73: Can't reverse banana arm bolts ?

[buster73]

I'm just in the middle of an engine drop (see thread below) but wanted to post this issue separately to also reach those for advise who might not read my other thread (Engine Drop - Stealth Mode).

While having the tranny out of the car (73.5) I wanted to turn around the rear trailing arm bolts (inner banana arm bolts), so I can remove them next time without lowering the tranny. However it looks as if the bolts are too long to get them in reversed (nuts to the inside). I tried from all angles, but anything short of widening the holes in the chassis mounts (which of course is no option) seems not to help. At the moment the trailing arms are still connected to the hub and spring plate, so I can't move the arms around too much. I was wondering if it is possible to get the bolts in, after the trailing arms are disconnected from the hub and spring plate and can be moved freely. As this would add a brake bleeding job and a rear wheel alignment to my task list, I would hate to try and find out it does not help. Anyone has experience in this issue ?

[Chuck Moreland]

Not with the factory bolts.

Try a socket head cap screw (aka allen head). The smaller diameter of the head may do the trick. Some creative use with a grinder can be used to bevel one side of the head to get a little extra room.

This is interesting because my 73.5 had the bolts in the favored direction, and the required dimples on the torsion tube. I thought this was in all 73s. It must have been phased in mid year.

[Tyson Schmidt]

Hayden from WEVO has a solution. He made new bolts that will clear. You'll probably have to contact him directly if Pelican doesn't have them in stock yet.

[Early_S_Man]

I reversed mine without any issues ... and it is an early '73 model!

[Tyson Schmidt]

Originally posted by Early_S_Man
I reversed mine without any issues ... and it is an early '73 model!

I did that on my old '72 also. It involved a little careful work with a ball-peen hammer to the torsion tube, using a '74 as a model. But I wouldn't recommend that anyone.

Warren, I'm betting you did it with different hardware, no?

[Stu Wilkinson]

On my 70, I carefully hammered an indentation into the torsion bar tube in the right spot to let the bolt enter the hole at the right angle to push through. I then resealed the area.
MY 911SC which has the bolts mounted the heads to the outside, already had these indentations.

[Bobboloo]

I was able to do this on my old 72' but can't do it on the 73' I currently have.

[Early_S_Man]

Tyson,

No special hardware ... just a couple of licks with a 4 lb copper-faced mallet on a 3/4" diameter steel tool made from rebar ... on each side!

[Tyson Schmidt]

Originally posted by Early_S_Man
Tyson,

No special hardware ... just a couple of licks with a 4 lb copper-faced mallet on a 3/4" diameter steel tool made from rebar ... on each side!

Yep, and it seems we're not the only ones!

Sure beats pulling the engine/trans. It did feel a little wrong while I was doing it, but it turned out looking just like what the Factory did on the '74 and later cars.

[rlh930]

I have dents in the torsion tube of my '73 to clear the bolts. Even this isn't enough; to clear, one of the flats on the head is ground at an angle. That flat must be oriented towards the tube to allow the bolt to be removed. The dent in the tube is not very big, more of a dimple really, so I don't think it affects the tube's strength.

[buster73]

Thanks guys,

good information - as usual. My car is January 73 (one of the first CIS built) and according to the PAG parts catalog all 73 cars should have the modified torsion bar tube. Guess there must have been an older part lying around on the factory shelf when my car was assembled. I'll think about the modified bolts . Not sure if I dare to reshape the torsion bar tubes, but I'll have a beer over it.

[randywebb]

or a cap screw maybe

what is the serial # on your Jan. built car?

[buster73]

Originally posted by randywebb
or a cap screw maybe

what is the serial # on your Jan. built car?

Next week I will do some measurements and hope with a cap screw, shortening the bolts (74 are 2mm shorter) and possibly shaping the head on one side I might get around. I sure will contact Hayden at Wevo in case he found the "perfect bolt" already (think to remember his orange 911 is a 72) . My cars serial # is 911 310 1506 (CIS models started @1500).

[randywebb]

Good Luck with it - mine is 911 310 2669

[Grady Clay]

This is one of those changes that Porsche claimed occurred
with the model year ’72 to ’73. I have seen ’72 models with
the dimple and ’73 without. Certainly by mid-year ’73 all the
911s had this change. (Dimple red circle, bolt head green arrow.)
04a.jpg
“
"
© Dr. –Ing. h,c, F. Porsche A.G.

If you mod an earlier torsion bar tube for clearance, you
should carefully inspect the interior of the tube for rust
damage. Under no circumstances should the torsion bar
ever be able to contact the tube – even slightly will lead
to the torsion bar failing.

There is an even more important change that occurred in
this area with the '74± model year. Porsche added two
small reinforcing pieces between the torsion bar tube
and the aft end of the tunnel (yellow).
IMG TorsionBarTube03a.jpg


These transfer the load from the trailing arm (banana)
to the chassis without bending the torsion bar tube.
This is a very desirable addition. Someone
should manufacture an aftermarket part as it is only
available from Porsche as part of a replacement torsion
bar tube.

Best,
Grady

[911pcars]

Grady,
What's the suggested modification on earlier tubes? Notch and weld? Heat and hammer?

Thanks,
Sherwood

[nick-moss]

I have not found a 911 yet (1966 to 1982) that I have not managed to fit the stock bolts from the outside without any force or modification

[captainrb]

Buster.. the easiest way is like the other guy said Smart racing has a special bolt and nut set up.But expensive. Wevo part number 552160 and cost $99.65 . I had same problem with my '73,when I replaced my steel trailing arms with aluminum ones. I used a grinder and beveled the head and the shank. I lost only a little on the head due to beveling maybe 10% of the flat area of the head. It is my option that this is a good fix and bolt strength is not reduced.Somehow altering this tourque tube may cause trouble down the road due to torsion bar chafing. Good luck.

[randywebb]

Originally posted by 911pcars
Grady,
What's the suggested modification on earlier tubes? Notch and weld? Heat and hammer?

Thanks,
Sherwood

also, what gauge steel? just a simple plate in the shape shown?

[buster73]

The shown reinforcement plates certainly make sense. Would be interesting to know if they were introduced because the notching of the tubes will make them somewhat more prone to bending by loads induced by the trailing arms in the longitudinal direction of the car. Should run the numbers through a computer one day. Could of course be coincidence and they were just introduced to compensate for better/wider tires, better brakes and overall higher performance. Anyway I guess a good modification for any early car if someone is welding the tub.