95 LWB - Brake Booster Pump Failure
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Thread: 95 LWB - Brake Booster Pump Failure

  1. #1
    SOPHOMORE ROVER
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    Question 95 LWB - Brake Booster Pump Failure

    I'm rather certain the brake booster pump has fried, but I wanted to post here and see if anyone had any other ideas to try.

    Background:
    I'm driving the truck and while stopping, the pedal looses resistance as if ABS/TC engaged. ABS and TC lights illuminate and it then feels as if there is a leaky brake line. When hitting the brakes, post incident, I have to push very hard and the pedal is soft. It depresses ~30% before truck begins to slow and ~50% to stop.

    I stopped and inspected observing no leaks, but brake fluid is slightly low. The low fluid is directly related to my front pads as they are worn. The BRAKE light does not come on.

    The ABS pump has occasionally been running while the truck is off. The last time I noticed this was when I parked at my office. With the truck off the ABS booster was still pressuring and I assumed that it was fancy new technology, in comparison to a 1990 RRC, which allows the brake pressure to remain perfect 100% of the time. In the 1990 the pump needs to recharge the system once the truck is started.

    Symptoms:

    • ABS booster pump does not turn on
    • Pedal required hulk-like strength to even think of stopping (basically full manual pedal)
    • No leaks
    • ABS and TC light are permanently illuminated
    Troubleshooting to date:
    • Followed RAVE electronic troubleshooting guide (pages 81-85 for ABS)
    • Relay show no sign of failure and swapping out the relays for others has no change in result
    • no blown fuses
    • grounds are clean
    • Removing the indicator relays (to turn off the ABS/TC dash warning) had no effect. Blaming lucas?
    • Checked and verified that I am getting 12v at the power plug which attaches to the ABS booster pump.
    • Tried this and the result was that I'm too late. A NEW, brand new, relay had no change in end result (
    • I just found this and think I should try a brand new relay (https://www.rangerovers.net/forum/8-r...ter-stuck.html) regardless of the testing I performed already.)
    Still left to answer:
    • Are the ABS and TC dash lights remaining lit because of the fault? - This wasn't covered in the RAVE description of what the lights do, OR, I misunderstood what I read.
    • Could anything else prevent the ABS booster pump from engaging? The wiring diagram made this look pretty simple and I'm certain I covered everything down the line.
    I'm open to suggestions so please let me know what you think!
    Last edited by rangerover; January 15th, 2016 at 04:45 PM. Reason: found another related link
    1990 Range Rover
    1995 Range Rover LWB
    2006 Range Rover
    2004 Discovery 2

    http://www.roverparts.com/News/archi...verSurgery.cfm
    http://www.defendersource.com/forum/...irs-60356.html
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  3. #2
    SOPHOMORE ROVER
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    Re: 95 LWB - Brake Booster Pump Failure

    Update - I have 12 volts + going straight into the brake booster with no results from the pump.

    I had to move it out of the garage and the pedal initially acted as if the pump was working then occasionally would depress into the foot well.

    At this time I'm convinced that the ABS Pressure Switch Unit has failed as the pump never engages. Because the ABS/TC light never thinks of disengaging I'm left wondering "what else?" Perhaps this is just one of those days where a RRC encounters multiple related failures (ie: ABS sensor + bad booster pump)...

    Again, if anyone has any other suggestion(s), I'm willing to read
    1990 Range Rover
    1995 Range Rover LWB
    2006 Range Rover
    2004 Discovery 2

    http://www.roverparts.com/News/archi...verSurgery.cfm
    http://www.defendersource.com/forum/...irs-60356.html
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  4. #3
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    Re: 95 LWB - Brake Booster Pump Failure

    Pressure switch does two things, it switches the pump on if the pressure is low and the low pressure causes the ABS and TC lights to come on. If you have 12V at the power plug to the pump but it isn't running, check across the pump for resistance, you should see a very low value. If you see an open circuit (very high resistance or infinity) the pump has burnt out. I had mine go on a P38 (virtually identical to a 95) and yes, you need both feet and all your weight on the pedal to get it to stop.
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  6. #4
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    Re: 95 LWB - Brake Booster Pump Failure

    Quote Originally Posted by Gilbertd View Post
    Pressure switch does two things, it switches the pump on if the pressure is low and the low pressure causes the ABS and TC lights to come on. If you have 12V at the power plug to the pump but it isn't running, check across the pump for resistance, you should see a very low value. If you see an open circuit (very high resistance or infinity) the pump has burnt out. I had mine go on a P38 (virtually identical to a 95) and yes, you need both feet and all your weight on the pedal to get it to stop.
    Awesome, thank you - I'll verify the resistance on the old later this week.

