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MG MGB Technical - MGB mark 1 clutch pedal stiffness
|Hello, my clutch pedal when changing gear it will feel really stiff and will be slow to return, then it will be normal, then you can feel some type of resistance. When stopped I manually press the pedal and a gurgle sound which could be normal, but also will be intermittent resistance. Any idea of this problem as it has been getting worse over the past two years.|
|More likely to be the clutch hose disintegrating internally causing restriction and small pieces of black rubber will end up in the slave cylinder. Changing the hose is a challenge and best change slave cylinder at same time. Check everything out under the car-don't take my word for it. Bleeding hydraulics can be frustrating.I've been through all this.|
|Change it ALL out. With a disintigrating rubber hose, you may have "fragments" throughout the slave cylinder, as well as the reservoir. |
|The hydraulic system won't normally stop the pedal coming back. The is fluid behind the primary seal (retained by the secondary seal) and if anything stops the fluid coming back in at the same rate the piston retracts, fluid is sucked from behind the primary seal. You can see this in the brake master which has a slow-return valve in the master outlet, which does exactly that, i.e. restricts how quickly fluid can come back in to the master, and that doesn't hold the pedal back. Fluid is pulled from behind the primary seal, then as the fluid returns from the lines the excess is pushed back into the reservoir via the bypass port.
It's more likely to be mechanical stiffness somewhere, in the pedal pivot, or possibly the piston in the bore. Eliminate the pedal before embarking on the hydraulics.
You can tell if the stiffness is in the pedal or the master cylinder by where the free-play is when the pedal is returning slowly, and indeed IF there is free-play while it is returning.
|Bit obvious and basic stuff I know but do you have over mats/carpets that could be catching pedal and do you have a pedal return spring that might be twisting itself somehow.|
I can't remember but does the pedal have a hole or bush that might be ovaled or loose.
Good idea to start at the pedal end and work your way forward, less potential misery at that end.
|The pedal pivots on a bush that is clamped into the pedal carrier, with a large washer or spacer each side of it.
The pedal has a fixed bush, but this is slightly shorter than the fixed bush in the pedal carrier. This means that the pedal has a very slight clearance to move from side to side on the carrier bush to keep it in line with the master cylinder push-rod. But if the two bushes dry out the pedal can become stiff, and if it has been assembled incorrectly the pedal can be out of line with the push-rod which can also make it stiff.
The pushrod holes in the pedal do wear oval, and the clevis pin wears. This could cause stiffness but is more likely to cause excessive slop and a low biting point.
The pedal footpad should have some side to side movement, and there should be some free play when pressing and releasing the footpad slightly, and both of those show the pedal is free on its pivot at least.
Your next mission, should you decide to accept it, is to remove the pedal cover.
|When I got my Mk1 I had that exact problem. Obviously the previous owner had tride to cure it because in the spares he gave me was a master cylinder and slave cylinder |
( both looked nearly new ) and new ones on the car. I replaced the flexi and the operation is now smooth and progressive.
|A J Dee|
|I'm with C H, Gary and Andy because I worked on an MGC recently where the clutch pedal went to the floor and disengaged the drive as normal. However, the pedal return stroke, although smooth, was exceptionally slow and rendered the car unusable. During investigation the pedal finally refused to return. All the likely causes were checked out before the culprit was found to be a degrading flexible hose. Needless to say all system components were cleaned out to remove any debris.|
This thread was discussed between 24/06/2018 and 26/06/2018
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