GregBBRD

There are actually three versions of the "late centering spring", but only two of which Porsche ever offered replacement pieces for. Not exactly where all the different ones started and stopped. There is the "early spring, which is held captive on the lower adjusting pin by a circlip. There is a washer between this spring and the lower adjusting pin. This spring has a "short detent section" and uses the "narrow" upper shift roller piece. The "middle" spring, which Porsche never offered a replacement part for, had the same lower dimensions and pieces, but had a "taller" detent section. This requires the use of the "wider" upper shift roller piece. The third design is what has been available. The lower washer and circlip are eliminated (the lower part of the spring is therefore dimensionally different than the two early springs), and the upper has the "taller" detent piece, which also uses the "wider" upper shift roller piece.

Note that the "early" spring has been NLA for quite some time and required the use of a "wider" upper shift roller piece, when using the "late" spring. Failure to change to the wider roller will result in the shift spring breaking quickly...and often.

BTW....I wouldn't suggest that driving the vehicle with the lower spring piece still in there is a good idea. The broken part of the spring flops either forward or backwards....or bounces around between the two places. It will rub on the gears. It is possible to "catch" this spring on the gears and turn a gearbox into scrap metal.

Mike Frye

Has anyone out there tried the new spring? I was one of the initial testers of Colin's spring and the first version of it was not so much a spring as a piece of steel cut to the correct dimensions. There were two of us that tested version 1.0. One put it into his trans and I tested it before electing not to. There is a very long thread over on Reutterwerk on it.

I never heard back from Colin after the initial tests so I am curious how the further testing went. I wasn't aware that he continued working on it.

Colin (or anyone who has first hand knowledge of the replacement part) can someone give us an update?

RET

I have been driving with my repaired preselector spring for awhile. No problems so far, and with the other new parts (rebuilt coupler and forward bushing), the shifting is precise: no more Ouija board gear selection.

I was not too thrilled about installing an OEM spring with its obvious (at least in my opinion) design defects (note the plural here). This concern was pretty academic as I could not find a NOS part and used was totally unacceptable.

After thinking up some elaborate but unworkable substitutes, I decided to simply fix the broken part using the best compromise of materials available, dimensional tolerances within the transmission (i.e. - next to none!), tooling in my possession, and fear of the unknown....

The basic idea of the repair was to eliminate the main points of failure and allow the new spring to flex evenly along its entire length and so avoid the fatal stress raisers of the OEM part. The OEM springs have an obvious fault in the square corners of the hole punched into the spring: it is exactly the wrong shape, and in the wrong place. The stress raiser formed there, combined with the tapered shape of the spring and the swaged piece that prevents the spring from bending beyond the bottom of the punched hole, causes the OEM spring to be stressed greatly at that point and results in failure of the part.

I replaced the tapered flat spring portion of the assembly with a piece of 1.25 inch wide and .062 inch thick spring-tempered spring steel with no taper (note: I think that 1.25x .050 would likely work as well). The original cross piece (the part that engages the shift selector arm) was milled down and brazed to a small square of steel which was slotted to retain it and this small subassembly is fastened with two 3/16 inch steel rivets only at the top end of the new spring.

I had drilled out the rivets on the old part in order to reuse the machined casting and used 3/16 inch steel rivets to fasten things together for the simple reason that I had them as well as carbide tipped drills to use on the tempered spring steel.

I also installed a hairpin clip on the end of the pivot bolt to retain the lower end of the spring should my repaired spring assembly fail… just in case.... at least the car would be drivable without the danger of the lower part moving into the layshaft gears, as the stock part will. There are seriously unpleasant consequences if the lower portion of the spring comes adrift inside the transmission.



Unfortunately, I don't have much expertise in uploading pictures, so....

The first picture is of part of the original broken spring, the adjusting/support bolt with retaining clip, and s brass mocked-up part used to test measurements.

The second picture is of a trail assembly of the part with AN bolts in place of rivets holding the spring to the lower machined casting, and the brazed and riveted top assembly.

The third picture shows the spring assembly being inserted into the transmission. Note that the shift selector shaft has been removed in order to make life a little easier... Note also the cord tied to it and snaking over the edge of the transmission - it has a small weight on the other end and its purpose is to make retrieving the spring assembly easier when it gets fumbled into the bottom of the transmission....

The fourth picture shows the spring assembly being held in position while the supporting bolt is installed from the outside.

The fifth picture should really have been the first: it is the transmission before clean up and surgery.

fraggle

BIG thanks for reviving this, I'm still lost as to what I should do when the inevitable happens and mine breaks. All I have is a single axis mill (my drill press), tons of time and lots of carbide and cobalt bits.

RET

Fraggle - One thing NOT to do: do not drive after the spring fails. Very bad things can happen.

The easy and quick part is repairing the spring. The time consuming efforts are what has to happen before and after that.

MCMaster-Carr was my source for the spring steel. I had little choice about using the already tempered strips as I have no way of properly heat treating untempered material. I would also suggest welding the cross piece to the top piece rather than brazing. I would not suggest welding to the actual spring itself, even with TIG, as this changes the carbon content of the steel as well as the temper, which I believe will recreate stress raisers,

Be advised that there is little (as in no...) room in the transmission case for any extra thickness or length.

UncleMaz

I have the early Borg Warner type described above by G. Brown, with the washer and the circlip.

How in the heck to you get that circlip off the end of the adjustment rod?