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TR6 TR6 BRAKE PROBLEM

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machinemd

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So I took my "new to me" TR6 for a quick ride today and experienced a problem that was described by the previous owner as a one time event last fall. After braking I noticed that I was getting no coasting, the front brakes were dragging heavy and the brake pedal had no play. I cracked the front brake fitting just a hair at the master cylinder, got a squirt of fluid out, tightened it, and the brakes were fine for the rest off the five mile drive. I did the same with the rear fitting and got no blow off of pressure. I get the feeling that it is the master cylinder, either the primary plunger failing to back off, or the tipping valve failing to open (is that even possible?). Of course the servo could be it and I don't have a clue what is in there to mess up. The flex brake lines? But both? There's plenty of meat on the front pads and the fluid is clean. Can the PDWA valve be a possibility? Any thoughts from the experienced minds? I remember reading a post about a broken spring but can't locate it. Is that a possibility here? Overhaul candidate or straight repair? Any thoughts would be appreciated.
Steve
 
Do front brakes on a TR6 use a 'restrictor valve'? TR3s & 4s have them - sort of a check valve that is supposed to reduce the amount of pad movement required before they make contact with the disc. Sometimes they work a little too good.

On 3 & 4 it is a cylinder about 2" long on top of the 4-way/5-way connector.

I'll confess I do not know 6s so maybe the PDWA thingy made this valve redundant.
 
Hello Machinemd,

surely the problem lies in the master cylinder?.
The flexible hoses would not be a "one off", as you say that the rest of the drive was fine (I assume you did use the brakes?), and the chances of both failing together?
The servo is common to front and back so all brakes would be affected with a servo problem.
(With servos, if the diaphragm sticks in the cylinder you get the same effect)
I don't think that there is anything in the Pressure Differential switch that could cause a problem. Was the light on after the problem?
If you feel capable, I suggest stripping the master cylinder to see if there is anything obvious.

good luck,

Alec
thirsty.gif


[ 04-18-2004: Message edited by: piman ]

[ 04-19-2004: Message edited by: piman ]</p>
 
Jeep,
We LBC owners don't have the luxury of just replacing our master cylinders. The Lockheed master cylinders used on Triumphs is no longer available, for those of you thinking it is time to renew. TRF had one or two left as of last month. Rebuilding is the only option.

Bill
 
My vote is that one or more of your 4 caliper pistons is stuck due to rust. Overhaul your calipers before you investigate the MC or PDWA. Make sure you generously grease the caliper pistons and rubber seals with the special red grease made for hydraulic systems. This procedure is straight-forward and the only potential difficulty is removing the pistons. That can be done with careful shots of compressed air.

If the age of the rubber hoses is unknown, I'd replace them while you're at it. It's cheap insurance.

Rick O.
72 TR6
 
My bad, Jeep,
The Lockheed (Girling) MC is still available new, though not always in stock. Like you, I replaced mine two years ago in lieu of overhaul. Had way too many of those. In fact, I redid my entire brake system and opted for the nickle/copper brake lines from Moss. Very easy to bend and adapt, although some maintain they aren't as strong as steel. My research shows they are safe to use for brake lines, not as strong as steel, but safe. I think in racing applications, they are not suggested. Anyone out there have experience with these? I have had them on two years and regularly inspect, everything holds, no leaks, seems ok....

Bill
 
Thanks for the input guys. I just picked this car up 2 months ago, haven't driven it much yet, so at this point am feeling it out. It's had a full body and interior resto but not a whole lot of mechanical work. The PO wasn't a wrench twister so relied on small garages in NH and just paid. It was obvious to me, because darn near every body panel is new and the crankshaft pulley is heavily rusted and painted, that this car at one time had just sat. The PO tells me he has owned and driven it for the past 4-5 years. The flex hoses look like they were replaced about 5 years ago and look good. The brakes feel great and in my mind even if the hoses were deteriorated inside it would hold a pressure between the hose and the caliper, not the master cylinder. I can't get it out of my mind tho that the brake pedal was rock solid. I can't swear that it retracted to the rest position when I took my foot off it but am reasonably sure. At this point I'm hoping short rides locally can reproduce the problem and I'll have enough tools and thoughts with me to nail it down. I don't have a clue if there's anything in the brake booster that could cause this. I have read Buckeyes excellent brake info but need to do it again when awake and alert. I'm a night time web junkie basically. I've had a Spitfire for a number of years. This is my first TR6 and I'm finding this is a completely different animal. Couple of questions for your well experienced minds. If the master cylinder primary piston for some reason stuck in the bore, wouldn't the brake pedal and booster retract when I took my foot off the pedal? And from parts and book illustrations I get the impression that the tipping valve is mechanically opened by the primary piston retracting. Correct? By the way, is the tipping valve included in o/h kits? I've been a manufacturers service rep on equipment for 25+ years and it's just my habit to analyze the problem and nail it not replace parts til it's corrected. Besides, I've blown my toy $$ for now and don't care to spend half the season waiting for delivery of one part after another. I've thought of a stuck piston but I believe it was both front brakes as the discs were hot after 2 miles and only braking a few times. Also the fact that when I took my foot off the brake pedal asny pressure in the lines should have been released, which it wasn't. If it definitely comes down to the master cylinder, I'm not at all shy about overhauling it if an inspection shows it's a good candidate. By the way, Kai Radicke indicated only a month ago I think on 6Pack digest, that his company Wishbone Classics has about 20 masters in stock.
Thanks, Steve

[ 04-21-2004: Message edited by: machinemd ]</p>
 
Hello Machinemd,

you are correct, the tipping valve is actuated by the piston. It is shown as included in my UK Moss catalogue repair kit, part number 517332.

Alec
thirsty.gif
 
Piman,
Thank you for that tip on Moss. I checked with TRF and they told me that the tipping valve was not part of their kit. I was ready to order the kit before tearing out and inspecting the master if the valve was included in the kit.
Steve
 
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