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MG TD TF 1500 TD Brake problem BBS discussion at MG-Cars.net
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MG TD TF 1500 - TD Brake problem
| > I am having a reaccuring problem: the brake lights come on and stay on > after I use the brakes on my '53 MG TD. After an hour or so the brake > lights will go out. > > I think the brake fluid pressure is building up in the system and not > releasing. The only place I know of an automatic release of the > pressure is in the master brake cylinder. So, I rebuilt the Lockheed > master brake cylinder, replaced all wheel cylinders and flex hoses. > The problem peristed. I bought a new Lockheed master brake cylinder. > The problem peristed. The brakes would also stay on and burn while > driving down the road (all four wheels). I rebuilt the brake pedal > pivots, rebushed the pedal assembly, backed off the clearance to 3/4 > inch free play (vs the half inch), backed off the adjustment on the > brake shoes. > > The brake lights still stay on after use. Any ideas? > Thanks > Rod |
| Rod Zander |
| How about the brake light switch hanging up? |
| Tom |
| hi Rod, not the normal way you tried to solve the problem. I think Tom is right, just replace the brakelightswitch!!! |
| Jan Mekes |
| After your pedal rebuild, do they still drag or not? Easy to tell- pump the pedal,jack it up and see if the wheels turn. If the wheels are free with minimal drag, the switch is bad (or maybe the turn signal relay if you have turn signals). |
| George Butz |
| Rod, I guess we all missed your statement in the middle of your message about the brakes burning while going down the road. I Imediatly thought of the switch also, but that would have no effect on keeping the brakes on and buring ... Take the car for a ride long enough to make the light stay on, stop on the side of the road and unscrew the master cylinder cap and see if the light goes out or if you can hear any pressure being released. I just checked with another TD owner, and we think that the vent on the master cylinder cap might be blocked. Also, is there any chance that there might be a mixture of both regular brake fluid AND silicone fluid, ??? That can raise havoc with the rubber seals.... |
| STEVE |
| Rod, when you rebuilt the Master Cylinder, did you make sure both the bypass port as well as the compensating port were open? The latter is much smaller in diameter than the former and is often overlooked by most since it is only wire diameter size. I use a peice of stainless steel wire to poke the rust, etc. out of the hole. Both holes are directly under the filler plug. If the compensating hole is not open, there is no way the pressure can be equalized when the brake pedal is released other tnan the normal leakage past the seals. If the orfice is plugged, pressure is not released keeping some pressure on the brake wheel cylinders and the brake light switch. Refer to page M4 in the Shop Manual. |
| Jim Merz |
| You can also release the brake line pressure by opening a brake bleeding screw. |
| Tom Patoine |
| Rod, You say all four wheels are locked and 'burn' as you drive down the road. As you deduce this must be caused by pressure in the system not being released when you take your foot off the pedal. If it was a single wheel that was binding I would suspect a collapsed flexi hose but since it appears to be affecting the entire system either the piston is not returning or the holes (note there are two) from the fluid reservoir to the cylinder are blocked. The piston will be sticking either in the bore or via the pedal mechanism - is there excessive free play in the pedal when the brakes lock on ? I would check to make certain all the rubbers and washers are the right ones and are in the right place and that you have the return spring in the bottom of the bore. Also look at the valve at the bottom of the cylinder - if this is faulty it will maintain pressure in the system when you take your foot off. As I mentioned above there are two holes from the reservoir to the cylinder. One is easilly seen since it is of relatively large diameter but the other is of a very fine bore and you may need a magnifying glass to see it. That's all I can suggest and since you have installed a brand new cylinder I may be talking rubbish but logic must lead to a master cylinder or linkage problem. Jan T '51 TD |
| Jan Targosz |
| The rubber cup might by old and sweld and can block the relief hole. Nothing a rebuild kit won't fix. |
| Jay Dyck |
| You say you bought and installed a new master cylinder. That kinda discounts that part then. If you reach under and pull the break pedal back with your hand do the breaks release? If so then brake return spring or the break pedal shaft needs lubing or reworking. The next step would be to flush the lines. Then rebuilding each of the brake cylinders. If the fluid is old they could all be gummed up. Chris |
| Chris Couper |
| It's possible theres a pinch or almost complete obstruction in the line from the master cylinder to the four way connector. The high pressure of the master cylinder can over come it and push fluid through. But, the return springs of the shoes don't have the same power to push the fluid from the wheel cylinders back into the master cylinder. |
| Blake J. |
| As Blake indicates, there must be a block between the 4 way connector and master,,, other than actually in the brake line, could there be a piece of "something" in the 4 way connertor that would block the easy relief of pressure from the lines ?? Please let us know what you find !!! Keep Your Stick On The Ice !! SPW |
| Steve |
