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MG MGB Technical - Clutch Problems? Won't Shift Into any Gear?

Took my 77B out for a spin this morning. It was running along beautifully. Stopped by an auto parts store to pick up a few things, hopped into the car, pulled out no problem and drove up to the light at the intersection. Pulled away from the intersection, went to shift into 2nd and would not shift. Tried 1st again, would not shift. 3rd and 4th the same. Stuck in neutral, can't shift into any other gear, how lucky for me. Managed to get to the side of the road and a pool of fluid began to form under the car coming from the slave cylinder. Opened up the master cylinder (which I top off monthly) no fluid. Only a little bit of brown sludgy looking stuff in the bottom of the resevoir (not good I'm thinking). Anyway had a great ride in the tow truck back to the house and I am seeking help from those of you that can direct me to my next step. Obviously the slave cylinder and hydrolics went bad but I am not sure how to proceed. Any advise and direction would be greatly appreciated.
JCH Hibbard

I'm not sure the best way to proceed (I guess get under the car and check the slave and slave hose?) but should you need to be topping up the fluid monthly? That doesn't sound right to me and maybe indicates there was something wrong initially?

Simon Jansen

gunsonr>If you are going to purchase a new clutch slave cylinder, be aware that many, if not all, of the aftermarket clutch slave cylinders are not designed to be rebuildable like the Original Equipment Lockheed clutch slave cylinder is. First, prior to installing it, make sure that both the hose (flexible pipe) and bleed nipple are in their correct locations. Because both holes use the same thread, it is easy to get them the wrong way around. The clutch slave cylinder often comes assembled in this manner so that it will fit into the box. The bleed screw should be near the high point of the clutch slave cylinder, with the rubber flex line attached to the lower of the two holes.

Inspect both the hole in the end of the pushrod as well as the clevis pin for signs of wear. It is common for both of them to have to be replaced. The bore should be closely inspected as well. If the bore is pitted, then rebuilding the clutch slave cylinder without sleeving the bore will work for a short time, but it will probably soon be leaking again. Next, inspect both the plain shank of the mounting bolt and the bushing of the clutch throw-out arm for wear and replace them if you find any. This will greatly reduce slop in the action of the clutch pedal and make engagement more consistent. The clutch fork should always be installed with its open end facing forward. The internal cylinder spring will take up any free play in the clutch release mechanism. The internal cylinder spring and diaphragm spring of the clutch pushrod push in opposite directions. While the diaphragm spring pushes the piston back into the clutch slave cylinder (and the hydraulic fluid back into the clutch master cylinder), the spring inside the clutch slave cylinder tries to push it back out again. It is the spring inside the clutch slave cylinder pushing hydraulic fluid back out that takes up the play in the mechanical linkages to the diaphragm, and the wear in the friction and drive plates, in order to give a consistent biting point. The pedal spring pulls the pedal off of the push-rod of the clutch master cylinder in order to stop it from rattling around and wearing the linkage, and to give a consistent pedal height. Do not omit the rubber boot when you reassemble the mechanism as its purpose is to protect the seal. Attach the rubber hose (flexible pipe) to the metal line first, and then to the clutch slave cylinder prior to bolting the clutch slave cylinder to the bellhousing. Use a new copper washer when you attach the rubber hose (flexible pipe) to the clutch slave cylinder.

Bolt the clutch slave cylinder onto the bellhousing, and then put a little brake cylinder grease on the very end of the pushrod so that it will lubricate the end of the pushrod as it bears against the piston. Remove the cap from the clutch master cylinder so that air can escape and you are not trying to compress the air space in the clutch master cylinder with the cap on when you install the pushrod. Insert the pushrod into the bore far enough to allow you to install the clevis pin through both the clutch actuating fork and the pushrod. If you have replaced the original pushrod with a new one and the new pushrod will not go in far enough to allow you to install the clevis pin, remove it and compare its length with that of the original pushrod. Some aftermarket pushrods are
Steve S.

Thanks Simon and Steve your description is very helpful and thorough. I have a question concerning the sludge type fluid left in the master cylinder. I had always checked the cylinder regularly to top off if necessary and the fluid always looked good with very little fluid needed. Am I to understand that providing there is no problems at the master cylinder level and the only problem is down below at the slave cylinder, that I can clean out the master cylinder through the bleeding process by using denatured alcohol? Would I poor it into the cylinder and bleed it through to the slave below? I will have time to get under the car in a couple of days to see what is going on but I did notice for sure that when I depress the clutch pedal fluid leaks out at the slave cylinder and there is very little resistance at the clutch pedal.
JCH Hibbard

Yes, you have the flushing process correct. However, just to make things easier, you should wipe up with a paper towel as much of the sludge in the master cylinder as you can prior to pouring in the denatured alcohol. You can purchase denatured alcohol at any houshold paint store. Flush the systen before you put in the new slave cylinder. From your description, it sounds as if the seal in the clutch slave cylinder is shot.
Steve S.

I know it's too late now, but if you'd just gone back to the parts store and got some brake fluid, filled the reservoir, and pumped a while, you possibly could have saved the tow. I sure don't know the situation, so I'm probably being rude, but that's what I would have tried. I'm sorry if your situation didn't allow that, just trying to give someone else an idea to carry a can of brake fluid along for just this purpose.

My cars have habitually leaked in a lot of places, and I do carry a bit of brake fluid along. I check more often than monthly, too. More like every other time I drive it. If it's been a month, I'll check it. Sometimes it doesn't need it, sometimes it does. And I can't say it's related to weather or use.

