Michael Benno

I have some play in my clutch pedal I am trying to diagnose. Check out this video of the free movement before the pressure of the hydraulic fluid:

I am pretty sure it needs to be re-bleed since I replaced the clutch line this past spring. But part of me is wondering if the clutch master cycling is going bad. What are the symptoms of the MC going out? When I used the power bleeder to reverse bleed the clutch, I did get a few drops push through the seal on the MC. I wiped them up and haven seen any new weeping. I do get a little stiff return of the clutch pedal on the first two uses on cold mornings.

Thoughts? Start with bleeding and see where if it goes away?

This is a close up of my Master Cylinder. There is some signs of the brake fluid eating the paint but no signs of dripping on the the carpet.




This is the clutch line I replaced (sample pic)


This is the what I replaced the clutch line with (sample pic)

jtrygstad

Replace it.

Michael Benno

Mrmerlin

what you have to understand is that the pushrod at the pedal has to have some play at the tip where it pushes on the piston, it needs about 1 to 2 MM of play.;

To bleed the system with the GB flex line remove the slave from the bell housing open the bleeder and let out any air hold the bleeder at the top position.
Then lower the slave so the push rod of the slave is closest to the floor,
press the pushrod into the slave slowly about 3 to 4 times and hold it each time for about 30 seconds then let it go .
this should purge any air from the lines and give you a properly operating clutch pedal.

Michael Benno

Hey Stan thanks for the tips. I did as you recommended with bleeding the slave and it did seem to help remove some of the play in the system. I have a little better action on the clutch pedal and realized I still have the same problem with clutch engagement at the top of the stoke. I inspected the clutch wear at the port on the bottom and it looks like it's well past it's wear point. :-(




For reference the WSM has a slightly different take on the pushrod adjustment, Is there a particular reason you are recommending some play where as the WSM is recommending pre-load?

Mrmerlin

Usually when trying to make sure the clearance is removed , it has some load, its usually too much as its difficult to feel,
if you have a small amount of play in the rod,it will guarantee that your not going to have the piston not returning to full stroke,
thus being able to provide a full stroke of fluid to the slave.

NOTE things change when the clutch system gets hot,
I have never had a problem doing this and many problems with a piston thats too far adjusted.
You also have to know that the rear side of the MC where the push rod enters is a washer,
so you can be tricked by thinking that you have removed the play when infact your preloading it more than suggested.
because you dont see the washer move.

NOTE also take the clevis pin out and see how much wear the clevis and pin have,
they might need to be replaced

NOTE in your picture you may still have enough clutch as if the TOB and release arm have been changed to the GTS parts this could change the sight for the wear limit and using an older PP.
or the release arm bushing is worn out
The whole clutch system should be inspected to see if it has been modded to work with different parts.
Otherwise you should have an idea what clutch parts you do have
IE grinding the pads on the release arm or the TOB so one surface is flat

Michael Benno

Thanks again. I'll hold off on my "preparing to replace my clutch" post until after I have inspected the parts. I'll pull the cover and do some inspection. The clutch was replaced I 2005 so there is a chance the parts were updated. Can you give me an overview of how I would identify the part differences?

I reviewed PET and noted that the bottom cover is the same from 1987 - 1995 so I don't understand how the the GTS parts could impact the wear limit if the inspection hole is in the same place.

Mrmerlin

The GTS parts dont always get updated together and sometimes other parts get used or reused because they seem to be good,
Earlier versions of the release arm had different contact points compared to the GTS parts where it would contact the TOB face.

So sometimes the mechanic would modify something to get it to work, IE use some early parts with GTS parts.
Ideally you would replace the whole clutch with GTS parts,
its expensive but thats what they are making now
These parts include.
S4 single disc slave cylinder, its the longest slave and pushrod they make.
NOTE if you have a 86 slave then the clutch will not release as its not going to provide a long enough throw
Release bushing
Guide tube that fits the new TOB
TOB that fits the new release arm
pilot bearing
Release arm that properly fits the new TOB
Pressure plate,
Single clutch disc.
Greg Brown flexible line from the sway bar mount to the slave. This replaces the old flex/hard line combo
One tube of the Porsche clutch spline grease its dark brown and very sticky use a tooth brush to coat the splines on the disc and stub shaft.
NOTE Greg Brown also makes a super hard 300M stub shaft it costs less than the factor stub shaft and is better quality

GregBBRD

When you remove the slave, apply some high pressure grease into the cup that the rod from the slave inserts into....that rust is metal grinding away.

Remove the air filter and make sure the plastic bushing in the T/O lever is present. Without the plastic bushing, the arm will be metal to metal with the pivot ball.

If you are getting any leakage from the master cylinder, under any circumstance, it needs to be replaced. When you get the new master, remove the guts from the old master (in situ) and see if the bore of the old master is perfect (they frequently are.) If the bore looks fine, just install the guts from the new master into the old master....this will save you many hours.

Michael Benno

Regarding the Clutch Master Cylinder, per the advice of Greg, any fluid means the seal is bad so I'll replace. Greg that's a great tip about rebuilding it in place. I'll consider that. But I think I'll want o replace my blue hose too, so since I'm in there, I may as well give the CMC replacement via the string method a try, Not 100% committed either way.

Regarding if my clutch is worn or not, I inspected the parts and was able to mostly verify I don't have any GTS parts in there. The TOB sleeve is steel, so its not the plastic GTS sleeve. The upper clutch case is the earlier 1997 -1991 part (PN 928.116.402.0R). The clutch fork ( PN 928.116.832.07) is not the GTS PN either.

@Greg, I was able to verify the plastic bushing was there but I noticed it was loose in the fork. So maybe that bushing trashed and it's causing the position of the fork to appear more forward than the clutch wear alone would. How the hell does one replace that without removing the upper clutch case? Can I get to it from the top?

the flyin' scotsman

I applied this method many years ago now.......works perfect.

Kevin in Atlanta

I've been chasing a slight loss of clutch pedal overnight. I bled the clutch after SITM and it had been ok until my recent trip to Baltimore and back.

The pedal always improved once I had drive a while.

Last night I decided to take a closer look at the clutch master. I pulled the boot to see if there were any indications of a failing master.

The master was rusty and there was some old dried residue. No smoking gun.

But, when I went to check the preload it was excessive. I dialed it back until it wiggled a bit.

Today on my first drive the pedal was near perfect. I don't understand the science of how the pedal improved overnight. I assume it was the seal out of position.

So, no preload good, very good. Excessive preload bad.

I really was coming to terms that a new clutch master was in my future. Glad to report that will not be the case.

I assume a previous owner added 5-6mm of preload.

HTH somebody else chasing the same issue.

Mrmerlin

NOTE you need a good back to adjust the MC pushrod,
ESP in the GTS with the knee baffles.

Kevin in Atlanta

Well, it was the '88 - lucky for me and I premedicate with Advil. :-)

Mrmerlin

88 still has the parcel tray in the way.
Bayer Back and Body also works very well.