Strange clutch cable connection

[fdeville]

After a complete rebuild of my 1976 911 2.7, I installed the engine totday in the car. Project lasts for 5 years already btw...
When trying to connect the clutch cable to the (also rebuild) 915 type gearbox, my mechanic told me that the connection is not standard as it should be.
So I checked my pictures I took 5 years ago, when removing the engine en gearbox. On the picture you can see how it was connected. So not correct according to my mechanic. He told me I need to replace the cable with a cable from a 1974 or 1975 with a clevis type 911.423.205.03. He is usualy right but before starting this extra task and buying replacements parts, what do you guys think ? Anybody else having this type of connection like in the picture ? Should I indeeed change it ?
Thanks !
Filip

[Flat6pac]

That’s a 77 and later clutch cable.
The arm is wrong for the cross over pipe on exhaust. That arm is pre 75
The 75 clutch cable goes around 90 degrees on the arm so it adjustment faces the passenger side of the car. I have the proper one available
Bruce

[Walt Fricke]

You have the cable used on the transmissions which incorporated the "harp" spring into the system. The harp spring cleverly reduces the force your left foot needs to disengage the clutch, and is indeed an improvement from its predecessors (as long as the spring doesn't break). The ring end of your cable is made to fit over a sort of hook on the harp spring assembly.

Someone made that sturdy sheet metal bracket bolted to the differential cover. The stock bracket to hold the Bourden tube of the long cable assembly is an aluminum piece which bolts to two of the diff cover studs (which are longer for that purpose).

Your clutch release arm is from an earlier model. The cable end for that design is a threaded rod swaged to the flexible cable. One benefit of this design is that you can install and remove the cable from up by the pedal cluster. The threaded end goes through a hole in a V shaped block, with a nut on its rear side for holding and adjustment. The V fits into the grooves you see on the clutch arm.

The "proper" clutch arm Bruce refers to has a 90 degree groove in it. The cable for that design is longer, and the cable bends around the groove, with its threaded end going through a hole in the arm's casting before the retaining nut is attached. It is my understanding that this is perhaps the worst of these three cable designs, because bending the cable around apparently places more stress on where the cable swages into the threaded end. Bending at the end of a swage increases the likelihood that one of the cable strands will fatigue and break. After one breaks, the next one breaks faster, etc.

I'd not use that design on my cars, "proper" or not. But I've never used this part in its intended configuration. Maybe premature cable failure is urban legend or something like that.

The V block part on the arm you have moves just enough so that the pull on the rod end is always straight as the arm moves.

What you have might work just fine, or perhaps it's life is more limited.

Here is a diagram showing all three of these various kinds of clutch arms - the 4th is the one with a bend in it, and may be for the 1977 Turbo.



This is what I did when the only clutch arm I had on hand was the unfavored kind. I just modified it to accept a straight cable pull. Worked fine, but on a track car so the hours don't add up as fast as on, say, an urban daily driver.



In its stock form the cable threaded end goes through the hole where I run the stud welded to my part, with a nut on its end to hold it in place. I included this picture because it is what I have showing what the "proper" part for your year car apparently is.

Here is what the arm I happen to like (if not using the harp spring)looks like with the V block. The cable is not standard (part of a hydraulic slave system I made), but you get the idea of a threaded rod through the V block.



Here is a not very good picture of the stock aluminum bracket to hold the end of the Bourdon tube. It normally bolts directly to two of the studs on the diff cover. I needed it to be farther back, so I fabricated that short metal piece you can see so it could be mounted one stud farther to the rear. Perhaps if I had just the right clutch cable I could have used it in the right more forward configuration, but the one I had for my GT car was longer - hence using a tube to get the nut (a butterfly makes adjustment a bit quicker)back where needed.



Here is the harp spring system. You can see the aluminum bracket bolted to where it belongs. On at least one earlier model of 915 transmission the end of the Bourden tube was held in a slot cut into a transverse rib of the tranny housing. Later, Porsche milled parts of these ribs off for clearance of the cable end and to attach the small bracket:



Now you know more than you may have wanted about the subject, and perhaps it will help you decide what to do (or just confuse you more).

[Walt Fricke]

Oh - if you really want to know what parts were supposed to come with your car, download the PDF parts catalog for it from the Porsche website. They have these for free. Sometimes some interpretation is required to sort out what came with what - the page I posted came, I think, from a Turbo catalog, but I had it in JPG handy.

[fdeville]

Thanks guys for such a mass of information. based on this info, my conclusion is that I have to buy another cable (91142340105) plus the end V-shaped bloc (91142320503) and replace the strange home made part on the transmission with the standard one.
From your experience, is it easy to replace the cable through the tunnel (with the transmission already in the car) ?

[Flat6pac]

There should be a hole on the section with the numbers on to seat the cable cover.
Bruce

[MBEngineering]

HI fdeville

to make things easy, you need one of these to fit the cable to


https://www.wevo.com/Products/ClutchProducts/915Products/WevoClutch915Products-XT206ClutchCableBracket.htm

the pivot/adjusting part for the cable to connect to the arm is 911 423 205 03

you will need 2 nuts for the end of the cable for adjustment and locking

you may need to ding the exhaust crossover pipe to clear the end of the clutch cable

[fdeville]

Thanks all again.
I took a picture of the underside of the rebuild transmission (picture above was from five years ago, before rebuild). It seems like I have the right connection on the transmission, the guy who did the work apparently knew what he was doing .

[Walt Fricke]

Mike - so Porsche used that "bend the cable 90 degrees" arm because of a clearance problem with the threaded rod sticking straight back?

[Walt Fricke]

FD - I wouldn't call scrabbling around in the tunnel by the pedal cluster/driver's feet detaching the old cable, adjusting, and connecting a new cable there especially easy. But do-able. Your car is old enough that there is no console in front of the shift lever sitting on the tunnel? At least you don't have to remove that before you pull the carpet back so you can use the oval hole in the top of the tunnel to do the work there.

[MBEngineering]

HI Walt

yes and then found that the clutch cable bent round the end of the clutch arm was good in the drawing room, but not in practice, the cable snapped with lots of gear changes and town driving, so the exhaust has a flat section in the cross over pipe, not a prob' if the exhaust has been back dated to the older heat exchangers






IF the bent round the arm cable is to be fitted, get a Porsche one, as the aftermarket ones I have found are not as thick on the inner cable and do not last.

I would take the SC cable out and fit the cable and parts to the arm fitted on the box now, looking from your last photo, the cable mount on the bottom of the gearbox was maybe damaged and the Wevo one put on the hold the outer cable,

SO fdeville, just what is fitted to the bottom of the gearbox to work the clutch arm?

the 1st photo from the start of the work has a early arm and a made bracket to a SC cable

the 2nd photo has the new wevo bracket and ? (no cable) ,so what cable is there now to work the clutch