Well, I have been on a journey trying to get my brakes to work right in my '99 P38 since I bought it about 6 months ago. I had a Disco 2 for about a decade, but I have never owned a P38 so didn't know about the ABS system. If I had owed a P38 before, it would have helped me diagnose the problem faster.

Actually, the journey started with the previous owner.

First, the symptoms.

The brakes worked, but the pump ran for 30-40 secs every three pumps. The brake pedal would sometimes feel like it was pumping up when I was braking, and would occasionally get very very firm and, when it was very firm, it tended to lock up the brakes if I stomped it too hard.

I googled extensively and never found anyone with these symptoms.

The previous owner took the truck to a mechanic who put in a 'rebuilt' ABS pump and new accumulator. Unfortunately, I didn't find this paperwork until after I did the first thing I tried, which was to replace the accumulator :/

Shockingly, the new, new accumulator didn't help. I bled and bled the brakes until I was pretty sure that air wasn't the problem.

So I timed the ABS pump and realized that it ran for 45-50 secs after being depressurized, which folks online said was a bit too slow and that the 'rebuilt' pump was on its way out.

So I bought a used pump and accumulator. I installed them, and bled everything again. I tried the new 'used' accumulator just to see what the difference was, but it made weird noises when the pump ran and then the pump ran with almost every pedal push, so I put the new, new accumulator on the new used pump and it seems to be pumping up and working fine and within the recommended times.

Except the pedal was still weird and the brakes didn't really work right, and the pump ran for 30+ secs every third pedal push.

Around this time I learned that there was a short period where the P38 was equipped with ABS Modulators that were faulty and could spontaneously fail, leaving you with no brakes at all, and that my truck was from that time frame. I checked the date code on the ABS Mod, and sure enough, it's dated from '98, so is likely original and, even if not original, it's very likely one of the problem modulators.

So I bought a used later model modulator (the new part is SXC 100010 vs SXC 100000 the old part) and installed it, then bled everything AGAIN.

It's finally working right. The pump runs for 15 secs every three pumps, which is a huge improvement, and all the pedal weirdness is gone.

One takeaway is that even with the weird ABS pump system, the pedal should feel like any other vehicle and shouldn't make weird noises. I thought the pumping up was maybe just how these things work. Wrong.

So anyways, I'm posting all this for posterity so if anyone else has a wonky P38 brake pedal, they will know the modulator is failing.

 

Thanks for your great write up. I hope I don’t ever need to use this information, but thanks for sharing it with us.