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MG MGA - Clutch or MC problem?
|Advice needed please. Reversing up car ramps to investigate occasional sticking handbrake I stopped to check position on the ramps and then revving and releasing clutch to get up to final position the clutch bit sharply and engine stalled. Thereafter I struggled to engage any gears and the clutch pedal pressure seemed lighter than normal. Fearing some catastrophic mechanical breakage at the clutch I finally managed to select a gear and found I was able then to drive forward (only tried first to second gears) and in reverse but with the clutch needing to be absolutely floored and engaging sharply with the slightest release of the pedal. Thought I would check the easy things first and found the push rod travel at the master cylinder is about 1 inch 25mm while at the slave cylinder Im getting at best 5/16 say 7mm I see that Barney suggests full pedal stroke should produce 5/8 16mm of motion at the slave cylinder push rod. The car was fitted with Hi Gear T9 setup using MGB clutch and ancillaries including new Slave Cylinder 18 months ago and has done little mileage since then. Given the small relative movement at the Slave Cylinder and the light pedal pressure Im suspecting issues with the MC though would have expected a problem here to be gradual rather than immediate as in this case. While the clutch pedal pressure is light (and doesnt improve with pumping) the brake pedal pressure is fine and all appears well there. Regardless it is probably time to replace the MC as according to the cars History file it could easily be 10+ years old and I can now see some seepage. Any advice gratefully received.|
I think my starting point would be to bleed the clutch slave cylinder first.
|Diagnostics first. It is good that you immediately realize the deficiency of travel at the slave push rod. That means it is a controls problem, not an internal clutch issue.|
Press the clutch pedal with one finger to check amount of free play. This should be more than zero but minimal, like less than 1/2 inch. If you can push the pedal about half way down before you feel resistance of the master cylinder piston, that's a master cylinder or master push rod problem. Check first to see if the master push rod and clevis and clevis pin and top end of the pedal lever are still in tact. If something there wore through or broke this could cause a lot of free play before it pushes the master push rod. You might need to replace the clevis pin or weld and re-drill top end of the pedal.
If the master linkage is good and giving full travel to the master push rod, my next guess is the piston is stuck half way in the bore and not returning all the way. A master cylinder repacking kit should solve that problem, as well as curing the leak.
|Just to report back that a replacement Master Cylinder courtesy of Bob West (AP unit) resolved my issue with the clutch. Surprised that I had absolutely no warning of the MC failing, glad it was the clutch side rather than the brakes. Took the opportunity to replace the fixed and flexible Clutch pipes and was dreading bleeding the system but all went well using a gunsons Eezibleed.|
You have bought the best MC, well done. I had many problems with my 'cheapo' MC before I too went down the Caparo AP route with Bob. Nicely machined unit. Faultless MC operation ever since.
|Kevin - Did you investigate the actual fault in the old MC ? I replaced the rubbers in my original one about 6 years ago and still OK at the moment - fingers crossed it stays that way!|
|Steve, I'm pleased I purchased well as I have seen MC's on EBAY for £75 whereas Bob's came in at £120 + VAT and P&P so still a realistic price. Cam, no I havenít stripped it down but will do so as I'm keen to see how it failed. Just wondering how old the replaced one was, the history file, which goes back to 1995 shows no work done on the MC. The markings, in case any one can age it, are Lockheed 7/8, numbered 3*1836 one side and stamped Q89 on the other.|
|Is there a supplier of the AP unit over here?|
I had mine sleeved by Apple. I'm not v happy. The finish is a bit coarse and after installing new seals it won't return with the internal spring pressure. I know the piston is a nice fit, so its not that sticking.
|Art, I was looking for a MC a few months ago and found that the usual suppliers on this side of the pond seem to carry the TRW unit. I ended up ordering a Caparo/AP unit from Bob West.|
Edit - You could try Chris Hollum in Montreal.
This thread was discussed between 12/08/2012 and 15/09/2012
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