Rear toe out of adjustment range - possible fixes?
 

Problem:

The toe adjustment on both rear trailing arms won't bring the toe back from "way out" (positive toe) to toe-in or even to zero toe.

Background:

The trailing arms are on a '73 that I am just getting on the road after a purchase some 3 years ago. I noticed a roaring noise on having just gotten the car on the road with a rebuilt engine. On closer look back in the garage, I discovered an excessive wear pattern on the inside of the right rear tire, and set up my string alignment equipment to measure front and rear toe. The fronts are pretty close to zero. But the rears are both toed *out* by approximately 40' (that's about 2/3 of a degree *per wheel*)!! Camber on both rears is about a negative one degree, where it ought to be.

With the car on the lift, and checking the position of the toe adjuster on the spring plate, the adjuster was already at the end of the toe-in position. Adjusting the effective length of the spring plate is what affects the toe, with shorter resulting in more toe-in. The adjuster is at the end of it's range in shortening the spring plate.

http://forums.pelicanparts.com/uploa...1194220939.jpg

Anyone have any ideas here? Is there some way I'm not seeing to deal with this? There is some wear in the adjustment slot which might be good for an additional 1/16", but that's not going to be nearly enough. My back of the envelope math says I need a good 1/4" just to get the adjustment back to zero toe and I'd like to get maybe 5' to 10' of negative toe.

FWIW, the PO had installed Delrin? bushings all around on the car, banana arm included. Yeah, I know, that is not the best choice for a place for a solid polyurethane bushing, but I don't see how that would affect this particular problem.

I have a set of SC aluminum banana arms and spring plates nestled away in the attic. I can go that route if I have to, but I'd rather first understand why I have this problem. I like to know what it is I'm fixing, and there's no real assurance that the SC arms are going to fix the problem. And of course, swapping the trailing arms out is not just an afternoon job.

Maybe some one has some thoughts on this........

Bump......

Surely there are folks out there who have experience with alignment of the 911 suspension who might have some idea that would be of help in sorting out this problem. Maybe the subject of the thread didn't attract the attention of the right people?

I don't want to put more miles on these tires until the problem is addressed and fixed, and short of replacing the trailing arms, or maybe relocating the holes in the spring plate, I'm currently at a loss as to how to proceed.

Never mind...I just reread your post.

Since it's on both sides, it's got to be something they have in common. I'd look at the bushings first.

Keep 'em coming folks!

Rich,

Thanks for the input.

Note in my first post that the PO had installed Delrin bushings. I doubt that even 50 miles were put on the car before I bought it, and from the ride, Delrin must be one of the hardest plastics known to man! However, I am not discounting any possibility here, so before it's over, I may have to pull the spring plate off just to check and see what's inside.

HI Jim

Your description is thorough and it sounds like you know how to measure toe. But just to be sure, how are you setting up your strings?

Assuming you measured properly, and the toe is equally off on both sides, I would take a good look at your torsion tube. It may be bent towards the front of the car.

Some types of impact to the tire will force the control arm forward, bending the torsion tube in the middle. Rust damaged tubes bend more easily.

If it is bent even 1/4 inch over its length, it will have a big impact on toe. Use a straight edge to check for straightness.

Generally inspect the torsion tube and the trailing arm mounts. Any evidence of replacement, repairs or modification?

Report back what you find.

My money is on the bent torsion tube.

----------

I don't think the plastic bushings are the cause of your toe problem. But they are likely the cause of your harsh ride. It's not the hardness of the plastic, it's the friction and binding they are causing.

Plastic bushings should NEVER be used on the trailing arm inner link.

Chuck, thanks for the response. My strings are down while the car is up on the lift, with me checking for something I may have overlooked. So after another good hard look at the arm/spring plates, I am going to put the car back on the floor, re-settle the suspension, and set the strings back up and re-measure. I am going to take photos of the process to post so all can see how I got what I am finding.

Stay tuned.

I did read that...the key word there is "PO". Never EVER trust a PO's installation of anything.

I hope it's not the torsion bar tube.

Hi Jim:

Just a note to all the kind folks who might read this thread for information,....:)

Delrin is a type of nylon and as such, should never be used for suspension bushings due to its propensity to absorb moisture. This makes them swell up and bind,...:) Although cheap and easily machined, its really a poor choice of material.

