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Folkes, as promised a quick write up on my ABS pump repair using the innards from a Merc 190E ABS unit.
The symptoms are NO ABS, but also no indication on the dash, no warning lights/buzzer, just 4 black lines down the road! I did the usual, cleaned sensors in the hubs, bled the system, charged battery, checked connections, no joy.
The failure is the 2 small half inch pistons are seized or partially seized in the ABS pump. These are operated by a cam on the end of the electric motor.
There is no way to know unless you strip the unit down, so no guarantee this is the fault, but the donor units are cheap and there is no cost, just time and effort and brake fluid, it is up to you if you want to give it a try.
First purchase a Bosch 0265200043 abs unit from a merc 190E, also used on other merc vehicles, from the bay - approx £20 , 30USD maybe a bit more.
If you want to try the dis-assembly procedure, why not try it on the merc unit first.... then move on to the car, this will also give you a chance to check the state of the donor unit.
Remove your ABS pump from the car....
Unplug the connector, it is a bit tricky to get the pipes off and mounting nuts undone, best use a brake pipe spanner to save rounding the unions. There will be some spillage, I clamped the breather on the brake reservoir to slow the flow and create a vacuum which helps, there isn't a massive spillage. Brake fluid, as you know, eats paint so best put rags and a plastic bag under the abs unit as you go.
Once out of the car unplug the 2 relays from the top, and undo the bolts holding the plastic top assembly, which holds the relays, on the top of the motor. Undo the electrical connection from the end of the motor. Hinge the plastic assembly up towards the end of the abs unit.
The objective is to remove the motor and the 2 pistons which it acts on, the motor will come away easily, just undo the long screws that run through the motor and pull it away. But the pistons have to come out from the sides of the unit.
Undo the 2 threaded caps that cover the pistons (cant remember the size, 12mm allen key?) be careful as the pistons are made up of springs and a filter and my pop out, keep a note of the order of their assembly. They are likely to be rusted blobs of gunk!
Clean out the bores that the pistons run in ready to accept the new secondhand ones.
Re-assemble with the parts from the new secondhand Merc unit. First try the new pistons in the bores to make sure they run freely and spin the new merc motor to make sure it is not stiff. Lightly grease the cam on the motor, then bolt up the motor. Do this without the piston threaded plugs in as they put the pistons under tension and so will get in the way of the cam on the end of the motor. Then install the 2 threaded plugs over each piston.
fold down and bolt up the relay holder and motor connections, that's it.
re-fit, bleed the brakes and test.
Last edited by tdiquattro; 01-12-2015 at 03:37 PM.
One question - did you try to cross reference or check with Bosch to see if the MB is the same as the Porsche pump and motor? I know you said, in a different thread, you weren't sure that's why you pulled the piston as opposed to simply replacing the whole unit. I'm just curious if you looked into it and couldn't get an answer and therefore proceeded to just replace the parts. I searched last night and couldn't find anything that would suggest or deny that they are the same.
In case anyone wants to investigate further the P Car pump is Bosch 0 265 200 052 and the MB pump is Bosch 0 265 200 043.
You are right, I looked long and hard and couldn't find any difference, but the part number put me off. Maybe they are the same "inside" they don't look any different.
So yes, I only did it to be safe. Oh and they are the same C2 and C4 part numbers to answer the earlier question, so the repair should fit either.
We hooked up my C2 to a Bosch ABS tester last week and much to my surprise the ABS didn't work. On stripping the unit down I found exactly the same problem highlighted here. The pistons were eventually freed and the pump reassembled and all is well with the ABS.
The whole exercise got me thinking. Firstly how many of us drive around not knowing if the ABS is working or not. Secondly, the pump and these pistons are 'dry'. They are not lubricated by brake fluid. The only reason they would seize like this is because they haven't been operated on a regular basis?
Indeed. Since mine failed and was fixed (unit replaced) I test it out to keep it working.
Good to know that you now have a tester available.
Same here, having had two different failure modes on the ABS over the years. There's a local road with a loose surface I take a detour down every time I go out for a drive.
I think I triggered the ABS once at Spa, on the sighting lap when a Caterham brake tested me! But generally I don't trigger the ABS on track and when I do I damn well want it to work!
The Bosch tester is now with Unit 11 Steve, a rare thing by all accounts. For sure it makes ABS diagnosis so much easier. The guys are making up another cable so the C4 and 928 systems can be diagnosed and that should be all bases covered
The Bosch tester is now with Unit 11 Steve, a rare thing by all accounts. For sure it makes ABS diagnosis so much easier. The guys are making up another cable so the C4 and 928 systems can be diagnosed and that should be all bases covered
Rare indeed mate...might even be only two in the country...and none left in Greece now!
01-12-2015, 03:03 PM
964 ABS Pump cheap repair
