Bleeding Rear Brakes - BX

Roscoe · Post by **Roscoe** » 14 Oct 2005, 13:01

I'm going to bleed the rear brakes on my TZD tomorrow - have given both rear bleed screws a good soaking with WD40 tonight and will give them another one in the morning before trying to get them loose. Since the rear brakes are in the same circuit as the rear suspension, are there any tricks to bleeding them, such as a jack under the suspension arm putting pressure on it with brake pedal depressed...or something along that line. I've read the Haynes description but it seems to be missing something as it talks about suspension on full high...or I'm missing something...

alan s · Post by **alan s** » 14 Oct 2005, 13:13

I've found the best system for me anyway, is to set it all up high, then sit a Jap car scissor jack under the arm or brake rotor so as to take the weight with an axle stand just barely below in case the jack slips.
Worked well enough for me to purge about a litre of LHM through via the rear brakes on a car I was servicing a few weeks back.

Alan S

Roscoe · Post by **Roscoe** » 14 Oct 2005, 14:02

Thanks Alan
I'll give that a go tomorrow...hopefully another dose of WD40 in the morning will soak in and I can crack them loose. Also going to swap accumulator spheres with my 16V (one with engine gone) to see if that makes any difference to the ticking speed.

fastandfurryous · Post by **fastandfurryous** » 14 Oct 2005, 14:25

to be absolutely sure that they are completely bled, and not to waste LHM:
Fit a very long length of clear hose to the brake bleed point, and pipe it back to the LHM tank. You can press the brake pedal in the car, bleed several litres through and watch the air go past you! Car must be in "High" to ensure that the rear circuit has full system pressure.

You'll be amazed just how much LHM you can bleed, and there still be air (or, more likely nitrogen) coming out. If you bleed it for long enough, you will of course bleed the entire rear suspension circuit, which can only be a good thing.

Roscoe · Post by **Roscoe** » 15 Oct 2005, 13:25

I bled the rear brakes to try and resolve a fast ticking problem - took about 1/2 litre of LHM out of each side - hardly any air in the fluid. Also swapped accumulator spheres with one off my 16V that only ticks every 50 seconds or so. Results are: rear end still rises a bit on braking - not much though. On normal height, ticking is every 2-3 seconds, on highest setting it varies from 8 seconds to about 15 seconds. I can't see any large flows of LHM back into the reservoir but haven't taken off any of the return lines to see if they are flowing and then chasing it that way. So other than that, I'm baffled. Doesn't appear to be accumulator sphere, but ticking is faster now since I've regassed front spheres than it was before. I've done the Citarobics, checked the pressure reg. bolt is tight, and the car rises from flat in about 10 seconds or so, stop light goes out within a couple of seconds, so it seems the system is working OK. What next - weak pump, bad flow divider...?

fastandfurryous · Post by **fastandfurryous** » 15 Oct 2005, 15:50

you need to bleed about 3 litres of LHM from the brakes to be sure that the lines are clear of air.

alan s · Post by **alan s** » 15 Oct 2005, 19:29

I'm fairly sure that Jeremy has cured this syndrome in the past by seating the ball bearings that reside within the pressure regulator...................over to you Jeremy!!

Alan S

jeremy · Post by **jeremy** » 15 Oct 2005, 20:23

LHM can escape from the accumulator in 3 ways - onward to the safety valve - where its meant to go, down the valve in the centre of the sphere seat or back the way it came - through the non-return valve.

the non-return valve is a ball bearing retained by the plate you can see on the sphere seat. to re-seat it, undo the bolt securing the plate, take the plate out and collect the ball which may fall out. (you need a tray or something similar. Stick it back in the hole with a dab of grease, tap it smartly using a brass ounch and re-assemble.

You must NOt use a steel punch - you may put a flat on the ball. I've done the valve on my TD BX with the regulator in situ - took about 10 or 15 minutes and that must have been 3 or 4 years ago.

A good accumulator should be able to raise the car when, having turned the engine off you go and sit in the boot. car should sink, then rise again after 30 secs or so. If you raise the car fully the ticking rate should drop as all spheres are now functioning as accumulators as the height correctors are open.

Remember when working on hydraulics that these cars can kill - make sure its properly supported.

