P38A Brake pedal / modulator

Got an issue.

Brake pedal has gone down but will not come all the way back up. Brakes work fine, no errors or warnings. Brake light on all the time because the pedal hasn't come all the way back up. Today I stripped all 4 wheels off and checked the brakes for binding or similar. All seem to work fine - should do, most of them are nearly new! Reassembled and then looked at the pedal itself. It just won't pull back out of the modulator.

I've got an old modulator in the shed. Took the bottom off and all I can see is the tops of the solenoids / valves with the ribbon cable connecting the wires. There's a brass Allen bolt on the front of the modulator but damned is I can shift it. Thing is wedged tight. Broke a reducer trying to turn it with my breaker bar.

The rear of the modulator where the shaft goes in looks like it might undo but it didn't. Monkey wrench just cut up the ally.

Does anyone have any pictures or instructions for dissembling one of these things so I can have a look inside and understand what might have gone wrong. I've a horrible feeling a bit of a rubber seal or plastic has given way and jammed somewhere but I need to know what I'm looking at.

Just looked at Rimmer Brothers and there is only the 99 onwards modulator available for models with traction control. No idea if it'll work with an older ECU but at £2,300 a unit it is one hell of a gamble.

Ideas welcome, as always.

Cheers.

Found these guys. Not far from me and WABCO specialists so might be worth chatting to: www.ringroadgarage.co.uk

I have a feeling that a long time ago on RR.net someone posted up pictures of the internals of one of the AB modulator blocks. I know there is a thread there about the internals of the master cylinder and a stainless steel upgrade kit from plastic parts. The guy that does them is in Aus, but think it comes with full instructions.

I know another owner who has an upgrade kit to fit, so will see if he can share with me a set of the instructions for stripping the modulator.

I have one of these kits, but never got round to fitting it yet. Don't recall any instructions coming with it - just a load of o-rings and the modified stainless steel washers.

I think he called them a "BBS Kit". Can dig out the guys details if you're interested. One of these jobs I'll get round to at some point.

I've just had another look. The car drives fine just the bl**dy pedal won't come up far enough to push the brake light switch. The brake-switch is attached to a plate taht looks adjustable but unfortunately the same plate acts as a stop to the throttle pedal. So if I adjust it to switch the brake light off the throttle would be revving. I put my foot under the brake pedal and tried to force it up to no avail. Also grabbed and yanked it as hard as I could but no movement. Bit of a mystery.

I also went back to the spare modulator in the shed. Undoing the smaller Allen bolts near where the brake line connect reveals valves with purple nitrile o-rings. Looks like tubes have been machined right through and there's a valve at each end with spings holding them apart. Presumably pressure one side opens one lot of channels and pressure the other side blocks them and opens another lot.

The big brass bung with Allen key in it at the front shifted with some heat and a scaffold pole. That revealed a circular plate behind it, possibly the end of a piston. It pushed back inside the modulator but I couldn't get it out. So, dead end there. Went back to the rear of the modulator where the piston from the brake pedal goes in. Monkey wrench with a scaffold pole just lead to my vice being ripped out of my bench. F*cking thing is stuck fast. Unfortunately that's the only way I can think of getting in to it now. Not sure how I can hold it in place short of parking the car on top of it.

Second hand modulators are all over eBay for under £50 so think I'll just have to risk a second-hand unit and hope it doesn't go tits up too. I guess that means I'll have a modulator spare so may just take an angle-grinder to the old one! Job for next weekend if it isn't p!ssing it down.

The brake switch is adjustable - I know it doesn't fix the brake pedal problem though. But if you remove the brake switch, you can pull the plunger all the way out to it's stop (it's on a ratcheting mechanism) and then when refitted and the brake pedal is released, then the pedal will push the brake switch plunger in to the required depth. Which will stop the brake lights from being permanently on!

I would think a second hand modulator would be OK. I tend to judge some parts by how much the replacement cost is for a new one vs the second hand price as to how likely they are to fail... Eg: £2K plus for a replacement modulator block to me says that they aren't a high demand unit, so doesn't attract a high production run to make them, so pushes the price up. And the fact that a second hand one goes for £50 to me says that they probably don't fail often, otherwise people would be snapping them up, they would be hard to find, and expensive if you did find one second hand.

I bought a replacement for my '01 as the brakes work fine on it, but I think there is an internal leak in the master cylinder. I think for the later one I have with 4 wheel TC, I still only paid about £80 for it second hand.

I'm beginning to wonder if they're near the end of expected life-expectancy.

My original one ('95) started acting up a few years ago and I replaced it with a scrapper from 1998. Now that has started to act up after 18 years. Coincidental? Don't know. Given the price I'll try another one while I try to break into the thing and work out what has happened. There doesn't seem to be a lot inside it to go wrong other than those o-rings and that plastic part on the ANR2238 and ANR2239 models.

