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 syustems, 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 syetem the dealer would replace the entire pump and accumulator as a ($1,000) unit; in latter days te 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 -- but if you can verify or amend this please email me with the details!

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.

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.

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.

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.

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).

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

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’.

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!!

More Information

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