throwout bearing and extended slave cylinder rod?

[9D1GSX]

A friend brought me his car today because he was having problems with his clutch not releasing. He has an ACT 2600 with very low miles on it, so before he brought it to me he replaced everything between the pedal and the slave cylinder with nothing working any better or worse.

When I pulled the rubber boot off the clutch fork all kinds of metal flakes came out and when I pulled the transmission, the throw out bearing was in about 5 pieces. It was attached to the clutch fork properly at one time because I found the wire clip with both the pieces of metal still attached but were both broken off. The fingers on the pressure plate had a pretty good groove around the insides about a 1/4 in. from the ends (more than normal for as low miles as it was).

One thing he had on the car was a slave cylinder rod that was longer. I was reading on a DSM site that they did not recommend using these because they put constant pressure on the throw out bearing and would wear them out quickly.

Has anyone else had similar problems and fixed with good results? Does anyone know about these extended slave cylinder rods and if this really could be the cause of what happened? thanks

kyle

 

[Taboo]

Originally posted by 9D1GSX
I was reading on a DSM site that they did not recommend using these because they put constant pressure on the throw out bearing and would wear them out quickly.

Obviously, someone's been talking out of his ass. x 1000 Do you have a link to that site?

Not only that the longer cylinder rod puts constant pressure on the t/o bearing, so does the 100% bone stock slave cylinder with the stock rod. The t/o bearing simply rides the pressure plate if the clutch is disengaged or engaged and varying the initial preload of the pressure plate by increasing or decreasing the pressure within the hydraulic system by the adjustment rod of the master cylinder changes the engagement point of the clutch.

The hydraulic system requires a certain amount of initial pressure for the clutch to function due to the limited stroke of the master cylinder. Since the diaphragm of the ACT2600 requires more pressure to fully disengage, it also requires higher initial pressure within the system - which can't be efficiently created even with the adjustment rod of the master cylinder fully maxed out.

One could install a longer adjustment rod to be able to preload the diaphragm in efficient manner, but the stroke of the master cylinder might be maximized before the clutch pedal reaches the floor and the pressure needed to fully disengage the clutch is realized. That's what's eliminated with the longer rod of the slave cylinder that creates the increase of the initial pressure without affecting the stroke of the master cylinder.

Does the increased initial pressure promote a faster wear of the t/o bearing? No. Even the increased initial pressure is still MUCH lower than the pressure that needs to be created within the hydraulic system to disengage a completely stock pressure plate. The t/o bearing has absolutely no problem to handle even the load required to disengage ACT3200.

The grooves in the fingers of the pressure plate indicate the t/o bearing seizure and it's consequent failure as result of lack of lubrication and has absolutely nothing to do with the longer rod of the slave cylinder.

 

[9D1GSX]

Thanks taboo, the site was Road Race Engineering.

http://www.roadraceengineering.com/clutchandflywheeltech.htm[/URL]

It's at the very bottom of the of the page.

 

[Taboo]

It really surprises me that this kind of misinfo comes from RRE.

There would have to be 0 psi of initial pressure within the hydraulic system in order not to put any constant pressure on the t/o bearing - which means that one would have to bleed the clutch without ever adjusting the rod of the master cylinder.

Once you start pushing the piston of the master cylinder in (after the clutch was bled) - in attempt to raise the clutch engagement point, you create initial pressure in the system and consequently put constant pressure on the t/o bearing - no matter if it's a stock clutch or ACT3200. If you don't and keep 0 psi in the system to begin with, the clutch won't ever disengage.

The longer slave cylinder rod has the same exact effect as adjusting the rod of the master cylinder by several threads. Heavier clutches requires higher initial preload (which doesn't mean that the fingers of the pressure plate are actually compressed), which does put higher constant pressure on the t/o bearing, but there is NO WAY around it - if you want the clutch to disengage. One may simply choose between 0 pressure on the t/o bearing + incompletely disengaging clutch + worn synchros and gears OR higher pressure on the t/o bearing + correctly disengaging clutch. There's nothing in between. You can either sacrifice the clutch disc and tranny to save the t/o bearing or chance possible faster wear of the t/o bearing in order to save the clutch disc and the tranny.

