| Author | Message | ||
     Carl Jensen Experienced User Username: carl_jensen Post Number: 18 Registered: 2-2005 |
1975 Shadow LRD20648. Life is full of surprises. Recently my master cylinder appeared to fail and this forum was great in helping me through the diagnosis, replacement and bleeding of my new cylinder. What happened is that my car had gotten very hot and started to smoke, and then the master cylinder light went on as my brake pedal went to the floor. I later saw that some grease from the left-rear wheel area had gotten onto the exhaust shield which caused the smoke, and figured that my recent maintenance of greasing the rear drive shaft joints had been sloppy. I was wrong. I took the car out today and once it was hot there was again some smoke coming from the left-rear wheel and voila! - the master cylinder light again went on. I immediately retuned home and in the garage I saw that the left-rear brake disc was so hot that it was red! Apparently this is what caused the previous failure of the master cylinder since I belive that the disc getting so hot probably boiled the brake fluid in the adjacent brake lines and calipers. I am relieved that it wasn't the master cylinder after all and will get to work diagnosing the current problem. Pending further examination, I'm not sure if I will need to rebuild the calipers that may be sticking (rebuilt a few thousand miles ago). I suppose that repacking the wheel bearing and other regreasing will also be necessary. In case anyone is interested, I will report back later. | ||
| Paul Yorke Frequent User Username: paul_yorke Post Number: 90 Registered: 6-2006 |
Carl, Have the trailing arm hoses been changed? | ||
| bob uk Unregistered guest Posted From: client-81-108-190-48.brig.adsl.tesco.net |
Boiling the fuild in the caliper will not damaged the master because that part of the circuit is a cul de sac any steam goes back up the line when the pedal is released thou the master and into the tank and on its travels comes in contact with cold fluid. By the time it gets to the master the steam will have condensed. The boiling fluid does not circulate around the system. The system is designed to handle these temperatures ---- by regulation ( the Law) However because you most likely have a bunged up flexible hose which is acting like a one way valve there is even less chance of hot fluid getting back to the master and rubber is a good heat insulator. How to tell if a hose is bunged up. The fluid does not dribble out of the caliper nipple under gravity. ( the tank is higher than the nipple and therefore has head ) The brake drags. Opening the nipple releases the brake. The caliper pistons are stiff to move ( I can just push a piston back by hand on a good day with a good caliper.So a lever should make it easy) If the nipple is opened and the piston moves easily then it must be the hose.------------ or the master is incorrectly adjusted but then it would do it both sides wouldn'it. Shadows appear to eat brake hoses so any doubts fit new they are about £12 each. Actually they don't eat hoses it is just seems that way because the newest Shadow is 27 years old and the oldest is 42 years old and because the system has lots of them you are bound to have hoses failures. Plus hydraulic constant flow systems demand good fluid flow which you won't get with old hoses. Also there are two hoses that connect the front subframe lines to the car. They go from the front of the rat trap to 2 "t" pieces on the subframe.These get over looked they are also £12 each. (Message approved by david_gore) | ||
| Carl Jensen Experienced User Username: carl_jensen Post Number: 19 Registered: 2-2005 |
Paul & Bob - thanks for the input. Hydraulic hoses were all replaced about 6 years ago, but I will replace the ones you mentioned regardless. And Bob - thanks for the diagnosis advice. I will use it this weekend. Greatly appreciated! | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 739 Registered: 9-2004 |
Hum,hoses are common but the warning light comming on has gotton the old brain thinking there may be two or three faults present. To my knowledge the early conventional master cylinder circut does not have a warning light. I am just thinking that there may not be any free play on the master cylinder for what ever reason. This will hold pressure to the i think lower caliper cylinders on the car causing heating of the rear brakes. As for the warning light this applies to faults in the high pressure system on your car. | ||
| Jon Rothwell Frequent User Username: jon_rothwell Post Number: 43 Registered: 4-2004 |
We had a similar proben with my in-laws 1974 Shadow. One rear brake was binding up so we changed all the hoses (we were going to do it anyway so had the parts to hand), however the problem persisted. We then pumped the pedal and tried to move the car by just pushing it on a flat surface, sure enough it was stuck fast. Cracking the connection at the master cylinder allowed the car to roll freely till the pedal was pumped again. We took out the master cylinder and found it to be pretty crudded up, so we rebuilt it with new seals. After a week or so of running fine the problem came back, so we tossed the master cylinder in the bin and fitted a new one. Problem solved! We were thrown for a while by the fact that only the left hand rear caliper was binding, but it's been over six months now and the brakes are better than they ever were. | ||
| Paul Yorke Frequent User Username: paul_yorke Post Number: 94 Registered: 6-2006 |
(sorry for the similar posting) On Shadows and sticky brakes. If any dragging of brakes is found then hoses should be the FIRST suspect. Even if sticky callipers or pads are found, this can ALSO be a sign of restricted hoses not 'exercising' the callipers properly. The only mechanism pulling the pads from the discs is the 2mm seal in the calliper trying to return to it's original shape when the pedal is released. As you can imagine, there's not much force there. Any restriction or resistance will negate that effort and the pads will drag. As the hoses close up further, they will be actively held on. When the hoses closes up completely, it will only allow fluid through under very heavy braking, but then the fluid will be trapped at the calliper and the brake will seize on compltely. By that time the pads will probably be hardly moving in the calliper or possibly seized. This often prompts the 'logical' conclusion that the pads were seized causing the seized brakes. Freeing out the pads will seem to cure the problem ( or working on the master cylinder ) UNTIL the next emergency stop. The hoses to the left hand rear trailing arms are usually the first to go. ( Heat from the exhaust?) Sticky brakes here should set alarm bells ringing. If when you check your hoses, these are new and the rest are old, Change the rest. Seizing on is something to be watched out for, and drivers should not 'drive through it' hoping they free out. If it's occurred after particularly hard braking then park for 15 minutes (or longer if necessary) and the fluid MAY seep slowly back through the restriction. Finish the journey without hard braking and change the hoses immediately. ( or next morning if you are tired!  ) Driving with the brakes seized will 'cook' the calliper seals first , then boil the grease out of the rear wheel bearings. If you really go for it ( which the powerful R-R V8 will let you ) you can get it hot enough to set the grease on fire or completely seize the rear bearings! Change ALL the hoses together. Don't forget the two rat trap to front sub-frame hoses. It's a good time to renew the brake fluid to. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 742 Registered: 9-2004 |
With the master cylinder at fault it will hold brake pressure within the lower rear brake calipers after pedal application. With the car on level ground after applieing the brakes with engine not running a few times,try and push the car to see if it rolls freely if not then a fault in the master cylinder lower pressure system is probable. As the car is used on a run the lower caliper cylinders bind holding the pads on the discs,the discs will expand as they heat up. This effect will carry on with less braking drag as the pads burn and discs glow hot before disaster strikes. Another check if it is the fault without the engine running. Apply the brake pedal a few times and release then slacken a lower rear caliper bleed screw and check for fluid comming out under pressure. If so and the fluid stops and the car then rolls freely then the master cylinder is in need of free play ajustment or attention. Worth a test first. If all is Ok then it will probably be the more common hose failing as Paul has said. Oh Bob that steam in the fluid,water pooling in the lowest part of the system. Time for more frequent fluid changes. But not silicone although some brave souls say it works well. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 743 Registered: 9-2004 |
Yes the above carried out after the high brake pressures are depleated first. |
