This'll Test you - Torsion tube length 1975/76 911 narrow body ?

[Sharkbitemarky]

Hi all,

New here ! I'm part way through a restoration of IB 911 Coupe and I am working in the area of the left rear torsion tube end, I have been trying to work to +/-1mm or better.

I am finding it very difficult to find a dimensioned drawing of the torsion tube I can read (most seem blurred/low res in this area) or just a measurement/s of the length of the rear torsion tube and tolerances.

In an ideal world I'd like to know the measurement of the length of a rear torsion tube left to right from the nominal surface of the outer weld that joins it to the inner wing and/or the length of a new replacement torsion tube. High res drawing would be great.

Another great measurement would be from the outer face of the inner spline boss to the outer edge of the torsion tube, both sides would be great (should be around 729mm-738mm) but would like it to +/-1mm or as good as you can get.

Many thanks
sharkbitmarky

[T77911S]

i have a drawing for a 72 that shows 501.5 from center to outer, its hard to read too

[Sharkbitemarky]

Originally Posted by T77911S

i have a drawing for a 72 that shows 501.5 from center to outer, its hard to read too

Many thanks, I think I may have seen the same low res drawing however, its not clear where the exact measurement points are taken from e.g. what is the outer, the weld, the bottom or top of the bushing pocket, or the top of the spring plate threaded stand off spacers.

Cheers
SBM

[Trackrash]

Not sure if this helps...

[Sharkbitemarky]

Originally Posted by Trackrash

Not sure if this helps...

Nice Res, do you think the max 1079 diamension is from the face of the threaded spring plate stand-offs ???

Getting close.

[Tom '74 911]

I have a stripped '74 and '75 in my shop. I will try to run a tape measure through the torsion tubes & get some dimensions for you. It might take me a day or two to get down there...

Tom

[Trackrash]

This might help. It looks to me like it is to the mounting standoffs.

[3rd_gear_Ted]

Here is a place for all 7 pages associated with the G body

https://www.carmanualsonline.info/porsche-911-1968-1-g-body-diagrams-workshop-manual/1#7

[Sharkbitemarky]

Thanks to all, incredible support, hope I can repay sometime.

It looks like 1079mm +/-0.5mm from the face of the spring plate mounting stand off's from a drawing/design perspective.

"Tom '74 911" I'd really appreciate some actual measurements.

Thanks again.

[Sharkbitemarky]

Originally Posted by Tom '74 911

I have a stripped '74 and '75 in my shop. I will try to run a tape measure through the torsion tubes & get some dimensions for you. It might take me a day or two to get down there...

Tom

Tom,

Some real measurements would be great.

[Tom '74 911]

Originally Posted by Sharkbitemarky

Thanks to all, incredible support, hope I can repay sometime.

It looks like 1079mm +/-0.5mm from the face of the spring plate mounting stand off's from a drawing/design perspective.

"Tom '74 911" I'd really appreciate some actual measurements.

Thanks again.

I just measured the torsion tube on a '75 911 and it mirrored the factory dimensions provided above. Using the lip inside the tube that acts as the spring plate bushing "stop" and measuring outside-to-outside, I got 975mm. From the outside of the same lip to the spring plate cover stand-off (the 3 longer ones), I got 52mm. And 975+104=1079mm, which is exactly what the factory drawing shows...

Let me know if where I took measurements makes sense... (or doesn't).

Thanks,
Tom

[Tom '74 911]

Also, something to note - there may be some differences between various years. The Celette bench set-up sheet has a note regarding additional washers to be used for models before August '76. The washers are 4mm thick and are used as spacers between the torsion tube fixtures and spring plate cover stand-offs. So presumably, models after August '76 are 8mm wider (4mm each side) between the outside edges of the spring plate cover stand-offs... so 1079mm+8mm=1087mm

I've never had a car newer than '75 on my bench, so I've never been able to test that.

[Trackrash]

Originally Posted by Tom '74 911

Also, something to note - there may be some differences between various years. The Celette bench set-up sheet has a note regarding additional washers to be used for models before August '76. The washers are 4mm thick and are used as spacers between the torsion tube fixtures and spring plate cover stand-offs. So presumably, models after August '76 are 8mm wider (4mm each side) between the outside edges of the spring plate cover stand-offs... so 1079mm+8mm=1087mm

I've never had a car newer than '75 on my bench, so I've never been able to test that.

That is interesting, since I have SC torsion arms on my '71. Seem to fit OK. Might have something to do with the extra thickness of the spring plates with the adjustable extra part?

[Sharkbitemarky]

Tom,

What the hight of the stand off/spring plate fixings, I have about 20mm ? Difficult due to paint thickness....

Another great measurement would be from the outer face of the inner/middle spline boss to the outer edge of the torsion tube, both sides would be great (should be around 729mm-738mm) but would like it to +/-1mm or as good as you can get.

Thanks to all.

[Sharkbitemarky]

Hope this pic helps dims Z and Y are my main interest as I am trying to determine how accurate the internal spline boss is mounted in relation to the centre line of the torsion tube. Measurements W, X and V would also be good to understand.

Thanks to all for your help.

[Tom '74 911]

Originally Posted by Sharkbitemarky

Hope this pic helps dims Z and Y are my main interest as I am trying to determine how accurate the internal spline boss is mounted in relation to the centre line of the torsion tube. Measurements W, X and V would also be good to understand.

Thanks to all for your help.

I sketched a drawing almost identical to yours yesterday when I was taking measurements, intending to provide a lot more data. What I decided is that due to the unevenness of the weld, using the end of the torsion tube (labeled "weld" in your drawing) as a reference point would not work. Measurements would vary as much as 3mm+ depending where I put the tape measure... So "W, X and V" are tough ones to establish consistently - and not really possible down to your 1mm tolerance. I think the same could be said of the sheetmetal around the standoffs - due to bumpy undercoating, measurements would vary wildly - well maybe not wildly, but a few mm for sure.

That's why I chose to use the reference points and provide the dimensions I did. I felt they were the most critical and consistent locations to use. I don't think it matters how long the standoffs are relative to the sheetmetal behind them, as long as they are located the correct distance apart, and symmetrically from the centerline.

I did also try to get some kind of dimension similar to your "Z & Y", but wasn't able to find any lip inside the tube to be consistent with the tape measure. I will revisit that one for you and look again with better light.

I do think though that a few mm in either direction is probably not critical for the location of the center splined area. My guess is that there is probably some tolerance built in to that & it's likely longer than the splined area on the torsion bar ends to accommodate being slightly off. And I don't think there is any way to assure that the torsion bars themselves are centered perfectly & symmetrically when installed either...

I can be a "perfectionist kind of guy" with the best of them, but at some point, you have to acknowledge that close enough is good enough. : ) : )

Thanks,
Tom

[Sharkbitemarky]

Tom,

Thanks again, appreciate your best estimate measurements of W,X,V,Z & Y I fully understand re weld and paint variations.

Cheers
Mark

[Tom '74 911]

I found that there is a very nice lip at the center splined section of the tube from which to measure...

Z = 425mm
Y = 424mm
W & X = 18-20mm

I did not measure V...

Also, I measured from the center splined section to the lip inside the tube that acts as the spring plate bushing "stop" (same place as my previous measurements) - the left side = 391mm and the right side = 390mm

So I'd say the splined section is pretty well centered in the tube.

[Sharkbitemarky]

Tom,

Thank you.

Mark