S3 Rear brake grabs when reversing

Having a problem with a rear brake on my S3. When adjusting the brakes I found that the osr wheel would spin freely forwards, but lock up when spun backwards. Same under power with vehicle on stands: fine in forward gears but in reverse osr wheel locks and all drive to nsr. I’ve stripped the brakes, replaced the cylinder which I assumed was sticking, & fitted new adjuster, springs & pads (Mintex).(I've seen threads which suggest that the leading and trailing edges are different, but on the Mintex pads the lining is exactly the same distance along the shoe on leading & trailing edges.) I get the same result when re-assembled. I’ve pulled the half-shaft out to eliminate any transmission component; its definitely the brakes. It seems that the rear shoe, which is the leading shoe in reverse, grabs and locks the wheel when the wheel is rotating backwards, and when I examine with the drum off the rear piston isn’t being pulled fully back in by the spring at the bottom, allowing the leading edge of the rear shoe to grab the drum. I’m at a loss to understand this. Is the new (Britpart) bottom spring just too weak? Any suggestions please?

Have you tried putting a shallow chamfer on the ends of the brake shoes

Spring attached to the correct shoe?

The bottom spring just links the two shoes, Is the ring plate in place bottom of rear shoe?

tottot said:

The bottom spring just links the two shoes, Is the ring plate in place bottom of rear shoe?

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I was thinking of the top spring, and is it actually fitted or fitted to the wrong shoe?

As it is the trailing shoe giving the problem I would say he has the top spring in the right place on the leading shoe.
Plus one re chamfer on shoe lining ends.

What they mean about the chanfer, is to change the shape of the friction material at each end of the shoe. At the moment it's a square block right angle shape. Using great care, and wearing appropriate safety PPE, remove this corner so it's a 45 degree slope.

I've used a Stanley knife to do this.

Ring plate in place.
When I checked there was a small chamfer on the edge of the lining, but I enlarged it: no change. So as a temporary measure (because I need the truck out of the garage) I fitted an extra spring to pull the trailing shoe in. Put it all back together & went to bleed brakes at front, came back to find pool of brake fluid under osr wheel. New Britpart cylinder fitted last week leaking at piston seal! Realised I’d got the Easibleed on 40 psi, so perhaps my fault. Disconnected Easibleed & dismantled brakes, when I removed shoes the cylinder popped out under pressure! Could I have a master cylinder problem that’s failing to release fluid pressure?

Anyhow, I had another wheel cylinder, so fitted that. Went to bleed – Easibleed on 20 psi now, no fluid! Even with bleed nipple removed! Still pressure at front brakes! What is going on? Pumped pedal, now fluid but this cylinder leaked at piston too!

So much for getting the truck out of the garage today!

I know Britpart aint great but this is ridiculous! Any thoughts about master cylinder please? Could that have been problem all along?

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FirstLW said:

Ring plate in place.
When I checked there was a small chamfer on the edge of the lining, but I enlarged it: no change. So as a temporary measure (because I need the truck out of the garage) I fitted an extra spring to pull the trailing shoe in. Put it all back together & went to bleed brakes at front, came back to find pool of brake fluid under osr wheel. New Britpart cylinder fitted last week leaking at piston seal! Realised I’d got the Easibleed on 40 psi, so perhaps my fault. Disconnected Easibleed & dismantled brakes, when I removed shoes the cylinder popped out under pressure! Could I have a master cylinder problem that’s failing to release fluid pressure?

Anyhow, I had another wheel cylinder, so fitted that. Went to bleed – Easibleed on 20 psi now, no fluid! Even with bleed nipple removed! Still pressure at front brakes! What is going on? Pumped pedal, now fluid but this cylinder leaked at piston too!

So much for getting the truck out of the garage today!

I know Britpart aint great but this is ridiculous! Any thoughts about master cylinder please? Could that have been problem all along?

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Mcyls these days are pretty poor especially if a cheapo, though to be fair thats what I use, I get a year or two out of one, mine always seize up from lack of use and that sounds like it may be your issue?
So yes it could have been your issue all along, I assume you have free play at the mcyl push rod?

Iirc the wheel cylinders have very light springs behind the pistons?

When I chamfered mine it was not as steep as 45deg more like taking 2mm of at end tapered over 10-12mm length,
I would use a lot less pressure in the easibleed, also on dual circuit brakes you might have the Pressure differential warning actuator valve PWDA. It has a sliding shuttle valve so if loss of pressure in one side it will shut that side off so you can still brake ,
They need special bleeding otherwise it can move the valve and cause problems,if applicable have a look at the brakes section to find info on chamfering linings , bleeding and the PDW valve

http://www.retroanaconda.com/landrover/manuals/series3wm/6_brakes_bodywork_electrical.pdf

steve2286w said:

When I chamfered mine it was not as steep as 45deg more like taking 2mm of at end tapered over 10-12mm length,
I would use a lot less pressure in the easibleed, also on dual circuit brakes you might have the Pressure differential warning actuator valve PWDA. It has a sliding shuttle valve so if loss of pressure in one side it will shut that side off so you can still brake ,
They need special bleeding otherwise it can move the valve and cause problems,if applicable have a look at the brakes section to find info on chamfering linings , bleeding and the PDW valve

http://www.retroanaconda.com/landrover/manuals/series3wm/6_brakes_bodywork_electrical.pdf

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My guess would be the differential valve too. I had a problem with mine when I renewed the brakes.

Col

What age are the brake hoses?

Try swapping the rear drums over

Double check freeplay at the master cylinder. I had a similar problem on my recent rebuild where the OSF would bind, regardless of what I did behind the wheel, new slave, etc.

Turned out the new master cylinder (which had the correct freeplay on fitting) had absolutely none, so was always applying a little pressure.

Would also explain why you can't bleed it/get any fluid through.

New Bearmach master fixed it.

Easi bleed should be max 5psi.
Collapsed hose internal can act as non return valve.also master free play so valve opens and lets fluid back to resevoir.

I am pretty sure the PWDA does nothing more than put a light on if you get a brake line failure. The sliding shuttle thingy is what turns the lights on.

LordOWar said:

I am pretty sure the PWDA does nothing more than put a light on if you get a brake line failure. The sliding shuttle thingy is what turns the lights on.

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I think some are meant to split the brakes in the event of a failure on one circuit, and some also have a switch as you describe.

This describes it so and it’s maintenance
https://www.autoexpress.co.uk/land-rover/100803/pdwa-valve-rebuild-on-a-series-iii

steve2286w said:

This describes it so and it’s maintenance
https://www.autoexpress.co.uk/land-rover/100803/pdwa-valve-rebuild-on-a-series-iii

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That is interesting.

Pretty sure my 90 has one but no switch, mates earlier 90 was a different shape and in a different position.

lynall said:

I think some are meant to split the brakes in the event of a failure on one circuit, and some also have a switch as you describe.

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Mine has the switch - which is shoved by the shuttle as it moves to split the brakes. I had to reset mine after enthusiastic bleeding when I did the full rebuild.