No rear brakes

[Jared]

Hi Jec,
Do I have a master cylinder problem on my '88 Teves system?
The original symptoms were a heavy brake pedal and amber warning light on the dash.
After some fiddling about we have front brakes but no pressure to the rear.
Is it possible the master cylinder is gunked up?
Can't see a way of stripping it or servicing it.
Any suggestions please?

[ptjs1]

Jared,

What does "no pressure to the rear" mean? Are you saying that application of the pedal doesn't cause the rear brakes to engage? What was the "fiddling about" that you've done?

IMO, the Actuator (the "master cylinder" is only a chamber at the front of the Actuator) doesn't tend to gum up or fail. Teves ABS problems almost always lie elsewhere.

Start with the basics. Turn on the ignition. Does the pump run? How long does the pump run pressuring the accumulator before it cuts out? Does the ABS light then extinguish? How does the pedal feel? Have you done a blink test to understand if there any fault codes being stored in the ABS system?

Cheers

Paul

[Jared]

Hi Paul,
My regular mechanic is working on this for me.
The pump runs but does not cut out. The brake pedal is heavy. The ABS light stays on.
He's wondering if there is a blockage in the pump and is there a way to clear it as you can't get into the workings as it is a sealed unit
Thanks
Jared

[ptjs1]

Jared,

If the pump runs constantly and the pedal is hard, it's likely to be one of 2 components.

The pump faing to generate pressure or the accumulator unable to hold pressure. There is also a PRV but if that was failing, the system would be overpressurising if the pump keeps running.

Just as a guess, it seems more like the accumulator is failing, although the pump running constantly could point to the pump itself.

It's not that practical to test either of them easily, particularly the accumulator. If you could swap for a known used unit to test, the accumulator is probably easier to source than the pump as there are some compatible units from other vehicles. Be very careful when removing it.

Good luck

Paul

[Jared]

Grand, thanks Paul

[PaulGover]

...
The pump faing to generate pressure or the accumulator unable to hold pressure. There is also a PRV but if that was failing, the system would be overpressurising if the pump keeps running.

Just as a guess, it seems more like the accumulator is failing, although the pump running constantly could point to the pump itself.
...

Just a thought, but if the accumulator was failing to hold pressure, where's the pump output going? There should be a flood of brake fluid somewhere!

Is there any reason to suspect the system needs bleeding or attempts have been made to bleed it recently? I know from experience bleeding the rear brakes is a right pain with the Teves system; took a couple of litres of fluid to get mine working. Of course, bleed the accumulator supply as well (that's easy).

If it's not a problem with bleeding, I'd wonder about failure of whichever pressure switch should turn the pump off - not got the manual to hand, but I'd guess it was in the pump itself. Alternatively, the pump input is not getting fluid from the reservoir; it's more complex than it looks from outside, with various baffles, but I'd guess it would only block if there were serious gunge in it.

The "master cylinder" is a very complex beast; I got a replacement from a breaker's yard some years ago, and dismantled to previous one. At one time it was possible to get an overhaul kit for it, but not from Jaguar. But reading the workshop manual, you'd really, really need a clean-room to do it, and there are some seriously delicate parts inside, if I recall.

[ptjs1]

Paul,

Some good points:

I think you're probably right about the accumulator. You'd perhaps expect leaks if the pump keeps running?

I'm not sure but I don't think it would be the PRV keeping the pump running as the symptom of a hard brake pedal SEEMS to imply that pressure isn't being generated or held.

I guess that air in the low-pressure circuit to the pump could cause these symptoms but that only seems to happen if the system has been opened or the reservoir emptied or run dry. (Jared, has that happened?)

You're right about the Actuator! Complicated beasts! But they don't tend to fail (IMHO).

As you know, generally, in these Teves systems, it's the valve block that picks up the sediment. With it's position early in the circuit, I wouldn't expect the pump to gunge up (unless the reservoir has picked up a lot of sediment and dirt somehow?)


Good luck Jared!

Paul