Chassis Rail Straightening
 

Have you been working under your 928 and keep noticing the dents in the chassis rails from inappropriate use of a jack?
After being inspired while reading through this thread https://rennlist.com/forums/928-foru...rrived-65.html, I decided to do something about mine.

You can access the inside of the rails from inside the car via holes in the floor. Lift up the carpets and press on the material that the factory has stuck on the floor to locate the holes, then trim the material and peel it off.

https://cimg9.ibsrv.net/gimg/rennlis...52598c34a7.jpg

I used a bench vice with a couple of pieces of angle iron to press in the sides of the rails before trying to flatten the base. My bench vice is quite heavy, so I used the floor jack to hold the vice up to the rail then tightened it to press the sides in.

https://cimg2.ibsrv.net/gimg/rennlis...45ee64a29b.jpg

https://cimg3.ibsrv.net/gimg/rennlis...a623125920.jpg

After pressing the sides back in I used a hammer and a punch along with a 20mm wide x 120mm long and 5mm thick piece of steel (this will fit through the holes in the floor) to bash the bottom of the rail back down as best I could. You won't be able to do a perfect job due to the restrictions of access through the holes, but I think the steel plate helped with spreading the force from the hammer along the rail away from the hole. It also kept the bottom of the rail flat, whereas the punch would have left round marks in the rail. I also used a 100mm length of 5mm steel rod to try to push out any kinks in the edges of the rails.

Here is a before photo
https://cimg4.ibsrv.net/gimg/rennlis...d0655bab46.jpg

And some after photo's.

https://cimg5.ibsrv.net/gimg/rennlis...074553d8b6.jpg


https://cimg6.ibsrv.net/gimg/rennlis...1702973632.jpg

https://cimg7.ibsrv.net/gimg/rennlis...9bf9a23c3e.jpg

https://cimg8.ibsrv.net/gimg/rennlis...6109cfc63a.jpg

After completing the work I sprayed the inside of the rail with cavity rust inhibitor, and covered the holes with adhesive tape and sound insulation. I need to repair the stuff the factory sprayed on the underside of the car to prevent damage from stones.
A magnet on a telescopic rod (like a portable radio aerial, see photo below) comes in handy when one of the pieces of steel slides down the chassis rail and you need to retrieve it.

Tools Used.

https://cimg9.ibsrv.net/gimg/rennlis...e6c85d1df8.jpg
If you look at post number 970 from the thread I mentioned in the start of this post, I would have preferred to use a tool as big as William's. That's a much more adequate weapon. :bowdown:

As I mentioned before, it's not perfect but it is an improvement.
Maybe someone has some other tips.

That's pretty awesome, G.P.!
Thanks for sharing that idea.


Seth K. Pyle

I never thought these chassis rails were not fully boxed. Now it seems logical because the floor must have been stamped out of one piece. Fully boxed would have been a lot stronger in my opinion. But good work because what you did is a true eye opener

Yes, those rails were not intended to support the car. Many erroneously believe that they are part of the "frame" (our cars don't have a frame), and use them as the jack supports.

I like the idea of the vice to squeeze the sides of the stiffeners while the bottoms are driven down to about where they should be. I made a tool some time ago to do the hammering downward. It is made of about 3/4 inch round bar bent into a kind of seven-shape and the bottom of it, the top of the seven, is milled so that it has a sharp enough edge to fit the inside of the hat sections. The top of the seven shape is long enough to reach to about half way between the holes in the floor. It works pretty well to beat the bottom of the sections down, but the vice looks like a neat way to pull the sides in.

If I could find the tool I made I would post a picture of it, but I don't remember where it is right now.

I did this several years ago on my 928. I cut an H in the floor from above, and drilled a small hole for a punch where there were dents. I then used a string to pull the 1/4th inch thick forward and backward. I then filled the H with lab metal and then installed full pan sound deadening.

Awesome. Thanks for posting G.P.!

Did you happen to take any pictures of this? I have a dent near my jack pad (https://rennlist.com/forums/928-foru...ad-repair.html) that I would like to fix so that I can jack my car up easily again...

This kind of box section damage is quite common, and I must admit I've done it myself before I knew better! I've started cutting un-bent box sections out of parts cars for future restorations..I'm starting to view these like nice dashboards and un-cut console trims.

Whether body-on-frame construction or unibody, I don't care. Use of the word "frame" is semantical. Even on a unibody, so many manufacturers ID parts as being a frame rail, frame horn, inner and outer rails, etc. The word "frame" gets used for both body-on and unibody. Shops charge for "frame" labor, at a different rate, for structural work whether car or truck, unibody or full frame. It's a word.

That is a nice professional looking repair. :thumbup:

Thread clean-up time.

If you guys want to argue about what a frame is or isn't, start a new thread and have at it. Leave this one to discussing the repair of whatever anyone wants to call these parts.

I think this is a very practical method for returning this chassis section to something close to its original form. But I gotta ask, what is the problem that this solution is addressing other than aesthetics?

Same could be said for a large dent in the door :)

It is a painful site when you have it on the lift. I may be anal, but I couldn't live with it either.

It's one of the first things I check when looking over a 928.

Made this sticker a while back , a bit crude, but they get the point when they shove the jack under there !