I recently purchased a '93 GTS with 120K on it. I finally got the shift action itself tightened up after replacing all the bushings. My next project is the amount of driveline lash there seems to be in the lower gears. Starting out in first, shifting to second and then third each results in a noticeable forward backward wobble with each shift after the clutch is fully engaged. I replaced the motor mounts with solid rubber ones and that seemed to help a little.
I had an 82 s that didn't exhibit this issue, then again the synchros were worn on that car so I had to shift a lot slower.
Do the 5 speeds all have a fair amount of lash? Might it also be worn rear suspension bushings contributing to this issue? Other bushings?

 

The driveshaft acts like a torsion bar and twists quite a lot with the torque of the 5.4.....still not sure what you are describing and how fast you are shifting.

 

Never thought of the driveshaft acting like a torsion bar....I suppose that could be it. It must twist a fair amount to introduce that much wobble though. Best way to describe it is like the lurching you get when you're first learning to drive stick shift. But even when on a trailing throttle in say second gear, when you get back on the gas you get a forward backward wobble sensation. It just seems more noticeable compared to other manual transmission cars I've owned that had similar power levels.

 

I have that problem in traffic , clutch out /just over idle . lurching / bucking , jerking . The only way to stop it is push in the clutch . The driveshaft acts just like a big spring . Of course the sourse of the problem could be the jerk behind the wheel.

 

I like that according to the 1980 owners manual the minimum RPM shift into 5 th is at 48 MPH or 2,400 RPM......3rd to 4th 2,700 RPM. Porsche does not want the engine lugged at low RPM primarily because of the driveline twist and spring effect.

 

Interesting...I tried the higher shift points and it does seem to help. Just hadn't expected that as a side effect of the design of the driveshaft. Thanks for the input.

 

Make sure your engine mounts have not collapsed.

 

[quote=Andy C;8859439]

 

The 4 cylinder little brothers of the 928 use a big rubber diaphram as part of the clutch assembly to absorb the twisting untwisting of an engine only firing half as often as the 928. Porsche also in one Tech Notice stated that ONE cause of broken driveshafts was when a 32 valve was driven on 4 cylinders ......like after a partial ignition failure.
If you ever try to loosen the front crank bolt on a 5 speed by putting it in gear with the brakes on......you quickly see how much twist is in the driveline before the bolt breaks loose.

 

What about the trans mounts?

 

I've got pretty significant driveline lash in my 5-speed GTS, with new factory engine mounts and tranny mounts in the last 3000 miles. Much more than in my GT, which also has new-ish (7000 miles?) MM and tranny mounts as well. For a while I thought it was some quirk of a non-smooth Sharktuned fuel map, and that may be contributory, but it's interesting that other folks are seeing it too. Anyone with a supercharged 5-speed have issues with lash? Or is the problem only proportional to low rpm, high torque situations?

 

My GTS does the same thing. Kind of bucks forward to backward. Thought it might be vacuum related or something??
Drove Herman K's car and it does NOT do it at all, its much smoother.

 

Be smooth, gentlemen. Be smooth.

 

Oh, I'm smooth, all right . Still bucks pretty good. I can get it to buck in pretty much any gear if I'm in the 2000-2500 rpm range, with very light throttle application. I know the answer is to stay out of that rpm range, but that can be difficult in stop-start-stop-start land here.

I'll see if I can get a video of the behavior to illustrate.