Technical Rear brakes locking on... Uno dual braking system.
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Technical Rear brakes locking on... Uno dual braking system.
Load leveling valve would reduce the brake master cylinder pressure coming to the rear brakes so making it less likely to lock up if working correctly, usually the more tension on a loading spring will increase the effort to the brake connected to it.
Any chance wrong rear brake cylinder diameters, or slight leak on rear brakes onto brake linings causing grabbing,or warped brake drums, or rear brake springs weak or loose or fitted wrong, that can cause it , or brake shoes wrong way around? Over fifty years I have seen all of those things causing lock ups etc. Plus things like wrong size wheels/tyre's/tyre pressure's. Take your choice
Normally if looking at the brake assembly with the brake cylinder at the top, the top of the leading edge of the shoe in the direction of normal rotation forward has less brake friction material on the brake shoe at the end nearest the brake cylinder.
If everything else is correct, it is possible to reduce the "self servo action" which leading shoe employs to increase design efficiency, by filing away the leading edge slightly on both side leading shoes, this will make it less prone to coming on so fiercely, but should not normally be necessary. (if doing this use a hand file and don't breathe in the dust, even though asbestos no longer used, it is still not advisable!)
The only time I have needed to do that was on brand new Moskvitch cars in the the 1970s when working for a dealership as part of the many things needed to make them slightly safer to drive, note the word slightly!
Thanks for this, RR had a leaking wheel cylinder which I have now replaced. The shoes have been assembled correctly (I am a mechanic). So suspect the master cylinder even tho it was replaced 5000 ks ago. Many thanks again.Load leveling valve would reduce the brake master cylinder pressure coming to the rear brakes so making it less likely to lock up if working correctly, usually the more tension on a loading spring will increase the effort to the brake connected to it.
Any chance wrong rear brake cylinder diameters, or slight leak on rear brakes onto brake linings causing grabbing,or warped brake drums, or rear brake springs weak or loose or fitted wrong, that can cause it , or brake shoes wrong way around? Over fifty years I have seen all of those things causing lock ups etc. Plus things like wrong size wheels/tyre's/tyre pressure's. Take your choice
Normally if looking at the brake assembly with the brake cylinder at the top, the top of the leading edge of the shoe in the direction of normal rotation forward has less brake friction material on the brake shoe at the end nearest the brake cylinder.
If everything else is correct, it is possible to reduce the "self servo action" which leading shoe employs to increase design efficiency, by filing away the leading edge slightly on both side leading shoes, this will make it less prone to coming on so fiercely, but should not normally be necessary. (if doing this use a hand file and don't breathe in the dust, even though asbestos no longer used, it is still not advisable!)
The only time I have needed to do that was on brand new Moskvitch cars in the the 1970s when working for a dealership as part of the many things needed to make them slightly safer to drive, note the word slightly!
Not casting aspersions
, just saying all the things I have seen that cause your issue over the years, it is difficult to know what level of knowledge people have when they start a thread.Just curious, what is pointing you towards the Master cylinder?
I sold it to a cousin who told me about the issue not long later. On investigation, he told me it ran out of brake fluid (due to the leaking RR wheel cylinder probably). He was unclear about what oil he put into the reservoir to top up when I queried and I now suspect it may not have been brake fluid! Is this the cause perhaps? Contamination? During the process to replace the faulty wheel cylinder I put in brake fluid and did not take notice of the oil being bled out... with regards to fluid colour (usually a light tan)...Not casting aspersions
Just curious, what is pointing you towards the Master cylinder?
I think you are right, trouble is it could knacker all the hydraulics.
Years ago we had a customer who thought he would top up the levels under the bonnet and filled the brake master cylinder on his nearly new Rover with engine oil !!! It expanded the rubber seals and destroyed them, in those days you could get seal kits, so we had to flush the entire systen and change the seals in all the four disc calipers, the master cylinder and in those days the brake servo was hydraulic also so that as well.
Thats what I was fearing and couldnt bring myself to say it!!!! The cuss couldn't say what oil he used and like in your case, I suspect he didn't realise the difference as well.... I have been carrying a 5/16 ring open-ender to undo the LR bleeder to release the pressure to allow me to continue travelling...
It would help if he told you what oil so you could neutralise it and flush out the crap before putting any new parts on.
Is it only affecting one wheel or is the pressure holding at the master cylinder on the whole system. If flushed out totally , I wonder if you could get a master cylinder repair kit of seals?
Just a thought depending on what substance it was, it's possible it is blocking the return washers behind the seals in the master cylinder, if it hasn't damaged the rubbers but just blocked the return, then stripping and cleaning may just work. I assume the pedal is coming back far enough to uncover the reservoir openings. I am only thinking that in the same way when people over adjust a brake pedal switch and it doesn't allow the pedal to totally return eventually the brakes lock on.
Its affecting the rear brakes only so far (both sides). I was always taught not to rekit master cylinders but in this case you could be right about the return system and worth investigating. Thanks for that...
Late 1960s it was common place to fit seal kits to every thing , but I agree with you better to fit complete unit to avoid law suits
