Changing brake fluid

[t-tony]

Just to clear up any misunderstanding, putting a "prop" on the brake pedal does not, and isn't intended to, put any pressure in the braking system. It is simply there to place the pistons in the master cylinder in such a position that fluid cannot run from the resevoir and empty the system. That is all it does.

Tony.

 

[Jimbob_OD]

So now I’m really stumped. Swapped the ABS pump for a new (second hand) one and there is still the same issue - fluid going from the master cylinder into the ABS pump but nothing at all coming out of the unions to the rear lines.

Im at a total loss now!

 

[Jimbob_OD]

But the bullet and got a mobile mechanic out today. Tried and tested everything but atill no fluid out of the ABS pump to the rear lines.

He thinks it can only be a faulty ABS ECU module locking the valves closed.

 

[t-tony]

Can you not operate the ABS pump via a code reader (you can with a Foxwell) . If you should be able to, but can't, then it's got to be the pump?

Tony.

 

[Jimbob_OD]

I replaced the pump with a new (second hand) unit. I just swapped the pump, not the ECU module to avoid having to re-code.

The mechanic today was able to cycle the ABS pump with his scan tool (don’t know what make/model but it looked a pretty high end one) but despite that there is still no fluid going to the rear lines from the pump.

He was at a bit of a loss given then I’ve replaced the pump and we tested all the other bits and pieces. He reckons it can only be a fault with the ECU which is causing the valves in the ABS pump to stay closed, preventing fluid passing through.

 

[Zephyr]

Are you sure the isnt a clot in the lines under the chassis? just saying, not an expert nor claim to be.

 

[Jimbob_OD]

@Zephyr Yeah, we detached the rear lines from the ABS pump and manually flushed them through with a fluid pump - all ran freely.

 

[Zephyr]

and your car does not have a proportioning valve, correct? (Again just trying to give some ideas here).

 

[Jimbob_OD]

No, no proportioning valve. We’ve tested the master cylinder and all the lines manually, bypassing the ABS pump. The issue is definitely with the pump or its ECU module. As I’ve swapped the pump, I think the only thing it can be is an ECU fault.

 

[Zephyr]

As a last resort before digging into the ECU I would try to locate the abs system and abs pump relays and bridge the ends of each one of them to see what gives…
sorry but no more ideas.

 

[Jimbob_OD]

Yep, the mechanic tested all the fuses and relays too - great minds and all that…

thanks @Zephyr

 

[Jimbob_OD]

Well, the saga continues.

New ECU arrived and fitted. Still the same problem.

I’ve tried blowing compressed air through the inlet port for the rears (with the pump off the car) and it is completely blocked/stuck shut. No air comes out of the ports which would go to the rear lines.

Is it really possible I’ve had two pumps with exactly the same issue??!

 

[Zephyr]

Very very strange. Since your brake lines are ok and have no clots or bends, have you tried "out of the box" ideas, such as engine on and running? Very strange...

 

[Jimbob_OD]

Yep. Engine on. Engine off. Key on. Key off. You name it, I’ve tried it!

 

[Zephyr]

Last thing that I would suggest is put everything back, fill the tank to the brim and suck from the rear bleeding screws instead of blowing from the tank.
Or call a priest... sorry.

 

[Jimbob_OD]

Thanks for all your advice @Zephyr.

 

[Zephyr]

Very curious to see if there was a solution to this...

 

[Jimbob_OD]

I’ll keep you posted @Zephyr.

The replacement ABS pump has been sent for a refund and a new (used) one is due to arrive Monday.

I took the old pump to a trusted local mechanic, who after testing it with compressed air, was adamant it was faulty with either a blockage or a stuck valve at the inlet port for the rears.

I’ll probably not get a chance to fit and test the new unit till Tue or Wed evening after work but I’ll post the result in here.

 

[Jimbob_OD]

@Zephyr It’s not good news.

Fitted the new pump, pressured it up with a pressure bleeder.

There is a good flow going into the pump for the rears but nothing coming out.

With the system under pressure I can totally disconnect the lines to the rear calipers from the ABS unit and there is nothing coming out.

Time to call a priest - I think the car is possessed.

 

[Zephyr]

I am thinking loud now.
what can cause an abs pump to send fluid only to the front?
Could it be the traction control? Could the system be puzzled and think that the front is doind a skid? I do not know.
are all the fuses of the traction control ok? Are they different from the abs ones?
Since the rear brake lines are free, no clots, and fluid passes through them with the pump disconnected we exclude them.
So its some sort of electrical curquit that controls the pump and its telling it not to send fluid to the rear...
What can be the cause?
A fuse, bad wiring, the ecu, a sensor and what else am I missing?
Can you just hotwire the pump off the car and see what gives?
Have you scanned the car with a modern reliable reader?
Maybe I am just writing a bunch of bs, but this is really extremely strange.
I googled "bmw e36 rear brakes not bleed" and then tried also "z3" and then just bmw and some cases came up but the one and only that looked like yours was a dead end because the OP never bothered to come back and report if it was ever solved...
I think maybe you should gather the ZedShed think tank for brainstorming with this one. And maybe find a willing person to lend you his ecu for testing...
Terribly sorry I can not help much.