Clutch or transmission

kavadarci · kavadarci's Garage

Hi,
I have this interesting sensation when in any gear and very little gas pedal the car goes forward but not smooth, jerks back and forth ever slightly. Adding more power fixes it and never happens again.

is this clutch or transmission problem?

Fairview · 05-21-2018, 06:02 AM

Quote:

Originally Posted by kavadarci

Hi,
I have this interesting sensation when in any gear and very little gas pedal the car goes forward but not smooth, jerks back and forth ever slightly. Adding more power fixes it and never happens again.

is this clutch or transmission problem?

Hopefully neither one! What about a constant velocity joint going bad? Would that exhibit the light load symptoms you describe? Others more experienced than me will opine, but I’d suggest starting with checking out the cv joints.

Jeff

john walker's workshop · 05-21-2018, 07:17 AM

Typical 1976 issue. Very hard to get rid of. Fuel/tune related.

Fairview · 05-21-2018, 07:22 AM

Quote:

Originally Posted by john walker's workshop

Typical 1976 issue. Very hard to get rid of. Fuel/tune related.

So John, is it a lean surge condition? BMW motorcycles of a certain vintage suffered from lean surge, so I can see how that diagnosis makes sense in this case. And yes it only exhibits itself in light throttle conditions. I didn’t realize some 911s did,too.

john walker's workshop · 07:55 AM

Yup. If the control pressure was decreased, allowing for a slightly richer run, that would help. A couple of times, removing the side vacuum hose from the WUR fixed it, but you can spend days trying everything in the book with no joy on 99% of them.

kavadarci · kavadarci's Garage

Interesting. Cv joints are all new.

Fairview · 05-21-2018, 03:24 PM

Quote:

Originally Posted by kavadarci

Interesting. Cv joints are all new.

It is highly improbable that you’d have gotten a new but bad cv joint, so it is even more likely that a John is correct- lean surge under light load conditions. The fuel to air mixture is so lean that the engine is hunting back and forth trying to run. My BMW motorcycle used to do the same around 2000 rpm with slightly opened throttle. If you ran faster or slower it was no problem. I cured it with a little black box that is made by Techlusion. It tricks the fuel injection brain to think the mixture needs to be slightly richer. Maybe somebody has done that for the affected 911s?

Hope you can get it fixed. Jeff

P.s. that is one tidy Porsche underside you have there!