    I bought a used pump from another RRC owner and fit it to the truck. Worked perfectly and I'm back in action. (Also replaced both relays to be safe)
    1990 Range Rover
    1995 Range Rover LWB
    2006 Range Rover
    2004 Discovery 2

    http://www.roverparts.com/News/archi...verSurgery.cfm
    http://www.defendersource.com/forum/...irs-60356.html
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  7. #5
    FRESHMAN ROVER
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    Re: 95 LWB - Brake Booster Pump Failure

    Thought I’d tag onto this thread rather than starting my own as I have very similar symptoms on my 95 SWB with ETC. My ABS system has always been ‘sketchy’ in that when you first pull off after starting the car, the brake pedal will audibly pulse and click (you can feel it pulsing against your foot through the brake pedal) and the braking performance is affected in time with the pulses like you’re briefly losing the power assistance each time it clicks, sometimes it’ll pull sharply to one side. This pulsing typically lasts only for the first few minutes of driving before it clears, sometimes it doesn’thappen at all. Once the pulsing stops the brakes seem to work well so I’ve been content to live with it. I did a brake system bleed according to the RAVE manual however this did not eliminate the pulsing.

    The pump also seemed to run far too often, it would prime for maybe 5 seconds max when you turn on the ignition, and then would run for a second or two each time you push the brake pedal. No sign of any leaks and never had any warning lights on the dash however I suspect that if I looked behind the cluster I would probably find the bulbs missing.

    Anyway today (while driving in monsoon rain!) the brakes suddenly seemed to lose all power assistance, hulk strength was employed and I managed to stop at a gas station. I couldn’t hear the pump running when the ignition key was turned on. I managed to limp the Rangie back to my workshop so I could get it out of the rain. All fuses were intact, the two black relays seemed ok when tested, I switched them around to no avail. Jumping the power supply to the pump at the relay plug causes the pump to run continuously and the brakes became mega-powered! I’m wondering what could have suddenly failed to stop the pump from running, perhaps after a prolonged of progressive deterioration which caused the brake pulsing? Could the pressure switch be at fault?
    "What was that? An exhibition? We need emotional content!"

    1995 Range Rover Classic SWB 4.6
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  8. #6
    FRESHMAN ROVER
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    Re: 95 LWB - Brake Booster Pump Failure

    MillSpeed,
    based on your description above I believe you have a combination of issues going on.

    the short run time at start up and the run of the pump with every brake application tells me that your accumulator has failed, and will need to be replaced.

    It also sounds like your pump has now failed. this is not uncommon when operated with a failed accumulator as it causes the pump to have to work much more frequently and doesn't give it any cool down time since it has to cycle every time you touch the brake. replacing the pump should restore your power assist, but you will still need to replace the accumulator or the new pump life will be short too.

    For the clicking and brake pulsing you are experiencing after startup, I think the most likely scenario is that you have a wheel speed sensor that is loosing signal and triggering the ABS to pulse. when a single wheel signal is lost the ABS interpolates it as having one wheel that is locked up and skidding. The ABS then pulses and releases brake pressure in an attempt to get that wheel to start rolling again. this is why you have the sensation of loosing power assist, since the computer is releasing the brakes. In my experience this is most commonly a front sensor as the air gap is critical to getting a good reading, and air gap can be affected by play in the wheel bearings and/or swivel pin bearings, though it could be due to other issues or the rear axle sensors. It the ABS light comes on, then you should be able to pull the codes, which may give you more direction on identifying the faulty sensor.
    Simon

    95 Range Rover Classic
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  9. #7
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    Re: 95 LWB - Brake Booster Pump Failure

    Thanks Simon for the advice!

    To update, I pulled a used pressure switch off a P38 pump assembly and fitted it to my Classic pump which is now running and the brakes work great after bleeding the pump and ABS unit. The pulsing was absent for about a day but then it came back, it seems to be much more infrequent now though. Lots of air came out when I bled the various nipples on the pump/ABS unit, the rear-most hydraulic booster seemed to keep passing air until I eventually ran out of fresh fluid and had to stop. The accumulator definitely seems to be goosed; the pump cycles for about a second every 18 seconds when the car is sat idling, and runs every time the brake pedal is pressed. A new accumulator is on the way, and hopefully once it’s installed I’ll be able to properly bleed the ABS unit and the rest of the system. I’ll also be pulling all of the wheel sensors and giving them a thorough cleaning.
    "What was that? An exhibition? We need emotional content!"

    1995 Range Rover Classic SWB 4.6
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