, the issue is with the mounting bolts that hold on the bushings/mounts below the sway bar in this picture....
I have had a Trans Am 1 1/4" bar on my '70 BBB car for the last 30 years with the Rancho bushings I bought. I am not gentle on my car and LOVE to hang it out in corners, 60's on all corners. I have just a touch of oversteer under power so I am able to make the front end work pretty hard. I think I used header bolts to replace the factory bolts because the Rancho brackets were too large to use a full headed hex bolt. I believe allen head bolts would clear even better. I did grind a washer down on one side to give it a bit more surface to bite. I do not believe there is an insert in the frame but I think there would be room enough to tap it out to the next large bolt size without any problem. Barring that, I suspect you can use some sort of collapsing anchor (similar but NOT a drywall anchor) to make the kind of solid connection you are talking about.
Thats exactly what the cutlass has. Hotchkis supplies allen head bolts, and the washer was ground down. But alas the problem i guess is with the frame. I know exactly the type of anchors youre referring to, they have a special name that just isnt coming to mind. I didnt even think of that if there is no sleeve. Thanks for the suggestion. Open to more suggestions though
Yea i was thinking of using a nut but had no practical way to get it in there (thats what she said)..... :laugh: ANyway, thought u might like to see some pix of the carnage creating event.
If you are not concerned with originality, I would cut some windows in the side of the frame rail to allow access to install nuts with washers on the back side.
We always used these on our fleet of trucks.,which are a different version of Paul's nutserts. http://www.emhart.com/products/helicoil.asp
There's how you fix it: There's a complete article of frame modifications done by the author at his site: Engineered Innovative New Stuff That You Need I haven't done this myself, but it's something that's on the "to-do" list.
I have a nut insert tool kit. The kit that I have has inserts with fairly soft metal. I typically use it for light duty applications like attaching an MSD box to the firewall, etc. I am not sure they are strong enough for the kind of loads that the sway bar will put on them.
i drilled & re-tapped the frame with a metric tap a little larger than the original bolt size & the replaced with a grade 8 metric bolt. that was 8 years ago.
So we happened to be filming the car when the break happened and we noticed a few things; My freind pushes the cutlass pretty hard in the corners, but i loaned him my 17" wheels with Falken tires (really soft compound) for the autocross. Normally with his 15s the rear end would swing out and that was it, but with the 17 he had a ton more grip which tested the limits of the bolt threads. Upon further research, Hotchkis aparently has a solution for this problem, that they include in the TVS kit for an additional price. We dont know what it is yet, but will find out shortly after a phone call. Failing that, we will go with the recommendation Phil posted by welding a plate on the frame. Kind of concerned about how this would affect the geometry or the suspension preloading though. The holes will be enlarged and retapped with either a metric tap or a 7/16 bolt. Ill post pictures when this happens, but likely wont be for a while.
