Clutch Problem
 

I have a bit of a nagging problem with my clutch pedal.

When I brake with anything more than moderately hard pressure, by clutch pedal falls halfway to the floor. It doesnt happen every single time I brake hard, but most of the time. And it is more likely to happen if I brake and turn and use rev-matching for gear changes.
The pedal will return to normal on the first pump but this is becoming a major annoyance now. There are no problems during normal daily driving.

The clutch was replaced on last friday with an Exedy standard replacement kit. NOT HD. Included a new pressure plate and thrust bearing. My spigot bearing was inspected and is fine.
And the clutch hydraulics were bled and fluids replaced just earlier this week. I did it myself using the reverse bleed method with a syringe. I am confident there is no air in the lines.
HOWEVER, this problem I am having was occuring before the clutch change and fluid bleed also.

Any thoughts from the pros as to the cause?

Stab in the dark - Clutch slave cylinder?

Darren

^^ What he said.

Under normal operation. the clutch is fine. It disengages and re-engages normally and smoothly.

What I dont understand is how differing degrees of braking can affect the operation of the slave or master cylinders

Edit: There are also no leaks anywhere on the clutch hydraulics.

Have you got fat feet or wear Ronald McDonald sized shoes?

Firewall flexing? Something catching up near the hinges of the brake and clutch pedal?

I don't get it. When you push on the pedals the fluid is supposed to be compressed through the lines to engage the other end into action. Meaning if you push on your brake pedal and your clutch pedal travels, it must be trying to disengage the clutch. It doesn't make any sense at all.

Both systems (I believe but google may be failing me here :P ) are vacuum assisted. I'm not sure if there is some kind of link between the two systems but perhaps some kind of proportioning valve is faxored and may cause a problem.

Once again, I preface this with the statement that this is a complete stab in the dark.

Darren

Clutch hydraulics are not vacuum assisted.


Just for kicks I have re-bled the clutch system last night and took extra effort to make doubly sure that there is ZERO air in the system.

Still the same problem.

Im all out of ideas

I have just replaced the Master Cylinder with a known good one removed from a late model WRX.

Problem persists.

[QUOTE=superman]. How did you bleed your clutch??
i hope you know when you bleed a clutch which has a ABS system you have to do it right.. you must start from the right hand rear then left hand front then left hand rear and finish on the right hand front.. hope that will help you..[/QUOTE]

WTF???
The ABS system has nothing to do with the clutch...

Heh, the new ABS Clutch .. Mine actually feels like that in the morning!! :D :D Shudders like hell for the first few mins.

hehehehe
shouldnt that be ACS, Anti-lock clutching system...
lol

WTF? I thought you were an experienced mechanic or something?

First of all, were talking clutch here not brakes.
Clutch hydraulics has nothing to do with ABS.
And Thirdly. I dont even have ABS. Good ol 1990s. ABS was an option on the Series 1 Legacy. But was standard equipment on the Series 2.

You should start by checking the wiper fluid, make sure it's at least 50% full, then drain your fuel tank and sump....fill them with the same water you use for washing your tyres, I guarantee the clutch will never bother you again.

Soz the master cyl didn't work but at least you've got a spare now.

Try this. Seems to be either the release arm for the release bearing or a flexihose on the slave cylinder fouling. Let us know if it helps [url]http://bbs.scoobynet.com/drivetrain-11/110923-clutch-pedal-feels-soft-after-heavy-braking.html?showfull=1[/url]

Well, my clutch fork release spring is still there and fully operational. Release (thrust) bearing was replaced with a new one.

I'll check for kinks or problems in the hose

Nice find there phizzle

i think he means that the clutch line goes from the reserviour and master cyl to the slave via a remote bleeder, mounted higher up behind the rh strut tower..looks sorta abs'ish. Except not

woops i was writting on a different site for abs brakes... the wrx club...
sorry good to see the funny side to it...
i was going to write to you about the clutch,
i was going to say check your clutch line that goes to the master cylinder it might be blocked..
good to see some guys on here pick up on mistakes.....

Just checked this morning. No kinks or problems in the flexible hose.

its has to be 2 only things.
1 your slave cylinder which is near your gearbox or the master cylinder.. you need to replace both... and that will fix your problem...

Get under the dash and have a good look at the clutch/brake pivots and the bolts mounting them under the dash.

They may be binding together ( unlikely as they are seperate assemblies I know) but nothing else seems to be working for you.
It seems strange it only occurs under heavy braking which leads me to believe the brake pedal is pulling the clutch pedal down somehow.

