AOW162435

I recently flushed and bled the brake system with ATE Super Blue, and a Motive bleeder ( ~ 15 psi). A few days later, I did the same to the clutch circuit. I must have allowed the fluid level to drop just enough to induce air into the clutch supply line, as my pedal went to the floor after performing the initial flush. After posting my findings here, I realized that another flush with a properly-filled reservoir should do the trick. So I went through the motions again and indeed regained my pedal.

After this work, a drive confirmed that the brakes feel even better than before, but the clutch action has changed. For what it's worth, the clutch operates correctly (allows normal gear changes), but has developed an odd feeling that I'll try to describe. Depressing the pedal feels just fine, smooth and with the same resistance as before. But when the clutch pedal is slowly released, I feel a strange 'rubbery', 'stepped' resistance. Imagine a piece of rubber pushing against the side of the clutch pedal arm - as the arm travels through its range, the rubber causes intermittent 'grabbing'. Of course, there is nothing interfering with the arm - but that's how it feels. Chris Walrod was kind enough to share some thoughts on this, and suggested that the rubber line at the slave may be in need of replacement.

I have ruled out my flushing/bleeding procedure, as I've done this countless times on other cars over the years, and tend to be very methodical and careful. I ran more fluid through the system than was necessary - just to make sure no air existed in the circuit. I remember reading a short write-up on the pedal cluster, and how the clutch pedal pivot points and master cylinder should be lubed. So I removed the time-warp floorboard and thoroughly lubed any and all pivot points. I found that the rubber bellows covering the clutch master cylinder shaft was split but nothing seemed to be in bad shape. In fact, the entire pedal cluster looked new.

So with my spotty description of the issue, would you:

- Perform another thorough flush of the clutch circuit, as air may still exist in the line?

- Replace the slave cylinder and rubber line?

- Replace the clutch master cylinder?

The lack of smoothness while releasing the clutch pedal makes it next to impossible to leave the line smoothly. Is there any chance that the new fluid caused the existing seals in the master and slave to somehow change? Before this, the clutch action was perfect

Sorry for the excessive , but this really is vexing! I welcome your thoughts.

Andreas

viperbob

When the clutch starts that notchy feeling when releasing, it is 99% of the time the slave cylinder. Replace it (and the hose if it look worn or just replace it anyway) and you should be back to normal.

dhicks

Andreas, we could do them together if you like. Let me know when you are free
David

AOW162435

David,
I'm stil in 'hold mode' for the big event....

Bob,
Could the fliud change have caused the slave cylinder to give up the ghost? If so, why?

Andreas

viperbob

Andreas, what happens when you flush the fluid is that you can dislodge some debris that has accumulated in the system. This can be from the slave cylinder, master cylinder, or just the decay of the fluid itself. This debris can also then act as a lubricant for the slave cylinder around the seals and piston. When you flush the fluid, you then remove this and with worn seals or worn metal sleeves you start to get more friction. Yes it is counter intuitive, but normal. Why do you think they do not recommend changing automatic tranny fluid in many cars? You will find a great number of problems occur right after changing fluid. Same reason.

AOW162435

Bob,
Thank you for the thorough response. I actually subscribe to that notion with the auto tranny in my '01 4WD 4Runner. 103,000 miles since purchasing it new and not a single issue with the tranny. In fact, not a single issue with the truck period.

Your explanation certainly makes sense, so I'll source a slave and rubber line. Do you have any thoughts that the clutch master may also be at fault? I'd rather not disturb this unit because of the nice tight factory hose clamp crimps Naturally the slave will be far more annoying to replace...

Andreas

viperbob

You'll find Andreas that the slave tends to be the culprit. The master cylinder seems to have a much longer life than the slave. Just take your time with the slave when reassembling. Remove the rubber access cover in the side of the tranny. This will allow you to feel that the rod is in the proper spot in the fork. I also use it to hook my fingers so that I can compress the slave onto the studs and get a nut started. Also, it is not a bad idea to have a stubby 13mm wrench. The nuts are not too tight, but access with a full size wrench is limited...

Good luck...

epj993

Andreas,
I found it a lot easier to replace the clutch slave by removing the left heater tube. Takes another 10 minutes, but will allow you to get both hands on the slave. I tried this after struggling for 45 minutes with one hand. With the tube out of the way, you can have the slave tightened down with 5 minutes. Also makes it easier to bleed.

Good luck!

AOW162435

Parts ordered! Thanks for the great info. I will post an update once the surgery is complete.

David,
It's just practice so we can do your's properly

Andreas

dhicks

OK......you are so kind to practice on yours so that we can do mine properly!!! Thanks....see you soon

Robin 993DX

Andreas,

There might be another possibility, the clutch pedal mechanism have two different stages, one stage you are fighting the pressure of the clutch pressure plate itself when you step on the clutch and the other stage is the return spring assembly on the clutch pedal assembly.

Have you tried to make adjustment to this adjustment bolt? The purpose of the adjustment bolt is to smooth out the transition between the clutch pressure plate and the tension spring on the pedal, so it is a seemless transition.

Also FWIW, in the 996 shop manual it did mention to flush the clutch slave cylinder with the clutch pedal depressed.

Here is a picture of that adjustment bolt.

AOW162435

Robin,
I did not mess with the bolt you reference, as the clutch action was butter smooth prior to the fluid flush.

When you state that the 996 manual mentions that the clutch circuit should be flushed/bled with the pedal depressed, do you feel that this applies to the 993 as well? When I performed this, I used only the Motive bleeder at ~15 psi and kept the reservoir full. Should I consider a different procedure to flush? It sure is convenient with the Motive!

Andreas

Robin 993DX

Adreas,

I think you should mess with the adjustment screw to see if it makes any difference. And yes I believe the procedure should apply to the 993 as they are pretty much the same design.

FWIW, I did flush my clutch slave cylinder on my 993 without depressing the clutch pedal and never experienced any issues. I only read to depress the clutch depal when flushing the clutch slave on the 996 shop manual recently.

CarmG993

Andreas - you described what I feel also. I have not flushed my system but I get a knotchy feeling when the clutch is brought back up. Basically a step feeling as you described. My other issues is that sometimes it feels (doesn't happen) like the clutch doesn't want to come back up, even though it does. The feeling can be pretty unnerving. I was told by one shop that the pressure plate was probably gone and a new clutch was probably needed. Now reading your post and the responses, I may go the route of first adjusting the tension (Thanks Robin), seeing how that feels. If it doesn't feel any better, bleeding the system. If still the same feel, I will replace slave.

viperbob

Carmen, change the slave cylinder. That notchy feeling will go away, GUARANTEED. I have seen this SOOOO many times. The shop that told you it was the clutch, never go there again. I'm serious......