I have recently restored a 1960 MK2 and installed a new remote servo (Lockheed) together with new master cyl, brake lines and hoses and new calipers. The system is filled with Castrol brake fluid (not silicon).
The problem I am having is that at the first application of the brakes there seems to be too much servo. An extremely light pedal pressure quickly slows the car. If I apply the brakes 10 or 20 seconds later they work as they should with completely normal braking action. However after several minutes the same over servo condition reappears just for the first application. The fault is persistant and doesn't change regardless of speed, engine revs or ambient temperature.
I have flushed and bled the system many times with no change.
I have checked all the vacuum lines and it has a new reservior and check valve.
I live in Southern California (80 degrees today) but I plan to visit the UK in Feb to see Mum at which time I can purchase new parts if that is what is suggested.
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If you are anywhere near Northampton, when you visit, there is a Jaguar man who specialises in old Jags. Can't remember his name, but his garage is in the middle of a village called Earls Barton, between Northampton and Wellingborough. Good luck.
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Where have you tapped into to get your vacuum what size of pipe and internal restrictions does it pass through does it pass through. If you brake with you left food and do not take your foot off the throttle is the effect the same. Regards Peter
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Thanks oldpostie, if I can't get it solved before my Uk trip I'll look him up.
Thanks also Peter D for your input. The vacuum lines are 3/8 inside diameter and were all replaced during restoration. I tried your other suggestion and held the engine at different speeds while applying the brakes and still had the problem. Your question about the vacuum got me thinking about how the system is supposed to work and I may have an answer, let me know what you think.
The normal state of the main servo is for there to be atmospheric pressure on both sides of the main diaphragm. When the brake is applied, one side of the diaphragm is ported to the intake mainifold and the difference in pressure (max 7 to 8 psi) is what supplies the servo actuation. I think that if there is a leak in the reation valve it would create an imbalance in the servo. Pressure would be applied by the main servo diaphragm but wouldn't affect the hydraulics until the pedal was pressed when the system would behave as if a panic stop was being applied. This would explain why the second braking appears normal because the leak is a slow one and it takes time to empty the main diaphragm. I'm going to order a new reaction valve, it may take a week or so to get it and I'll let you know the result. Thanks for triggering my grey matter and I would be interested in you thoughts.
Keith
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Many years ago I rebuilt a remote servo for a Jaguar MkIX, which although smaller, is similar to the MK2 one. One thing I do remember is that there is an adjustment for the clearance between the cylinder pushrod (from the diaphragm) to the cylinder piston. The manual I used gave a very good procedure for the adjustment, which required a depth gauge, for which I used a vernier caliper IIRC. The manual made the point that if the clearance is wrong, the booster operation can become unpredictable, or even 'kick back' on the pedal. There are very few things in the servo that need to be adjusted, but it might be good to check whether this adjustment is correct. HTH.
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I assume the pipe is the correct stuff I have seen radiator hose used and it can be sucked flat. With the inlet vacuum at over run being high it could collapse some pipes. Normally the servo has an accumalator side of the diaphram thus the check valve to stop vacuum bleebing back into the inlet manifold. Now when you apply the brakes the other side of the diagpham is allowed to move by sucking in air and allowing the diapham to move towards the vacuum side thus creating the thrust. This system is used as the vacuum side replenishes itself on overruns and cruising and maintains a vacuum should you stall or require the brakes when the throttle is still open, thus the test I got you to do. I have experinced an incorrectly adjusted piston clearance and it feels like the brakes are slapped on, this is due to the Vacuum being bought itnto play before the normal piston pressure has initiated the movement of the slave cyclinders prior to vacuum assisted pressure. Regards Peter
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finaly got around to fitting the new reaction valve to the servo. Brakes are working perfectly. Thanks again for all inputs
Keith
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