Trailing arms move in two planes (directions) and plastic bushings of ANY kind should never be used in those applications due to severe binding problems. One should either stick with the OEM rubber bushings or install weather-sealed monoball cartridges.

Hope this helps,

Steve,

If Delrin is a no-go what do you recommend for track only PCA club racing other than metal bearing and the like? Consider both front and rear busings. I was given the impression that Delrin was the firmest and way to go for minimum suspension movement. Now you rained on that, so to speak.

I learned the hard way about trailing arm plastic bushing and am surprized they are still sold. Luckily, all I received was a great learning lesson in handling and a shorteded weekend.

Thanks for you insight and your contributions to the oil threads.

Jim

I had poly graphite bushings on my car. I can tell you that the one for the banana arm mount was a PITA. It will resist the suspension settings you try and put in. That bushing has to not only rotate, but it twists to get the toe and camber settings. I have aluminum arms now with a monoball. A monoball is the best as it does not "give", but still has the freedom of movement to allow suspension changes to be made easily. A rubber bushing for the banana arm is better then the hard stuff. You should be able to use the harder poly bushings for the front and the spring plate.

Steve,

Thanks for your input. Quite honestly, "delrin" was dredged up from my memory. I know the bushings in the '73 appear to be made from some white plastic looking material, and that name popped into mind. But all I can really see is the flange portion of the bushings, and there may be another bushing material that resembles the "white plastic" description. I will be replacing the ones in the banana arm regardless of wherever this current toe-out problem leads.

John,

The trailing arm is certainly resisting my attempts to adjust out the excessive positive toe. So you may be on to something there.

I set my strings up again tonight and remeasured the toe out. I had the car up on the lift and struggled with a readjustment, getting absolutely all the shortening of the effective length of the spring plate I could get. When I did the remeasure, I had taken maybe an eighth of an inch out, which might equate to 20' or so, leaving another 20' to get it within the limit of zero, but still short of where I want to go, and not seeing how I can improve it with the current setup.

I'll get some photos posted tomorrow of my string setup.

Hi Jim:

LOL,..I'm glad I "rained" on that idea as that saves you a LOT of headaches and stomach lining. :)

There are a LOT of products on the market that are truly useless in both design & execution. Such items sold by those vendors/manufacturers simply entrap the unsuspecting in the quest to make a buck and have no scruples about it.

The operative words here are "Caveat Emptor" and this situation underscores the need to consult as well as support the folks who truly know this business as thats how their collective knowledge & experience is available to you. :) :)


Mr. Williams:

Most common Delrins are white or light tan in color and easy to ID due to their hardness,...:) :)

These used to be VERY popular in the 60's & 70's due to the lack of other options and low cost.

Steve,

Thanks but a bit late. I installed the delrins this summer after years of hearing from my former mechanic (60&70s era) how great they were. I am unfamiliar with delrin and with it's hardness never contemplated a moisture problem. Due to circumstances they've yet to be tested.

I had removed a set of the old Weltmeister race bushing that had not been properly fitted and obtained the Smart Racing bushing but felt they were too soft for a dedicated track 930.


So, it's back to the learning pit again. Any suggestions? What's another day in the garage?

I will agree on getting the best advice but that in itself can be difficult with the overall noise level.

Thanks

The other Jim

Maybe at this point starting a separate Delrin bushing thread would be appropriate. I would like to get back on the topic of finding the problem with the rear toe adjustment.

Just for review, regarding the string alignment, here is the set up I used to determine the toe setting. The diagram was copied from Ray Scrugg's alignment booklet. The string set up is really pretty simple: parallel (to each other) strings, set up parallel to the fore-aft center axis of the car. For those familiar with only the fancy computer alignment machines, this may seem pretty crude, but with a little care, one can get very accurate results.

http://forums.pelicanparts.com/uploa...1194490328.jpg

Here is my string setup. The tubes are electrical conduit with grooves pressed into the ends. The grooves define exactly equal lengths on the tubes which the strings (also equal length) ride in.

http://forums.pelicanparts.com/uploa...1194491037.jpg
http://forums.pelicanparts.com/uploa...1194491102.jpg

The string lengths should be close, but when I checked mine, there was about an inch difference. But doing the math to see if that really made a difference, it affects the parallelism by only 0.010".