Personally, I do not believe in the increased t/o bearing wear as result of constant pressure theory for three reasons:

1) The clutch system was designed to put constant pressure on the t/o bearing from the factory. If it wasn't, the master cylinder would not have an adjustment rod that actually regulates how much of constant pressure one puts on the t/o bearing in order to raise or lower the engagement point of the clutch.

2) Even with very heavy clutches such as ACT2900 or 3200, the constant pressure is much lower than the actual pressure required to fully compress the diaphragm even of the stock clutch. If the faster wear theory was true, the heavier clutches would toast the t/o bearing faster than the stock clutch anyway.

3) I've been driving with the longer slave cylinder rod and the same ACT2600 disc/PP and t/o bearings for three years without ANY failure whatsoever. There's no theory against that.

 

[Defiant]

Originally posted by Taboo

Personally, I do not believe in the increased t/o bearing wear as result of constant pressure theory for three reasons:
1) The clutch system was designed to put constant pressure on the t/o bearing from the factory. If it wasn't, the master cylinder would not have an adjustment rod that actually regulates how much of constant pressure one puts on the t/o bearing in order to raise or lower the engagement point of the clutch.

I don't know that it's putting much pressure on it, but it seems like it'd be touching, and probably enough to spin the T/O bearing- which is MUCH larger than a wheel bearing, not dealing with brake heat, and taking loads in only _one_ evenly-distributed direction. The diaphragm fingers will push the throwout lever, pushrod, piston and fluid back to the master cylinder and into the resevoir, and possibly gain a tiny bit of clearance as RPMs go up and the fingers press back from centrifugal force.

Otherwise, I'm with you- until the T/O bearing dies, it should be happy as happy. And they make a lot of noise long before they die.

 

[Taboo]

Originally posted by Defiant
I don't know that it's putting much pressure on it, but it seems like it'd be touching, and probably enough to spin the T/O bearing-

The t/o bearing IS touching the pressure plate and spinning ALL THE TIME - any time the engine runs. There's always some initial pressure within the hydraulic system pressing the t/o bearing against the pressure plate - even if 100% bone stock, otherwise (if one starts with 0 psi of initial pressure) one couldn't create enough pressure to fully disengage the clutch due to the stroke of the master cylinder and the master cylinder/slave cylinder piston square area ratio.
The t/o bearing rides the pressure plate even with no fluid in the hydraulic system since the piston of the slave cylinder is being pushed out by its spring, consequently pressing the t/o bearing against the pressure plate.

Originally posted by Defiant
The diaphragm fingers will push the throwout lever, pushrod, piston and fluid back to the master cylinder and into the resevoir, and possibly gain a tiny bit of clearance as RPMs go up and the fingers press back from centrifugal force.

Nope, this doesn't happen. Once there's a higher than o psi of initial pressure within the system (achieved either by the longer rod of the slave cylinder installation or adjustment of the rod of the master cylinder), the plunger of the master cylinder closes the reservoir feed hole and converts the originally open hydraulic system to closed.
However, with very high pressure needed to disengage heavy clutches, the pressure within the system may overcome the sealing abilities of the plunger of the master cylinder. There's a very easy fix for that:
http://www.taboospeedshop.com/cmc.htm
The sealing abilities of the plunger increase with the pressure within the system as result of installation of the assist spring. Basically, the more one pushes on the clutch pedal and the more pressure he creates inside the hydraulic system, the more the plung seals and holds the pressure. As a result, the fluid has nowhere to go.

 

[badboyr66]

Thanks for the info taboo, I was kinda curious about all this myslef. by the way, hurry up with those skyeline style tail light kits!!

