tweaked RR steel banana arm, how to determine?

[zotman72]

I have had my '72 911T for 16 years. About 8 years ago, the car was upgraded to 21/26 torsion bars and new bushings. As I just made it into a Vintage/PCA race car this year, I decided to swap in bigger bars (22/30), rear ER Polybronze bushings, and monoballs on top for the front struts this past week before my last race of the season. Last Friday it went to a respected local shop for aggressive track 4 wheel alignment and corner balancing. This Boulder tire shop has done good work before for me on my other race car and for several Porsche friends. Generally I do not question their work or opinion. Fair prices and good results.

Well they told me that my car was had issues getting the settings I wanted and corner balancing was not possible. Rear camber was marginal on the right side ( R -0.7 and L -2.1) and fronts were not great (R -0.8 and L -1.2). He said corner balancing was not possible as car was would not adjust. Small adjustment creating big changes.
They said that the car either has a tweaked right rear trailing arm or the tub is bent. The car has never been in a shunt/wreck in my ownership but it does have some history of bodywork in the past.

So Friday I did get an used right rear trailing arm Friday to R&R mine, but I am not convinced this really is the issue. I can do the R&R task but it is up there as a major PITA 911 job. I might add that the front mount bolt's head is on the tranny side The replacement banana arm from DARTAUTO is somewhat sketchy too.

What I need for a Pelican buddy to provide some specific meaurements for me to check for steel trailing arm or some means to determine whether my arm is in fact bad/bent. Visually it looks fine.



Thanks in advance for your wisdom and assistance lads!

Oh I did search the forum first before my post.




Here is the car in all its glory, racing last month at High Plains Raceway.

[arrivederci]

I have a good steel arm that came off my '72 buring away in my garage - I'll take some measurements for you later tonight.

[joefrantz]

Bill

I've also got one if Josh's doesn't work out.

The factory manual shows a small jig for checking the arms -- maybe someone in town has one.

I'd also check with Grady -- he saved a lot of his Porsche specific tools, and he had most of them.

Joe

[G450X]

The alignment shop said my left front (not too bad), and my right rear (bad) out of spec.

I'm in for a banana arm replacement myself (as well as a front left strut/a arm just to be safe)

I was worried about the tub as well, but a frame shop said it was straight.

This does not look like fun.

[zotman72]

I am going to try another shop this week here in Denver rather than Boulder. The right trailing arm is OK, I am certain. I took off the four mounting bolts and separated the arm from the swing plate this afternoon. Once free from the spring plate, I centered the mount bolts and ecentrics and tighten them all up. The alternative shop will be told nothing and we will see what shake outs from them. My race is next weekend so hopefully this can be sorted out.
Well if there is a problem with the banana arm, it will be a winter project as the engine and tranny have to come out to get the forward mount bolt out. Stay tuned.

[arrivederci]

Originally Posted by zotman72

Well if there is a problem with the banana arm, it will be a winter project as the engine and tranny have to come out to get the forward mount bolt out. Stay tuned.

You can get by with a partial drop -- done it before on my '72. On my '81, someone had put the bolts in backwards, so I used my sawzall-brand wrench instead of doing a partial or full drop.

[Hotrod911T]

You don't need to drop the engine and trans to replace the rear trailing arms. Just cut the front mounting bolts off with a sawzall and use the WEVO 911 Banana Arms E-Z Pins for the install.

Welcome to Windrush Evolutions - WEVO - Porsche Products

As long as you are at it, you might consider replacing the steel trailing arms with aluminum ones. I had the same trouble with bent arms on my '69 and I couldn't get more than about 1.5 degrees negative camber in the rear. When I installed the aluminum ones (using E-Z pins), I could easily get 3 degrees negative camber with no other changes. The aluminum arms may break, but they won't bend.

Rod