Here are photos of the toe measurements on one rear wheel. By the way the suspension was settled out beforehand by the use of slip plates.

http://forums.pelicanparts.com/uploa...1194491644.jpg
http://forums.pelicanparts.com/uploa...1194491700.jpg

That's 1/4" over 17" of rim diameter, and equates to close to 50' of toe out. The larger of the two measurements is to the rear edge of the rim, and the smaller to the front edge, resulting in toe-out and not toe-in.

More coming in the next post........

Chuck,

I couldn't figure out how to get a straight edge up to the torsion bar without dropping the engine. So I rigged up a way to get an indirect measurement. I made some photos, but will post them later if there is a need to clarify my explanation. I made up 3 "plumb bobs" with some string and steel nuts on the ends. These were draped over the torsion tube in three places, one on the right, one on the left and one close to the middle of the tube, between the tube and the car body, on the forward side of the tube. I then clamped a 3' metal ruler so that one edge would line up against all three plumb bobs if the tube were indeed straight. However, they did not line up; I found that the tube center is about 3/16" forward of the ends, indicating that it could be bent forward in the middle toward the front of the car.

If this is indeed the case, have you any experience with straightening the tube? It looks like the engine/ trans would have to come out, and some sort of fixture constructed to pull back on the center of the tube to get the 3/16" out.

Jim, I beleive you are measuring toe properly. Just wanted to be sure ;)

I've never tried straightening the tube myself. There might be a creative way to do it with a porta-power or some comealongs.

A good frame straightening shop with the right equipment could certainly do this.

You could also cut it out and weld in a replacement tube.

Check the tube for rust. If structurally rusty, replacement would be the best option.

Chuck,

Thanks. I was hoping that someone, like yourself, had some ideas on how to approach straightening the tube. Thinking that I might be faced with this, I had envisioned an "A" frame with the legs of the "A" against the outermost ends of the tube and either hydraulics or a come-along between the peak of the "A" and the center of the tube. If I were lucky, and the tube is not rusty (as it doesn't appear to be), I might be able to give it a short stout pull and measure to see if that had any results, and not have to even pull the suspension. I have a friend with a local body shop who I plan to contact for suggestions.

If anyone else out there reading this has any thoughts on other ways to approach this problem, feel free to keep the comments coming. Otherwise, it's looking like an engine drop and a frame shop.

Uncharted territory for me, good luck. Keep this thread updated with the details of the fix. It will be good info for someone else down the line with the same or similiar problem.

Most likely culprit is the delrin/eurathane banana arm bushings. I'd start with that. I doubt the t-bar tubes are bent.

Testing bent torsion tube theory
 

On the presumption that a bent torsion bar tube might be the source of my toe-out problem, here are the results of a preliminary test. Not yet enough to prove that the bent tube is the problem, but it seems to support the theory.

It had been suggested that another way to approach bending a bent tube back into place was to spread the rears of the banana arms apart toward the outside of the car. If nothing in the geometry of the triangle formed by the banana arm, the spring plate and the distance between the banana arm support and the mounting point of the spring plate and the torsion bar tube occurs, then the torsion bar tube must bend in the desired direction to correct the toe-out, that is, toward the rear of the car.

http://forums.pelicanparts.com/uploa...1196809709.jpg

I figured that a brute force approach could not harm anything at this point, so I proceeded to spread the ends of the banana arms using a hydraulic PortaPower. To measure progress, I made a reference measurement of the exposed part of the hydraulic ram, and dropped a plumb line to the floor under the lift, attached to the transmission mount. If the transmission mount moves, it is because the torsion tube moved.

http://forums.pelicanparts.com/uploa...1196809782.jpg

http://forums.pelicanparts.com/uploa...1196809871.jpg

http://forums.pelicanparts.com/uploa...1196809951.jpg

http://forums.pelicanparts.com/uploa...1196810007.jpg

There are some intermediate measurements, but a beginning and end reveals that when the rear ends of the banana arms are forced apart by 1 1/8", the transmission (and torsion tube supports) move to the rear of the car by 7/32", almost a 1/4"!

