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MGB MGB Troubles

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79MGB16

Senior Member
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Mgb Problems
Car: 1979 MGB non-overdrive 4 speed transmission

The problem is with the clutch. We have just rebuilt the master and slave cylinders. If you start the car in 1st 2nd or reverse with the clutch all the way down, the car lurches forward or back. The car will somethimes shift through the gears fine clutch in or out with the engine off. With the engine running the car will grind reverse if you try to put it in, and it is like it is locked out of the other gears. It won't go in. Could this be a problem inside the transmission itself(nothing to do with clutch)??We measured how far the arm that comes out of the slave unit is moving, it is only 1/4 of an inch. Could anyone tell me how far it should move? The transmission is full of oil, and we have bled about a quart of fluid through the clutch system. What is the proper bleeding procedure for this car? I need to know if there is anything I need to do before I break down and spend some money.
 
Reasonably sure the problem is in the hydraulics. I'm guessing the master wasn't bench bled. Therefore needs more bleeding. It's messy, but if you can force fluid into the slave cylinder bleeder and expel the air from the master cylinder you would be better off. Bob

[ 12-01-2003: Message edited by: Bob Claffie ]</p>
 
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Its really a pain to get it bled properly but that is definitely your problem provided everything is right on the rebuild.
 
Regarding the non functioning clutch,it might also be a problem in the clutch pedal assembly. The material in the pedal itself is quiet softand the pivot hole is prone to wear into an oval shape. The pivot pin is also soft and wears excessively. with all of this wear at the short end of "lever" arm it really cuts down on the fluid diplaced by the master cylinder piston. I learned this the hard way
 
OK, now that you jogged my memory, the shaft coming out of the slave cylinder and its pin also wear quite badly. I have replaced the pin a couple of times in the last 20 years.
Bob
 
I am pretty sure the problem is not that it hasn't been bled completely. We have bled 2 bottles of fluid through with the same results. I will check the pedal assembly ect. This weekend, but could someone please measure how far the arm on the slave moves when the clutch is fully depressed. Mine is only moving 1/4 of an inch. Thanks for the help so far.

Thanks Again
Robert
 
The next logical question is "How does the clutch pedal feel?" There should be a fair amount of resistance. If it feels like you are pushing on air, YOU ARE. The volumm of brake fluid used in bleeding has no relationship to the success of the operation. I've had some bleed very easily and others that I thought would never come around. My car is already in winter storage so I can't measure the throw but as a wild a$$ guess you should be looking at 3/4 to 1" movement. Patience. Bob

[ 12-02-2003: Message edited by: Bob Claffie ]</p>
 
Personally, I just took a Mitey Vac and filled the resevoir from below, thru the bleeder screw. I just put the suction end into the bottle and the exaust (for lack of a better word) onto the bleeder screw!! It took all the air with it and it took less than 5 minutes!!
thirsty.gif
driving.gif
 
Check how much slack there is between your slave cyl rod and the clutch fork with the fork pulled back against the resistance of the clutch. You should have very little, even none maybe. If you have lots, then you may need a longer rod or an adjustable one.

I have made adjustable ones for almost every british car I have owned ( the Japanese figured this one out decades ago! )Your major cyl travel could be wasted taking up this slack. The bonus here is that you could then adjust as needed as the clutch wears.

It goes without saying ( but I'll say it anyway )
that your cyls are a match for bore and stroke..IE
too large a bore on the slave will result in too little travel...
 
I really really like my EZ Bleed power bleeder. It pushes the fluid through from the reservoir, and keepr the reservoir topped up while it does it.

