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Discussion Starter #1
I have an odd one that I so far cannot diagnose. Working on my ’99 4.6 with 215k miles. The issue as best I can describe is that it seems the ABS is activating under normal braking conditions. The pedal gets a bit stiff and the light vibration is felt, although no lights. This first started a couple years ago after getting the system back to proper operation. Maybe 20 percent of the time. Occurrences have steadily increased to about 50 percent now. And just recently I had a new issue. During braking the pedal dropped about an inch and a momentary loss of brakes was experienced. Possibly a momentary loss of brake pressure.
I little extra detail. When purchased a few years ago the truck had the three lights. After replacing a front sensor I was plagued with intermittent ABS errors pointing the sensors. Different sensor with each corner being involved at various times. Finally it produced a consistent left rear. Turned out the axle shaft was swapped with an older non ABS (no ring). After the new axle shaft The ABS system was in proper operating condition for about a year. The rotors and pads replaced regularly, rebuilt calipers all around (normal maintenance). When the above issue started all brake lines, hard and soft, were checked. Pump was checked. The pressure switch failed and after replacing that specific issue was addressed but the possible activation issue unchanged. I was thinking the modulator since I had rebuilt older units with the plastic valve discs. I happened across a good used modulator and swapped in. Things seemed fine for a couple hundred miles, but perfect operation was short-lived and I am now back to the puzzling cause. Basically all components have been swapped due to maintenance or diagnostic indicators. The control module has been swapped with a known good one and has been used in another vehicle which performed normally.
Any Thoughts?
 

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1995-2002 Range Rover P38A
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As Swiss Tony would say:
"They all do that mate, it's a feature!"
Both of my P38s will activate the ABS on a particular rut on the downhill track from my workshop when the front wheel hits it. I wouldn't describe it as a light vibration through the pedal though- it's a heavy vibration accompanied by the rattle of the solenoids operating. When I first encountered this my instinctive reaction was to reduce pedal pressure then reapply. That then felt like I'd momentarily lost braking force. The answer was, as the book said, keep the brake pressure on and constant. You get self cancelling cadence braking otherwise.
I've found that if the wheel sensors have moved slightly out, but not enough to cause a fault- the sensitivity of the ABS increases. You might want to try a tap on each sensor with a soft faced hammer to reseat them against the ring.
You've replaced pretty much everything except the accumulator- I'd be looking a bit suspiciously at that as well.
 

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1995-2002 Range Rover P38A
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95, could you please elaborate on bleeding using software? I am familiar with power bleeding somewhat but not using software. Might this require the use of a Nano Unit?

Thanks
 

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1995-2002 Range Rover Classic
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I use autologic and have used factory test book, both of those systems offer a brake bleeding procedure. in there it gives datailed instructions on bleeding the brakes, I/E where to start how many times to hold pedal, when to activate etc.
I don't have experience using other software thus can't vouch for them.
 

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1995-2002 Range Rover P38A
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I don't suppose you would be able to get a couple of pictures/screen shots of the ABS power bleeding instructions?

I've bled mine the 'RAVE' method, but still feels like there is air in there... Nanocom has the option to do power bleeding in it, but looking in their manuals, it just simply says it's for power bleeding the system, and may need to be done more than once if there is a lot of air in the system...

As for actual directions about if you need to press the pedal, how many times, what bleed nipples etc to use, it's most uninformative! As far as I know the Nanocom functionality is based on the Testbook system, so I would imagine the instructions should be the same...

Regards,
Marty
 

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Discussion Starter #7
Sorry, been offline for a while. I had to replace an accumulator on another truck, so waited to bleed mine until finished with the other since I’d have everything out to perform bleed. Interesting results. I did find some air in the left front. Guess was tramped even though I thought was thoroughly bled. Rain hit and I had to take care of stuff outside. The next day I got the truck off the lift and the pedal was soft and too much travel. Had to wait another day until I had assistance and did a full bleed again. All was great on the test drive (about 20 miles). Then the next drive the issue seems to be returning. Not as severe, but definite vibration. I may swap the modulator with another unit if I get some free time. Seems to be a valve issue. Also, traction control activated when I pulled out turning (from parking lot onto roadway). Two pulses while wheel was cut hard. Had on older Classic that did the same on occasion.
I usually use my old Rovacom for all my P38 work and recently picked up the Nano for the L322. Blackbox Solutions mimics most of the TestBook. As far as brakes, they do not provide the step by step instructions and only functions are ABS Power Bleed and ABS Modulator bleed. I don’t have the P38 activated on the Nano, but should be the same. I have used the Lynx and another system that provided the step by step actions. I was with an acquaintance when he destroyed his modulator using a generic system from his full service shop. Possibly Actron, but I don’t remember. I do remember the system pressurized somehow with valves incorrect. Fluid was pushed up into reservoir and spilled all over. The master cylinder seals were shot and he said the was some other internal damage after tearing down modulator. His unit did recognize the Wabco system, but I am curious if it was software or user error.
But that does bring up the tangent question. What do you use for tools and/or procedure when bleeding brakes?
 

