atb

Okay, first mistake was getting the part through a local vendor, but at the time the part was needed in a hurry.

This is a clutch master for a '79 with big booster.

It looks exactly like the one that came out of the car, and the box says *** made by FTE, part # 928 423 173 06.

The part was installed, and there was some issue with the clutch not fully disengaging. When measured against the original part, the new part only had about 27mm of stroke compared to about 36.5mm of the original. John Davis measured his '84, and it too had 36mm of plunger travel.

At the slave, the actuator rod only moves about 12mm compared to the 17.4mm spec in the WSM.

Has anyone come across this particular problem with this particular part?

atb

Perhaps I should add in here:
1) Does anyone have a clutch master sitting on a bench that they could measure the plunger travel?
2) Does anyone have a 928 in the air that they could measure the clutch slave actuating rod travel?

Thanks.

Tom. M

Did he get all the air out of the master?...bleed it from the inside...and plunge the slave a few times to free up any trapped air...could be a trapped air issue.

The only problem we have had in the past was Sean K's clutch..it was actually actuating too much..and pushed the release arm over/off the release bearing...

Did he adjust the double disk intermediate plate? it's only 5mm off (12 vs 17mm actuation)...not much...but an out of adjustment int. plate would cause issues..

atb

Probably not air, there is a mechanical "clunk" when the pedal bottoms. Ken noted that the pedal travel felt short when he installed the new unit, and disconnected the linkage to make sure the pedal wasn't binding. The pedal went to the floor. We checked John Davis' new one - still in the box - and it too only travels about 27mm, and as noted above the one in his car travels 36mm. One thing to note is that both Ken and John's original master cylinders are/were leaking around the seal. Could this provide the extra travel? Is an air tight master only supposed to have 27mm of travel?

Tom. M

It still could be air...the master may travel the full length and bottom out..but the slave only moves if fluid is being pushed from the master..if part of the master travel is taken up by compressing air (rather than moving fluid) it will not move enough fluid to actuate the slave.....

Do the master's cylinders have a washer up at the top end (where the clutch rod goes in)?..

atb

I'm with ya now Tom, I wasn't totally clear in my original post. (Although the thread title says it all )
I'm was more curious as to the difference in master cylinder piston travel between the new and old part, as opposed to diagnosing the malfunctioning clutch.
I think John led him through the usual steps, except for removing the washer. I don't think Ken was down with taking apart a brand new master cylinder.

I'm really just curious if anyone else has come across this shorter throw master cylinder in any application.

atb

Well here's the latest. Ken checked with a local parts vendor who I guess pulled parts off the shelf until he found one with the correct throw. It turns out that the boxes from ***/FTE were mismarked. The box has the correct Porsche Part No. as noted above, but the manufactures' No. (hence the part) is incorrect. The manufacturers No. on the box is KG19070.1.6.
The last digit should be a ".2" The .6 is a 27mm throw piston, the .2 is the correct 36.5mm throw piston. The misnumbered part is not just a local phenomenom, so if you recently replaced your master cylinder and you're still having engagement issues, check the manufacturer part No. for correctness.

RyanPerrella

ive heard of this problem before of aftermarket master cylinders not having full travel. I find it hard to believe but i have heard of this problem before.

Sorry, thats all i have to contribute. You may want to search, I would have read about it on here so there is probably some info in the rennlist abyss