Transmissions with Porsche Syncros

2531 Views 4 Replies 0 Participants Last post by aaron masters (Unregistered Guest), Oct 22, 2003

Discussion Starter · Oct 22, 2003

I wanted to share my “shifting

I wanted to share my “shifting” experience and see if the more experienced group out there thought it was normal.

This is a 72 US C4 with 42K on the odometer when I bought it – 15777 – I have very little history on the car prior to 1992. Body was in great shape (some cracking paint), but does have a cigarette burn in the carpet to the right of the passenger seat - apparently done on purpose.

When I got the car, shifting into second was an exercise in “grind avoidance”. First thing I did was pull the transmission – put in 5 new syncro rings – Reverse was virtually new so I just flipped it over. I put in a new 1st/2nd slider and 3rd/4th slider ($400.00 each) and filled it up with Redline shockproof fluid.

So – now that everything is new – it ought to be perfect, right?

Shifting into second and third at my casual (BMW rate) I still get a distinct gear “hit” where the syncro rings are not quite resolving the rpm difference. Shifting slowly – works fine. Also, shifting hard/fast works great as well – so I need to be really patience or I need to slam the gears- the casual shift situation does get better as the box heats up – as I have heard it should.

In my pursuit of perfection – I switched over to Swepco oil - the stuff all the Porsche people recommend for Porsche style syncros – The above situation slightly degraded – what I believe is that the Redline shock proof tends to be thinner at room temp. and it takes a while (It is natural mineral oil) for the Swepco to heat up and thin out. Also the Redline has a more “cushiony” feal – I will go back to it next time.

Comments?

Aaron

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Discussion Starter · #2 · Oct 22, 2003

Aaron,

A couple of question

Aaron,

A couple of questions...first.
How long ago did you do the transmission (miles-wise)? and...

When you did the transmission, were the syncro "teeth", on the gear assemblies, that the sliders engage inspected carefully for damage?

Were the clearances, with the new synchro rings measured on the gears (cone clearances)?

I just need a little more to go on...Thanks.

Regards,
David

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Discussion Starter · #3 · Oct 22, 2003

Hi Aaron,

almost sounds lik

Hi Aaron,

almost sounds like the syncro dogs are in the syncro brake channel backwards, preventing the ramping up and squeezing (expanding) of the syncro brakes against the inner slider surface. It is extremely easy to get them in backwards and the WSM gives an ambiguous picture of the correct positioning/direction if I remember correctly.

Regards, JRV

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Discussion Starter · #4 · Oct 22, 2003

*very important note:

O

*very important note:

Of critical importance to shifting issues is clutch adjustment and/or degree of release along with pilot bearing condition.. It is not uncommon for a poorly adjusted clutch and/or a warped clutch disc or PP or worn Pilot Bearing to cause shifting irregularities. Even the slightest contact between the Disc and PP/Flywheel or Worn Pilot Bearing can prevent the mainshaft from slowing down when the peddle is depressed. When any of the above occurs it can and will cause grinding when shifting.

It is possible in some cases to isolate the above conditions by feel if one carefully concentrates on feeling each phase of clutch actuation and shifting.

Regards, JRV

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Discussion Starter · #5 · Oct 22, 2003

Thanks for the questions – and

Thanks for the questions – and the input.

The transmission now has about 15K on it. I tend to be fairly gentle on the drive train, but I would think that any break in would have occurred.

The Syncro rings (hard steel ring, about 4 inches in daim, with a ½” gap and rough surface on the out side, one for each gear) are all new except for reverse. The old ones were visibly warn and now reside in my old parts box. The sliders were new from Ruttlands.

Regarding the dogs – I recall 4 components in and around the syncor ring channel. There where 2 half circle pieces that were apparently made of spring steel that applied outward pressure on the syncro ring when the syncor ring started to engage. One for either direction – (are these what is referred to as the “dogs”.) I do not recall in detail if there was a direction in which I put these.

There were two “T” shaped forgings, (I think these are the dogs), I remember one being longer than the other. One of them drove the half circle pieces (mentioned above) from the driving shaft. The other allowed the half circle pieces to push/rotate the Syncor ring. Thus, when the syncro ring started to engage, depending on direction (down shift or up shift) one of the half circle rings would be compressed in the “Syncro slot” causing the Syncro ring to expand and engage more strongly with the teeth on the slider. I do remember a distinct difference between where the “long T or dog” and where the “short T or dog” were place but I do not remember what the positions were. I put them back in as the manual depicted – it has a good picture of the Syncor assembly.

Also – I should add, My Gear “hit” is probably a relative issue. Anyone know anybody in the Sacramento area with experience that could drive the car and tell me if I’m over-reacting.

Thanks,

Aaron

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