cthagreekgod

Hey guys, this is a pretty rookie question, but I'm not 100% sure of how this works.

What is ultimately responsible for the clutch pedal returning to the top. My clutch keeps losing pressure, until I eventually can't shift and the pedal stops returning.

Here's why I ask, and maybe this will clarify my qustion a bit:

I've got a 1990 4runner, V6. Had the Master replaced in Aug 2003. Had problems again in Jan 04 again (It seems to happen everyt ime it gets really cold, I'm in canada here, so like -40 celsius), so I brought it back to the shop. They replace my clutch, saying that it was the clucth that was the problem. The slave was never replaced. And now I find myself in January (well, feb now, but it started last month) losing pressure in my clutch pedal again, eventually I lose the ability to get in and out of gear. I bleeed the system and it is ok for a few days, but then it starts to go again. I just ordered a new slave seeing as it is the only thing that hasn't been replaced. But I am wondering if it might even be the problem, or if I'm way off base here.

Unhappy99

Does the pedal return to its top stop? Or it is sticking down? And another question: Does the pedal feel different between warm and cold? i.e. does the engagement height change?

If there is a difference in engagement height and feel between warm and cold, you have air in the system.

For the pedal it to stick down, the clutch master cylinder piston is jamming in its bore. This means it has either gone bad, or was not bled properly when installed. (Air in the system)

The clutch masters must be bench bled VERY WELL before being put on the car for a final bleed. They must be twisted, turned and banged on with screwdriver handle to get all the air out.

cthagreekgod

Thanks for the reply.

I defnitely notice a difference in pedal height when I use it frequently. That is, it's gets softer after a long stint on the highway where I haven't shifted in a while. I know there is air in the system. The first time I bled it, I thought I got it all out.

So, is it likely I just ordered a new slave for nothing?

Do you suggest I remove the master and try to bench bleed it while I am going through the replacement of the slave?

shiftless89

Also be sure to check your hoses/lines the tiniest pinhole will let air into the system and cause similiar problems

Unhappy99

If air in the master is your problem, then it is likely to have worn out the bore already. I went through 2 masters in 5 months due to them not being installed and bled correctly at the dealership. The pedal felt mushy until it seized in the bore. Finally did it myself with an Autozone master and never had problems again.

cthagreekgod

Thanks guys, much appreciated...

cthagreekgod

I noticed that the fluid in my reserve and the fluid that is being expelled is full of debrism sort of a black dust. Obviously in a closed system, there should be nothing but clear fluid. Is this a sign that one of the seals has degraded and is now turning to debris in the system?

Tonight I bled the system and I still can't get the clutch to activate (I can't shift without pumping...).

Unhappy99

The black debris indicates your master cylinder has gone bad. The debris is a combination of neoprene seal material and aluminum dust from the scraping of the piston against the bore.

When you get this one replaced, disassemble the old master. Take a look at the piston and bore and you will see shiney wear marks, and perhaps even an out of round piston. This means air was still in the master when it was replaced last time, and the piston wasn't square in the bore, causing early failure.

Bench bleed, bench bleed, bench bleed....Took me about 30 minutes of tapping and bleeding before I was convinced all the air was out.

Steveh29

It's a pain to bleed the hydraulic clutch. Here's a link that I've found useful when bleeding mine.

http://www.v8archie.com/arch4.htm

I had the rubber hose from the firewall to the engine go bad several times on my truck. Very irritating.

wrenchmonster

Alright. First of all, yes bench bleeding is important, but not imperative. Pressure bleeding/vacuum bleeding is better in my opinion. Though if you have the master off anyway, why not? If your fluid is getting black, that can be caused by the master OR the slave cylinder as the fluid exchanges between the two. The slave cylinder is more likely the culprit here. Take the boot of the slave cylinder and see if there is any moisture outside the assembly? Look at the back of the master cylinder for the same thing. Also, check the return spring for the pedal itself to make sure it's not worn out. Check the clutch pedal to make sure it was not mal adjusted after your clutch job.

-Wrench

kyle_22r

i didn't bench bleed my clutch master when i rebuilt it, works fine. i did pump quite a bit of fluid through it as the stupid line on my bleeder bottle kept falling off

i'm pretty sure that the clutch diaphragm spring is what's responsible for pushing the pedal up. the fluid and the master and slave cylinders basically function as a link to push on the spring.