T-Series More clutch failure symptoms

[100DashSix]

I recently replaced my clutch hydraulics (including master and slave cylinders), after my MG lost the ability to shift. I test drove it and was able to shift, but the clutch engaged lower than normal, and after some driving it got harder and harder to get into gear. Thinking that the low engage point could explain it, I took the clutch pedal out and fixed the ovoid hole where it connects to the push rod...but now I can't shift at all!

Travel of the clutch fork at the slave cylinder is just about 1/2", maybe 1/8" to 1/16" of an inch shy of 1/2" travel. I'm included to believe that it's being fully actuated, and there is pressure on the clutch pedal.

Does this sound like a clutch failure? What component may have failed? The car has 98,000 miles, and the PO <span style="font-style: italic">may</span> have rebuilt the clutch, but possibly not. Is my only option to pull the engine and transmission? What else should I do while I'm at it?

 

[Deleted member 8987]

Sounds like air in the line.

 

[100DashSix]

But why would the slave cylinder pushrod actuate the fork up to a 1/2"?

 

[DrEntropy]

For a check of the travel at the slave, have someone first push the clutch pedal right to the board one time and hold it. Measure the "throw" at the slave. Then have the helper pump the pedal thru several strokes and hold it, measure again. If the throw increases you have likely got air in the system. If not, the T/O bearing or other mechanical pieces of the clutch are suspect.

A thought: Some replacement slave cylinders have shipped with the bleeder in the underside hole, and need to have it ABOVE the hose connection. Just sayin'...

 

[Hap Waldrop]

Keep bleeding the slave, you will get there, this is one of the biggest PITA jobs on these cars, on my race cars I made remote bleed line to make this job easier, and stay married, as my wife is the pedal pumper

 

[100DashSix]

I'll bleed it again, but is 1/2" not enough travel at the slave cylinder pushrod?

When I installed the new slave I put the bleeder screw on the top hole, as the old one was, with the hose connecting in the back.

 

[DrEntropy]

Another possible "trick" which may help is to use a set of welding clamp style Vise-Grips to hold the slave piston all the way in, then bleed the system. Just be sure to keep the reservoir topped up after you reconnect the rod to the fork. :wink:

 

[Deleted member 8987]

As a general rule, when a clutch goes, the disc wears (or disintegrates), the pressure plate moves towards the flywheel more, the "fingers" and T/O bearing move back, arm moves further into the slave.

You still have normal free-play and such.
Dis-engagement usually not the issue...engagement is.

Now, if the pressure plate failed, one edge will usually fail into the disc, and there is no way you can get it to dis-engage.

Your symptoms sound like air.

How much free-play at the pedal do you have right now?
Use your thumb to tell.
When you engage the plate fingers, your thumb ain't gonna be able to depress the pedal any more.

 

[DrEntropy]

If the T/O bearing has worn down to the nub the pedal travel/slave travel will not be enough to disengage the clutch.

 

[100DashSix]

Ahh, I see, TOC. At the moment I have 2" of pedal travel before it becomes significantly more difficult to depress the clutch with my thumb. I could see that being air-related... It _feels_ like my old clutch, but maybe that was improperly bled too.

I have a one-man bleeding kit that has a one-way valve, which should be air-tight. I'll try that some more, even though I bled the heck out of the clutch already. I'm assuming there should be almost no pedal travel before I can no longer use my thumb to depress it?

 

[DrEntropy]

1/2" to 1.0" max, methinks.

Could you get someone to repeatedly stroke the pedal so's to measure slave throw?

 

[100DashSix]

So, Doc, if the car's in neutral and running, with the clutch fully depressed, and if I can't shift it means the transmission is free-wheeling--and the TO bearing could be worn too low to disengage the clutch? From the sound of it maybe the air in the system is making the slave pushrod travel insufficient.

Again I'd like to know what distance the pushrod SHOULD travel. I've looked online, and it varies from 1/2" to 3/4".

 

[100DashSix]

Whoops, just saw your reply. Anywhere from 1/2" to 1? Hmm. Yeah, I had someone depress the clutch and took measurements over and over. 1/2" displacement of slave pushrod at most.

 

[DrEntropy]

I'm leaning to the T/O bearing then.

Usually even with air in the system the throw at the slave will increase with a few pumps of the pedal. If it's consistent you likely have it bled correctly.

 

[100DashSix]

I just bled it for another 30 minutes, and the pedal travel is still 2" before I can't push down with my thumb. I can't check the slave push rod travel right now, but the pedal feels the same.

The only way to check anything else is to pull the whole engine and transmission, I take it? I'm going to need a lot more storage space...

 

[Deleted member 8987]

On the MGB, it's self-adjusting.
Yeah, maybe, but worn pivots, too, can cause this.
If there is 2" of free play, and the slave is working, M/Cyl is picking it up right away, theoretically fluid fills the void and the slave piston stays put.

I don't think the pressure plate is pushing it back, as you'd feel it.
The slave would be popping apart if too much throw.....yet, that said, I have seen folks with a spring return on the slave arm, like on a manually-adjusted clutch, that will pull the slave piston back and kill off the self-adjusting feature.

You don't have a spring on the clutch arm coming out of the bell housing, do you?

You can over-center and lose mechanical advantage if the TO bearing is worn away, but that should not give you two inches of free play.

 

[100DashSix]

There's no spring attached to the fork arm coming out of the bell housing, and I'm pretty sure the master cylinder is picking up the pressure right away--it's a new master and slave cylinder, and new, stainless steel flexible hose.

When you say that the pivots could be worn, do you mean the bushes that allow the clutch withdrawal lever to pivot? That also looks like a job requiring pulling the engine and transmission.

 

[Deleted member 8987]

Yeah, and that might do it.
Do you have the tunnel off?
You can watch the actuation of the slave with regards to the master.
The slave should pick up and move virtually immediately upon pressing the master pushrod.
Slight lag as you cross the recharge port.
But, if you're pushing the pedal down 4 inches and no slave movement, that's a hydraulic (or pedal mechanical) issue.

If the slave starts right away, and you still go 2" to remove freeplay, fork, pivot, TO Bearing, and al that.

Do a clutch while you're at it.

Remember the First Rule of Automotive Repair that states:

Just because it's a new part doesn't mean it's a good part.

 

[100DashSix]

I don't have the tunnel off, but I can confirm the slave cylinder push rod starts moving as soon as the pedal is depressed (even in the 'free play' zone) by getting a helper to push the pedal.

So, seems pretty clear that something internal to the transmission is failing, and pulling the transmission & engine is in my near future.

Anything else I should do when I pull the engine free? The head also weeps a bit at cyl. #3. Should I pop it off and have it inspected?

I wish I had a sandblaster. I could redo the engine bay...

 

[100DashSix]

OR maybe this is the perfect time to convert my car to a V6 with a T5 5-speed.