One problem I have had was my clutch like broke one day and, it would not fully release. So whe I pulled it, it looked like the springs on the clutch had made contact, or had just blown apart. The car sate for 3 years before i saved it. So ok, could happen, but lightening never strikes twice in the sa...er, WTF. I had replaced the clutch and 500 miles later, it feels like it did it again. I knew then I have the flywheel machined, I made sure they machined the step. But I am wondering if it is just out of spec all together. So now I am looking into a new ACT flywheel. This thread kinda sounds like what happened to me in a way. Any insite?

oh ya...taboo , I WANT THOSE LIGHTS!! oh ya, and the hood :laugh:

 

[Taboo]

The spring failure on our stock (or even ACT street) discs is quite common. Although there's no proof to it, I'd suspect fatigue of the material due to inadequate spring rate (and increased torque of the engine) being the cause of the spring lenght reduction over a period of time, consequently leading to the springs braking off the mounting tabs and falling out of the disc.

 

[badboyr66]

I am still questionng the step height.....so how bout those lights?

 

[badboyr66]

I am taking it out soon so I will be able to check it and u thing that ACT fw is any good?

 

[diambo4life]

The alleged victim of this discussion is my car. We managed to put a new ACT 2600 in there and there was almost no change. This is with the stock slave cylinder rod. After fiddling with it for some time, Kyle suggested putting back the longer slave cylinder rod which we did. We bled the line and disengagement problem disappeared. So, the longer rod helped a ton. Kyle witnessed it and so did I.

 

[habitatguy187]

Waaaay back from the dead but this is some very interesting info on extended slave rods. I had decided to get one due to exactly what happened to diambo4life happening to me also. No clutch disengagement, TO bearing in 5 different pieces. Pulled trans and replaced TOB, still no clutch disengagement. I even have the speed bleeder with the check valve so air can't come back into the system. I'm hoping that the extended slave rod will fix my problem.


I did have a question though. In his first post Taboo mentioned adjusting the master rod after bleeding the clutch. I was trying to figure out if I bled the clutch with the rod adjusted all the way in, then adjusted it all the way out, if it would be any different than just bleeding the clutch with the rod all the way out from the start? Any thoughts?

 

[twicks69]

Waaaay back from the dead but this is some very interesting info on extended slave rods. I had decided to get one due to exactly what happened to diambo4life happening to me also. No clutch disengagement, TO bearing in 5 different pieces. Pulled trans and replaced TOB, still no clutch disengagement. I even have the speed bleeder with the check valve so air can't come back into the system. I'm hoping that the extended slave rod will fix my problem.


I did have a question though. In his first post Taboo mentioned adjusting the master rod after bleeding the clutch. I was trying to figure out if I bled the clutch with the rod adjusted all the way in, then adjusted it all the way out, if it would be any different than just bleeding the clutch with the rod all the way out from the start? Any thoughts?

Brad, adjust the master cylinder rod outward (towards the pedal assembly/ away from the firewall), then bleed the hydraulic assembly, then thread the rod back towards the firewall until you find your proper adjustment. Do this with the vehicle OFF to find the proper pedal throw required. Then check with the car on after you have it adjusted to make sure that you don't have it over-extending the clutch during disengagement.

 

[habitatguy187]

Brad, adjust the master cylinder rod outward (towards the pedal assembly/ away from the firewall), then bleed the hydraulic assembly, then thread the rod back towards the firewall until you find your proper adjustment. Do this with the vehicle OFF to find the proper pedal throw required. Then check with the car on after you have it adjusted to make sure that you don't have it over-extending the clutch during disengagement.

You're saying that maybe I'm over-extending the clutch causing it to not disengage?

 

[twicks69]

You're saying that maybe I'm over-extending the clutch causing it to not disengage?

Potentially correct.

 

[habitatguy187]

I've never thought about that because the first 2" or so of the clutch pedal is pretty soft. I tried bleeding it again a few days ago (with it all the way out) so I'll turn it in when I get home and see what happens.