Roscoe · Post by **Roscoe** » 15 Oct 2005, 23:13

I tried reseating the ball using a very large brass screw ground down to fit and flat on the end but maybe didn't whack it hard enough..gave it a few taps with a normal hammer only. I also didn't remove the ball to check on the condition of the seat behind it, will do that as well. I can do it in place as well since there is lots of room to get to on the diesel. I tried the 'sit in the boot' test with two of us and although the car sank, it did not rise again at all after a couple of minutes...which is why I changed the accumulator sphere but it still made no difference. Will bleed more fluid from the brakes and reseat the ball on it's seat again and see how that goes.

jeremy · Post by **jeremy** » 15 Oct 2005, 23:24

Why did you do the boot test using 2 people? I know its companionable but the back of these cars should be very soft and the thing should sink several inches with a very light pressure. I was surprised when mine dropped about 3 inches when I put my foot on the rear bumper the other day to tie my shoelace!

The ball should be reseated by one smart tap. It doesn't need a heavy blow and a number of blows will probably cause damage as its unlikely that the ball will seat in precisely the same place every time. Hence the instruction - 'one smart tap.'

alan s · Post by **alan s** » 15 Oct 2005, 23:28

I gave the one behind the bleed screw a whack on the sons car too.
When we had his engine out, I flushed through the F/D and P/R and made 100% sure I had all the filters nice and clean by soaking in petrol and blowing through with compressed air. It's a fairly big mileage car and the hydraulics on that have always worked a treat.
If you can get to the brake valve, bleed it too. I did this on the Trs and it made a difference, but that's one of the attractions of a Trs over most other models; there's a few things that are more accessible.

Alan S

Roscoe · Post by **Roscoe** » 16 Oct 2005, 00:38

Don't even mention the brake valve on a TZD - behind turbo trunking, turbo....etc. It's hard enough to see let alone get your hands on. I also can't do the one behind the PR bolt with the PR in place as there is a bracket covering it, so would either have to remove that and try and get enough room between it and the rad or pull the PR off the block - will take a gander at that but it looks ugly.
For the boot test, I tried it on my own at first, the car sank about 3 inches or so but never came back up, so I thought I'd use two people, car sank a bit more but still didn't rise back up. I'll have to see what happens if I try the manual height lever and put it on high after the engine is off - see if it does anything there.

jeremy · Post by **jeremy** » 16 Oct 2005, 08:07

The reason I asked about the 2 people was in case the rear suspension on your car was suffering from some other problem. The quick way of testing the height corrector linkages etc for this purpose is to do the est with the engine running - then you should know what to expect. - it should do exactly the same.

The ball under the pressure relief screw can be re-seated in the same way but will mean removing the regulator from the car or removing the radiator to get at it. I didn't do this one as I did the current regulator on the car, and also this one is not subject to constant chattering as its held in place by the screw and probably is only opened a few times during the car's life. The other reason was that as far as I know I was the first to do the reseating and I had no idea if it would work! (I first saw the procedure in the overhaul instructions for Laycock overdrives - and I cannibalised an overdrive for my Triumph Stag from 2 - and the hydraulic pressure was so high it would go in before I'd taken my finger of the switch and take 15 seconds for the thing to release!)

The ball under the pressure release screw is a different size.

Roscoe · Post by **Roscoe** » 24 Oct 2005, 12:47

I was playing around with the car some more tonight - been gone for a few days so haven't had time to look at it. Bled a lot more out of the rear brakes via a long clear tube back to the reservoir - still no sign of air in LHM. Did the boot test again - this time with engine running first - sat in boot, car sank a few inches, about 15 seconds later it rose up again. Got out, car rose higher, a few seconds later it settled back to normal height. So this tells me my height corrector is working properly. Next I shut the engine off, sat in the boot and after about 15 seconds again, it rose back up - got out and car rose higher, then settled properly. I tried it again, but this time the car didn't rise, so that indicates there is only enough reserve pressure to do it once. I tried it after starting engine, getting height stabilized and then shutting engine off, waiting a couple of minutes and sat in boot - nothing happened. Car sank and stayed down until I got off, then it came back up. So it looks more like an internal leak - next step is pull return lnes one by one to see which is flowing...This is starting to make my Mitsubitte van with it's 'simple' leaf springs look very attractive!

citronut · Post by **citronut** » 24 Oct 2005, 19:22

the best way to test your A/C sphere is after running engine with hight set at normal ride level,switch engine off,then move hight lever to highest setting and the car should rise up a bit,this tells you that there is reserve presure,its unlikly to do it twice without starting the engine again
regards malcolm