P38A Brake pedal / modulator

Can't seem to get these bloody smiley faces to work?

Forgot to mention, the pistons that control flow to the brakes with those big springs don't come out. Can push them up and down the chambers but not out. Guess they were put in cold or maybe before the 2 halves of the unit were bonded together. Probably the former as you can see some channels were drilled after the top and bottom halves were joined.

Typical LR & Wabco . . . .designed to be replaced as a unit, and not serviced.

Grrrrrr said:

Brake pedal switch not adjustable on mine.

Click to expand...

It is if it's the correct part.

Adjusting it is part of a technical bulletin I've just read. If you've changed the modulator from the one that was fitted in the factory, you should have adjusted the brake light switch to fit the new modulator.

According to RAVE, you pull the switch from the mounting plate, pull the plunger all the way out, press the brake pedal all the way in, refit the switch and allow the pedal to come back up. It should then set the plunger to the correct position.

Are you sure your modulator is working just fine, and all you need to do is adjust the switch?

MrGorsky said:

It is if it's the correct part.

Adjusting it is part of a technical bulletin I've just read. If you've changed the modulator from the one that was fitted in the factory, you should have adjusted the brake light switch to fit the new modulator.

According to RAVE, you pull the switch from the mounting plate, pull the plunger all the way out, press the brake pedal all the way in, refit the switch and allow the pedal to come back up. It should then set the plunger to the correct position.

Are you sure your modulator is working just fine, and all you need to do is adjust the switch?

Click to expand...

I have a spare brake-light switch on my kitchen table. Not sure why. Never got around to putting it in the shed. Plunger is well and truly jammed and doesn't move more than the usual movement to depress it. EDIT: the switch is the original switch off the car from when I got it so presumably a Land Rover one.

The modulator I have in the shed seems to have a 3 stage movement when pressed. There's about 10mm of travel with little effort, then about a half of the travel takes more effort and the final part takes a lot more effort.

Another modulator arrived today so will have a look at that. If it wasn't raining I'd go out and double-check the brake-light switch fitted too. Maybe tomorrow. Still got the folded cardboard "fix" for now.

Full marks to @martyuk and @MrGorsky for the brake light switch adjustment. It IS adjustable but it takes considerable more force than I initially dared to give it. In my defence I've got previous on snapping and shearing all sorts of steel fastenings so that poxy plastic switch was a prime candidate for breaking. You really need some needle nose pliers, grip the shaft just under the mushroom part and then sort of bend it forwards (towards the plug side) and pull upwards at the same time to pull it out. It makes a graunchy ratchet sound and extends out.

So, 5 minute repair in the end and free too. Got another spare modulator to play with but hey ho. Once I've tested the first one to destruction I can refurb the second one with knowledge gained.

It looks like the metal clip that goes over the pin that holds the modulator to the brake pedal popped off the end of the pin. This allowed the brake pedal to come back too far, knocking the brake-light switch in. The pedal then must have re-clipped on another pedal push leaving the switch too far receded to operate. It is interesting to note that on the original modulator from the car the metal clip is U shaped and goes over both sides of the pin so this cannot happen. Both the later modulators only have the clip on 1 side.

Live and learn.

MrGorsky said:

It is if it's the correct part.

Adjusting it is part of a technical bulletin I've just read. If you've changed the modulator from the one that was fitted in the factory, you should have adjusted the brake light switch to fit the new modulator.

According to RAVE, you pull the switch from the mounting plate, pull the plunger all the way out, press the brake pedal all the way in, refit the switch and allow the pedal to come back up. It should then set the plunger to the correct position.

Are you sure your modulator is working just fine, and all you need to do is adjust the switch?

Click to expand...

Nothing to do with modulator, all you are doing is setting the brake switch to the back stop on the pedal.

Just for the record and so it is here when I've forgotten where I put the piece of paper, the WABCO part number for the STC2778 part is 4684130120. Their technical support lot in Yorkshire are really friendly too. Best not put their number up here though in case they're deluged. They've made neither part in 15 years and have lost the plans.