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Gary Lloyd:
Personally, I just took a Mitey Vac and filled the resevoir from below, thru the bleeder screw. I just put the suction end into the bottle and the exaust (for lack of a better word) onto the bleeder screw!! It took all the air with it and it took less than 5 minutes!!
thirsty.gif
driving.gif
<hr></blockquote>
 
Your pushrod should move 1/2" to 5/8", if it doesn't it probably needs bleeding some more - provided the hydraulics were rebuilt right. Not saying they weren't, it's just one of the variables. Another good way to bleed that I've used is to run a tube all the way from the bleeder back to the reservoir and pump like mad with the bleeder opened just enough to let the fluid and bubbles flow. The air gets pushed out of the bleeder by the constant and quick fluid movement, goes up to the reservoir, and air bubbles stay there and pop. Good luck, Wade
 
The pedal feels hard. I am really confident that it has been bled as much as it can. My grandpa, father and I spent two days bleeding it until nothing but clear clean fresh fluid came out. We cleaned everything before we put it back together, and the system is clean because the fluid coming out is as clean as the stuff we put in. Just the slave isn't moving enough if it is supposed to move about an inch. Its only going 1/4th of an inch. Maybe the parts just weren't rebuildable. Do you guys think a new master cylinder and slave would fix the problem? Have to spend my money this week and I miss my b. I am sick of driving my parents car. Thanks for everyones help so far.

Thanks Again
Robert
 
We didn't have the parts bored either. Maybe this is why? Perhaps they were too far gone for the rebuild kit to fix. What are your opinions. Also I think the clutch fork did have some slack, but the slave still isn't moving far enough. How did you make your adjustable arms or where can I get one?
Thanks
Robert
 
It's conceivable that either or both of the cylinders were too worn for rebuilding. With bad scoring or heavy wear it is possible that the new seals just aren't up to the task. I am a little disconcerted when you claim a hard pedal. If that is true than I have to agree with you that more bleeding may not be the answer. What was the reason for rebuilding them in the first place? Did clutch problems appear all of a sudden or had they come on gradually. Inquiring minds want to know. Bob
 
The problem came all of the sudden. I was driving to katy to pickup a wheel for my motorcycle, when all of the sudden I couldn't downshift or upshift. I managed to limp the car home, where it sat for 2 weeks until I rebuilt the slave. That made the car drivable again until last week, when it became a down hill spiral until it won't go into gear again.
where is the cheapest place to get the master, and slave, cylinders?
Thanks for all your help.

Robert
 
I know this is a desperate move but have you considered the flexible hose between the master and the slave? They occasionally degrade on the inside causing various problems (usually won't allow the fluid to be released). I have had them go on two different MG's and for $10 or $15 might possibly help. My personal opinion from what I've read here, it isn't the length of the rod or the wear of the pivot parts. Is there any chance you ran over something to kink the lower metal pipe? I think we are all grasping at straws at this point. Bob
 
Hi Robert,
If rebuilding the slave fixed it for a while & then it failed again, replace the slave. You can find a slave cylinder here;
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29011#top
Good luck,
D

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by 79MGB16:
when all of the sudden I couldn't downshift or upshift.
I rebuilt the slave. That made the car drivable again until last week, when it became a down hill spiral until it won't go into gear again.
Robert<hr></blockquote>
 
Rebuilding the slave didn't fix it. It only made it more drivable. I still couldn't down shift at speed and it wouldn't upshift at anything else than 2000rpm.

Thanks Again
Robert
 
I just had another thought. The throw-out bearing in our cars is the friction type. How long has yours been in there? They wear gradually unless you are one to keep your clutch pushed in at traffic lights.
Now this is more extreme than what you are saying but when I first got my MGB, I did this and it wasn't too long before it started making a little noise and started shifting like you described. I didn't know what to think of it but went on driving. Then suddenly I heard awful metal splintering noises and suddenly had no clutch release at all.
I was able to drive home by starting the engine in first gear and carefully syncronizing the revs with the gears when changing them and cutting the engine off when I had to stop.
To try to shorten a long story a little I found that the throw-out bearing had completely worn away and came off the fork and the fork had gone into the pressure plate and destroyed it. Also the little metal pad the throw-out bearing goes up against on the pressure plate was worn away.
New parts fixed it but the fork wasn't available so I had to weld a new end on it shape it for a new bearing.
Bob
 
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