If that doesn't work I ordered the extended slave rod yesterday morning. I was thinking that maybe since I didn't shim the pivot ball I actually need one. I'll keep everyone updated. And thanks again Tim.

 

[DSMified92]

Jacks Transmissions LLC — Tech Articles FWD


that might be a help to everyone i know it helped me big time i learned alot. and the reason why ## pedal feels good at first then doesnt is because u need to shim the pivot ball because you are hitting the clutch fork against the bell housing probably

 

[JackM]

Taboo was completely wrong in the previous posts. I would never, under any circumstances, install an extended rod. It does damage to the TOB, pressure plate and engine thrust. The way the system works is the pressure is released in the system when the pedal is all the way up. When that pressure is gone the TOB does not put pressure in teh pressure plate any longer and just sits there like it's supposed to. The extended rod bottoms out the piston inside the slave. When this happens the system cannot return to its home position when you let off the pedal and it puts constant pressure in the system at all times which will cause failure. You need to figure out what is wrong with your clutch setup instead of sticking a band aid like an extended rod on it that will do more harm than good.

The extended rod is a scam that damages not only your clutch, but your engine as well. I am still suprised people sell those things.

Jack

 

[habitatguy187]

^^^ Well that sucks. Too bad I've spent well over 10 hours and a couple master/slave cylinders trying to fix this problem. What would be the reason for a brand new oem TOB failure in under 4k miles? Hopefully I've been over-extending my clutch and adjusting it back towards the firewall will fix the problem. (which I doubt it will since the first 2" or so of the pedal is pretty mushy) If not then I'm putting the extended slave in.

 

[habitatguy187]

Update time:


I did what Tim suggested about turning the clutch master rod in towards the firewall more, no go.

I got the extended slave rod and put it in, no go.

I had a friend help me manually bleed the clutch, thinking that maybe the speed bleeder valve went bad, no go.

So I decided to pull the trans again and shim of the clutch fork, it's the only thing I haven't done yet. Pulled the trans out and inspected everything and it all looked good, so now I have to shim the fork. I'm also going to replace the master and slave again since they're still under warranty. Not sure when the next time I work on it will be but I'll keep everyone updated.

 

[twicks69]

Darn, that sucks, I would really like to see what the problem is.

 

[habitatguy187]

Darn, that sucks, I would really like to see what the problem is.

I'll figure it out eventually and let everyone know.


There is something curious though that I forgot to mention and remembered when I tried the ext. slave rod yesterday; When I push the clutch pedal in about half-way the TOB screeches pretty decent, push it in a little more and it stops. I lubed it up really good so I'm not sure why it's doing that. Any thoughts?

 

[habitatguy187]

Update: Got suspended from work today so I decided to work on the car some more. Shimmed the pivot fork and put everything back together. I'm sure I used too many washers (2) because I could barely squeeze the regular slave rod in there, even with the master gone and there no pressure in the line.

Now all I have to do is pick up the new master (they didn't have that one in stock this morning) and fill the trans up with trans fluid and I'll fire it up. I'm pretty excited cause I'm sure this is going to work, I don't see how it couldn't there's such little room between the slave and fork, I'll probably just have to adjust the clutch all the way in .

I also ran out of firewood for the wood burning stove in the garage and I've got church tomorrow night so I doubt I'll get anymore done until Thursday night.

 

[habitatguy187]

Well I finally got around to working on the car again. Filled the tranny back up with the 4k-already brown fluid that was in it, bolted up the new master, and bled the system.

At first I only had 1st gear, it was really notchy, but it was something at least though. After a little more bleeding I also got a super notchy 2nd. I scratched my head and got the idea to cut out the carpet and sound deadener underneath the clutch pedal. Tried again, all gears are now engaging extremely smoothly. (car still on jack stands)

I'm happy that it works but it still sucks that I have to have the engagement point so low, I'm wondering if autozone gave me a nt slave cylinder. (I put the stock slave rod back in) Either way, it works so I'm happy!