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MG MGB GT V8 Factory Originals Technical - Clutch problem on the Factory V-8
|I am in the middle of the shakedown period with my Factory GT V-8 after the restoration, chasing all the loose ends. One problem I have had is that my clutch is not fully disengaging, the trans is acting like a 3-synchro, not letting me enter first unless the car is at a standstill. Also, unless I am very slow on the gearchange, second gear will "graunch" upon engagement. Third and top gear are fine, both upshifting and downshifting.|
All the clutch components are new, except for the throwout bearing fork. I assumed this was in good condition because the clutch worked fine before disassembly. I replaced the master cylinder, mostly for cosmetic reasons (the old one was rusty and ugly). On advise from Beer of Houghton, I put in a 4-cylinder MGB clutch master cylinder (they assured me it would work fine).
I am only getting about 7/16-1/2" travel on the slave cylinder plunger. I have bled the system twice, once using the Paul Hunt reverse bleed technique with an Eezibleed unit attached to the bleed screw, and once with the "pump the pedal" technique. I am reasonably certain I have all the air out of the system.
I went ahead and ordered a new V-8 spec clutch M/C from Brown and Gammons. I assumed that the V-8 cylinder had a larger bore, allowing more fluid transfer and consequently more travel on the slave plunger, but when I got the new master cylinder yesterday, the bore is actually smaller! This besides the fact that the new cylinder is a generic Euro-copy with a lousy looking plastic fluid reservoir (grump!).
My theoretical knowledge of hydraulics is sparse, but shouldn't a smaller bore master cylinder give even less travel on the slave?
Any suggestions would be appreciated, once this problem and the funny grunt from the front suspension and the clicking in the tranny and the overheating in anything approaching moderate traffic volume are fixed, the car will be a joy to drive!
Thanks in Advance,
|Your logic sounds right to me (smaller bore = less volume of fluid sent to the slave calendar).|
All I can say is that I have measured the standard four-cylinder MGB clutch slave cylinder to be ½ inch on several occasions. Perhaps someone with a factory V8 can measure theirs to find out if they travel further.
|Paul - try the clutch with a small socket between the plunger and the slave - let us know whether you can change gear normally.|
This is normal for TRs where the slave was not properly matched to the master.
If you try to install that new V8 master cylinder you will find that it won't fit, that large plastic fluid reservoir cap will foul the firewall. Send it back to B and G.
|1/2" travel is what I have, but I also have a dragging clutch from time to time, also a vibration when slipping the clutch but in reverse only. I have ascertained that it occurs when the car does not get much use - it had been fine when used every other day or so but parked up for six days while in Ireland I found that although I reversed off my drive OK I could not get any forward gear other than fourth, which I used to start it rolling then could select first OK. After that first drive where I purposely slipped the clutch when changing gear it has been fine. I remember Roger Parker saying that the clutch could develop a film when not used and recommended a bit more drastic slipping than I used - brakes on and plenty of revs. I am convinced it is nothing to do with clutch slave travel as the main biting point is always in the same place even when the clutch is dragging slightly with the pedal fully down.|
Where mine differs from Paul is that if I am very slow going through the synchro it will graunch, and I can enter first while rolling but not at a standstill.
Again from Roger Parker (and my web site) are these bore sizes:
MGB M/C: 19mm
MGB slave: 32mm
V8 M/C: 17.8mm
V8 slave: 25.4mm
With both master and slave (do you have the V8 slave, Paul?) having different bores, and different forks, relative travel between 4-cylinder and V8 is no easy thing to derive!
A constant dragging, or very low engagement, can also be caused by work linkages and clevis pin at the pedal.
|Clutches not used for long periods also have a significant degree of moisture take up from the atmosphere and the 'warming' of the clutch Paul mentions I have said before has benefits in removing this.|
This thread was discussed between 09/05/2001 and 10/05/2001
This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.