http://forums.pelicanparts.com/uploa...1196810071.jpg

http://forums.pelicanparts.com/uploa...1196810126.jpg

Now how does that affect the toe, you may ask. Since the car was on the lift during this process, I had to resort to eyeball "measurements" to see the result on the toe. So I sighted down the outside edge of the rear tire towards the front of the car. Before the "Spread", I could not see the front tire. After, I could see a portion of the front tire. I checked this for both rear tires. The Portapower was relaxed, and the test was repeated - same results. The transmission moved back to the starting point when I relaxed the PortaPower, then back to the same 7/32" when it was extended. "Toe sightings" were repeatable.

http://forums.pelicanparts.com/uploa...1196810177.jpg http://forums.pelicanparts.com/uploa...1196810237.jpg

The toe problem remains at this point, however, as everything moves back to it's original position as soon as the spreading force is removed. What has to happen now is to drop the engine, weld up a fixture to hold the PortaPower, and try to take the 7/32" bend out. I'll post photos of the progress.

By the way, the fixture will consist of an "A" frame, with the legs of the A at the ends of the t-bar tube and the point of the A at about the distance of the rear engine mounts. The pull on the t-bar tube will be at the center of the tube towards the rear of the car.

You can file the slot in the spring plate larger to accomidate more movement of the banana arm forward. Many racers do this to the camber slot to get more camber.

-Andy

Hi Andy,

I've given some thought to modifying the spring plate. To change the toe adjustment, one would actually have to move the hole in the spring plate forward. The toe eccentric bolt uses a hole in the spring plate, and the slot is in the banana arm. Filing the slot larger in the banana arm would make the toe-out only worse, so the solution here would be welding up the hole in the spring plate and re-drilling it closer to the torsion bar end. Or, one could weld up and move the toe slot in the banana arm, moving it more toward the wheel.

The camber adjustment on the other hand, has it's hole in the banana arm, and the slot in the spring plate. I haven't thought through the camber mod you speak of, but if the racers use this I'm sure it must work for camber increase.

My eventual plan for this car is to replace the steel banana arms with aluminum banana arms I already have on hand, along with the adjustable spring plates, also on hand. So if I have to resort to modifying my current spring plate set-up, I'll have to modify my adjustable spring plates as well.

So I'm hoping to address this problem by going to the source if at all possible. I still haven't entirely ruled out the delrin bushings as the source, as some have suggested, as the root of the problem. But testing out this theory would require that I replace them with either the rubber bushings or the monoball ones, and I won't know until the replacement is complete whether this would solve the problem.

I would highly recommend that when you put the alum banana arms in you use the mono balls. Not suggesting that will fix your problem. For that one bushing, delrin is not good. I had the poly graphite and they would resist any suspension changes I tried to make.

Jim, I'm learning a great deal from your systematic research into the problem. Thanks for sharing this with us.

John,

I would agree that from all I can find, monoballs would be the best choice for this particular bushing. My car came to me with delrins in ALL possible places to put suspension bushings, and they ALL will eventually be replaced. However, I am not convinced at this point that the delrins in the banana arms are the problem. If I force the torsion bar tube to move back to where I think it belongs using the PortaPower, the resulting movement toes the wheels in.

If the delrin is really as hard as it seems to be, then the bushing is probably not deforming under the load the PortaPower is subjecting it to, and thus the tube is what is being deflected, as the movement of the transmission shows.

I double-checked the available adjustment room provided by the slots on the spring plate/banana arms on both wheels, and there is no more adjustment available at the spring plate.

So... the basic issue at hand is fixing the toe problem so I can drive the car, and finish the break-in of my engine.

I am having the same issue with not getting enough toe at the back of the car. The mechanic told me to grind out more clearance at the adjustment slot, as they are at the end of their travel. Any one ever done this?

Jim,

I agree, you need to verify and fix the problem you have with the steel arms now. It sounded to me like you were going to upgrade to the alum stuff later. I was only saying when you do that, you should use the mono balls. If you are going to the trouble to upgrade the suspension pieces, don't use the wrong bushings again. This has been a great read, and can't wait for the final installment when it's all fixed.

Is it possible to weld some strengthening brackets to the torsion tube to maintain its positions when the banana arms are spread? I know the factory did some gussets / brackets for strengthening the torsion bar tube.

