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MG MGB Technical - Slave or master
|I'm having problems selecting a gear after fitting a replacement clutch.|
The pedal is stiff to depress and the release lever at the bell housing only moves some 10mm.
There doesn't seem to be any fluids leaking. Assuming one of the cylinders is faulty,is there any way of determining which one to replace / overhaul first ?
Thanks in advance.
|If it grinds when selecting reverse then the cl;utch is the problem i.e. dragging i.e. not releasing fully. 10mm is a little on the low side, the normal figure quoted is 1/2" to 5/8" i.e. around 15mm. But if it's not grinding when trying to select reverse (engine running obviously) then it is something to do with the selection mechanism i.e. gearbox.|
If you disconnected the clutch hydraulics instead of just demounting the slave cylinder then you probably have air in the system. One way to confirm this is to put the car into gear with the engine stopped, hold the clutch down and start the engine, then start lifting the pedal up slowly. If the clutch starts to engage much lower than usual then the hydraulics do need bleeding. Incidentally make sure you have the handbrake and ideally the footbrake on before doing this and plenty of space in front (for a forward gear) or behind (for reverse) in case the engine catches and launches the car.
The clutch can be a right pain to bleed, the easiest way I have found is to connect the right front caliper nipple to the clutch nipple (they are the same size) then use the brake pedal to reverse bleed the clutch system. Should only take a couple of pumps. If the clutch master is full siphon some out first, and make sure the brake master doesn't get lower than half-full.
If there are no leaks (check up at the top of the pedal as well as round the slave) then usually the only symptom is that while you hold the pedal fully down the clutch starts engaging on its own. That indicates a problem with the master seals. Other than that a pedal which doesn't go fully down, or a clutch that doesn't fully engage again afterwards, could be the flex hose delaminating internally and acting as a check valve one way or the other.
|Paul Hunt 2|
The problem is selecting any gear, ie permanently engaged.
I have bled the system from the slave cylinder bleed nipple... it didn't seem difficult. Are you suggesting that this doesn't do the job properly ?
Also, I have checked at the top of the pedal and there is no leak, if I understand you correctly do you think, therefore, it is the master cylinder that is at fault ?
To give you a bit more back ground info. The car was stored in a barn for 17 years, so both master and slave cylinders have not seen much action recently !!
|Dave: if the clutch disengaged alright before you replaced, the most common problem is fitting the disk backwards. The slave cylinder does not move very far to disengage the clutch and if the driven disk is installed backwards, the pressure of the disk against the pressue plate will prevent the clutch from disengaging.|
I thought that at first, but have since gone over my steps on a spare engine and clutch assembly. It seems incredibly awkward to fit the friction plate the wrong way as the locating dowels are too short that way.
When I changed the clutch I had the engine out, if I have to do it again, is it easier to leave the engine in place and drop the gearbox to get at the assembly?
|I had real trouble getting the air out of my slave cylinder when i changed it. In the past i have asked a friend to depress the clutch peddle while i have released the bleed nipple. My nabour advised using a power bleed systemm that you attach to the car tyre to provide pressure and fit the cap to the master cylinder to force the fluid through when you release the bleed nipple. It worked.|
|Dave - the crucial thing is as I asked before, is it grinding when selecting reverse? The forward gears aren't very indicative as with synchro they don't grind even when the clutch is dragging. So if reverse grinds, then it is the clutch dragging i.e. not releasing. If reverse *doesn't* grind, just refuses to go in, despite several 'clutch up, clutch down, try again' attempts then it is probably gear selection that is at fault.|
A problem with the master is only indicated if normal changes are OK, but when sitting at traffic lights or junction in gear with the clutch pedal fully down (a bad habit anyway) the car starts creeping forwards on its own, or if you have the footbrake down as well the revs gradually drop and the engine stalls.
You can't drop the MGB gearbox to change the clutch without major surgery to the tunnel and fixed crossmember, it is a case of engine out or all out.
|Paul Hunt 2|
|Dave: Depending on the manufacturer of the disk, it is possible to install the disk backwards and have the pins on the pressure plate line up well enough to install. The test of hydraulics versus mechanical problems is if you can pump the clutch pedal a couple of times quickly and get it to disengage, you have a hydraulic issue, otherwise it's mechanical. Mechanical problems will include either installing the disk backwards as I've indicated, or worn clevis pins, or worn clevis pin holes in the clutch pedal and/or the master cylinder operating rod. The Slave cylinder push rod and clutch throwout fork rarely get severely ovaled holes, but the clevis pin does tend to wear.|
|Thanks Paul & John|
Yes it does grind when trying to selecting reverse and going on Johns advise, it probably is mechanical...dam it...they should make all friction plates idiot proof!
Back to the engine hoist.
|A quick update|
John you were right, I have just had the clutch out and it was fitted the wrong way !
If you hadn't known that different plates could fit backwards i would have been scratching my head for ages.
This thread was discussed between 20/07/2007 and 24/07/2007
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