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1995-2002 Range Rover P38A
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I generally bleed mine using the directions in RAVE, and do it to the letter.

I swapped the modulator on my '01 with one that I'd stripped, cleaned, and rebuilt with new seals etc - and after getting it all bled, it drive brilliantly... until the other day - about a week after having done it all, I would get the pedal go soft and if I applied the brakes, then the pedal would keep dropping, with no extra braking action.

Had a second set of hands (well, feet) today, and re-bled the first part with the master cylinder, and I got a decent bubble of air out of that, and the pedal feeling got better straight away. Took it for a drive, and again it felt better, but when I went to reverse and apply the brakes, again pedal started sinking.

I was just curious about the power bleed as I've always seen it as an option in the Nanocom etc - but also have figured that it can't just be as simple as turn the option on and hope for the best!!

Tools that I use during bleeding is generally just an old jar with a bit of brake fluid in the bottom, and some clear hose. That and an 11mm crowsfoot spanner to loosen/tighten the bleed screws. Then get someone else to do the pressing/releasing of the pedal - and will generally communicate with them as to when to press/release etc and turn ignition on/off when doing the parts that require that.

Marty
 

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I don't suppose you would be able to get a couple of pictures/screen shots of the ABS power bleeding instructions?

I've bled mine the 'RAVE' method, but still feels like there is air in there... Nanocom has the option to do power bleeding in it, but looking in their manuals, it just simply says it's for power bleeding the system, and may need to be done more than once if there is a lot of air in the system...

As for actual directions about if you need to press the pedal, how many times, what bleed nipples etc to use, it's most uninformative! As far as I know the Nanocom functionality is based on the Testbook system, so I would imagine the instructions should be the same...

Regards,
Marty
Marty, in the garage we have 2 autologic units the old blue machine which is now obsolete as far as updates or repairs and the new orange unit which well is new.
the new unit has limited brake service on the p38, the old blue unit allows the procedure I mentioned, where you enter the brake bleed procedure then instructs to open the driver side bleeder, hit the on screen button and bleed. then proceed to all others.
then is asks to perform a valve power bleed where you push the brake and hit the on screen button and it cycles the abs valves.
finally autologic screen suggests to follow with traction control valve bleed based on the screen instructions.

it is similar to d2 power brake procedure with the addition of traction control valves.
this procedure is not possible on pre 95 units, all bleeding is done manual on those..on the classic you will bleed the master cylinder by using the three nipples next to the reservoir, maybe this last procedure is the one needed on the p38's I have never performed "it" on p38's.
may be worth a try...
 

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Thanks for the reply...

Mine's an '01, and have the option in the ABS section for 'power bleeding'. I'm just wondering if it's worth a shot, as I don't seem to be losing fluid anywhere - and I thought yesterday that a) they wouldn't have added the functionality for no reason, surely (though it is Land Rover, so who knows!) and b) as the modulator block I swapped it had been out of a vehicle and pulled apart - there was no brake fluid at all through any of it, until I filled it up - which is fine, but I wonder if there's still air displaced in the block maybe around the ABS or ETC valves as they haven't been activated (and aren't activated in the normal RAVE bleed procedure).

At this point I don't have a lot to lose - it's either try that, try another full manual bleed, or swap back to the old modulator - which again will then need a full bleed too!..
 

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this past winter in the us east coast was my first winter with the p38, all other years I have driven my 95 classic or one of the other cars of the family (subaru or honda).
during the earlier summer the p38 begun showing brake concerns, the accumulator would take a long time to charge and every other time you would feel the pedal fade as you were braking, it was a very interesting way of stopping.
anyhow I renewed the accumulator and the system auto bled the pedal begun to feel a little more comfortable but not completely there, also the accumulator begun to charge faster, less than a minute.
the last bit of winter precipitation we got included about 2 inches of ice, on my way to work I had to climb an icy hill. it is there were the traction control went to work and soon there after I was low on brake fluid according the cluster indicator.
turns out I never physically bled the system and by happenstance winter driving and activation of traction control valves bled the system internally.
I still have a funny some what soft feeling pedal and plan to bleed the modulator valves, braking is better but not there completely. now my 95 on the other hand, it has never had a brake fade, the pedal is always firm and stops on a dime.

I will update as soon as I do the physical bleed.

BTW mine is a nas 2000 HSE 4.6...with 190,000 miles. black exterior with tan leather interior, I think your is identical.
 

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Discussion Starter #12
Quick update. thinking wiring issue and going to run through all. Went out on a test drive and it acted up rather badly. Pedal got rock hard braking not consistent. After hitting a bump ABS and ETC lights. Braking became perfectly normal (except I assume ABS was not functioning). Pulled into driveway and immediately hooked up diagnostic - could not communicate with module. For fun I swapped control modules and almost the exact same test drive repeated. Put the module in another truck and I got a low voltage on left front sensor. I had time to confirm sensor wires back to module. All good. Will hit others in a few days.
 
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