P38 ABS Accumulator
Replacement on a Range Rover
Official Versus Unofficial Procedure
Gaining Access to the Accumulator
Removal of Old Accumulator & Attachment of New One
Reassembly & Testing
Other Owners' Experiences
Photo at right: Location of ABS accumulator on Dan Czarniak's Bosch-engined P38 (1999 & up). Location is similar on 1995-98 models. Photo courtesy of Dan Czarniak.
The Range Rover ABS and Traction Control system is second to none. Originally designed by WABCO, a major manufacturor of heavy truck braking systems, it accounts for much of the Range Rover's superiority over lesser vehicles. The flip side is that it is fairly complex and like most Range Rover systems, not immune to failure.
Aside from ABS sensor misalignment, by far the
most common problem is the wearing out of the ABS accumulator that sits
on top of the ABS pump and acts like a battery to hold a charge of high
pressure brake fluid in the system ready for action. The accumulator is
essentially a compressed air tank with a flexible rubber diaphragm at
the bottom; the ABS pump compresses the air inside the accumulator to
provide a store of hydraulic pressure energy for the ABS and traction
control systems. As noted in ABS Pump and
Accumulator Diagnostics, if
your pump runs too long (more than about 45 seconds) after engine
startup, the most likely (but not only possible) problem is the
accumulator developing a slight leak.
In the early days when ther was a problem with the
system the dealer would replace the entire pump and accumulator as a
($1,000) unit; in latter days the accumulator became available as a
separate part and the repair became much easier and less expensive. The
following illustrated description of the accumulator replacement
operation was kindly provided by Dan Czarniak who performed
the operation on his lat model Bosch-engined Range Rover P38 in 2008.
The procedure for earlier (GEMS) P38s is exactly the same. I think the
procedure for the 1992 and up
Classic Range Rovers and 2003 and up Range Rover models is also similar. They introduced the awesome Wabco system, generations ahead of what
other makes offered, to the Range Rover family, and you will notice the
Wabco label on the new parts sourced by Dan.
Replacing the ABS Accumulator was an easy one. The potential problem is that you might not know that you need a new one. Whenever I started my vehicle, I was used to the sound of the EAS pump – or so I thought. As it turns out, the EAS pump and the ABS pump are very close to each other. So, in truth, I don’t know what I was used to hearing, but the sound was familiar just the same.
One day a guy who is an accomplished LR mechanic
(Dennis Altman), though not for the purpose of fixing my RR. In the
taking advantage of a friend’s good nature, I started my P38 and opened
the hood, and asked him to tell me if he sensed anything noteworthy.
“Hear that sound? It’s your ABS pump. It
should be done running by now. You need a new ABS accumulator”, he
The sound was one of the pump sounds to which I had become accustomed.
“Replacing it is easy”, he said. Coming from a mechanic, those
words are better than “May God have mercy on your soul”, but it
only means that replacing it would be easy for him. Those words did not
necessarily bode well for me.
I figured that continuing to place an undue burden
ABS pump would lead to the pump’s undoing. And a new ABS Pump would be
expensive. So I searched around online and bought a new ABS Accumulator
in a hurry. The best price I could find for
an OEM one was about
$ 210 (US), plus shipping. The Part Number is: STC2784.
There is no cheaper
‘alternative equivalent’ to the OEM ABS accumulator that I am aware
of. (As of July, 2008).
The accumulator is a
little bigger than a
baseball, but weighs maybe 2.5 lbs.
Brand new accumulator with packaging; not the O ring that is needed for the correct seal.
Unofficial Replacement Procedure
I followed the manual’s procedures. ‘Remove ABS accumulator’. Seems easy enough. Well, the old one does not want to go gently. Note also that the inside of an ABS accumulator is pressurized to 80 bar. I had to look that one up. 1 bar = 0.986923267 atmospheres. So let’s round that to 1 bar = 1 atmosphere. That little round ball is pressurized to the tune of 80 atmospheres inside. I decided to handle it respectfully.
I then reviewed the
manual pages dedicated to the replacement
procedure. A frightening phrase leapt off of the page at me: bleed the
have never bled the brakes. I have never seen or heard it described as
other than unpleasant and time-consuming. [But see this shortcut method devised
by other alert Rangerovers.net readers!] Things were not looking
searched the Rangerovers.net P38 Forum to gather
as much information as I could find on
replacing the ABS accumulator. The search results yielded very
news. The general consensus was that it could be done without bleeding
brakes, and routinely was. I decided that I would replace it the
its arrival, in the event that I ended up having to bleed the brakes.
