Clutch pedal engagement point

[dingbatt]

Hello fellow mudders!

I've been absent from here for a while now but I have had a niggling problem for ages that I really would like to resolve.

Here's the low down:

1981 HJ47 troopy. A few years ago I swapped in a H55F transmission. You can find a link to that thread here:

https://forum.ih8mud.com/threads/old-yella-gets-a-5th-gear.302432/

I've had problems with the clutch pedal engaging high in the pedal stroke (like the top few inches) ever since that transmission swap. However, it has not affected clutch function much except recently when the clutch began slipping under load during hot days on a road trip through central / northern Western Australia. I figured that that was due to premature wear on the friction plate due to no slack in the slave pushrod. But I can't be sure. Anyway, I pulled the transmission recently, put in a new exedy clutch kit and also replaced the HJ70-series clutch fork that was in it with a HJ47 one so that I could re-attach the spring on the slave cylinder. I was hoping this would have sorted it, but it has made no difference. Clutch still engages high with spring or no spring, new clutch or old.

I don't know what to do next. I have tried everything I thought it could be but none have worked. I've done all the adjustments as described in the FSM.

The only conclusion that I can come to is that the problem is hydraulic. It doesn't matter how much you adjust the pushrod on the master cylinder or the pedal, HYDRAULICALLY, the movement of hydraulic fluid hasn't changed. Only mechanical freeplay has.
And if you adjust freeplay on the clutch slave pushrod, the hydraulic weight when the clutch is actuated will take up any of that freeplay straight away within the first couple of pedal pushes. The spring on the clutch slave is not strong enough to push the fluid back, and even if it was the clutch pedal feel would be extremely heavy. The only thing strong enough to push the fluid back is the pressure plate itself, and that only seems to push it back only to the point just prior to clutch disengagement!

In which case, maybe I have problems with lines or clutch master (clutch slave is new, clutch master has been rebuilt)

Has anyone experienced anything like this before? Can anyone help me out with suggestions / ideas / theories, anything. I'm all ears!!

Thanks!

Matt

 

[40's rock]

I have a similar issue in a pedal that engages high....took the slack out of the slave push rod....next thought was to bleed the line and adjust the pedal via the rod adjustment under the dash. Seems that should change the pedal position vs the master cyl. allowing it to engage sooner
I did the high gear with emergency brake on trick and mine stalled, so I know its not slipping.

Bump to the top.

 

[dingbatt]

Yeah clutch function appears fine. However I think that either the clutch wears out prematurely OR because the throw out bearing is always pushing on the pressure plate, as the friction plate wears out it stops engaging sooner than it should.

Did the adjustments you make fix your problem?

 

[Solace in Solitude]

I have a similar issue in a pedal that engages high....took the slack out of the slave push rod....next thought was to bleed the line and adjust the pedal via the rod adjustment under the dash. Seems that should change the pedal position vs the master cyl. allowing it to engage sooner
I did the high gear with emergency brake on trick and mine stalled, so I know its not slipping.

Bump to the top.

My clutch also engages higher than I like - I've gotten used to it, because it drives well.

I have a new slave cylinder to install, but haven't gotten to it yet - so, I'll be watching this thread with baited breath!

Good luck!

 

[sggoat]

Seems like the prob originally started with the tx swap--any issues after that are really moot. My uneducated guess is it's related to the swap, and is mechanical in nature--my .02

 

[dingbatt]

Goat,

Definitely seems that way. But I think I've ruled that out... since that transmission swap I've changed every variable that I can think of. The engine has even been swapped for a newer 2H from an HJ60. So its been the same high engagement point with varying combinations of clutch fork, clutch slave cylinder (I've tried both HJ47 and HJ70 ones), engine, clutch kit. Still high.

There's something I'm missing here...

 

[platypusREX]

Isn't supposed to be like that?

 

[dingbatt]

Isn't supposed to be like that?

Like what? engaging in the first few centimetres of pedal stroke? I don't think so. Even if it is, I don't like it and want to change it!

 

[taro]

Talking out loud, but wouldn't you want some slack in the push rod if you wanted to lower the engagement point?

I recently had my slave cylinder fail and replaced it with an aftermarket one. It works okay, but the line to slave cylinder connection leaks slightly and so any adjustments to the push rod gets "absorbed." When I ordered a new clutch cylinders and line, beno told me that a washer that fit on the line was often overlooked, but caused problems. Are you leaking any brake fluid at all?

I have a similar issue in a pedal that engages high....took the slack out of the slave push rod....

 

[adistler1]

How much tension should there be at the slave pushrod/clutch fork? I don't have a problem with my pedal engaging high, it's about midway, but on hot days, like the original post says, I get a bit of "slipping" or shuddering" coming out of first. I was wondering if it could be that I need to adjust that pushrod or maybe bleed my lines better...

 

[Blue77FJ40]

Check with the FSM. It starts with the pedal height measurement. Then it covers free play measurement. That may be enough to lower the engagement point. That said, on the '40, the engagement point is gonna be higher than most people are used to. Me included, and i've driven only stick all my life (except rentals).

 

[taro]

I don't have a problem with my pedal engaging high, it's about midway, but on hot days, like the original post says, I get a bit of "slipping" or shuddering" coming out of first.

