911SC Torsion Bar Issue

[Steam Driver]

I recently discovered an issue (I think) with the rear torsion bars on my project car. I had not pulled the end caps off of the torsion arm support tubes until just recently; I was looking to see if I could ascertain the size bars in my car. What I found was this.

On the right side I could not see the end of the bar. It is recessed in the fitting on the arm 25mm, plus or minus. (See photo below). On the left side the end of the bar was almost flush with the end of the tube, recessed about 5mm or so.

I am pretty sure this car does not have stock bars; the end of the bar I can easily see is marked "27," which may (or may not) indicate the size of the bar. I also know the car suffered some serious damage back in 1987 when the right (not the left) rear suspension "collapsed."j I have no idea what precipitated that. However all of this seems to have been satisfactorily repaired back than and I know the PO drove it at least for another then years and 11K miles.

So any idea as to what is going on here? The car isn't currently on the road so not an immediate issue, but I am concerned as to the wisdom of driving it like this, if it is indeed a problem.




Later: I got under the car this afternoon and inspected the torsion bar tube and surrounding underbody. No evidence of accident damage or subsequent repair. No cracked or missing paint, undercoating, or welds. And I confirmed that bars are indeed 27mm. End of bar I shot on left side is marked "L," with "27MM 684" stamped on the end.

[Driven97]

Those look like aftermarket spring plates that get you TB access without having to pull the whole plate. On stock or you can't see how far the torsion bars fit in. Doesn't seem right to me from the pics though

[Trackrash]

There is no "stop" in the center of the torsion tube. It is therefore possible to install the torsion bars un-evenly side to side. Most likely not causing a problem.

Looks like you need new bushings. 27 is not a very common size of torsion bar, but not out of the question.

[Steam Driver]

Bars are indeed 27mm; I confirmed that this afternoon. Bar on left side is stamped "L" followed by "27MM 684." So what you're saying is I may have issues finding replacement bushings?

I did not do the suspension work on this car, the PO did. As near as I can tell from his invoices the bushings have about 21K miles on them. I have no invoice for the suspension work (he wasn't a DIY'er; far from it) but when he bought the car circa 1985 it had 4K showing at his first routine service invoice. That was on it's second speedometer head to get rid of that stupid 85mph thing. I don't know if he did that or someone previous to him. The last dealership record in the Porsche book showed 25K miles, then all of a sudden the reading is 4K.

[uwanna]

Originally Posted by Trackrash

Looks like you need new bushings.

He's absolutely correct, your rubber bushings are shot. The difference in the upper
distance to the mounting plate and the much larger space below shows that the
upper portion of the rubber bushing is "squished" down.

[Steam Driver]

I will address that, but would that have any effect on the original question?

[mikl911]

If you unload the pressure on the torsion bars, both sides, you can drive the torsion bar in with a pipe and a big hammer to equalize the spacing.

[mikl911]

I love the cork in the thermostat!

[Mark Salvetti]

Originally Posted by Steam Driver

Bars are indeed 27mm; I confirmed that this afternoon. Bar on left side is stamped "L" followed by "27MM 684." So what you're saying is I may have issues finding replacement bushings?

No, the bushing should be a standard size. The OD of the bushing fits under the cover held on by the four bolts, the ID of the bushing slips over the shaft. Changing the torsion bar size has no effect on the bushing size.

There are actually two bushings on each side; there is another one on the inside that fits into an opening in the body.

This ER video that shows how their bushing removal tool works will show what I mean. And you don't need the tool to get the old bushings off.
https://youtu.be/Lup9iiXiLco

Mark

[Steam Driver]

Mikl911, are you saying the two bars abut in the center and are free-floating? If that's the case it would explain the staking at the outboard end of the arm fitting. But is equal spacing an issue?

My concern is with spline engagement. If they are free-floating it must not be a concern. I was always under the impression they butted up against something in the torsion tube at the inboard end.

[brentrussell]

They can be pushed all the way through, mine are butted together Left and Right.
To ensure as much engagement as possible I would have them even, with the car jacked and no pressure on spring plates you can tap them to even up the measurements.

Brent

[chris_seven]

Rear Torsion bars for cars with 915 Transmissions are 625 long.

I think you have spring plates from a G50 car.

[Steam Driver]

Are you sure about that? All of the torsion bars listed by our host are 26.56 inches long, which 674.62mm. And they cover multiple years from 1965 through 1989. A length of 625mm would only exacerbate the problem(?) being discussed.

[Driven97]

G50 torsion bars are definitely different from 915 torsion bars, but I'm unclear on what the difference is, and my Google-fu isn't strong enough this morning to figure it out.

[chris_seven]

26.56" is a front bar.

Rear Torsion Bars from 1965 to 1987 - Cars with 901, 911 and 915 transmissions are around 625mm long. They may vary up to 627.5 depending on diameter and model year but the variation is only manufacturing tolerance and I would think that the effective length is always the same.



The Spline count on a G50 bar differs into the torsion bar tube and doesn't fit into the early cars.

The Spring Plate on a G50 car is substantially different as the torsion bar also differs.

I don't have any G50 bars to hand so I can't make a measurement.

[Steam Driver]

This gets weirder and weirder. Given its vintage I'm pretty sure the gearbox is a 915. And the bars are 27MM X 684 (assuming that's what the "684" stamped on the ends means. Other than that I don't know. I'm just concerned about the uneven insertion into the spring plate. Other than that it was working fine.

[chris_seven]

The bar just can't be 684 mm long - 2 1/4 extra length just doesn't work.

https://swayaway.com/product/race-torsion-bar-set-65-86-porsche-911-rear-vw-24-1116%E2%80%B3-26mm/

The splined end of the spring plate has also been 'messed' with as normally there is Welch plug in the end and there is a machined recess to allow its fitting.

Soemone has machined a taper onto the end od the spring plate.

[Steam Driver]

That's because those aren't stock spring plates. They are Sway-A-Way adjustable.

[Trackrash]

Bottom line, if the splines are fully engaged in the spring plate it won't matter if they are not evenly spaced on the ends. I guess the only way to confirm it is to disassemble. Unless, that is, someone else has a set of SAW torsion arms and T bars sitting around for comparison.

[chris_seven]

Originally Posted by Steam Driver

That's because those aren't stock spring plates. They are Sway-A-Way adjustable.

How do you stop road dirt is there a cap?