MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Gears grinding - clutch or hydraulics?

Last Friday I had trouble getting into reverse (grinding) and as the day went on other gears started to catch. By the evening it was all distinctly worse, with the clutch failing to disengage; the car was still pulling forward with the pedal was fully down.

Next morning I was all steeled to pull the engine, but it changed fine from cold and I went through the hydraulics first.

Movement of the pushrod at the bellhousing was only about 6mm so I:
* bled the system (no change)
* checked for leaks (none found)
* checked the master cylinder for bubbling when the clutch is pumped (none)
* checked for the pushrod slipping back when the pedal was held down (no movement I could see)
* changed the pushrod at the master cylinder where the clevis pin hole had become oval (was I glad I didn't throw away that old brake master with its good pushrod).

The last move got me to about 9mm or 0.35" total travel. That got me on the road again this morning, but I had a slight grind getting reverse as I pulled up just now and I'm suspicious that the problem may be returning; I'm also suspicious that it gets worse the more I drive.

My dilemma is whether the clutch plate/bearing is the issue or are the hydraulics still suspect?

Any advice would be very welcome.

Many thanks,
Steve
Steve Postins

I would still suspect hydraulics. 0.35" isn't enough. I found the only way to get mine working properly was to drain all the fluid out and fill it from the slave upwards using a gunsons Eezibleed. Paul Hunt tells you how to do this on www.mgb-stuff.org.uk
Mike Howlett

Thanks Mike. It was the Eezibleed method I used, so I guess the master cylinder is the most likely culprit.
Steve Postins

It sure sounds like a bypassing master cylinder to me. Ray
RAY

Check the pushrod travel at the bell housing when the car is cold and again when it is hot and acting up. If the travel is reduced hot, the master cylinder is likely leaking internally when the fluid heats up and thins out.
John H

Sounds like good news. It's been bothering me that it improves after a rest but that would explain it. I'll get the hydraulics ordered and hopefully will have it resolved quickly.
Many thanks!
Steve Postins

Have you checked all the pivot points (clutch pedal, clutch fork) and push rod for wear? Is there a difference if you pump the pedal before trying to shift? How old is the flex line? Old flex lines can slighty balloon, absorbing some of hydraulic energy that would normally go to the slave cylinder.
Kimberly

I've checked the linkages and will replace the master, slave and hose at the weekend, to try to ensure the job is done. The brake master cylinder went a few months ago so I'm guessing the other hydraulics have reached their expiry too.
Steve Postins

Slave piston travel should be 1/2" to 5/8". Dealing with wear at the master (oval push-rod and pedal and worn clevis pin) can make a significant different to slave piston travel but this sounds more than that. If, once you do have a gear engaged, you find the clutch slowly engages all by itself even when the pedal is held to the floor then either the master is leaking back (master seals) or the slave seals are leaking which should eventually give visible leaks. Short travel *without* automatic engagement sounds more like air in the hydraulics. One wouldn't normally expect to have this unless there were problems at one end of the other, but I'd still bleed it to see if I could get full travel back, and see if it reoccured. If it did, without visible leaks, then I'd replace master, flex hose and slave. If you get visible leaks at the slave then I'd replace that ansd the flex hose. Before removal pump the fluid out of the master through the slave nipple until you get clear fluid, to flush out the metal pipe. When refilling *reverse* fill. The easiest way to do this, especially with the large clear dual circuit brake reservoir is to conenct the slave nipple to the right-hand caliper nipple, open both, then use the brake pedal gently to fill the clutch system - or at least until you can see the fluid through the fill hole of the master. As I say with the dual circuit brake master it hardly lowers the level and is easy to keep an eye on, but is still worth doing with the single circuit metal can although you have to keep a closer eye on the level in the brake master.
Paul Hunt 2

Thanks Paul.
I've replaced the master, slave and hose and found fluid in the boot for the slave. I missed this on first inspection because I'd just sqeezed it without removing the rod, so that's a lesson to me.
I reverse-filled with an EeziBleed and now have just 8mm/0.35" movement at the clutch fork, but a firmer pedal and no catching on the initial gear changes. I'll be doing a few miles tomorrow to see how it goes.
Steve Postins

Well, all seems fine. After leaving the car for the night the fluid level in the master had dropped half an inch but has not moved since, so I suspect this was air finding its way out of the system. I haven't been able to check if this has increased the pushrod travel, but the clutch bites halfway up and it all works so I'm very happy. Many thanks.
Steve Postins

That's interesting. I've heard the 'leave it overnight and she'll be right' theory of bleeding both clutch and brakes before but can't see how air gets back down from the top of the loop into the master, which is what both seem to have as standard. My front brake pipes have an additional up and down loop at the calipers! Particularly with the clutch you could leave it overnight with the pedal held down, then releasing it next morning should shift quite a bit of fluid back into the master, carrying any air with it.
Paul Hunt 2

This thread was discussed between 26/11/2007 and 05/12/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.