P38 ABS Accumulator Replacement on a Range Rover


ABS Accumulator location on a Range Rover 4.0/4.6Introduction
Diagnosis
Parts Needed
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.

Introduction
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.

Diagnosis

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 visited (Dennis Altman), though not for the purpose of fixing my RR. In the spirit in 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 said. 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.

Parts Needed

I figured that continuing to place an undue burden upon the 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.

ABS Accumulator

ABS Accumulator

Brand new accumulator with packaging; not the O ring that is needed for the correct seal.

Official versus 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 brakes. I have never bled the brakes. I have never seen or heard it described as anything other than unpleasant and time-consuming. [But see this shortcut method devised by other alert Rangerovers.net readers!]  Things were not looking good. Then I 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 encouraging news. The general consensus was that it could be done without bleeding the brakes, and routinely was. I decided that I would replace it the Saturday following its arrival, in the event that I ended up having to bleed the brakes.

Depressurizing the System
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’.

When I removed my old ABS Accumulators, there was no ‘fssst’ sound or squirt of brake fluid or anything of the sort. It was remarkably uneventful.

Gaining 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.

Gaining access to the Range ROver abs accumulatoro

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.

Paper towels placed around accumulator to catch brake fluid

I could not remove the old accumulator by hand. A strap wrench wouldn’t do it either. (If I live long enough, one day a strap wrench will surprise me by actually showing itself to be good for something). A metal oil filter wrench did the trick.  I then saw why I would not have to bleed the brakes: the brake fluid was filled completely to the top already! No need to even top it off (see photos below).

 

ready to insert new accumulator

accumulator removed

I put some brake fluid on the o-ring on the new one and screwed the new accumulator into place by hand.

New accumulator and O ring

CLose-up of new O ring seal on ABS accumulator

Photos showing installation of new O-ring seal (provided with new accumulator) prior to installing the unit.

When it was all the way in, I realized that the manual does not provide any information as to how tightly it should be attached. (no torque value or anything to that 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 it just a smidgen. Just enough so that I saw that it had moved. That was how I defined ‘pretty tight’.

New accumulator in place

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!!

Other Owners' Experiences
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 did 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 orfice 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 2002 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.

 


 

 

 

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Page revised February 2, 2012