Cheers
Ken

nope. checked for that a while back. No binding or catching on the two pedals.

I think Doug may have solved this though. But more discussion and investigation is necessary.

Ludwig, just skimming through... I'd have to say clutch slave cyliner as well. It was actually supposed to be a recall on early model WRX's so I've heard.

I am having similar problems with 'binding' on my RS since fitting a new clutch. Not during braking like yours, but it does stick when changing through the gears rapidly and friction point feels as though it varies ever so slightly some days- everything pointing towards slave cylinder.

(Would have had it fixed by now and been able to report results if some lady didn't think pulling out in front of me during christmas was such a grand idea) :(

i found that my clutch would stick on hard changes. found out that it was the spring that was missing on the top of the gearbox housing.

I think Doug has cracked it.

Some Subarus have it and some do not. A counterweight on the clutch fork. I am missing mine. It seems the thrust bearing and the bottom of the fork below the pivot point has enough weight in it to overcome the weight of the top of the fork and the fork spring such that in heavy braking the thrust bearing moves forward pulling the fork along with it such that the next time I step on the clutch pedal, the slave cylinder has to take up that extra free play before the clutch will begin disengaging. Thats why it feels like there is no pressure in the lines for the first half of pedal movement after I come off a fast brake.

Ive picked up a counterweight off Doug tonight. so tomorrow It will go on and test that theory. I think it is the answer though.

It explains all the symptoms (*Dr House voice)

[URL=http://imageshack.us][IMG]http://img181.imageshack.us/img181/4863/itsnotlupusjc0.jpg[/IMG][/URL]

Good to see it's (almost) sorted.

Shit happens.

The new counterweight has not solved my problem. Symptoms Persist

I really am stumped by this. If the clutch pedal moves downwards then it should be trying to disengage the clutch. I think it must be getting to the friction point and stopping there because of the resistance. Now seriously, as I said in my first post on this, although hard to check, is your firewall flexing at all when you go for the brakes? You said you've checked for any snags up in the assembly so that's out. Maybe give it another bleed to be sure. It has to be something ridiculously simple. I've never heard of it before :confused:

Does this happen at 88mph? Maybe the google mobile is trying to go back to 1955? :D

Start replacing parts if nothing else is obvious, next I guess would be the slave cylinder....if you haven`t done this/all of them already !!, freeplay in master rod ? can you rattle the fork with the return spring removed ? no pre-load ? pedal box ok? bushes worn ? greased up ?

Have you tried removing the clutch pin and re-installing to see if it feels right ? is it greased ?(Not anti sieze ! use proper HTB)
Remove the rubber boot(and pin for more room) and get a torch and have a look down there.

More description of the problem ? details, try replicate issue in diffrent situation...

Was it a new clutch and release bearing&clip ?

All new clutch, pressure plate, thrust bearing

Master cylinder is off a GD WRX. and in good conditon (so was the old one)

No ratttling in the clutch fork.

I have replaced everything on the clutch system now except for the slave cylinder and flexible hose. But there does not seem to be anything wrong with them. I will probably replace them very soon.

I should clarify something.

The clutch pedal doesn't fall on its own. It stays up there in the correct position. But after you brake heavily, its like half of the pedal travel has no pressure in it. So it feels like its fallen to halfway. Only at the halfway point does it have pressure.

Clutch fork should rattle(slightly, i.e no preload) back and forth when return spring is removed.

Area clear around fork and slave(no hoses, wiring/whatever touching or able to contact it under braking) Stay rod installed and tight ?

Did you rub a little grease into spline before you re-installed box(you`d be surprised how important this is !)

Did the box slip back in easy(onto the spline, then still easy into the spigot before you put a bolt anywhere near it ? or did you have to lever it and work up a sweat to get it home ?

Pull the pin and see what you can see/feel, and while your there play with the slave pushrod and see if its rock hard(try squeeze it back with your hands, it shouldn`t budge unless you bleed it back) slave bolts tight ? Rubber boot good, installed right way round and correctly in place ?

Well the fork pivots forwards and backwards if you pull the spring off. Normal movement though.

Nothing touching any moving part of the clutch hydraulics

Box slipped easily onto the clutch spline and spigot bearing.

You can push the slave pushrod back with your fingers. But its quite firm and anyway, its normal because if the pedal is not depressed the return valve on the master cylinder is open. Bolts are tight. Rubber boot is old but fine and correctly installed.