Doug

After looking at this for a few weeks, I don't think that you can simply grind out a slot and fix the toe-out problem if the adjustments are at the end of their travel. The toe adjustment slot, in the banana arm itself and not in the spring plate, needs to be moved forward. This means not only removing material from one side of the slot, but filling it back in (by welding) on the opposite side. It is the filled-in side that causes more toe-in when the eccentric is turned.

Also the two slots at the end of the spring plate will need to be ground out more (lengthened), that have the locking bolts passing through, as they will be at the end of their travel . Then, the camber slot in the spring plate will need to lengthened so that there will still be a full range of adjustment for camber.

Another approach would be to cut a slice out of the spring plate, and weld it back together. You would d@mn sure want to trust your welder, though. A broken weld here would be a disaster at much of any speed at all on the road.

I would advise researching all that would need to done before going down this path.

It would be interesting to see what the factory did. Do you have any info on this? One issue might be getting access (with a welding torch) to a solid place on both the body and the tube to do a decent weld. The bracket would need to be near the center of the tube, right above the center of the transmission. I have learned from the factory manual that replacement of the torsion bar tube requires cutting open part of the flooring in the car above the ends of the tube, in order to complete the required welding. The photos show cutting open a flap and folding it back much like opening the top of a can of beans, then welding the flap back into place. Welding in a bracket might require the same. I don't have the engine out yet, so I can't really visualize/remember what access there might be above the transmission.

Very interesting thread. Subscribing,

ianc

You don't actually have to fill in the unused end of the toe adjusting slot. Just file in more room on the end you need and then bolt the thing down. The bolts on the end of the spring plate and the two adjusting bolts will hold the arms inplace once they are tightened. In other words the slots don't have to maintain the position they only have to allow it.

-Andy

Jim, sorry I don't have photos. I have seen Pelican threads relating to "RSR" chassis strengthening techniques. I posted within one of the threads. Tyson Schmidt shared some information within, as well. I'll do some searching for a link.

I cannot remember to what areas you have proper welding access with the engine in (it has been a while).

I was thinking you could weld two brackets on either side of the transmission mount between the torsion tube and the body.

Does the 7/32" movement of the torsion bar offer enough to set your alignment toe properly?

Jim,
Check out this thread
http://forums.pelicanparts.com/porsche-911-technical-forum/259557-structural-reinforcement-post3195258.html#post3195258
And this one:
http://forums.pelicanparts.com/showthread.php?t=342844&highlight=RSR+weld+plate&p age=2

this might sound like a dumb idea after i skimmed over the thread, have you considered taking the car to a panel beater who has a 911 jig to check that everything body wise is straight.

i remember seeing a car that didn't have any castor adjustment left (it was a mercedes however) and that was mainly because the body was bent.

Andy,
One of us is not thinking the same as the other. The toe slot is in the banana arm, opposite the hole for the toe adjuster in the spring plate. For toe-in, the eccentric, rotating in the hole in the spring plate, has to push the banana arm forward, that is toward the front of the car. On my car, the eccentric has pushed against the side of the slot which is toward the front of the car, as far as it will go. In order for the eccentric to have something additional to push against, this side of the slot must be filled in. The side you *need* doesn't need filing, it needs filling in. If you have some way to adjust the relative length of the spring plate *without* the adjuster (eccentric), then you wouldn't need it at all. The other thing you are overlooking is that the bolts at the end of the spring plate will not allow the banana arm to move any further forward. They are already at the end of their travel.

There are no 911 jigs within, I'm guessing, 200 miles of my car, likely even further. I do have the factory plan and elevation drawings which spell out the locations of the points I'm measuring from, namely the torsion bar tube centerline and the transmission mounting bolt holes. From that I have determined that the tube is bent. The next step is to try and remedy that. Since I have no idea how to locate anyone with a Celette jig, I figure if this is going to happen (straightening the tube) I'll have to do it myself.

signing-up. Thanks for the reports on this Jim.

Jim,

Very interesting thread. Really enjoy the creative ideas.
I was wondering how the torsion tube was bent forward. Could the car been hit from the rear before?

Have you consider using Elephant Racing's adjustable spring plate or just use coil-over with 935 adjustable spring plate? Expensive, but less work.