Tactcil feedback: I can feel my shifts

[Chuck Moreland]

When driving Babbar, my '73 - When I shift I can feel it in the accelerator pedal. Slap it in gear and I can feel a little tug on the pedal. It is most obvious on 3rd and 5th.

I suspected the accelerator cable was wrapped around the shift linkage. A careful inspection convinced me this was not so.

Then I thought the hand throttle was rubbing against the shift linkage. Again, I'm pretty sure this is not the case.

Current theory: The throttle linkage has a pivot shaft that is anchored into the transaxle. Shifting causes a small movement in the transaxle, which is then felt in the throttle linkage.

I have new sport mounts on the transaxle. Original mounts on the engine which are about to be replace with solid mounts. If my theory is correct, the solid mounts should reduce the tug I feel at the pedal.

None of my other 911s have had this behavior. Does anyone else feel this? Any alternate explanaitions?

[Tyson Schmidt]

I think you're right.

But I doubt that the solid rear mounts will help. The trans mounts control fore/aft movement, and the engine mounts control twist. The rear cross mount flexes so much in the fore/aft movement, that it would undermine the solid mounts.

If you put in solid trans mounts, you would eliminate it. But I do not recommend solid trans mounts. Too noisy.

[Chuck Moreland]

I see your point about the flex in the cross mount canceling out the solid mounts.

Does anyone else feel this? I know I don't have super sensitive feet.

[wevoid]

Chuck,

I pretty much agree with Tyson, but it would also be worth looking at the clutch cable too.
The clutch cable mounts can start to break free in the tunnel and being adjacent to the throttle cable, might have an impact. The same might happen in the pedal cluster if starnge wear is present.
If the condition exists as Tyson suggests, it would occur when the torque is re-applied - coincidentally, same time as the clutch cable / pedal pressure goes slack.
I would look at the clutch cable and pedal assembly too.

Regards

Hayden

[Chuck Moreland]

Hayden

The pedal cluster is freshly rebuilt, the clutch cable is new. It's not the clutch I'm feeling.

I feel it when moving the shift lever, just when it clicks into gear. It's not related the clutch pedal.

[wevoid]

Chuck,

In that case, I agree with Tyson. Should be easy to visually validate your suspicion.
Have someone select 3rd and 5th while you look at the engine. In either gear, the shift lever is trying to push the motor/trans backwards in the car. If you can feel it in the pedal, I suspect you will be able to see it in the engine bay, or feel it by spanning your hand between the engine and the chassis somewhere convenient.
We once had a customer who installed new transmission mounts and used the incorrect length bolts ( 2 cars prepared together, same symptom). The bolts bottomed in the thread bucket in the chassis before they really clamped the transmission mount to the chassis. The result was that the engine could move back and forwards by the amount of clearence on the bolts trhough the transmission mounts, this was quite a problem when our dog gear transmissions used the gated shifter handpiece.
If selecting 3rd and 5th requires enough force to noticeably move the engine and transmission on new sport mounts, I would be concerned about the durability of several parts in the gear selection mechanism.

Regards

Hayden

[BlueSkyJaunte]

Waitasecond--it's drivable??? Pics, man, pics!!!!

[Chuck Moreland]

Hayden, that theory seemed to show promise so I checked it out today. However the bolts are securely clamping down the steel sleeve in the center of the mount.

To my surprise, I found the rubber part of the mount can slide up and down on the steel sleeve probably 4 millimeters. This had me concerned, until I found the engine mounts do the same thing.

Laying under the car with my lovely assistant shifting gears, I couldn't detect any significant motion of the transaxle. Shifting doesn't take any unusual effort.

I don't know if I have a problem or not. It doesn't interfere with driving the car. It's just odd so I suspect it is a symptom of some problem.

Bluesky

The car has been driving for a couple of weeks, though it's not complete (are they ever complete?). The car still needs its rollbar, harnesses and roadwheels. So I'm holding off on the full "Jack O" type pictorial till it's done.

I had to get it rolling for a sneak preview at German Autofest, where these spy photos were taken:

[VincentVega]

:P