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MG MGB Technical - Clutch pushrod

First some background...
I've had issues with my clutch since rego inspection last year, and the mechanics that replaced the steering, front suspension and a few hoses (including the clutch hose) had a lot of trouble bleeding and adjusting the clutch.
It always had a lot of slack in the pedal, and I'd never really worked out why and it was good enough to pass inspection so it was forgotten about until now.
A few weeks back the clutch pedal started having trouble returning, and seemed to click or pop at the last stage of putting my foot down. I found I was often flicking it back into return position with my foot under the pedal, or it would remain stuck for a second without my assistance.

Finally I took the car down to the only mechanic I trust (who unfortunately is rarely available because he is so popular) and got him to check the problem and told him all about the inspection last year. He reminded me I should have brought it to him in the first place... duh.
Cut a long story short, the problem is in the pushrod (part 17H 7985, yay I found my part catalogue) at the master cylinder which you can see when you remove the top panel of the box surrounding the link assembly from the pedal. The hole in the fork where the clevis pin pivots with the pedal was no longer round. In fact, saying it was elongated would be an understatement. It had worn into a long slot running about 45 degrees up, pretty much in line with the movement of the clutch pedal attached to it.
Removing the old clevis pin to replace the parts was easy. BTW the old pin was no longer a round pin, but resembled something similar to a cam-shaft with all the wear caused on it by rubbing back and forth inside the slot.

I don't have a circlip tool (yet) so I can't get the old pushrod out. Replaced the clevis pin and spun the pushrod around 180 degrees so the slot it now at right angles to the direction of the clutch pedal movement. It seems to have fixed the problem for now, but I am under no illusion this is a permanent fix. As soon as I get the circlip tool I'll be replacing the pushrod.

I grabbed a complete set of seals for the master cylinder in case I need them when removing the pushrod, but I'm not sure if there is anything else I need to worry about when I get around to finishing this job.
I assume draining the master cylinder will save me spilling fluid everywhere when I remove the pushrod. I also guess bleeding will be necessary when I put it all back together. The problem there is I have seen plenty of guides on bleeding brakes but nothing about how to do the clutch. Is it any different?

Cheers,
Dave - Sydney Australia
D O'Brien

Changing the pushrod does not mean you have to drain the cylinder - as long as the valve body & seal don't come out of the bore you can just swap the rods over.
Chris at Octarine Services

I have found that the easiest way to bleed the clutch is simply to use gravity. Just open the bleed nipple on the slave cylinder underneath the car and put a clean glass jar underneath. Then pour in the fresh fluid until there is a steady stream going into the jar. Close off the bleed nipple and then try the clutch. If it works then easy, if not then go back to the pumping method
Cheers
Steve
SW Tompson

You'll probably find the pedal hole is also elongated and you really should do all three things at the same time. I calculated I had about an inch of extra travel on mine before I welded up and filed out the pedal and replaced the clevis and fork.

Reverse bleeding is really the only way to do it and get it over with quickly. I filled my system after a rebuild using a gunsons EeziBleed on very low pressure connected to the slave nipple and it didn't need bleeding at all, getting the full 1/2" to 5/8" travel straight away. Unless you have rebuilt the system or otherwise previously flushed out all the old gunge and old fluid don't reverse bleed without flushing it through first or you'll push the gunge into the master. An alternative to using a Gunsons is to connect the right front caliper nipple to the slave nipple and open both, then use the brake pedal to reverse bleed the clutch. You will have to keep the brake master topped up and remove excess from the clutch, of course.
Paul Hunt

This thread was discussed on 22/09/2004

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