Brakes completely jammed

[WheelsOfSteel]

Hi everyone, posting on here for the first time. I have a 1968 Minor which has been brilliant until it developed a serious brake problem recently. When driving it makes a rhythmic brushing sound and begins to hold back, until the car eventually stops dead and won't move at all. The pedal becomes extremely hard even though I haven't been using the brake. I took it to an MG garage last week and it seemed to be fixed, they said it was the clutch pedal that was interfering with the brake but I don't think that makes any sense. A week later and it's even worse than before. Does anyone have an idea of what the fault could be?

[palacebear]

Brushing sound like it could be a brake shoe/lining that has become detached and is preventing a brake drum from turning. Alternatively the master cylinder might be seized causing all the brakes to bind and would explain the hard pedal. First jack the car up securely. Release the handbrake. Try turning each wheel. If none of them turn I'd suspect a master cylinder fault as above or a seized brake pedal link rod (I think it's attached to the clutch pedal link rod which partially explains the MG garage diagnosis). Probably worth taking the drums off and checking the shoes/linings for damage, incorrect fit or broken retaining springs etc., and that there aren't any seized wheel cylinders. Also as a matter of course, check that the handbrake linkage is releasing fully.

[shoebone]

The brake pedal does indeed pivot on the clutch pedal shaft and may be holding the brake pedal down enough to cause the brakes to drag, everything gets hot, fluid expands, brakes lock on with a hard peddle. Does the brake peddle try to go down when you push on the clutch?. Best solution is to remove the clutch shaft and clean, grease, or replace as necessary.

[oliver90owner]

Poster gives no indication of how long the car has been ‘brilliant’. Days or years?

If one thinks about how the brakes operate - they stay in operation while pressure is maintained on the pedal and rely on springs to retract the lininings from the drums when the pressure is released.

If the brake shoes are not retracting, the master cylinder is not relasing the pressure, or the brakes are jamming mechanically, rather than hydraulically.

First thing is to determine which is causing the symptoms. I suspect it may well be the linkage between pedal and master cylinder.

[kennatt]

you can very simply prove or disprove the clutch/brake pivot. Once the brakes have jammed on. stop and reach down and pull the brake pedal back up,If it frees up its the pivot needs attention ( it is a known problem)

[RobThomas]

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This is the left side but it is the same story...the pivot for both the clutch and brake pedals is the shaft that runs between these 2 holes in the chassis leg, just forwards of the master cylinder. There are 2 bronze (Phil?) bushes that the shaft pivots within and the 2 pedals are meant to swing separately on the shaft but can become grunged up so that the pedals stick. If you push the brake pedal down it will drag the clutch pedal upwards as your foot comes off but there will still be brake pressure left on since the brake pedal has not come all the way up. If so, the brakes drag on the drums until they get soooo hot that they expand and jam the brakes on. The pedal will now be 100% solid since the brakes are trying hard to ram the pedal back upwards, unsuccessfully.

Carpet up, large Philips screwdriver (or Pozidrive...long story) to lift either the little cover over the master cylinder or even the whole big black cover plate, unclip the return spring, unbolt the clamp on the shaft and get the pedal shaft out.

https://www.youtube.com/watch?v=7pOOCC1zkwk

https://www.mmoc.org.uk/Messageboard/vi ... .php?t=882

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[Mark Wilson]

I replaced my pedal and shaft last week, but on a part completed car with no engine or box. The clutch pedal and shaft are one piece on a 1968 car, and I think you might struggle to remove it with the gearbox in place.

[The vast minority]

Welcome,
the likley causes of the problem have been covered well but for future ref: If a mechanical thing is talking to you like this you really don't want to just keep going until it wont go any further.
You are also risking damaging the clutch and possibly even the half-shafts with this rather brutal approach. your fuel consumption will also rise dramatically.

I dont think anyone else mentioned this but you could always feel the wheels very soon after your noise starts, the one with the binding brake will get hot very quickly.

Good luck with the fix.

[philthehill]

Rob
The bushes are oilite or similar.

Original floor screws.................Philips cross head screw driver No2. Thread 1/4" BSF.


The following can be done to alleviate any seizure in the bushes and/or shaft.

1. Fit a grease nipple to the brake pedal.
To clear the floor the grease nipple has to be positioned as per the photo which still allows the nipple to be greased when the carpet is pulled back and the brake pedal slightly depressed.

2. Centre bore the clutch shaft with a single 1/2 way through cross drilling where the shaft bushes rub and fit a grease nipple at the inner end.

I did this with a new aftermarket shaft mounted in the lathe but take care when drilling as I found hard spots in the metal which can (and did in my case) resulted in the good quality drill breaking even though lubricated and using only light feed pressure.

[oliver90owner]

Phil,
Are the bushes ‘grease-ite’ or ‘oil-ite’?

[philthehill]

The pair of NOS bushes I have are oil-ite (oilite)
The bushes will accept either oil or grease.
After market bushes may be made from alternative but similar materials.
Phil

[WheelsOfSteel]

Hi everyone, thanks very much for the responses. I took the car back to the garage in the morning, about a mile's trip, and very soon the brakes had become extremely hot to the touch on the front two wheels. I also checked to see if the pedal could be pulled upwards but there was no movement so I suppose the bushes are out of the equation. I'm getting new cylinders on both sides at the front to see if that solves the problem. I wasn't able to share a picture of the car the other night, but I eventually figured out how it's done

[shoebone]

Do you have the original drums on the front or have you been upgraded to discs?

[oliver90owner]

There is a very simple check before replacing anything.

Open the front bleed screw(s) ( carefully!) and see if the brakes free off.

Sorry, but assuming here the robbing merchants at the garage are milking you for as much cash as they can get, while not bothering (or haven’t a clue how) to diagnose the fault.

I very much doubt that changing the wheel cylinders will be a solution to your problem.

[RobThomas]

Phil,
Are the bushes ‘grease-ite’ or ‘oil-ite’?

What a shame they aren't Brakefluid/water-ite. That seems to be what most are covered with. Quite a nice mix to start corrosion in steel.

[ManyMinors]

As Oliver says, it is most unlikely to be the wheel cylinders jamming on while you're driving. I've suffered from similar problems twice in the past. Once it was the brake master cylinder, the other time it was the flexible hoses which had perished internally so were acting as a valve. As suggested above, just carefully undo a bleed nipple and see if fluid comes out under pressure. Don't bother buying the cheap "pattern" wheel cylinders and don't bother not replacing the flexible hoses at the same time.

[Dogsdad]

This has happened to me.
Master cylinder not freeing off properly caused exactly the same symptoms.
Brakes gradually came on until the car would not move.
Releasing fluid freed them off so came home the last hundred yards on the handbrake.

Richard M.

[ianmack]

‘What a shame they aren't Brakefluid/water-ite. That seems to be what most are covered with. Quite a nice mix to start corrosion in steel.‘

I dribble a little oil down the brake pedal at service time. Probably not entirely thorough but it only takes a moment and I haven’t had any seizure problems.

[simmitc]

My first thought was to ask the question that has been posed but not answered: Do you have the original drums all round, or has the car been fitted with a front disc conversion? If the latter, then there is a seal in the master cylinder that has to be removed or modified. If this is not done then you get exactly the symptoms that you describe. However, this applies only if discs have been fitted.

[oliver90owner]

Original post indicates that all was well and the fault developed. I doubt that would be the case if that scenario had occurred.