don_xvi The '89 328 with the Teves ABS does not have a vacuum booster. The power brake function is provided by high pressure brake fluid. The normal system operating pressure range is between 140 and 180 bar. A small reserve of system pressure is maintained by an accumulator sphere. During normal operation and braking, the pressure supply pump cycles on and off to maintain system pressure.The cycling of the supply pump is controlled by the pressure switch which is the subject of danman's investigation.
I may be way out of line here as I do not know the ABS cars, but... It sounds as if a hydraulically boosted system is being described here. I had a BMW that had it's brakes boosted off the power steering pump. I was replacing many components on the car, including the master cylinder, and just couldn't get the brake system to feel right-it was always as if it had air in it. I finally took it to a shop, and they replaced the accumulator, which fixed it. Could that be the issue? Unfortunately, I don't think there is a way to test them, only replace it and see if it works better. It's a ball filled with nitrogen I think, and I suppose if it leaks out that's it. I don't know about the rest of the issues, i.e. the auxillary pump, but if there is an accumulator, it can fail, can't be diagnosed, and feels like air in the system.
Hmm, OK, Sowest, that sounds like a pretty comprehensive description, and matches with a lot of what I saw when I was looking at those parts diagrams, but then I found one titled "with antiskid" that showed a conventional vacuum booster. In light of this... ignore everything I've said as it described a normal ABS-equipped car! I'm curious... can you hear it when this booster pump runs as a normal part of operation or is it quiet enough that you're not aware of a buzz after every few stops? Good luck.
don_xvi Hi. Yes, the Teves system is a strange animal. It does work well, but it seems overly complicated to me. When they go bad, the repairs and the price tags makes one long for a good 'ole vacuum booster. The pump can be heard when the key is first turned on, but when the engine is running and the car is driving, the hum of the electric motor gets lost in the din. FamilyCar Hi. The accumulator can fail. On the Teves system a pretty reliable check can be made with a test gauge. The sphere is charged to 80 bar above the diaphragm so when the pump starts on a discharged system, the pressure jumps quickly to the 80 bar level and then the pressure rise slows as the pump compresses the upper chamber up to the operating pressure. "danman" might have a bad accumulator, but his primary problem is that the system pump is not kicking back in after the initial start-up. The fact that he is able to get multiple brake applications before losing pressure should indicate that the accumulator is actually working.
I think we just have a problem with words here, but to clarify: The diagnostic codes are brought up by grounding pin 26 on the ECU by inserting a fuse into the empty holder. This holder is often next to the diode block, but one does not actually ground the diode.
Sowest, Any idea what might trigger the "ABS" light to come on during a running condition (after the initial start up and pressurization? In other words, is it low pressure on the pressure switch or some other triggering event? Thanks.
Hi Cliff The pressure switch unit has three switches. One controls the start and stop of the pump motor, one turns on the "ABS" light when the pressure falls to a level where the ABS function no longer works and the third turns on the "Brake Fail" light when the pressure is so low that brake failure is imminent. The system does have failsafe manual braking even when there is no pressure. I think the failsafe braking is only on the front brakes.
Here is a VERY simple test. Turn the key to the "on" position..let the pump run and stop. Now shut off the key and remove it from the ingintion switch. Pump the pedal. You should be able to pump the pedal 15-20 times BEFORE it gets really hard to press. If you pump it say 5 times and it gets hard (I know it sounds dirty) then your pressure accumulator is shot. You have found your issue..very common on the teves ABS equiped cars, Jag, Porsche,GM etc all used the same system.
I don't mean to hijack the thread here, but it looks like I may need a new accumulator (based upon the symptoms and information in this thread). Any reco's on replacing the accumulator? Where to buy? How to de-pressurize the existing and install the new accumulator? Thanks in advance.
Hi Cliff The accumulator is screwed in with an O-ring seal. Pump the brake pedal with the key off to discharge any system pressure. I would think 30-40 times would be more than enough. More will do no harm. I don't have a real recommendation for a source for a new accumulator. You could call around to local dealers of the cars in the post above to see if something is available locally and get an idea of prices. I found that there was nothing in stock in my locale as the system is pretty old now and dealers have pretty minimal inventories. I would probably call GT Car Parts (623) 780-2200. They are pretty good at doing the source of supply research and price things fairly.
I'm glad my thread is so useful to everyone and I'm not the only one with brakes woes! I still think my issue is the pump/switch (though I haven't tested yet) and not accumulator because the pump does not turn on again when system pressure drops. If my accumulator was leaking, I would think that the pump would have to run much more often!
Thanks sowest, much appreciated. I notice that my accumulator on my 3.2 mondi looks to be the same shape/size as that on the Jag/Rover systems of the same era with one exception - my mondi accumulator has a small hexagonal fitting on the top about the same size as a 13mm nut with a depression in the middle that looks like it may take a fitting, possibly for re-charge?? It could just be a hexagonal fitting for ease of removal of the accumulator however (w/o provision for a re-charge port, basically). The other accumulators I've seen of equivalent size/shape don't seem to have this fitting on the top. Anyway, I'll check 'er out. Thank you!
