OK, nobody has ever answered this shifting question fully

[Jerome74911S]

This is not the first thread on this problem; I know because I started one of them myself, and I read the other threads. The question involves gear shifting that gets more and more difficult the longer the car is driven, which is to say, the hotter it gets.

• My shifting, when hot, will first get difficult getting out of gear, and as the trans gets hotter, then it will also become harder to get into the next gear. It does not crunch going into gear until I have driven 4 to 5 hours. This means any gear.
  
  
• Most previous answers blamed an old clutch cable that is stretching, or even unraveling. My response to that is this: How does it then cure itself when the car cools off? The cable is not subjected to any appreciable heat, so why would that be a factor? My clutch is adjusted properly. Can a cable get stretchy, then not be stretchy after everything has cooled off?
  
  
• What about 'easy' other things, like the gear oil? I am using the Kendall that is highly recommended by many here.
  
  
• What else can be binding, or otherwise malfunctioning as it gets hotter? None of the symptoms are bad when the car is cooler.
  
  
• The transmission was recently rebuilt (8,000 miles) by a well respected shop that serves successful Porsche racers.
  
  
• I am able to double-clutch to upshift when hot, and double-clutch and rev-match to downshift when hot. Not necessary when cool.

The trans is a 1974 915.

[javadog]

You ever measure the clutch cable travel? Adjusting the cable properly?

JR

[DRACO A5OG]

PMed you

[Jerome74911S]

The adjustment is correct, but recently I tightened it up slightly when trying to address this issue. If adjustment is good, how would cable travel be wrong?

[javadog]

The adjustment and cable travel have nothing to do with each other. On the later cars, you actually preload the cable a little bit when adjusting the clearance. The cable travel is adjusted by moving the pedal stop on the floor board. I don't have a 74 and I don't know if yours has been updated to the later style release mechanism, so I can't comment on the specifics of your installation.

JR

[Jerome74911S]

Originally Posted by javadog

The adjustment and cable travel have nothing to do with each other. On the later cars, you actually preload the cable a little bit when adjusting the clearance. The cable travel is adjusted by moving the pedal stop on the floor board. I don't have a 74 and I don't know if yours has been updated to the later style release mechanism, so I can't comment on the specifics of your installation.

JR

Interesting thought. I tightened the cable up a bit in trying to address this issue. As I push the clutch pedal down by hand I can feel the point where release goes "over the top", so I'm puzzled to understand if travel is a problem for me. Original release mechanism is on the car.

[Matt Monson]

Sounds like the synchro rings are too big and are binding on the sliders.

[kodioneill]

Originally Posted by Matt Monson

Sounds like the synchro rings are too big and are binding on the sliders.

Agreed. Did the trans shop replace the sliders and syncros together?

[Jerome74911S]

Originally Posted by Matt Monson

Sounds like the synchro rings are too big and are binding on the sliders.

Another interesting thought, but the problem is getting worse with time. Wouldn't this issue have presented itself right at the start, or not?

[Jerome74911S]

Originally Posted by kodioneill

Agreed. Did the trans shop replace the sliders and syncros together?

The shop replaced the synchros and operating sleeves together, along with 2nd gear dog teeth and other odd bits.

[javadog]

I don't recall if there's a spec for travel on a 74 but on a later car it's about 25mm. Worth a measurement...

[pete3799]

Sounds like it may be a travel issue (clutch not disengaging all the way).
Were does the clutch start to grab 1/4-1/2-3/4 of the way up?

[Jerome74911S]

Hi Pete. The clutch engages about 1/2 way up, and it feels fine - nice and smooth and all.

I'll take a look at the stopper on the floorboard, but it does seem that the clutch is releasing completely, at least when cold. Why it changes when hot is the mystery.

Of course, my clutch is the old fashioned type, if that changes things. Easy enough to measure travel, though:




Are you going to be defending your dominant status in the rally next weekend?

[sacoffee]

It's a hydraulic clutch?

[DRACO A5OG]

Nope = 915 cabled

OP, see if after checking the arm has slop, it could give you a false reading.

I found an assistant to be very helpful in fine tuning the adjustment.

Jim

[pete3799]

Originally Posted by Jerome74911S

Are you going to be defending your dominant status in the rally next weekend?

Yup
Should be a cinch as my competitor can't shift his car

[E Sully]

On transmissions before the helper spring was added, clutch adjustment is different.
All adjustments should be done on a warm transmission. Free play is measured by pulling the clutch pedal toward the seat. 15mm-20mm max.
Travel is correct when reverse can be selected with out grinding. Travel is adjusted by moving the plate on the floor board.

[Jerome74911S]

Originally Posted by E Sully

On transmissions before the helper spring was added, clutch adjustment is different.
All adjustments should be done on a warm transmission. Free play is measured by pulling the clutch pedal toward the seat. 15mm-20mm max.
Travel is correct when reverse can be selected with out grinding. Travel is adjusted by moving the plate on the floor board.

Free play on a '74 is measured by pushing the pedal down, not pulling it up. That method perhaps applies to earlier cars (?) As for selecting reverse without grinding, I have no problem. I'll check the adjustment while warm - I always have done it while cold.

[E Sully]

Travel would be measured by pushing pedal down.

[Jerome74911S]

Originally Posted by E Sully

Travel would be measured by pushing pedal down.

That's true and I'm going to check travel length. But actually on a '74 (at least), free play cannot be measured by pulling the pedal as shown in the photo, because it rests against a fixed, non-adjustable stop that prevents pulling the pedal toward the rear as shown. Therefore, free play must be adjusted by pushing the pedal forward, as on certain other models.