1

123asd

Member
Chaps, i have a P reg disco 1 300tdi with abs that is giving me some bother.

With the engine not running the brake pedal is nice and firm, just like the one i had previously without abs.

Turn the engine on and the pedal goes soft like there is air in the system, the pedal goes all the way to the stop and while it is driveable the stopping leaves rather a lot to be desired. Stopping from speed the brakes bite alright initially then start to fade a little.

All pads are looking good, no excessive disc corrosion, not usung fluid. Wheel bearings feel good, abs light behaves as it should, lots of servo vacuum, check valve works. At the mot in November to my surprise it scored a pass albeit with not much to spare, i feel the stopping has got worse since then though.

When it stops raining i am going to bleed it again, but i cant quite reconcile a perfect hard pedal feel when the engine is turned off with a significant amount of air in the system.

Any pointers? I have a long run with a big trailer next week so am keen to get some improvement.



UPDATE

i replaced the master cylinder, bled the system and got it working almost to perfection. A week later the brakes are crap again, spongy, feeling like there is air in the system. The pedal hits the stop especially on long gentle braking towards a junction then needing a bit more at the end.
 
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I would say that you problem sounds more like a servo fault than ABS. I did check in RAVE to see if there was mention of "Power bleeding", but it appears not:-

Untitled.gif
 
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Many thanks. I used the easybleed at 10psi last time but have access to an assistant today so will go back to the old fashioned approach.

I understand there is an option in the electronic voodoo boxes to cycle the abs pump and modulator whilst bleeding but i dont have access to one and cant afford to throw £300 at one at present.

The people who make the modulator say it can be vacuum bled if you can activate the solienoids but i cant make any visible or audible sign of mine activating when i supply 12v to the appropriate pins. It does pass its start up checks though.


If it were a servo fault why would i be able to get the brake pedal to the stop? Loss of adequate servo assistance would, in my basic understanding, mean no or minimal change in pedal feel when running, and large amounts of force required on the pedal. I have a hard pedal with short travel with the engine shut down, but engine running i have long soft pedal travel to the stop.
 
123asd said:
If it were a servo fault why would i be able to get the brake pedal to the stop? Loss of adequate servo assistance would, in my basic understanding, mean no or minimal change in pedal feel when running, and large amounts of force required on the pedal. I have a hard pedal with short travel with the engine shut down, but engine running i have long soft pedal travel to the stop.
Click to expand...
IMO the hard pedal symptom for servo assistance failure is valid when vacuum is lost somewhere but there can be other internal leak within the servo unit which can be accessed only with vacuum assistance cos some chambers in the unit are "locked" with engine stopped... IMO the problem is there somewhere:
D1 brake fault chart.jpg
 
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I'd agree that this appears to be a servo fault - have you tried disconnecting the servo from the exhauster and driving very very VERY slowly, and preferably on private land a bazillion parsecs away from anything else ( you get the idea ) to see how the brakes feel then ?

( they are likely to feel stupidly heavy - potentially to the point where you are not able to operate them - so be bl**dy careful :eek:)

IIRC, the servo can be changed without removing the master cylinder...... (?)
 
If the pedal is "hard" without the engine then the master cylinder seals are ok.
The master cylinder is only retained to the servo unit by two nuts, the servo unit remains attached to the bulkhead.
If as you say the pedal goes to the full length of its travel with the engine running you have air in the system, if some how Air has got into the ABS matrix then indeed the valves have to be opened when bleeding the system, Land Rover use Testbook to do that, but there shouldn't be any air in the matrix unless the been work carried out on the braking system and air has been allowed to enter.

I've had both systems abs and non-abs and there is a difference between the two in pedal feel and travel, if you wish to compare.
When y ou bleed the system try it with the engine running at idle and I'm sure u know, it's the longest pipe first then the next ending up at the one nearest the master cylinder.
 
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Many thanks everyone for some top quality help.

The consensus seems to be air in the brake system but master cylinder likely ok, with a potential servo fault if i understand rightly.

