I had a local Pelicanite to suggest Elephant Racing's adjustable spring plates. But as I look at it, this is a band-aid approach, and a very expensive one. As was mentioned earlier in the thread, I have SC aluminum banana arms and their companion adjustable spring plates ready to install. If these steel arms/spring plates don't work, then their replacement isn't going to work either. And besides, I need to justify this lift in my garage, and that PortaPower from Harbor Freight, and my new welder, and............. :D

On the subject of how the tube may have been bent... I found some previous damage to the car (after the car was bought at a good price, not complaining), that suggests the car may have been hit in the area of the right rear wheel. Dent on the inside of the fender well, dent in the oil tank. If the rear wheel had taken a lick here, due to the geometry of the banana arm and spring plate, it is easy to see how this could have bent the tube, just enough to cause the problem I'm seeing, but not enough damage to the torsion tube to be seen with the naked eye.

Pretty much exactly as I predicted at the top of this thread.

While the ASP could compensate for the this problem, I'd rather see you fix the problem correctly - bend the tube back into place.

Then buy the ASP just because it kicks-ass ;)

Chuck,

That sounds like a biased opinion. :D

PS. I finally got the camber max I bought opened up to fit the 935 spring plates. Bad thing is I have not had time to finish up the work on the car yet.

While I don't think tightening up all the adjustment bolts at the limits of the toe settings, combined with hard Delrin bushings, would be capable of imposing flex on the torsion bar tube (seems as the spring plate bushings would nullify this), I have to wonder. I suppose while I was beginning the disassembly process, I'd just double-check the measurements on the plumb-bobs after decoupling the spring plates and trailing arms. Just for grins, as it were.

One other thought - especially if this car has been hit - while everything's apart, definitely double-check the inside of the torsion bar tube. They often show no outward signs of cancer. However, if you pull your torsion bars and then give a squirt in one side with an air line, you may be very surprised at what comes out the other side...

Fascinating thread, look forward to hearing how this works out. Good luck.

Chuck,

Here is a puzzle on the measurements of the torsion bar tube now that the engine/transmission has been removed from the car. Using the same method I used to measure with the engine in the car (getting 7/32" apparent bend), I now get only 1/8"! I have done this measurement 3 times, and it repeats.

All I can make of this is that the engine/transmission unit had deflected the torsion bar forward. When I installed this engine, I had to work at getting the rear cross-bar holes to line up with the engine mounts, by using a 2x4 to lever the cross-bar forward until the bolts would line up.

I really can't see any way that jockeying the engine into place could have caused that sort of movement in the torsion bar. But, this my first experience with this sort of thing.

Is 1/8" worth a try at bending the tube back to zero?

Here's another update:

I put the PortaPower across the ends of the trailing arms again after removing the shocks, so the PP could get a better bite. I decided that since I was going to trade the steel bananas for the aluminum ones anyway, I would spread the steel ones out until the torsion tube came in line, or something broke, or the PP ran out of pushing power. I did the latter. When I couldn't pump anymore, I quit. Now when the PP is relaxed, the plumb bob setup says the tube is straight.

But I don't know whether to trust the tube to stay there when I swap out the bananas. I'm thinking I've got nothing to lose but time, so I'll probably go ahead and see what happens. It might be a good thing to pull the torsion bars and check the interior of the tube while I'm at it.

Comments are still welcome at this point, but it may be a few days before I have anything new to report.

Hmmm... Given the flexibility of the rubber motor and transmission mounts (you aren't running solid mounts are you?), it seems difficult to believe that you would develop enough preload with a 2X4 to cause the torsion tube to deflect...

How about the measurement of the engine\trans from the trans mounts to the engine mounts? Could that be out of line at all? Still, the mounts would only exert a force with very little moment on the tube...

I guess I'd check the distance between the engine and trans mounts and try to find something to compare it with for a sanity check. Keep us informed,

ianc

I'd definitely measure across the trans and engine mount holes, and as long as you at it, pull the tb's to have a look. Heck, you've come this far. You might be able to figure-out a way to put a straight bar through the empty torsion bar tube, center it at each end, and use it as a reference for straightness. Just a thought. Great thread.

I have the banana arms ready to drop. The spring plates are disconnected, have been pulled from the torsion bars, and the torsion bars have been removed. The torsion tube is still straight and sighting through the tube, no visual evidence of a bend, and no evidence of rust. I have one Delrin bushing out of the torsion tube. It took about 45 minutes with a saw blade to cut a segment (by hand!) and then pry the segment out. I tried a propane torch to soften the bushing, but to no avail. Toughest "plastic" I've ever seen.

