Squareness of Tub Tolerances. . .

[Tom '74 911]

Hello -

I thought I'd start a post here as I feel like I'm at a dead end with my car and not sure how to proceed.

A brief history:
At the end of last June, I made a mistake during a hillclimb race and drove my car into some concrete k-rail barriers located at the outside of a right handed turn. 100% my fault. I hit pretty hard on the left front. The damage to the left front included all the bolt on stuff (fender, lights, bumper etc...) some bent suspension (front cross member, a-arm, possible bent left strut) also bent both left side wheels as I ended up with the left side of the car wedged against the barriers. The left front of the tub was pushed in by the battery box/bumper shock, windshield was blown out. . . it was a pretty hard hit.

Fortunately, all the safety equipment (Roll bar, Recaro race seat, 5-point belts, HANS etc...) did it's job and I crawled out shaken, but not stirred.

Further assessment to the tub revealed: the left front fender and hood pushed back against and bent the cowl at the lower left corner of the windshield, the driver's door was pushed back against the top of the rear jamb, there is a new crack in the paint on the roof behind the sunroof opening on the left side, there is a weird wrinkle in the floor just to the left of the pedal box, some of the sheet metal in the front trunk was bent due to the forces from the Rennline 3-point strut bar I believe.

I proceeded to strip the car of the engine, gearbox and all suspension - basically everything bolted to the exterior of the tub, so I could deliver it to a shop w/a Celette bench and someone with the knowledge to use it. The closest one I could find was 5 hrs. away!

So I delivered it to them, stripped and on a dolly to minimize their time (and my bill). After a few weeks, I picked it up, brought it home and started reassembly. My goal was to start by getting it back to the point of being able to roll under it's own power with most everything reinstalled, so I could corner balance and align it - to see if everything was straight.

Well, it doesn't appear to be straight.

I should note that the doors and hood close perfectly - better than before, although the gaps are not 100% - they weren't before the crash either though. The windshield opening was tweaked in the crash out of square and while the shop realized that and made it better, it's still not perfect either as the windshield doesn't seem to fit exactly square in the opening.

My measurements indicate that the left front of the tub is about 6mm higher than the right front.

When aligning it with the old struts (that survived the crash), the LEAST amount of negative camber I could achieve on the left front was -2.0 deg. This was with the strut top positioned all the way to the outside of the adjustment range. Prior to the crash, the was about the MOST amount of negative camber I could achieve with the strut top positioned all the way to the inside of the adjustment range.

So I bought some new struts thinking (hoping) that the spindle was bent on the old ones from the crash.

This helped, but the problem persists. Now the LEAST amount of negative camber I can achieve on the left front is -1.0 deg. So the strut was bent, but something still isn't right.

So enough of the history, where does that leave me? My tub appears to still not be 100% straight.

I have chased this for a long time and it's driving me crazy. I had a really sad summer w/out my P-Car (it actually bummed me out that it bummed me out - that a material thing could make me depressed; or the lack of a functioning material thing. . . )

FINALLY! My question: How close are the tolerances of the dimensions of these cars? I have the factory workshop manual sheets and there are tolerances listed on them - often 1-2mm. 6mm doesn't seem like a lot, but my alignment settings are way off. I see photos from other projects where folks are replacing front suspension pans and other critical components while the tub is on jackstands or on a rotisserie etc... not the most structurally stable platforms for locating critical parts and pieces. I can't see how one could replace a front suspension pan with the car on a rotisserie to a 1-2mm tolerance. I think the flex alone from being suspended on the ends would put the tub out of tolerance to begin with. . .

I think that I'm probably just trying to push aside the reality that the shop I took the tub to didn't get it 100% straight on the Celette bench. My understanding is that it's basically a giant go/no-go gauge for cars. . . but ??

I've thought about trying to find a tub to swap all my (many) go-fast part to, but in a perfect world, I'd stick w/my '74. . .

OK, I'm going to stop rambling now. . .

At the very least, if you made it this far, thanks for listening.

Tom

Here are some photos of some of the areas of damage. It doesn't look THAT severe but. . .

[Nickshu]

I am no expert, but I can tell you my experiences.

My 911 was in a nearly identical accident, except it was on the right side. It wasn't in a race, the PO put the car into a ditch and I bought it wrecked and did the repairs myself, working closely with a body/frame shop who had alot of 911 experience, including the factory frame alignment jigs. My damage may have been slightly better than yours as it did bend the cowl, but did not affect the roofline, however the windshield did crack.

The shop was able to get my "alignment" spot on at the suspension pickup points, however there are other areas which are out of spec including bumper pickup points, front A-arm mounts, and some areas of the front clip and floor pan. (Also damaged in the accident as PO high centered as part of the accident). I believe the factory reference which they measure from are the rear torsion tubes.