The sludge isn't very easy to see until the fluid's low, it sinks to the bottom.

I have been using Valvoline Synpower fluid, and have noticed no deterioration of seals (haven't disassembled, just no more leaks than when I used Girling LMA). I just bought a pint of Prestone DOT 4 at Wal-Mart, does anyone have bad experience with this? By the way, the last can of Girling LMA I bought was at Wal-Mart, haven't seen it there since (years ago).


<<I know it's too late now, but if you'd just gone back to the parts store and got some brake fluid, filled the reservoir, and pumped a while, you possibly could have saved the tow. I sure don't know the situation, so I'm probably being rude, but that's what I would have tried.>>

Tom, no offense intended, but I think that is very bad advice and potentially life threatening. Topping-up the brake fluid is one thing (I carry fluid for that purpose), but refilling and continuing to drive after a catastrophic failure of the hydraulics is quite another. He might have saved the tow but lost his life (or killed someone else) if the brakes subsequently failed.

M. D.


It has nothing to do with the brakes. It was the clutch hydraulics that failed. Of course it is brake fluid that is used in the clutch hydraulics, and hence the mention of brake fluid.

I don't see any danger in topping the clutch master to get you home. All you need is to get moving and then you can drive these cars without touching the clutch.

Completely agree with you that topping up brakes would be a no no.

67 BGT
I D Cameron

All good advise from everyone. Hind sight being what it is, I was still in reasonable walking distance (about 3/4 mile in the Florida heat) from the parts store but it never even entered my mind to go back for fluid. Honestly I was more concerned about what could have caused the failure and was trying to plan what I have to do this weekend once I get a chance to get back under the car to get this baby up and running. I haven't had the need to do any work on the slave cylinder before so I'm going into new territory but looking forward to it.
JCH Hibbard

Sorry Tom (and Iain). That'll teach me not to cross-over from the MGA board again (single master cylinder for brakes and clutch in an MGA).

M. D.

Had the chance to get under the car today to really see what the problem is. Slave cylinder definitely needs replacement but oddly I could not disconnect the clutch hose from the slave. The hose nut attached to the slave was frozen solid and none of the usual methods to loosen it would work. Finally had to disconnect the slave cylinder from the gearbox and then disconnect the other end of the hose from the cylinder line up inside the engine compartment. Ordered a new slave and hose today sure hope going back in proves to be easier than coming out.
JCH Hibbard

Is the hose good?

I wouldn't recommend adding fluid anymore, I'd just do it. If it saved me a tow. I have pumped and pumped before, finally getting a clutch without bleeding. I think if the slave is worn so much, the air just bleeds itself out, along with more fluid.

Even a half mile walk in hard heat may have had me calling the hook too. Pretty easy to give armchair advice, but having a quarter pint of fluid may save a tow. Safer than leaving it in a lot somewhere. Oh yeah it sounds like a recommendation again. Don't mess with anything on these cars, they're dangerous!

From what I recall on a 78 at least you have to undo the pipe nut from the hose above the bracket, then undo the hose nut that clamps it to the bracket before you can rotate the hose to unscrew it from the cylinder. The only other alternative is to loosen the hose in the cylinder first, then remove the cylinder from the bellhousing and unscrew it from the hose. Recently changed the clutch, had the slave fail, bought a new one and hose, but simply could not get the hose to pipe and bracket undone. Had to settle for using the old hose without butchering the pipe and bracket, but the old and new slave hose threads start in different places so the old hose ended up twisted when fully tightened. Fortunately a 2nd copper washer was enough to get it straight.
Paul Hunt

New slave cylinder and hose arrived a couple of days ago and are both now a new addition to my car. Interestingly, after reading about clutch bleeding nightmares I took some ideas from everyone's comments and here's what I did to bleed the system. I went to the auto parts store and picked up a siphon pump/fluid transfer pump. About $12.00. I placed a piece of hose from the pump to the bleed nipple on the clutch slave cylinder and on the opposite end of the pump placed a hose into the brake fluid. Two or three good pumps was just enough to get the clutch cylinder above about half full. I tightened up the nipple on the slave cylinder and topped off the master. Pumped the clutch pedal two or three times and I was back in business. Drove the car about 8 miles came back and checked for leaks, none present. So thanks for all of your comments and ideas, it was a great help.
JCH Hibbard

Regarding Tom's advice about carrying a container of brake fluid in case the the clutch hydraulics leak, that very tactic saved me a tow about 3 years ago. Got most of the way to work, then the clutch bite point got very low until it became very hard to shift gears. On lunch I walked to an auto parts store near my office. After work, I refilled the clutch master and managed to get back home. I parked the car until I could get a new slave cylinder (2 days).
Even though the clutch has nothing to do with the brakes on an MGB, I would say there is a bit of a safety issue in doing this. If your clutch pedal is on the floor, and the car in gear, the car can unexpectedly start to drive forwards (or backwards if in reverse) as the fluid gets past the seals or out the hole in the flex hose, whichever the case may be. So use caution if using this trick, and do it only to get directly home or to the mechanic.
Erick Vesterback

Erick, your timing for this comment is perfect. I just walked in from the garage after putting a pint of fluid in the boot for future trouble shooting. Thanks for the advice.
JCH Hibbard

This thread was discussed between 03/08/2008 and 24/08/2008

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