At least one reader has asked "Does the old accumulator sort of "blow up" when you unscrew it???". The entire brake system operates at very, very high pressure. So it would be fair to ask the same question about doing anything that involves opening the closed system through which the brake fluid circulates. For this reason it is important to DEPRESSURIZE THE SYSTEM FIRST. If the system has been properly depressurized, according to the directions in the manual, then there should be no difference between the pressure inside the brake system and the ambient air pressure. Ergo, no blowing up. Dan (being an insurance man) reports that he probably repeated the depressurization procedure 5-6 times in a row before removing the ABS Accumulator. Dan reports "What I now know is that the same care needs to be taken when doing anything that ‘opens’ the braking system’s ‘circulatory system’." Dan offers the following additional details:
The ABS Accumulator itself is made of metal (steel, I would venture) that is at least 1/8” thick. After I removed it and drilled a hole in the top (per the manual’s instructions) I had a go at cutting into it. I used a metal cutting wheel attached to a drill. It must have taken 20 minutes and 3 wheels to get all the way through the ‘skin’ of the accumulator. I wouldn’t worry too much about the accumulator blowing up. To come at it from the other direction, I doubt that you could get it to ‘blow up’.
I removed my old ABS Accumulators, there was no ‘fssst’ sound or
squirt of brake fluid or anything of the sort. It was remarkably
Access to the Accumulator
The part arrived, as did the following Saturday. To gain access to the accumulator, sufficient to comfortably unscrew it (which requires significant torque), Dan removed the main air intake components from the top of the engine. The photo below shows the parts that had to be removed.
Removal of Old Accumulator
Brake fluid is corrosive stuff, so it is a good idea to arrange a few paper towels or rags around the base of the accumulator area to catch any that might leak out when you remove it.
could not remove the old accumulator by hand. A strap wrench wouldn’t
either. (If I live long enough, one day a strap wrench will surprise me
actually showing itself to be good for something). A metal oil filter
did the trick. I then saw why I would not have to bleed the
fluid was filled completely to the top already! No need to even top it
off (see photos below).
put some brake fluid on the o-ring on the new one and screwed the new
accumulator into place by hand.
installation of new O-ring seal (provided with new accumulator) prior
to installing the unit.
When it was all the
way in, I realized
manual does not provide any information as to how tightly it should be
attached. (no torque value or anything
effect). I think that “How tight? is a
fair question to ask. I decided upon ‘pretty tight’. I went as
tight as I could by hand, put the oil filter wrench on it and tightened
a smidgen. Just enough so that I saw that it had moved. That was how I
Reassembly & Testing
I put everything back together and started it up. Bad news. The ABS light was on. For the following 15 minutes I ruminated and postulated. Then I remembered something that I had read on the P38 forum some time ago. The light stays on until the vehicle exceeds something like 3.7 mph (+/-). So, I hopped in and off I went. The ABS light went off accordingly. Success!!
Alert reader MK Tribbie reports (February 2010): I completed the job on my wife's 99' 130K mile P38 HSE. I had bled and re-bled her brakes several times trying to get a firm pedal. Additionally, when backing out of the garage in the morning, her pedal would essentially be ineffective to stop the truck while being backed out.
[The job] was easy. Just depressurize
the system, then simply unscrew it with the oil filter wrench. I
however fill both the reservoir opening to the very top and the
accumulator with fresh brake fluid before refitting the new
accumulator. I just put my index finger over the accumulator
and manuvered it into place and rapidly made the fitment and then
screwed it on (after fitting the new O-ring of course). Brakes are VERY
firm now. Job took a total of 10 minutes or less. I plan to do my
90K mile P38 HSE soon. This is the absolutely easiest 'big' job I have
ever done in my entire 12 years of Range Rover ownership.
I sourced the new accumulator from Atlantic British which was cheaper than my dealer who gives me a big break on spare parts. Even with the dealer discount, the AB part was about 100 bucks cheaper.
If you have corrections, comments or suggestions, email us.
Page revised February 2, 2012