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944 S2 Very Slow Gear Shift after Synchro Replacement

  • 1989
  • 944 S2
Mileage: 
220 000
Transmission
Australia, 
Alberta

I had synchro's changed about 500 mile ago by a very experienced local Porsche mechanic (although he would admit he is not a gearbox specialist). Gearshifts are good, smooth and reasonably quick at low to medium RPM (say upto 4,000 rpm). But slow or "gear clashing /crunching " above about 4,000 rpm (in the new gear). OK for the road, but it's also a track day car.

Specifically, for high rpm downshifts:

 - if I attempt a gear shift with normal speed and force, it feels to "shoot straight through" the sychro process and I get gear clashing; or

 -if  I shift very slowly it feels to "block" the full gearshift part way through the movement  above about 4,700 rpm (in the new gear)

It is worst into 2nd but a little slow into 3 rd as well, and worse on downshifts, but a little slow on up shifts as well.

Any pearls of wisdom?

As further background, I have tried four transmission fluids:

a) Liqui-Moly 75W 90 Full Synthetic

b) Swepco 201 (80W 90 I think)

c) an Castrol 80W natural mineral oil

d) Castrol 75W 90 full synthetic, said to have a similar "easy shift " additive as c)

Oils c) and d)  appeared to allow gearshifts at slightly higher rpm than a) or b) (4,700 vs 4,200 rpm for downshifts into 2 nd)

All above were after 30 minutes or so of highway driving, and with similar ambient temperature of about 45F to 55F.

 

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