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MG MGB Technical - Bleeding Brake Adjustment 67
|My 67 just had the rear banjo axle swapped out with another banjo, but with original steel disc wheels instead of the painted wires. I hung new brake shoes on the rear and new rotors on the front. The drums and pads were in great shape. Upon adjusting the rear and bleeding the front, I still have a pedal with more travel than normal until I pump the pedal once and then it is normal. I re-bled all 4 corners again, furthest first, added fresh fluid and no change. I turned the adjuster until it stopped the free turning wheel and then backed it off one click. Still one pump plus the second to get the pedal right? I am perplexed. Am I missing something in terms of adjustment because of those new rotors? The drums and pads are like new. I only replaced the rotors because I had a new set in the garage. Thanks for your thoughts.|
|Ralph - Are you using silicone fluid? If so, it may have become aireated and that will take some work to get the air out. Best let it sit over night and then bleed again. Another thought, when you changed the front rotors, did you press the pistons back into the calipers to remove the pads? If so, the caliper seal may be catching on a ridge of dirt build up on the piston and then pulling the piston back too far into the cailper. You will have to watch the pads on each wheel while someone pushes the brake pedal down to see if this is the problem. Finally, there may be some air in the system that hasn't gotten out yet. Possibly a pressure bleed is in order. Good luck - Dave|
|Sounds like air still in the system. On both my cars normal bleeding with either the pedal or a gunson's EeziBleed gives this result, I have to get someone to stand on the pedal while I rapidly open and close each caliper nipple in turn, and that always blasts an extra bit of air out compared to low pressure and flow of the other two methods. Either it needs the high pressure to shift the air bubbles off the walls of the system, or the rapid flow to get them to flow downwards in those sections of the pipe runs, or both.|
|Paul Hunt 2|
|Ralph tighten the adjusters until you cant tighten them anymore (This aligns the shoes) then back them off until wheels turn free. I don/t mean so tight you break something but very tight. Denis|
|Thanks guys. I really pressure pumped and stood on the pedal as these were bled. I can't imagine not getting the air out....but perhaps. I can run a full container of DOT 3 or 4 through and see. Denis, that is interesting regarding the adjusters. I did not align the shoes in that fashion but rather did the "turn clockwise until the wheel stopped" then backed the adjusters off one click. I will try the tightening method before re-bleeding. I began to wonder if perhaps the springs or alignment wasn't off a bit. The handbrake seems to indicate the shoes are contacting the drums in the correct fashion though. Ralph|
|try jamming brake pedal down overnight with the mastercylinder top off to let air come out |
i works on the bikes so will on the cars
|Ralph, just a couple of points here. Firstly you can certainly bleed the brakes with the adjusters tight if you wish and this will eliminate any doubt. Then, you are using silicon fluid and so do I and it is very easily aerated. Bleed the brakes gently and do not use force on the pedal or try to force it quickly to the floor as this will only aerate the fluid. You can see this quite easily as the colour lightens and you must avoid this. Paul Hunt advocates rapid pedal movements, now I dont think that Paul uses silicon fluid but in my experience this too will aerate the fluid and so will the Gunsons Eezibleed which I cannot use with silicon. Paul, you might like to comment here. The other thing is that you MUST have a clear tight fitting plastic tube attached to the nipple before opening it and the other end into a jar of fluid. Open the nipple half turn only and depress the pedal. Close the nipple. Lift the pedal. Open the nipple and depress the pedal and close the nipple before lifting the pedal. This is vital to prevent air being drawn in and the tube in the fluid will ensure this as well. If you follow this bleeding should work every time.|
|it seems ralph is using dot3 or 4 not silicon iain but the slow way like iain says is prob the best way to go for all types of fluid but dont mix fluids|
|If Ralph is not using silicon then it will certainly be easier but I really suspect that he has slipped up and is drawing air back into the system either at the nipple thread if he is slackening it off too much or due to a slackly fitting bleed tube on the nipple or directly from the bleed jar.|
I had a similar problem when I overhauled my '66 banjo and rear brakes, which might be what you're experiencing. If your brakes feel firm after you first adjust, and then later feel soft, here's what my problem was. The springs aren't strong enough to immediately pull the brake shoes back against the resistance of the brake cylinder pistons. So, when you adjust with the adjuster, there's some shoe clearance that you can't take up mechanically, because that clearance has been eliminated with the movement of the brake cylinder. Jack the car up and leave it overnight. Don't touch the brake pedal until you've adjusted out all of the clearance with the adjuster. This gets your shoe clearance where you want it. After that you can then do your bleeding. Hope this helps.
|As the owner of an early car, and assuming the lines run in the original orientations, you may have another option. I originaly bled the brakes on my 67 by opening the bleeder and letting gravity do the work.|
|Iain - I didn't say rapid pedal movements, just a single hard press down on the pedal while I open and shut the caliper nipple. Rapid pedal movements would probably be counter-productive to what I am trying to do. And no I don't use silicon fluid. |
Each to their own, but personally I want to get my cars back on the road 'now', not wait overnight only to find it is still iffy.
|Paul Hunt 2|
|OK Paul, point taken. I hadn't tought of that approach and it could well blast out that awkward corner which is otherwise difficult to reach. I thought you didn't use silicon fluid and whether your technique would work with it I don't know but suspect it might be OK. Quite frankly I am not entirely convinced by silicon due to its poor lubricity but dont really want to go back to paint stripper if I can help it. I too believe in getting the job done, this let gravity do the job or leave it overnight makes no sense to me but as you say each to his own.|
|Thanks for the suggestions. I tried the tightening of the adjusters and rebleeding with not as much effort at pumping the pedal and they are perfect now. When I was first fooling around with older american cars back in the 70's, we used to bleed the brakes like we were trying to force the air out or bend the brake pedal trying. The slow smooth press of the pedal worked much better for this 67 roadster. The adjuster tightening was useful in aligning those new shoes also. Ralph|
|Glad it worked Ralph. I just have a feeling that it was the silicon fluid that was the problem and it seems you really have to bleed the system gently with that. Enjoy it.|
|Vacuum cleaner and a drop out vessel. This is simply a largish bottle (whatever you find in the rubbish!)with two tubes stuck through the lid. One tube goes to the bottom of the bottle, this is the inlet and the other end attaches to the hydrolic line. Other tube goes nowhere near the bottom, and the other end goes to your vacuum cleaner.|
Mess free and much faster than all that pumping, including the 20min's you spend drilling two holes in the lid!.
Drop out vessels are commonly used in industry.
If you temperaraly duct tape your garden hose into the vacuum line this makes it long enough to control the process from up at the master cylinder, if you want.
|I think not|
This thread was discussed between 26/02/2006 and 07/03/2006
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