I am making measurements of the engine and transmission support locations on the garage floor using the plumb bob. I want to see how they compare with the info in the Porsche workhop manual. So far, they indicate that the right rear mount location is a 1/2" to 3/4" forward of the factory spec. I will continue measuring all 4 points with relation to each other, and compare with a generated center line, and transfer this to a drawing I can post.

I want to be able to put the engine/transmission package back into the car so that it only has to be raised into position and bolted in place, with no stress at all on the torsion tube. If the chassis mounting points are a little out of whack due to a previous hit, then I will modify the engine mounting bracket to compensate.

I am also giving some thought as Doug (DW SD) suggested earlier that some supports be welded into place to hold the tube where it is. Now would be the time if I'm gonna do it. Some added stiffness couldn't hurt things as I see it.

Not sure how much this will help, but here is a pic I downloaded when I was asking about doing some reinforcements to my car.

http://forums.pelicanparts.com/uploa...1197596578.jpg

Hey Jim I know it is a little late to recommend this but what difference if any would it make if you where to "relax" all of the suspension bushing points?

my point is to loosing the bolts on the trailing arms at the tube and the torsion bar covers this might give you a little more movement then you could go back and re-tighten every thing and of course recheck...

just a thought

Jim, another indicator of bent torsion tube - put the torsion bars back in, no spring plates. The tbars should be concentric in the torsion tube. If the tube is bent, they will be non-concentric.

Tony,

The tube got really good and relaxed last night. The only thing preventing the steel bananas from falling to the floor is their attachment to the tube at the transmission mount. The tube is still checking as straight.

Chuck,

Both T-bars line up reasonably well. The Left side hangs in place on it's own, pretty well in the center of the tube. The Right side needs to be wiggled a good bit for the splines to move into place, and with more wiggling doesn't seem to fit all the way into the mating splines so that it stays firmly in place. I'm thinking that there is possibly some greasy grit in the way, but haven't figured a way to get at it to clean it out.

I plan to weld in some supports for the torsion tube like the ones on the threads I was directed to for the RS.

Follow-on issue... How to get the engine/transmission reinstalled so that it doesn't have to be literally forced into position. I dropped some weights down from the mounting points in the body, then rolled the engine/transmission into position under them. Using the transmission mounts as the baseline, and lining these up under the mounts on the torsion bar tube, the rear mounts for the engine (at the ends of the engine cross-bar) are way off base. The left side is about 1/2" to the rear of the chassis mounting point, while the right end of the engine mounting bar is 1 3/8" too far to the rear. Either the engine/trans is too long or the chassis is too short...........

http://forums.pelicanparts.com/uploa...1197944409.jpg
http://forums.pelicanparts.com/uploa...1197944719.jpg
http://forums.pelicanparts.com/uploa...1197945095.jpg
http://forums.pelicanparts.com/uploa...1197945133.jpg

If I can figure out how to address this issue, I hope to have the toe-out problem solved. I may take the quest for a solution for the engine mount problem to a different thread, as the nature of this problem is not adequately described as toe-out. Anyone with any ideas, though, is welcome to post them here.

Jim, I've been reading the thread, as I have the same issue with my car. Perhaps I've missed it, but have you compared the stock measurements to your chassis? Your comments seem to indicate that the rear engine mount locations are wrong, and that installing the engine tweaks the chassis in ways that result in your toe problem. I would think those engine mount locations have documented measurements referenced off other points on the chassis.

If so, it's a bit disturbing to think what the ultimate solution is...as it involves significant pulling..and as those mounts are so close to the quarter panels..well, lets not go there~

If you need insight as to the chassis dimensions, find Damon who posts here as, I think, "series900". He's a great guy, and has a Celitte (sp?).

BTW, I love your front and rear bumpers. What are they? Thats a late winter project for me.

Jake,

I do have the factory manuals which give the measurements of various points on the chassis; for example, the horizontal distance from the centerline of the torsion bar tube to the transmission mounting points, and to the rear mounting points for the engine. From comparing these measurements to actual measurements on the car taken from the plumb bob tape markings on the floor, I have determined that the right rear engine mount is not where the factory drawings say it should be. Exactly how far off depends on whether I have done a real accurate job with suspending the plumb bobs in the exact center of the holes, whether the car on the lift is exactly level, ditto the floor under the car, etc.

What really matters though in the grand scheme of things is :
1) That I have an engine/transmission that needs to fit in the space provided,
2) The space provided by the mounting points on the chassis don't allow this without significant levering, forcing, and deformation of the engine mounting parts and the car's torsion bar tube, affecting the rear wheel alignment.

So forgetting for a bit how the car chassis compares to the factory measurements, what do the plumb bobs say about how the engine/transmission assembly compares to the actual mounting locations on the chassis?