Next thing to replace is the transmission mounts. They are old and we suspect excessive movement of the drive train could be a contributing factor. Regardless its old and soft. It needs to be replaced anyway.

Yes I suppose your right about the master having a return valve.

If nothing is leaking broken or loose it may be a freeplay issue, that may be adjustment or wear I guess, I doubt gearbox or engine mounts are the issue as that surely could affect and enclosed clutch system !

What do you reckon about worn crankshaft thrusts Justin? My theory is that the crank moves forward under heavy braking and as the flywheel/clutch also move forward the cylinder is pushed back via the fork pivoting. I installed the new clutch a week ago (problem was there before) the fork pivot was lightly greased etc. There was a wiring loom rubbing on the fork which I thought "Eureka" when I saw, but relocation had no effect. You cannot replicate the fault at all when stationary, but move 10 metres and stab the brakes and you've got the fault. You can get the same 1/2 pedal effect by manually pushing the slave rod back in about 3mm. So I reckon somethings pushing it back when you brake??? I have also adjusted the mastercylinder pushrod with no effect.
Also to note; it will not fault if you have a slight depression of the clutch pedal when you brake as sharp as you want, indicating to me that enough master cylinder stroke to close the port will prevent fluid from returning to the reservior.

Yeah sounds like the crank thrusts could cause that, so I take it its a early EJ20G hydr tappet follower motor ?

Do you get a lot of slap if you lever the crank pully back and forth ?? its usually very evident...its amazing they still run well enough like that !

Doodgy fix - maybe shim up behind crank timing pully to stop movement !! Don`t know what this would do to bearings etc, belt and timing tooth aligment should still be good enough as its finding its way forward under braking anyway !

Doodgy fix#2 - Try adjusting master rod up to keep port closed or almost closed and hopefully fork return will keep up with the pedal and not pump up clutch to much ! thus solving issue !(and possibly making a new one ;) )

[QUOTE=dtrally]What do you reckon about worn crankshaft thrusts Justin? My theory is that the crank moves forward under heavy braking and as the flywheel/clutch also move forward the cylinder is pushed back via the fork pivoting. [/QUOTE]

If you had that much freeplay in the crankshaft, you'd know about it via f*cked conrods and bearings.

Your crankshaft thrust movement probably won't ever exceed the freeplay in your clutch fork, even if its worn.

[QUOTE=BALISTC]If you had that much freeplay in the crankshaft, you'd know about it via f*cked conrods and bearings.

Your crankshaft thrust movement probably won't ever exceed the freeplay in your clutch fork, even if its worn.[/QUOTE]


I`ve seen some cars with ~4mm of movement on the crank :eek: its a freak`n huge amount...and it does make me wonder how they still run ok...but they do run smooth and quiet, the crank must get up and float in a workable position when revving !! and the rods would slop/float forward on the pins :happy2:
Also possibly the freeplay on the fork(contacting the thrust and rod of the slave) in the direction of the crank moving forward would all be taken up just after you step off the clutch and by the return spring......so it could have some affect. Theres really no other reason for this issue as described except a free-play somewhere in the system...

But yes I agree you`d have to call the engine bin material(oh except for the closed deck-ness :D ...rebuild material)....thats why I suggest doodgy fix #1 (at your own risk of course !)

What about dodgy fix #3. If crankshaft thrust proves to be the cause, live with the fault, boost the crap out of the old rocker arm engine and eventually fit a better design engine.
Justin, I had already suggested dodgy fix #2 but he seemed intent on solving the cause (or at the very least finding what it was)
Stay tuned.

Ive been kinda busy and havnt had a chance to really inspect if there is any movement along the crank.

If its fucked, im just gonna start a new build. 257 with forgies and My98 heads. Bolt it all up and VERSO it. I cant afford to wait until it finally dies and have my car off the road.

Well, I just had a look with the help of a friend trying to lever the crank pulley to see if there was any movement. And there is none. Other than the crank pulley moving around on its rubber mount, the crank itself wouldn't budge. Not even 1mm.

I may just have to live with this and just rest my foot on the clutch pedal when hard on the brakes to stop the fluid moving back up the lines. I would prefer it this way than adjusting the master cylinder push rod as that method would isolate the fluid in the lines from the reservoir not allowing it to refill the lines in the event of a leak in the clutch lines.

For now, I'll try a stronger return spring on the clutch fork and get those Group N transmission mounts. And maybe down the line if I still havent fixed this, I'll just get a new slave and flex line just for peace of mind.