The net result of this was that my alignment was spot on at the wheels, but there were some other "slight" modifications I had to make. For example, the left tie rod knuckle (where it attaches to the rack) hit the body at full right turn lock. This was solved by installing turbo tie rods, which are smaller in diameter. Also my steering linkage was hitting the body at a certain point in it's travel up under the HVAC area (took awhile to figure this one out). Also we had to cut off and reposition the bumper pickups on the front clip to give even gaps at the fenders.

Bottom line is while you can get the wheel alignment correct, the effects of the accident on the minor, non-structural sheet metal is difficult to predict and "adjustment" of these areas is not the focus of factory body references. Accomodations will have to be made as you go along to get everything to fit evenly.

The challenge for me was that by the time I found out about these minor issues, I already had primer, paint, and parts reinstalled. In retrospect I could have cut out more of the front clip, also the floor pan and welded new in, but all-in-all the car came out great in the end and I can accept some minor issues. Photos below.

[eastbay]

I done a few crash repair cars and I would not mess with a unibody car where the damage extends into the roof. (Well, unless I had my own frame machine even then..... Of course, you can cut off more or most of the bent stuff and weld on new, might be easier)

Not sure if you have seen this Factory restoration done by the PCA, but it shows how your issue was dealt with by the factory team.
Arrival and Dismantling - Revive the Passion - Porsche 911 Factory Restoration - References - Dr. Ing. h.c. F. Porsche AG

[1990C4S]

It's all here:

Body Guys - I Need Help

[Chuck.H]

>>When aligning it with the old struts (that survived the crash), the LEAST amount of negative camber I could achieve on the left front was -2.0 deg. This was with the strut top positioned all the way to the outside of the adjustment range. Prior to the crash, the was about the MOST amount of negative camber I could achieve with the strut top positioned all the way to the inside of the adjustment range.

On my '89, camber is very much dependant on the ride height, ie if I lower the car I get negative camber without moving the top of the strut. So the 'range' may be due to the ride height not being high enough?

Just a thought,
Chuck.H
'89 TurboLookTarga, 342k miles

[matt demaria]

Critical dimenions of the suspension is 1mm tolerance. All other tolerance is 3mm. Porsche is not very complete about listing tolerances above the suspension area, ie roof area. Most of body shop straightening around this area is more of an art. However your car seems to be folded up and has signs of some severe deformation. And it looks like it would not be cost effective to fix.
And yes I don't like using a rotisserie because of the body flex. I have seen too many convertables with permanently screwed body gaps because they were welded on a rotisserie.

[unclebilly]

If it was me, I would change out the tub - tubs are cheap, probably less expensive than the frame work you already had done.

6mm is 1/4" and for a road car, this is nothing. For a race car, you probably want it better than that. That being said, why are you worried about 2° of negative camber? Isn't this a good thing?

[Tom '74 911]

Thanks for all the responses so far - I appreciate that you guys took the time to read my introductory novel! I realize that a lot of it was rambling, but I think I just needed to purge. . . I've been frustrated and bummed about my car for a while now.

What I'm mostly worried about is that the front end no longer seems symmetrical. I can likely get my camber and toe settings where they need to be in terms of the final numbers, but the strut tops and tie rods will not be adjusted symmetrically to get there. So the right side strut top may be adjusted all the way to the inside of the range, the left side strut will be adjusted all the way to the outside of the range. The numbers will match on paper, but the location of the strut tops and length of the tie rods, won't match side-to-side. Does that make any sense?

I'm also not sure if the wheels are all 100% square to the centerline of the tub.

I do realize ride height effects alignment settings etc... I have been setting ride height first using the tripod method as a poor-man's corner balance check during that process, then moving on to camber, caster, toe etc... Then going back to verify ride height, and back to alignment etc....

I have talked to a few different folks about rollers or tubs to do a swap. At this point, it would've been the cheaper route to take if I'd done that right off. While I'm admittedly emotionally attached to my current tub, I'm not opposed to doing that if it needs to be done at the end of the day. My end goal is to have a drivable car - a very straight, well set up one at that - and if that's what it takes, then I'm willing to do it.

My only hang up w/getting a tub is that I'd really prefer it to be a '75 or earlier. I have a 3.6L engine and while I don't have to deal with smog where I live currently, I don't want it to be an issue later down the road.

So does anyone have a (100% straight and rust free) '75 or earlier tub or roller they'd like to pass along? Preferably located in the Northwest? I'm certainly in the market. . . Maybe I'll put an add in the classifieds. . .

