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We have a similar set up on the BMW e30 I race, and we've been having massive issues with our ABS- normally the front right locking up although sometimes the left too.... (it's a left hand drive car and the front right has about 170 lbs less weight on it).
What made this really confusing is that we could feel the ABS working in the rear, but we couldn't understand why the fronts were locking up- really hard. So much so we flat-spotted two tires at the last race
The symptoms are the ABS system appears to be perfectly functioning- no warning lights. Pulling a wheel sensor triggers the light immediately. I put in another controller (I had spare) and no difference.
I wired in some 12v LED's to the channel activation (FR, FL, R)- I could see when the wheel was locked up, the ABS system thought it was trying to unlock it... so definitely not a sensor or a controller issue.
Pulling off the connector at the pump and manually activating the pump and each solenoid didn't yield any results (although it has fixed other peoples issues in this thread).
Finally I bit the bullet tonight and replaced the pump with a spare... Early testing around the streets appears to show that it works! I need to get it to the track to really see, but no wheel locked up for more than about 1 meter.
So, if you're having ABS issues in 964's, e30's or any of these early Bosch systems, there is no sensor to detect whether the solenoids or the pump is firing. The test circuits are for whether the relays are working.
Here's a diagram for the e30 pump wiring- I'm assuming yours is similar:
In answer to a previous question, if the system is off, my understanding is that it has no effect on the brakes whatsoever... what is interesting however if there's a warning light, it does hold the solenoids open but keeps the pump off. FWIW I would try both modes to see if that makes a difference. Disconnecting a wheel sensor is the easiest way to make it go off.
ABS has become a way to cheat at brake balance, so what we found was that when it was going wrong, it really goes wrong since the wheel that shouldn't be getting full force, is!
Hello. Might anyone have experienced an ABS with this type pump having the top silver relay that pressurizes the ABS getting warm and hot when ignition off? Does the ABS computer run when ignition off doing self checks? I am suspecting a locked ABS problem as is described in this thread. Also I hear clicking coming from what sounds like the relay when the ignition is off, but only occassionally. The relay also will be cool after using car, then when I check the relay the following day it starts getting hot. Thank you.
The electronics can swap over to the Merc pump relatively easily. The only difference between the C2 and C4 pump is the simple addition of one pin for a warning light circuit on the C4 pump. That said, I've thoroughly dismantled/destroyed a used Merc pump and it was full of gunk. Even though the screens and ports for the pump part were clean, the ridiculously complicated solenoids had dirt and gunk all the way through them. The best pump is one that gets used.
No relay should ever get warm or click when the key is out of the ignition. The abs controller can easily get wet and cause all kinds of shorts and issues. That's where I would look.
The electronics can swap over to the Merc pump relatively easily. The only difference between the C2 and C4 pump is the simple addition of one pin for a warning light circuit on the C4 pump. That said, I've thoroughly dismantled/destroyed a used Merc pump and it was full of gunk. Even though the screens and ports for the pump part were clean, the ridiculously complicated solenoids had dirt and gunk all the way through them. The best pump is one that gets used.
No relay should ever get warm or click when the key is out of the ignition. The abs controller can easily get wet and cause all kinds of shorts and issues. That's where I would look.
Pic of some abs guts-
Thanks Nick. Switched out controller and cleaned pump ground thinking it is due to electrical resistance and to eliminate possible controller problem. Same heating of relay. I understood the abs pump has 3 relays inside and the pistons that could stick and then create heat when the computer tells it to operate. Also, it gets hot when ignition is on as well (or very warm). Tried a new high pressure relay and exact same problem. My next move will be to remove pump and open up to see if stuck as this thread shows. This problem draining battery at higher amp draw, though not overnight. The heating when ignition off of my relay seems to be in cycles like the computer is doing a system check. Have also monitored the battery amp draw and it does go form normal low amp draw to high when relay is warming. Thank you.
@-nick did you find the bolts that hold the body of the unit together to be safety bolts (heads shear off so they ca not be removed?) If so how did you remove them? My mercy pump is made with these types of bolts so I only got as far aa far as the shuttle valves- which were in perfect condition. Are there seals to be replaced? I definitely want to disassemble and clean before installation of either the merc pump body or the 964 unit.
I have the merc pump and thought I would dissembled it first- but I can only get to the shuttle valves (as everyone is posting) and I believe the problem on my pump is that the 3rd (rear) solenoid is not functioning. Has anyone been able to completely strip on of these?
Pete
How do you know if the rear solenoid is not working ?
Actually it was the front that locked up on me so those solenoids are not functioning. I still have not fixed the problem but am planning on flushing the whole system with alcohol and cycling the pump as I bleed. I tested the system with the tester and instructions provided by Cajonfan. Not sure if he's still making them or not but its a very easy to use system.
I disassembled the pump unit and as suggested on this topic the pistons were seized
I managed to remove them and clean them and they look to work as they should
But I broke one of the small orings around the pistons, and they also seemed to be slightly biiger than required, maybe they lost a little bit of their elasticity and it s better to replace them
I found that the orings made to be used with brake fluid should be made from a specific material and from what I found it should be EPDM
Does anyone know the exact dimension specifications of those orings ? ( I measured them but just to confirm as there are many measures close to each other )
Once the abs unit is fitted back on the car what would be the easiest and proper procedure to bleed the system without any special actuator tool? just bleeding normally the brakes? or jumping the electric motor or solenoids in some way but in that case what would be the sequence of things to do ?
I just wanted to update this thread with some new info regarding the difference/similarities of the various pumps. It turns out that internally there are differences relating to front/rear bias. So a straight swap of a merc pump is not something I would try. I got this info from a rebuilder: https://mtechniqueauto.com/shop/ols/...sche-abs-pumps. Seems to be quite the perfectionist and I was considering send my pump to him- then I decided on this instead:
Sorry! It’s a 4 channel 997 unit. 9m is making me a front end kit” includes all brackets, fittings, components, etc for electric power steering, their version of electric a/c, and 4 channel abs- complete with a stock wiring harness that is modified for everything.
07-06-2020, 06:42 AM
