Dave De Halle Posted April 23, 2019 Report Share Posted April 23, 2019 Not sure if anyone has any previous experience or can advise. I have undertaken a significant refurbishment of my 1972built /1973 registered TR6 including wheel cylinders, discs flexible hoses and master cylinder. Initially the brakes were fine (pedal is very solid with very little free movement), however a sticking brake problem has crept in over the last few days only becoming a problem after a few miles 10 to 15 and modest use of the braking system, when the car is left for 30 minutes the brakes free off again.Last week one of the rear brakes stuck evidenced by heat and hot friction material smell, this week both of the front brakes stuck sufficiently to blue the discs after completing approx 10 miles without problem then a further 2-3 miles after they started sticking. Whilst the original front callipers have been retained the flexible pipes have been upgraded BF Goodridge S/S braided , rear wheel cylinders replaced and the master cylinder replaced. Whilst fitting the new TRW master cylinder I bled the rear brakes first which was straight forward however the front brakes would not bleed until I removed the outlet union and cleared the drilling hole from the cylinder (by hand with a small phillips screw driver) after which the pedal pressure was very solid. After the initial rear brake sticking problem I removed the master cylinder cap to check the vent hole was clear, this appeared fine but was surprised to see a small amount of black sediment in the bottom of the cylinder, the cylinder was new and bled with clean new DOT4 fluid. I suspect there may be a blockage due to either a fault with the front master cylinder section (cleared to enable bleeding) or sediment left after manufacturing causing a partial blockage which can be overcome by the braking pedal effort applied but not overcome by the much smaller return rear brake springs/caliper relaxation forces, or only allowed to dissipate extremely slowly. I would be grateful if anyone has any similar experience or knowledge, Alternatively is it possible that the servo could be faulty as this is still the original unit Regards Dave Quote Link to post Share on other sites
Waldi Posted April 24, 2019 Report Share Posted April 24, 2019 Dave, the symptoms you describe indeed point in the direction of not bleeding properly as the brakes warm up and the fluid expands. Does the servo have the clearance as indicated in the WSM? Black deposits are not good in a new system. Waldi Quote Link to post Share on other sites
iani Posted April 24, 2019 Report Share Posted April 24, 2019 I had similar issues with a TRW master cylinder, swapped it out for a reconditioned original and all well. There have been lots of issues with TRW master cylinders. Quote Link to post Share on other sites
harrytr5 Posted April 24, 2019 Report Share Posted April 24, 2019 I reset my servo push rod with out very much clearance and after a test ride the brakes locked on.Released the master cylinder a tad and got home. Reset the push rod on the servo to the correct clearance and all was well. Thought all the faulty TRW master cylinders were no more. Regards Harry Quote Link to post Share on other sites
iani Posted April 24, 2019 Report Share Posted April 24, 2019 37 minutes ago, harrytr5 said: I reset my servo push rod with out very much clearance and after a test ride the brakes locked on.Released the master cylinder a tad and got home. Reset the push rod on the servo to the correct clearance and all was well. Thought all the faulty TRW master cylinders were no more. Regards Harry So did TRGB, they managed to sell me a dodgy one a year ago though, they took it back with no fuss. Quote Link to post Share on other sites
RogerH Posted April 24, 2019 Report Share Posted April 24, 2019 3 minutes ago, iani said: So did TRGB, they managed to sell me a dodgy one a year ago though, they took it back with no fuss. Hi Iani, PM on its way. Roger Quote Link to post Share on other sites
Mk2 Chopper Posted April 24, 2019 Report Share Posted April 24, 2019 1 hour ago, harrytr5 said: I reset my servo push rod with out very much clearance and after a test ride the brakes locked on.Released the master cylinder a tad and got home. Reset the push rod on the servo to the correct clearance and all was well. Thought all the faulty TRW master cylinders were no more. Regards Harry I had the same issue, new MC and difficulty bleeding front brakes and initial tests showed brakes locking up. The new MC wasn't set up correctly with the old servo push rod and once the MC was undone a tad it released the brakes, I reset the clearance of the push rod and never had another issue. Gareth Quote Link to post Share on other sites
Dave De Halle Posted April 24, 2019 Author Report Share Posted April 24, 2019 Many thanks everyone great help will start with servo actuation rod setting and pre check vacuum and no vacuum brake operations and then test again. Regards Dave Quote Link to post Share on other sites
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