Thanks,
Tom

[unclebilly]

These always come up, they typically range from free to $1000. I have several that will be cut up at my place right now but most have rust or some other damage.

[Porboynz]

I put my trust in the Celette jigs if correctly used. Looking at your photos I can not see the height adjust pin fitted to all the jig brackets, this may be because the photo is before or after the align is completed. There is a certain amount of spring in the body as well, you can bolt the brackets into position but when you loosen the jigs off again the body springs back to where it was. (maybe 5-10mm) You have to pull the body past the point it needs to be so it springs back to where it should be. Working in 3 dimensions on multiple jig points means you need a skilled operator, a pull here can disturb another jig point there. Once you get all the factory jig points correct, the suspension will also be correct and on a race car the door fits etc are secondary to the suspension alignment IMO.

[Chuck.H]

What I find funny (sorry Tom I know it's not funny to you) is that there are other threads here with 'my fender lip heights are all wrong' and 'my wheels don't stick out the same distance' and there are many replies like 'these cars are all hand built and no two are alike' and 'the cars often don't match side to side'...

So what I'm saying is maybe all this doesn't make that much difference - if you can get the wheels into alignment and reasonably corner balanced (something I've only been able to come close to on my unwrecked 491), you may be fine.

Jus saying,
Chuck.H
'89 TurboLookTarga, 342k miles

[Tom '74 911]

Originally Posted by Chuck.H

So what I'm saying is maybe all this doesn't make that much difference - if you can get the wheels into alignment and reasonably corner balanced (something I've only been able to come close to on my unwrecked 491), you may be fine.

Jus saying,
Chuck.H

Chuck,
You may be absolutely correct. My car always seemed to have a slight twist to it - even before injury. When set up properly, the fender heights did not match exactly side-to-side in the front or rear. And when set up on 4 jackstands, one of the front corners would hang slightly above the stand, not touching. . .

What makes me a bit worried is that pre-injury, the one thing that WAS balanced and symmetrical side-to-side was the suspension settings in the front. The strut tops and tie rod adjustment locations were just about dead-on symmetrical. Being a "right angle" kind of guy, that made me happy! Now that they're not, I'm a bit worried that the car will have non-desirable handling characteristics because it's not square. The last thing I want is a scary shimmy or twitchiness that wasn't there before as I head into the turn one braking zone at 125mph. . . so to speak.

But still - you could be absolutely correct in that as long as I can get the alignment numbers where they need to be, I could be good to go. . .

Tom

[eastbay]

Before giving up, I would talk to the frame guys about the issue and one more pull. The frame guys I have worked with before went out of their way to make things work for me.

Some good advice above on over bending

[1990C4S]

I think you need to be able to get to factory suspension settings as mentioned, get it corner balanced (as also mentioned) and confirm the pitch from wheel center to center on each side. Lastly you need two diagonal wheel measurements to be equal. The roof and doors are aesthetics.

Aside from the corner balancing you can get the car close enough with a Lufkin tape measure and a plumb bob.

[Tom '74 911]

Originally Posted by eastbay

Before giving up, I would talk to the frame guys about the issue and one more pull. The frame guys I have worked with before went out of their way to make things work for me.

Some good advice above on over bending

I have talked to the shop and the tech. that did the work on the Celette. He could not have been nicer and was willing to make things right. The problem is that I'd have to tear the car completely apart again and trailer it down to them - which is 5 hrs. each way (I live in the middle of nowhere!). It's just not that easy for me to get the car back to them. Also, from the shop's point of view, while they have a Celette bench, they had to rent the appropriate fixtures to do the work on my car. The fixture rental alone was a substantial part of my bill - maybe 2/3rds?. If I brought it back to them and they had to pay to rent the fixtures again, the entire job would end up being a net loss. . . I know, not really my problem, but. . . I don't play the part of the angry customer well.

If they were just down the street, it'd be a different story.

Thanks,
Tom

[Porboynz]

Its fairly common a body shop having to rent the jigs, who can afford to have jigs for every car made? I helped the body guy do mine and the sheet of instructions on how to set the Celette jigs up is year and model specific, reasonably straight forward but probably easier the second or third time like many things. If you replace the tub you will be pulling it down anyway right? If you are not going to do the angry customer angle then find a shop that already has the jigs and get a second opinion. Its not that hard to drop the engine and suspension, there are harder cars to do this on. As you say when you passing on the outside, late braking into a hairpin from 120mph its nice not to be thinking about the body alignment and any compromise in the suspension setup. Someone said a Porsche is a triumph of engineering over design (bit of a dig at having an engine behind the rear axle I suspect). Therefore its best to make sure the engineering does triumph.