I get that, but I always assumed it was from my rear main seal leaking :-/

 

[Weber Sarge]

You have to make absolutely sure that throwout bearing isn't riding the pressure plate all the time - I just remove the spring at the slave cylinder and check for play in the fork , if no play it isn't adjusted correctly . There is a highly detailed procedure in the service manual . Yes , oil leakage into the clutch can cause chattering , especially taking off from a dead stop .
Sarge

 

[sggoat]

Something is causing that clutch to be partially engaged--high pedal engagement plus slipping under heat tells me the thing is not completely disengaged when the pedal is full up. Based on your previous tests/replacements, I would suggest there may be something in the clutch springs themselves, not allowing full disengagement(even if the hydraulics release ok). There might be an alignment issue in there keeping the clutch from moving back as it should--you wouldn't notice this unless you got under the truck and yanked backwards on the fork rod--to see if the thing moved back more than the slave was trying to release it. This may not tell you anything at first, since you don't know how far back the orig tx/clutch went, but, I bet there are members on here who could measure the backlash on the slave arm to compare with yours.

 

[adistler1]

I get that, but I always assumed it was from my rear main seal leaking :-/

Hmmm... I just did a full rebuild from JimC. I wouldn't think my rear main seal is leaking. I do see oil coming from somewhere though...

 

[sadam_husain]

Check with the FSM. It starts with the pedal height measurement. Then it covers free play measurement. That may be enough to lower the engagement point. That said, on the '40, the engagement point is gonna be higher than most people are used to. Me included, and i've driven only stick all my life (except rentals).

yep that's the easy fix to it mate only takes 5-10 minutes to adjust the pedal freeplay and height so everything feels right

 

[dingbatt]

Talking out loud, but wouldn't you want some slack in the push rod if you wanted to lower the engagement point?

I recently had my slave cylinder fail and replaced it with an aftermarket one. It works okay, but the line to slave cylinder connection leaks slightly and so any adjustments to the push rod gets "absorbed." When I ordered a new clutch cylinders and line, beno told me that a washer that fit on the line was often overlooked, but caused problems. Are you leaking any brake fluid at all?

No leaks at all... She's tight. inuendo not intended.

Check with the FSM. It starts with the pedal height measurement. Then it covers free play measurement. That may be enough to lower the engagement point. That said, on the '40, the engagement point is gonna be higher than most people are used to. Me included, and i've driven only stick all my life (except rentals).

I've gone through the adjustment as described in the FSM to no avail. This can indeed lower pedal engagement height but any extra distance you get in pedal stroke before the engegement point is just taking up mechanical freeplay... just compressing the spring on the pedal before the master cylinder starts being compressed.

The problem is not the pedal end... its the slave pushrod / clutch fork end... I'll explain more below

You have to make absolutely sure that throwout bearing isn't riding the pressure plate all the time - I just remove the spring at the slave cylinder and check for play in the fork , if no play it isn't adjusted correctly . There is a highly detailed procedure in the service manual . Yes , oil leakage into the clutch can cause chattering , especially taking off from a dead stop .
Sarge

Sarge,
I think that you are on the money. The throwout bearing appears to always be resting on the pressure plate. If I remove the spring at the slave cylinder I don't feel any play in the clutch fork.
If I change the nuts on the slave pushrod to increase freeplay at the pushrod end, as soon as I drive around for a short whil and engage the clutch a couple of times that freeplay is lost, as the hydraulic system just takes up that slack. If I keep adjust that pushrod shorter and shorter, eventually I will get to the stage where the piston in the slave cylinder falls out the end. Trust me, I've learned the hard way!!

So why is this so on my machine and not on others? This I don't know. Is the slave spring too weak perhaps??

Something is causing that clutch to be partially engaged--high pedal engagement plus slipping under heat tells me the thing is not completely disengaged when the pedal is full up. Based on your previous tests/replacements, I would suggest there may be something in the clutch springs themselves, not allowing full disengagement(even if the hydraulics release ok). There might be an alignment issue in there keeping the clutch from moving back as it should--you wouldn't notice this unless you got under the truck and yanked backwards on the fork rod--to see if the thing moved back more than the slave was trying to release it. This may not tell you anything at first, since you don't know how far back the orig tx/clutch went, but, I bet there are members on here who could measure the backlash on the slave arm to compare with yours.

Totally agree that the pressure plate is partially 'engaged' or 'pressurised'. I don't think its due to clutch misalignment as I've gone through two clutches with the same problem and both times I used a proper alignment tool.

There is a possibility that I have a problem with alignment due to the clutch fork I hae installed. It is, as far as I know, from an early HJ60 with an atachment point for the spring on the end. From the photos I've seen of other 40 series clutch forks it looks different. Its possible that the geometry of this fork is causing the problem...

As far as I can tell it is that or hydraulic. I think.......

Cheers for the suggestions guys! I appreciate it!

 

[Weber Sarge]

What you describe covers one rare chance - something in that system is not allowing the clutch master cylinder's piston to return far enough to bleed off pressure to the slave cylinder . Same thing can happen with brakes if the rod behind the master is too long - it will not bleed off . I'd start off with making certain that clutch fork is correct and go from there - check that rod the clutch master , it may be mis-adjusted and not letting the piston return .
Sarge

 

[adistler1]

Finally got around to this and made the adjustments per the FSM. My pedal height was way off and had to come up about 2". Took the spring off and there was a bit of play in the clutch fork but not 3-4mm. I ended up backing the bolt off about 3mm and had the proper play. The truck shifts like butter now. I just have to get used to the pedal and the engagement point being in a different spot. Thanks for the help guys!