| I will let you know what i find when i am able to work on it , been out of town. thanks for the support and advice. Rod |
| Rod |
| Rod Sounds like you have a pressure build up after braking. This should be easy to check. What I think I would do is: pump up the brakes, then check the bleed screw on the right rear wheel. If fluid squirts out, with no pressure on the pedal, the pressure is not releasing. Pump up the brakes again, now check the left rear wheel brake bleed screw. If fluid squirts out again you know you have it in both rear brakes. Repeat this process, until you have done all wheels, both front and rear. I would also bleed all wheels as to change the fluid. For this you need a helper to hold down the brake pedal. If there is a delay in the fluid comming out after you have loosened the bleed screw, then this may be the line that is plugged. Check all four bleed screws like this. If silicone brake fluid has been used and you are using hydraulic brake fluid, this may have caused some of the rubber parts to loosen and be pumped into the brake system. But bleeding each should blow out the obstruction. I think I would also check the tension on the hand brake cable, they may be rusted in the cable housing and not letting your brakes release. Hope this helps. Let us know what the fix is. John |
| John Hambleton |
| Well I bleed all the brakes and the preasure build up seemed relieved. the lights would go out. Then if i pump them up again the lights stay on. I checked the breather holes in the cap of the master brake cyl. they seem fine and the light still stays on with it open, I bleed the brakes and light goes out. I operate the brakes and they seem to be fine, I take it for a short drive it is dusk the brakes work the lights go off then i realise that after a second or two the brake lights will come back on! I am really confused on this one. went to a parking lot with a bit of a hill and no lights on, tryed out the brakes they work, take foot off pedal after a couple of seconds light comes back on. over and over. the brakes do not seem to be dragging (though there is extra play i left in the adjustment so they would not lock up on me) I have not adjusted them back to factory specs. all of the wheel cyl. are new, new master cyl. new flex hoses, new emergency cables adusted as per spec.,the tubing is for the most part original it has regular brake fluid in it(mechanic who did brake job was to have put silicon fluid in) I topped of with silicon fluid before I realised this. the container says that silicon is compatable with all of the other fluids, What are the problems with using Silicon Fluids, or combining them? Thanks, Rod |
| Rod Zander |
| Rod, Check that there is play (clearance) between the brake cylinder push rod and the piston in the master cylinder when you are not applying the pedal. If the piston is not allow to come ALL the way back and relive the pressure, it can retain enough pressusre in the system to keep the light switch on but not enough to drag the brakes. You will find that the push rod for the master cylinder is adjustable for this purpose. Ciao, Ben T. |
| Ben Travato |
| There seems to be confusion (maybe on my part) as to there being silicone brake fluid, regular brake fluid or worse, a mixture of both in the system. Given the history of problems you have encountered I suggest you start again with new seals in the master and slave cylinders and replace the rubber flex hoses. Flush the solid pipes. Do not mix fluids in the future. I leave it up to others to debate the merits on silicone vs non silicone fluids. If you started with regular fluid then introduced silicone fluid it may have caused the rubber to swell and hence problems. Tony |
| Tony Cove |
| the problems all were happening prior to the mixing of the fluids that happened last week. what you suggested about the new or rebiuld cyl.,new flex hose, is what i have already done and still have the problem. Cheers Rod |
| Rod Zander |
| Sorry Rod the confusion was mine. I still maintain that if you have mixed fluid it would wise to flush and bleed the system. As advised above, the answer may be obvious if you can examine the pedal/master cylinder and switch area directly when the lights stay on. Tony |
| Tony Cove |
| I have had this happen when the cars was changed to silicone. The problem was solved by dismantling the master cylinder and removing .010" from the face of the aluminum piston. The rubber cup was too large and was just covering the small, fluid return hole in the master cylinder. By removing .010" from the face just behind the cup it allowed the rubber cup to clear the hole.Try it, you will like it. Sandy |
| conrad sanders |
| Rod, For what it's worth here...Sandy's comment about "rubber cup was too large" makes alot of sence to me. I have just finished replacing nearly every piece of rubber on my TF this year. Nearly 90% of the new "repro" replacements were on the "large" side of being a correct fit! So, is it that the old parts are shrinking...(like some of us older owners) or are the new ones being made just a bit on the large side? I don't know the answer to that...but I spent a lot of time with an emmery board, strip of emmery cloth, and in some cases a dremel tool scaling things down a bit just to get them on the car! I had a simmular problem with the TF a few years ago but it turned out my switch was sticking...a good cleaning fixed my problem...but I belive you said you had allreay done that. Cheers & best of luck, David 55 TF 1500 |
| David Sheward |
This thread was discussed between 10/10/2002 and 23/10/2002
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