Hi All

I have one jack pad on my car that has been deformed by a floor jack. As from the pictures attached, one sees that the lateral support running over to the side of the frame rail is depressed, thus moving the jack pad to a position in which it is not flat. The fact that it is not flat is rather annoying and is not optimal for jacking.

Has anybody ever attempted to repair something like this? I don't mind doing mechanical work, but I have no good skill to do any kind of body work much less frame work.

Thanks in advance for any comments on such repairs.

John

 

John,

Sorry they all get squished. Sucks that shops can't be more careful. I bought an adaptor from Pelican parts several years ago and have not had any problems at home but still find damage after typical oil changes and other shop visits. The jack adaptor is no longer available.


Michael

 

Thanks, Michael. I figured that most people would kind of say what you said. On the other hand, some people have actually tired to repair some jack mounts. I remember comments from Dr. Bob and Sterling, but with the search function I could not find them. Oh well, I will try to look again...

 

Are you planning on doing the work yourself or farming it out to a shop?

 

I would definitely farm it out. But, I would only have the work done, if I think the repair could be done without causing more damage.

As it is currently, with the later model Porken Liftbars with the centering rings, the car can be lifted. The earlier model liftbars without the centering rings would scare me though.

 

I've successfully knocked down damage to the frame rails, using a piece of flat welded to a 16mm rod, to form a 'foot'. You insert the foot through the inspection holes already in the floor and it allows you to knock the damage back down. The foot end allows you to broaden the impact point, and also to apply the impact forward and back from the access holes. If the foot is a reasonable length, and thick enough, you can get a good result. The flat forming the foot needs to be as wide as will just fit through the inspection holes with minimum clearance.

In locations where there aren't access holes, you can drill a 1" hole over the damaged area, and fit it with a rubber plug afterwards.

You need to have a reasonable knowledge of how hard to hit, and where to place a dolly, just like in other panel beating.

For the damage you've pictured you're going to have to use the technique I've just described from above, in combination with pull of the jack pad bracket to the outside, and knocking the outward bow of the lateral sides in as you progress, to allow the damage to return.

You have to picture how the damage progressed, and apply impacts and pressure to reverse the sequence of movement, to avoid stretching and distorting the metal more and making it worse.

 

I'm not sure I ever contributed anything on this subject. That might be why search didn't find anything.

The only sure way to get the pads correct might be to cut the old one off and weld a good donor piece in its place. While it's certainly possible to straighten the existing pad, the metal is weakened and would be subject to bending again with even less force. A good body shop can do the surgery for you. You'll remove some interior trim above the weld area, and will want to do some rustproofing depending on how/where they do the welding. If they cut the old pad off with some existing metal remaining, the donor pad gets welded there rather than to the tub itself. Stitch weld with a MIG, and you can manage the heat that passes to the tub better.

I'm not sure how garage lifts manage to damage these. Much more dangerous to them is a floor jack, where the forked cup on the end of the jack applies pressure unevenly when not centered under the pad.


You can make your own protectors to use between the jack and the pads, using one or two hockey pucks and a screw-on furniture foot. Pick a furniture foot that will just fit in the hole, and screw it into the middle of the hard rubber hockey puck. Drill a small pilot hole in the puck and lubricate the screw with a bar of soap. Whether you add another puck depends on how deep the cup on your floor jack happens to be.

Keeping the jack pads in reasonable condition may not seem critical right now, but it will become so the first time you find yourself on the side of the road somewhere, trying to use the factory jack to raise the car. The business end of the jack indexes in the hole in the pad, and without that function the car is extremely difficult to raise and very unsafe to work on. Owners would be wise to do a "test lift" with their factory jack in the comfort and safety of their home garage, so they can verify the fit and function of the factory jack. One of my early 911's way-back-when was a challenge, so I added a decent aftermarket scissors jack to the toolkit. I think I still have that jack, though the car ('76) is long gone.

 

Here's a pick of my adaptor, lost the rubber ring.






Michael

 

What people too commonly refer to as the "frame rail" under the floor of the 928 is actually just a floor stiffener. That is where most of the jacking damage occurs because it us just stamped out of sheet metal and not intended for jacking. That is why there are specific jacking points designed into the 928 body that don't get used like they should be.

For the subject damage to the actual jacking point (and I can't quite understand how it happened) I would first investigate what the point is like inside the pilot hole. If it opens up up inside like one might imagine that will give one a place to pull on the inside of the point to pull it back down. If there is no place inside the point to grab onto then my whole suggestion is moot.

If the jacking hole opens up up inside then I would take some measurements and machine a steel flat bar slightly narrower in width than the opening but as much longer than the opening as will lay flat up inside and just above the hole. I would round the ends of the flat bar. Then I would drill and tap a hole in the middle of the flat bar for a 1/2x13 thread, and I might even turn some groves in it that will match the upper edges of the flanges that appear to be formed upward into the hole.