Brake pedal switch not adjustable on mine.

Just for a laugh I rang Land Rover today. They said the ANR2238 (STC2779 no traction control) and ANR2239 (STC2778 rear wheel traction control) are both discontinued by Land Rover and not available. So, I said what about the SXC100010P1 4 wheel traction control modulator, would that work on an earlier model? He told me the car was older than he was and he'd have to go and ask but for the record the 4W TC unit was also discontinued and unavailable.

I also rang WABCO but they've yet to ring me back.

And I ordered one off a scrapper for £20. I think getting the old one apart is becoming a more urgent mission!

Grrrrrr said:

Just for a laugh I rang Land Rover today. They said the ANR2238 (STC2779 no traction control) and ANR2239 (STC2778 rear wheel traction control) are both discontinued by Land Rover and not available. So, I said what about the SXC100010P1 4 wheel traction control modulator, would that work on an earlier model? He told me the car was older than he was and he'd have to go and ask but for the record the 4W TC unit was also discontinued and unavailable.

I also rang WABCO but they've yet to ring me back.

And I ordered one off a scrapper for £20. I think getting the old one apart is becoming a more urgent mission!

Click to expand...

A few cars use the same unit i believe SAAB, Jaguar are but two.

Saab 900's I think use the same pressure switch. I'm not sure about the modulators though - but it would be handy if another manufacturer used them!

The local WABCO specialist in Buckingham said they did truck trailers and had no idea about Land Rovers.

The Land Rover dealer came back with a blank other than confirming obselete and none available from any heritage scheme as yet.

Just spoken to WABCO direct. They have no dicumentation on it other than a sketch of the outline. They say it was a bespoke item done for Land Rover and discontinued so long ago they have no record of it. No drawings even. Says it was probably done at a single plant and all drawings were at that one plant and lost a long time ago. For the information, the WABCO part number for STC2778 was 4684130120.

So, scrappers it is, possibly with the fix from that chap in Australia if you can work out how the chuff the damn unit comes apart.

It occurs to me that maybe I am wrong and the problem isn't internal to the modulator itself. The other components that are connected to the modulator from memory are:

Brake lines: is it possible inside of line is corroded and somehow a flake got sucked back into the modulator and jammed something?
Clutch master cylinder: is it possible inside of that rubber pipe disintegrated and somehow got sucked back into the modulator and jammed something?
The pressure valve thingy. What's inside that? Anything rubber that could disintegrate? Doesn't fluid circulate through that?
The pump. Does this have seals? Is it a rotary pump? Fluid must circulate through this? So any rubber seal in here that disintegrated could be pumped to the modulator and jam something?

Part still hasn't arrived but may try flushing the modulator tomorrow and see if anything is dislodged.

Are the internals anything like the Disco-1 unit ? http://inform.wabco-auto.com/intl/drw/5/5077.pdf?PHPSESSID=1cc447bd84cc001d43d026d0416a47ea

pwood999 said:

Are the internals anything like the Disco-1 unit ? http://inform.wabco-auto.com/intl/drw/5/5077.pdf?PHPSESSID=1cc447bd84cc001d43d026d0416a47ea

Click to expand...

Similar. It is actually pretty simple apart from getting the main piston out.

Today I bled the clutch. Black horrible pondwater came out! I only replaced the fluid in it about 3 years or so ago. So flushed it through. If I do the modulator I might do the master cylinder too (did the slave a few years ago when the spiral pins went.) Seems sensible when I'll have so much space to play with.

Tried a bleed on step 1 of RAVE to make sure no air in the modulator but no difference there to pedal movement.

Replacement unit hasn't arrived so I've done a bit of a Heath-Robinson fix for now: folded some cardboard over and cable-tied it to the brake pedal. Brake lights now go out. Brakes working perfectly. Must admit I'm reasonably nervous as to how long before something goes catastrophic.

Inside the brake modulator (this is the ABS only ANR2238 or STC2779 unit without traction control.)

Underneath for the connections to the valves ...




The pistons that control flow to the brakes themselves:



Finally the pistons that go right through the middle to the brake pedal. The outside Allen nut took a scaffold pole to shift it.



Under that is a cap (see above). Soaked in Plusgas then hammered it down a bit, banged it back pushing the rod that goes to the brake pedal, more Plusgas, same again. Eventually it worked loose and popped out.



Under that is a piston with a spring and insert.


Further down is a further piston.


Once that is out the rod that attached to the brake pedal can be seen moving when you push it in.


However, I couldn't dissemble any further from the front. Trying to dissemble from the rear was unsuccessful although you can see I gave it a go below!

Very thorough Grrrr, you certainly like to get to the bottom of things.

Proper man is our Grrrrrr, strip it down to see how it works, even if it won't go back together. By the way PP38vouge (I always thought it was vogue), your spelling is atrocious, there are 6 r's in Grrrrrr.

Sorry Alan, my bad.