ABS pump intermittent

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BigJessie

Active Member
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56
Location
Lancaster
Just changed the brake accumulator on our 1998 diesel P38. We bled the brakes by RAVE and straightaway they were sharp. Went for a run and parked up, but when we came to drive home the ABS pump did not come on, and the brakes were hardly there at all unless you stamped hard and long. Limped home by the back roads. Next day turned ignition on and ABS pump still not coming on. Left for a couple more days and just now have tried again, and the pump came on for 30 seconds and the brakes were sharp again.

I checked the fuse and the black relay and both seem fine. I suspect the pressure switch on the end of the pump is to blame. Is this right, as I would like to be sure before spending out on what seems to be available only as a very expensive second-hand part.

Thanks P38 collective geniuses!
 
BigJessie said:
Just changed the brake accumulator on our 1998 diesel P38. We bled the brakes by RAVE and straightaway they were sharp. Went for a run and parked up, but when we came to drive home the ABS pump did not come on, and the brakes were hardly there at all unless you stamped hard and long. Limped home by the back roads. Next day turned ignition on and ABS pump still not coming on. Left for a couple more days and just now have tried again, and the pump came on for 30 seconds and the brakes were sharp again.

I checked the fuse and the black relay and both seem fine. I suspect the pressure switch on the end of the pump is to blame. Is this right, as I would like to be sure before spending out on what seems to be available only as a very expensive second-hand part.

Thanks P38 collective geniuses!
Click to expand...
Could be the pressure switch or problems with the fuse box it could even be the motor itself. Lots of checks needed before spending money. The switch is or was available as a SAAB part I think
 
Datatek said:
Could be the pressure switch or problems with the fuse box it could even be the motor itself. Lots of checks needed before spending money. The switch is or was available as a SAAB part I think
Click to expand...
Thanks for this. I shall check the electrics again.

One other thing is that before I started her and the pump worked again I noticed that I had overfilled with brake fluid almost to the top, so took some out to get down to the correct 'FULL' level. Is there any chance that have an overfilled brake fluid reservoir would somehow impede the pressure switch and stop the motor coming on? I know it sounds far fetched, but after seven years of ownership I have realised that whoever created the P38 moved in mysterious ways...
 
BigJessie said:
Thanks for this. I shall check the electrics again.

One other thing is that before I started her and the pump worked again I noticed that I had overfilled with brake fluid almost to the top, so took some out to get down to the correct 'FULL' level. Is there any chance that have an overfilled brake fluid reservoir would somehow impede the pressure switch and stop the motor coming on? I know it sounds far fetched, but after seven years of ownership I have realised that whoever created the P38 moved in mysterious ways...
Click to expand...
The reservoir should be at the full level AFTER the pump has run. When left parked, fluid will bleed back into the tank raising the level well above the full mark. Over filling will not cause a problem other than a mess if the reservoir overflows.
 
Datatek said:
The reservoir should be at the full level AFTER the pump has run. When left parked, fluid will bleed back into the tank raising the level well above the full mark. Over filling will not cause a problem other than a mess if the reservoir overflows.
Click to expand...
Thanks so much - that's one less possible cause. Shall go and check the others.
 
BigJessie said:
Just changed the brake accumulator on our 1998 diesel P38. We bled the brakes by RAVE and straightaway they were sharp. Went for a run and parked up, but when we came to drive home the ABS pump did not come on, and the brakes were hardly there at all unless you stamped hard and long. Limped home by the back roads. Next day turned ignition on and ABS pump still not coming on. Left for a couple more days and just now have tried again, and the pump came on for 30 seconds and the brakes were sharp again.

I checked the fuse and the black relay and both seem fine. I suspect the pressure switch on the end of the pump is to blame. Is this right, as I would like to be sure before spending out on what seems to be available only as a very expensive second-hand part.

Thanks P38 collective geniuses!
Click to expand...
ABS light came back on after about a mile of driving when my pressure switch packed in
 
Well today the pump did not come on, and brakes were hardly there, and the ABS and brake warning light were on again. I pumped the brake pedal 30 times, then four more, and still the pump did not come on. Yesterday the pump worked fine, so I have invested in a new (used) pressure switch and hope that will solve the problem.

Thanks for your thoughts - much appreciated.
 
Well, I fitted the replacement pressure switch and the brakes are working properly again - at last. I'm a bit concerned that the switch is not available as a new part so we have to rely on used parts taken off scrapped vehicles for something as important as the brakes... but fingers crossed. Thanks for all thoughts and happy Ranging!
 
BigJessie said:
Well, I fitted the replacement pressure switch and the brakes are working properly again - at last. I'm a bit concerned that the switch is not available as a new part so we have to rely on used parts taken off scrapped vehicles for something as important as the brakes... but fingers crossed. Thanks for all thoughts and happy Ranging!
Click to expand...
See post#2 ;)
 
Sounds familiar - I usually remember these things long after they have become unimportant! But actually I shall keep my eyes open for which other cars use the same pressure switch.
Update is that the brakes are slightly spongey, so will need another round of bleeding. What joy...!
 
BigJessie said:
Sounds familiar - I usually remember these things long after they have become unimportant! But actually I shall keep my eyes open for which other cars use the same pressure switch.
Update is that the brakes are slightly spongey, so will need another round of bleeding. What joy...!
Click to expand...

Keep an eye on the rear brake lines. Any P38 that hasn't had them replaced should be treated with extreme caution.
 
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