Next I would recall for myself that the frame of the 928 is actually part of and inside the door sill/rocker panel area of the body along the bottom of the door opening. The frame is actually inside that area and consists of a longitudinal member that is very heavy steel and is captured in the sheet metal welded along the top in the door sill and along the bottom flange outboard of the jacking point. I would measure the thickness of the flange along the bottom on the under side of the car and outboard of the jacking point, and perhaps the depth of the flange, but that is not important, I don't think, and then I would obtain another piece of steel flat bar at least a foot long and perhaps 16 or 18 inches, and about 1 by 1 1/2 inches thick and I would machine a groove in it to match the frame flange all along the narrow side of it its full length. That I would intend to be using as a fulcrum for the lever that I would be devising to pull the jack point back down.

Then I would obtain a long piece of steel box tubing about 2 by 2 and at least a quarter inch thick and about 12 feet long. I would drill a half inch hole near one end that I could put a half inch bolt thru. I would also obtain the bolt, if I didn't already have one and it will be about 4 inches or so long--maybe only 3 or 3 1/2 inches long. Then I would put the first piece I made longways through the hole in the jack point and push it up inside so that it can be turned longways and then lay back down up inside across the jack point opening and would be laying snuggly on top of the inside of the opening. That should expose the threaded hole in the center of the opening. Then I would bolt the end of the long box tubing through the opening into the pull piece that is threaded.

Then I would place the long piece of steel bar with its groove along the frame rail flange with its center located opposite the jack point opening in such a way as to become the fulcrum for the long box tube that is now our lever. I would adjust the bolt some to get the components positioned so that I could lift the long tube at its outer end that is now about 10 or 11 feet from the door sill and I would lift it carefully is such a way as to pull the jack point back down where it ought to be. I feel intuitively that the frame rail we are levering against is stiff enough to resist the force which will be transferred to the jack point, and that it will be the jack point that bends and not the frame.

I suppose one might use a shorter lever and lift it with a jack, and that might be more precision in terms of gauging how much to lift and bend or straighten. Still, this all depends on the ability to put something similar to what I have described above up inside the jack point opening in order to pull downward.

Just my 2 cents worth.

 

There are certainly ways to pull the old pads back down, and Jerry describes a good one. In my experiences with other cars and similar damage, I've found that once damaged and weakened, the 'straightened' pads will un-straighten themselves again at the first opportunity.

If originality is important, I'd harvest some good pads from someone's parts-car tub that's otherwise headed for the scrapyard. I'll speculate that Mark Anderson has sent a few and continues to do so, and the pads would be available. If from a donor, have the whole section of the tub cut out so you can do the the cutting-wheel surgery yourself to match the profile left when you cut off the bent pieces.

If you are working with a good fabricator, it wouldn't be tough at all to box the pads on the remaining two sides that are just rolled with a lip. That would add some stiffness, and might possbly be a solution for 'straightened' original pads.

Carrying Jerry's repair process a bit further, consider that you can make wood 'fillers' that are matched to the tub profile ahead of and behind the pad. Build the plate he describes to fit inside the deformed pad, threaded for a bolt in the middle. With a piece of channel channel as a bridge between the filler blocks, use a Porta-Power hollow hydraulic ram with the bolt into the pad plate. That way you can just pump the Porta-Power ram to draw the jack point back down straight again. I'm sure there are other ways to get the pads bent straight again, just consider that they are weakened after they are bent and re-bent a few times.

 

Jerry, thanks a lot for those thoughts. I have to collect some ideas here. Maybe I take the car some time to the best shop I can find and ask them some more opinions.

My intuitive uneasiness is exactly what Dr. Bob clearly noted though. Probably, once bent they are permanently weakened too much. It's one of those situations in which the best solution is too just ignore it maybe.

The only reasonable action might be to fabricate for the this bent jack pad and the rear jack pad a permanent "custom" adapter that will allow me to use the Porken liftbars safely.

The front adapter would have to compensate for the bent pad and the rear adapter would just be a spacer so to say so that the lift bar is really flat.

Thanks again both of you.

 

After I posted my suggestion above I studied the OP's pictures a bit more carefully and I also went and looked at my own 90GT. Based on what I learned this is the front jack point, and I was thinking more about the rear one when I wrote what I wrote, and the frame of the 928 at that location is inboard of the jack point rather than outboard. Based on that, much of what I suggested is pretty much out the window. But not all of it.

In other words I think a similar lever can still be devised to do this but it will be revere from my previous idea in that the fulcrum will be on the end and about 8 inches from the pull point. We will be pushing down on it rather than pulling up. Too, the fulcrum devise I described will need to be similar, but only about 6 inches long.

The other major difference will be in the pull down devise. The inside of the pilot opening of the jack point is more of a cup than what I had in mind, so the piece I thought might fit up inside and rotate to pull with will not work. However, the metal that the outer part of the jack point is made of has a gap running between it and the frame member just above so some kind of devise can be fabricated out of heavy steel that will slip into that gap all along the jack point and also outside the jack point to at least the center of it and then with some kind of way to connect it to the lever. It will be kind of like a C-clamp but with a very very narow clamping range, or more like a question mark made in the style of the font that we see "928" made in = wide and narrow.

When configured and installed one should be able to push down on the lever and pull the jack point back into position. Given that the whole area that is now deformed and will not likely be returned to its original shape that is where there might be some residual weakness that remains, but on the other hand working this metal the little bit that we are going to do will actually work harden it some more and make it slightly stronger. I suspect that will offset; so I would not be too concerned about the end result from that standpoint.

Another 2 cents worth, or less.