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ABS Master Cylinder

2426 Views 14 Replies 9 Participants Last post by  alfa75 88
So I have invested time and money into a new abs pump and new accumulator from GM that was successfuly used in previous threads described. However, I am having trouble getting fluid out the line from the master cylinder and into the abs pump. The abs pump is connected and my fear is that the new pump will burn out if I start the car up too many times. Should I be worried about a pump burn out?
Should I replace the abs master cylinder with a good used one? I have unscrewed the bleeder screw behind the reservoir on the master cylinder and no fluid is coming out? What to do next to keep the ABS in working order?
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I believe you have to prime the ABS pump somehow to get the fluid to pressurize. On my car I had to use a pressure bleeder to create some pressure to get the fluid out of the master.

I'm sure the ABS workshop manual has the answer on the approved way to do it.
When I did a GM swap I just hooked it up and turned it on - done. No priming, pressuring, or anything was needed in my case.
I have used a turkey baster. I use it to pull out as much old as I could and put in new. (also swished some in and back out to get all the junk at the bottem.
then I poped off the rubber part. and shuved it in the fill hole turned on the pump and pushed on the rubber some. I also had the hi-PSI hose lose. as soon as it started to pump I tightend the hose. and then washed everything off with the garden hose.
tossed the turkey baster in trash.
Did you disconnect all of the lines that connect to the underside of the master cylinder or just the one behind the reseroir on the side?
just the big flex one where is bolts on the pump.
I have changed the master before and it was a real pain to get all the air out.
the back is easy but the front took a while.
if you put a stick on the break pedel to just give is a tiny bit of breaks the back will pump all day long. so just open each valve untill no more air in the back. while topping off from time to time.
the front will need some one to pump and somone to work the valves. like any other car.
There is plenty of fluid in the flex line that connects to the pump and goes out. But there is no fluid in the banjo connection flex hose that connects to the brake line and then onto the master cylinder. I disconnected this line directly from the master cylinder and no fluid is coming out. Bottom line, I can not get fluid out of the master cylinder into the pump. Is there any other way to get fluid into the pump? The conventional front brakes bleed fine but, will eventually go out after a few hard stops.
Have you ever been able to get the GM pump to shut off?

I suspect you may have reversed the power to the pump! The 2 pin Alfa power plug goes on the GM pump both ways. If the pump just keeps going and never shuts off (unable to build pressure) you may have it on incorrectly. Pull the 2 pin power connecter, flip it 180 degress, and stick it back on.
Pump and accumulator are fine. The switches were switched to confirm polarity and it is fine as is. Bottom line, fluid can't make it to the pump! I think it's time for a master cylinder replacement.
I'd take it in and have it serviced, or at least looked at.
ABS Problems

If in fact you end up condemming the master cylinder, I have one sitting on the shelf from my old Platinum. It is a known good unit, I tracked the car with no issues, and no longer have a need for it. Test the unit. If it is bad, I'd let mine go for cheap. I fortunately never experienced all the woes of the ABS that others do, but would offer one experience. The pump was working intermittantly, and by cleaning all the electrical contacts common to the system, the problem went away. Good luck to you, let me know if I can help!
The pump gets the fluid right off the tank the master cylinder has nothing to do with it.


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abs pump fluid supply

I changed out pump and master cylinder last spring on my 88 milano autocrosser. I used my old fluid reservoir, and found, at least on this one example, that the filter ... item 11 on diagram ... was pretty much loaded with black residue. I cleaned that all out. Used parts worked fine ... very fortunate.

mark m thornton
seattle washington usa
Man, so what happens when the supply of useable used units run out??

Is ABS an American option only on Milanos? I'm wondering if similar style ATE MkII rebuilt units can be adapted to fit. Dynatech should be able to provides a master for around $300.
I've got various ABS parts laying around from my non-ABS swap.
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