The rain has died away and i am going out to bleed the thing with the engine idling. i shall then report back.
 
Pre bleed servoless test run was very heavy on the brakes but a much more convincing pedal feel.

Stopped almost as quickly with a big heave on the pedal as on the stop with the servo working.
 
Turns out i didnt have as much dot in the garage as i thought, only 750ml so i took 750 ml through in total. A bit bit off each caliper with the engine running having got under the thing but it will need a more thorough bleed on tuesday as working tomorrow.

All the fluid that came out was nice and clean from its last bleed, no significant air bubbles found.

No change in performance.
 
I dont know where these theories with bleeding with engine running came from but it has no logic, wabco recommends on the contrary to make the pedal bleed even with battery disconnected, the modulator has 2 valve circuits for each wheel within, one N/O for normal brakes operation and one N/C for active braking(ABS) ... as long as you pedal bled it well the only air which can be trapped is within the modulator in the N/C valve circuit and that circuit opens only when ABS becomes active it has no effect on normal braking, to bleed that out you need tester but it doesnt affect pedal travel whatsoever...also the logical sequence is not about longest to shortest line as stated in a previous post but about primary and secondary circuits alternance:
brake bleed sequence.jpg
 
The logic in bleeding the brakes with the engine running is that bleeding the system by the manual method is easier with a servo assisting.
I'm amazed on you lack of knowledge on RRc and D1s brake system even though you say " all my advices are based on my own experience" and then show pictures of a D2 which has a different brake bleeding sequence as most of us know with RHD starts at the rear near side brake :)
 
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123asd said:
Chaps, i have a P reg disco 1 300tdi with abs that is giving me some bother.

With the engine not running the brake pedal is nice and firm, just like the one i had previously without abs.

Turn the engine on and the pedal goes soft like there is air in the system, the pedal goes all the way to the stop and while it is driveable the stopping leaves rather a lot to be desired. Stopping from speed the brakes bite alright initially then start to fade a little.

All pads are looking good, no excessive disc corrosion, not usung fluid. Wheel bearings feel good, abs light behaves as it should, lots of servo vacuum, check valve works. At the mot in November to my surprise it scored a pass albeit with not much to spare, i feel the stopping has got worse since then though.

When it stops raining i am going to bleed it again, but i cant quite reconcile a perfect hard pedal feel when the engine is turned off with a significant amount of air in the system.

Any pointers? I have a long run with a big trailer next week so am keen to get some improvement.
Click to expand...
sounds like master cylinder,
 
discool said:
The logic in bleeding the brakes with the engine running is that bleeding the system by the manual method is easier with a servo assisting.
I'm amazed on you lack of knowledge on RRc and D1s brake system even though you say " all my advices are based on my own experience" and then show pictures of a D2 which has a different brake bleeding sequence as most of us know with RHD starts at the rear near side brake :)
Click to expand...
youve no need to bleed in a sequence
 
discool said:
and then show pictures of a D2 which has a different brake bleeding sequence as most of us know with RHD starts at the rear near side brake
Click to expand...
the sequence is the same and the one from the pics is correct for all with wabco units...to start with the longest line has no logic... or if it has just explain it
 
Thank you everyone for your continued input.

As the book suggests a sequence and i know of no compelling reason to do otherwise i shall be sticking to the disco1 bleed order. I will also have no assistant for my next bleed so will have to resort to the easybleed.
 
sierrafery said:
the sequence is the same and the one from the pics is correct for all with wabco units...to start with the longest line has no logic... or if it has just explain it
Click to expand...
The theory was that air would still be trapped in the longest pipes if bleeding was started on the short pipes first, so that how I will do it as I never had any issues, that may be old school as all Rave states is "Fit bleed hose to any caliper bleed screw". That may be just a LR thing for the disco.

I don't normally keep vehicles longer than three years so the brake fluid change i only do is on vehicles I've kept, so that was my old RR and now only on my disco and a 40 year old Ford I also have in the garage,
 
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