If I use the transmission mounting points as the baseline, assuming that I don't want the torsion bar tube to move from where it is when the engine is reinstalled, either the rear mounting arrangement for the engine (yoke and cross-brace) or the right rear chassis mount must be moved a little over an inch. In the case of the engine mounts, this means re-configure that hardware over an inch forward, or for the chassis mount, pull the chassis an inch to the rear.

At this point, weighing both $$ and time to be spent, I have opted to go the route of modifying the engine mounting brackets to allow the engine/transmission to be placed into the car with goal of zero stress on the chassis components, namely the torsion bar tube. I have just finished modifiying both the yoke and the cross-bar, with the goal of making the mods as inconspicuous as possible. Those really familiar with these cars probably will spot that something looks a little strange with the mounts when the engine is back in the car.

I will post some photos of the bracket modifications shortly.

The bumpers were installed by a PO. I believe he got them through The Racer's Group, probably 5-6 years ago.

Jim, I was thinking about your situation this AM, and thought the crossbrace was probably your best option. I can see doing something cool and lighter, yet stronger...WEVO like, if you will.

My only concern was the amount of clearance remaining behind the engine. It sounds like you have this on the run.

(A side note, I've used laser "plumb bobs" in applications like this and loved them. They are getting really cheap now, and the time savings is significant)

Thanks for the bumper info...I LOVE the look of your car.

I'll go back to lurking now..keep the thread posted!

The toe-out issue resolved......
 

There has been a lot going on with the toe-out issue, and I had promised some photos.

After making all the measurements with the plumb-bobs, here is how things played out. First, I used the portapower on the steel banana arms, and pushed outward as shown in the previous photos. This got the torsion bar tube back as close to straight as I could measure, at least in the front to rear direction. Then out came the steel bananas and their spring plates, along with the delrin bushings in the ends of the torsion bar tube. I could find no way to pull the bushings out in one piece, so I took a hand saw to them.

http://forums.pelicanparts.com/uploa...1200519432.jpg


The bushings on the part that holds the spring plate to the chassis were glued in, and since this piece was badly rusted any way, I tossed them and used some others I found in the parts box, bead blasted and painted them.

I further checked the straightness of the tube by installing the bars as Chuck suggested. The left side bar was centered, but the right side had a slight droop. I could come up with no way to pull down on the tube, and wasn't sure that if I could, how this would affect the left side, so I elected to leave things alone at this point.

Based on a suggestion about welding in some brackets to reinforce the tube, ala RSR suspension mods, I found some pieces in the scrap metal box and welded them in place.

http://forums.pelicanparts.com/uploa...1200519543.jpg

Because there was apparently forward force on the tube by the out-of-place engine mount support, I fabbed a new cross arm for the rear engine mount. The right side bends forward, and that side was lengthened from a donor bar to account for the significant forward bend. A little unorthodox, but a lot cheaper than frame/body work, I'm betting. The modified bar is in the front.

http://forums.pelicanparts.com/uploa...1200519711.jpg

Next came the installation of the aluminum arms. The rubber bushings seemed to be still in pretty good condition, so they were retained. Time will tell whether or not this was a good decision. The bracket on the tube that holds the banana arm was pinched inward by the gorilla that installed the delrin bushings there, so the sides of the bracket had to be forced open somewhat to accept the aluminum arm. Thank goodness for the small portapower attachment with the jaws that spread outward like an oversize set of snap ring pliers!

Then a decision on torsion bars. Since I had a set of good rear SC bars at 24.1 mm, I decided to use these in lieu of the stock 23 mm bars. I took a guess at the unloaded spring plate angle and went with 33 Deg, based on guesswork and the Bilstien shocks which in effect add to the spring rate of the bars. With the engine now back in the car, this turned out to be too much angle, so a disassembly and another guess was called for, this time to 29 Deg which resulted in a more acceptable ride height. Oh, and I almost forgot to mention, the bottom line...! The toe can now be adjusted from (+) to zero and on to (-) through the spec range! Camber too...

A corner balance check with the scales revealed that as is, weights are within 3 lbs of correct balance, although this was without me in the seat. Well, that can be solved later with the height adjustment on the adjustable spring plate.

While the engine was out, the '73 915 transmission was traded out for a rebuilt later aluminum version, calling for different axles, also required by the aluminum arms' different hub flanges.

There are still all the required engine hookups, different clutch cable, added wiring for the electric speedometer drive, etc. to be done, before she's ready for the street again, but hopefully the toe problem will no longer be an issue. I'll submit a report after the first test drive for those interested.

Congrats - good, practical decision making and inventiveness at its finest.

Doug

Nice write up. So am i to understand you onlu needed to modify the right (passenger) side of the rear engine crossbrace?

I am jealous of your toe situation. I think I need to print out this tread, take a highlighter to it, and spend a long weekend in the shop under the car!