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MG MGA - brakes drag
|MGA 1600 disk front / drum rear.|
Rolls free when cold but as I drive and use the brakes they begin to drag. I've been concentrating on the back end. I loosend the rears and checked the hand brake, they seem free.
The front hub spinners are warm after driving, particularly the front left. The brake pedal seems very tight.
Could the front brake hoses be the culprits? I've used silicone fluid for close to 30 years.
No signs of leaks anywhere.
|I think the actuating rod in the master cylinder is too long and is not letting the system vent into the master cylinder when the brake pedal is released. The effect of this is that a small amount of heat in the brakes causes the fluid to expand which because the system is blocked (no vent) the brakes become applied. The statement by you saying the pedal is firm tends to be a classic symptom.|
|Robert (Bob) Midget Turbo|
interesting, I can look at that, thanks.
there have been no changes to the master cylinder so am curious as to what would affect that aspect. I'll look to see if there is play for the rod to fully engage and return to normal.
very firm pedal.
Could a clog be the problem?
|Yes, brake hoses sound like a very likely cause, particularly the front LH one!|
|I'd be looking at brake hoses as the culprit.Bob|
|I had that symptom on mine after the rebuild. It was the pushrod exactly as Bob suggests.|
|Ted and Neil,|
"Hoses are the culprit" - how can that be? The hoses could either leak, balloon, or might plug up. None of these conditions would cause the brakes to drag. So please explain your theories.
|Gday Peter, hoses can fail internally with no outward sign of it. The hose going to the rear axle had this happen,allowing flow to the wheel cylinders but not allowing it to release. Bob|
|Rubber in hoses swells and shuts off flow. High pressuse from foot flows down but slight pressure remains in cyls/calipers.|
Also could be stuck rubbers in mastercyl.
When brakes drag see what bleeder releases pressure.
|R J Brown|
|My money lies along Bob's thought process, but perhaps not the actual length of the pushrod, just the MC brake piston sticking and not returning fully back for whatever reason. This would leave the return hole in the MC covered. Overnight the piston would creep back and the wheels would spin freely in the morning.|
I suffered the same brake drag for several years without getting to the source of the problem. A new and better engineered MC was an immediate cure. It was worth about a 3mpg improvement.
|I think we are on to it, it seems to be the rod as Bob suggested. I thought I had it resolved last night by shortening the rod a few flats, had a good drive, but then I retightened a couple. Need to back it off again and retest tonight.|
found the following on a Moss board:
Many MGA owners seem to be experiencing problems with the brakes 'binding', especially right after a brake system rebuild. The common complaint is that the brakes begin to drag as the car is driven, which creates tremendous heat and eventually stops the car, possibly damaging your new linings, pads, and discs.
The Factory Workshop Manual (#210-410) gives explicit instructions on setting the master cylinder pushrod, which sometimes cures the problem. However, even with the proper 'free play' in the pedal, the brakes can still bind up. The problem is that the master cylinder piston is not coming far enough forward to uncover the bleeder orifice that allows the expanded fluid to bleed into the reservoir.
Solution: Add a shim between the master cylinder block and the cover plate! This shim allows the piston to come a little further forward, thus uncovering the bleeder orifice.
I cut my shim from .020" brass shim stock using the gasket ( #180-020) as a template, but allowing a 1.00" diameter clearance hole for the brake piston. I used two #180-020 gaskets, modifying one to include the 1.00" diameter hole, but leaving the other one standard
That is one way to do it. I too found that when tightening up the pushrod locking nut the rod lengthened slightly. It was quite fiddly getting it just right. That said, I did make my own brake rod because, when I converted my car from left to right hand drive I found the original way out in length. My screw cutting was probably very slightly off square, accounting for the 'lengthening' phenomena. I will make a new one some day and get it right, probably with a finer thread.
Prior to that, with the MC on the bench, I too noticed that when the piston was fully forward the hole was partially covered. I put the piston in my lathe and reduced its length until I got a better clearance. It was one of the issues I had with my cheapo MC. My new one is better engineered all round and has solved all my problems.
|Thanks, Steve, it appears there is hope.|
I know its elementary, but how much pedal play did you end up with when all resolved?
Never really thought about it. It just feels right. I will measure the pedal travel tomorrow.
|I backed off a couple of more "flats" on the adjustment and it appears to have resolved the problem!|
The pedal feels a little low, but probably because I've become so accustomed to it being right up top.
now to put the blower to its true test!
Thanks everyone! let me know about pedal play for curiosity. These are pedal cars, yes?
|Because the car does not have a servo the pedal on an MGA feels totally different to a modern car. |
Due to that I have a very hard pedal that does not travel very far. It is probably the highest pedal I have ever had in any car that I have owned.
The trick I think is to make sure the rear brakes are fully adjusted up and secondly that the front disks, (I believe you call these rotors) are running true. With disk brakes (Do you call them Rotor brakes?) if the disk is not true it tends to push the brake pads back into the calipers and then you need to push the pedal further to take up this slack.
Good luck and I am pleased you are almost sorted.
|Robert (Bob) Midget Turbo|
|Bob, yes we call them disk brakes and rotors. I do need to readjust the rear brake shoes. I had backed them off or loosened them up when I started this process thinking they were too tight. I also loosened the hand brake to make sure it was not causing the drag.|
|After 20 years of use (without a problem) why would the rod need adjusting now....?|
My thought from the beginning of this thread is still with the flexible hoses.
It's a safety thing... Replace them and I'll bet you can adjust your rod back to where it was to give you the pedal feel you are used to...
Just my thoughts...
|M T Boldry|
|Adjust the master pushrod until it will wiggle just a minimal amount. If it doesn't wiggle there is no clearance, and the brakes may lock up for lack of fluid return. If it wiggles too much you get too much pre-travel on the pedal. When you get it right you may find 1/8 to 1/2 inch of pre-travel on the pedal. You can push it with one finger for that short distance until you feel the force take up when the pushrod hits the MC piston.|
|Thanks for that Barney. Just measured mine at approx 8mm (about 5/16).|
|What might explain why it "was working but then things tightened-up" is that the front cover plate gasket can thicken or swell-up from age and/or moisture. When this happens, the piston cannot move forward enough to cure the problem which is caused by the lip of the innermost seal covering the compensating port of the brake cylinder. Adding more freeplay to the pushrod may not improve the problem. |
Adding a shim to move the cover plate forward is one way to remedy the issue but there is an easier way. Replace the cover plate gasket (Moss part# 180-020). Also, if a hole is cut or punched in the cover plate gasket large enough to allow the brake piston to contact the cover plate rather than the gasket will prevent this from occurring again.
Adding an o-ring on the pushrod that will just contact the INSIDE of the rubber dust boot when the pedals are relaxed will help somewhat in preventing water from following the pushrod past the dust boot and into the cylinder bore.
Works for me, anyway!
This thread was discussed between 14/04/2011 and 19/04/2011
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