Hydro boost issues e28 535

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Bcrazy
Posts: 6
Joined: May 16, 2023 3:33 AM
Location: Perth

Hydro boost issues e28 535

Post by Bcrazy »

New to the community, good to be here.
I have the 535i version of the E28. This has the hydro boost system. I recently bought the repair kit and installed it. I had a bit of a mishap during the installation as I scored the inside of the cylinder. So I bit the bullet and bought a a brand new Hydro boost unit from FCP Euro. After installation during the bleeding process, I noticed that all the brakes fluid was entering the hydro reservoir, so on top of having worst brakes, I now have contaminated power steering fluid.Why is this happening? Is the new unit defective? This was not happening with the previous unit and the brakes were good but not great.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: Hydro boost issues e28 535

Post by Aldo525 »

Hello,

I can't tell if the booster is faulty, but check the booster installation.

Image
Federico
Posts: 545
Joined: Sep 16, 2013 6:38 PM
Location: Argentina / California

Re: Hydro boost issues e28 535

Post by Federico »

This is really weird. Any fluid leaking out of the brake master or booster will drop out of the gap between them and onto the frame rail. I cannot imagine a scenario where the fluids would mix. Can you post photos of your setup?
Bcrazy
Posts: 6
Joined: May 16, 2023 3:33 AM
Location: Perth

Re: Hydro boost issues e28 535

Post by Bcrazy »

Thanks gents, I will recheck the schematic and ensure, that my lines are as they should be
Bcrazy
Posts: 6
Joined: May 16, 2023 3:33 AM
Location: Perth

Re: Hydro boost issues e28 535

Post by Bcrazy »

From the schematic provided by Aldo, the only way I can see fluid entering the hydro boost reservoir, could be only from the return low pressure line on the hydro boost when the brake pedal is returning to rest position providing a suction.....if that make sense
gadget73
Posts: 1176
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: Hydro boost issues e28 535

Post by gadget73 »

I don't specifically know the BMW setup but I am familiar with hydroboost in other things. There is no suction in these systems, its just a fluid return to the pump reservoir. I also can't see how the fluids mix. Leakage out of the back of the master I get, the seals fail, but how that would get into the power steering is definitely not something that makes sense to me.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: Hydro boost issues e28 535

Post by Aldo525 »

Bcrazy wrote: May 16, 2023 10:25 PM From the schematic provided by Aldo, the only way I can see fluid entering the hydro boost reservoir, could be only from the return low pressure line on the hydro boost when the brake pedal is returning to rest position providing a suction.....if that make sense
I don't believe that, the union between the brake master cylinder and the booster is "dry", there are seals in both systems and the union is simply mechanical and the bolts that join them. A crazy idea is that a line from the brake master cylinder is connected to an input from the booster, but that doesn't even have the same connectors (lines of 2 have been connected to 3 in the diagram below right). Another crazy idea is that someone mistakenly thought the ATF reservoir was for brake fluid and added a few ml to the booster system.

Image
Bcrazy
Posts: 6
Joined: May 16, 2023 3:33 AM
Location: Perth

Re: Hydro boost issues e28 535

Post by Bcrazy »

Yes correct, its seems a bit impossible to take place, and after the first schematic, I rechecked the lines and they all are correct, but when I was depressing the brakes during the bleeding, I found no leaks on any of the 4 wheels or at the master cylinder but, then I found the power steering fluid as unusually high.... :brick: :brick: So I am going to take it down again to hopefully find the mystery and resolve. I will take picture as I go. Thanks for your input Aldo
Blue Shadow
Posts: 10195
Joined: Feb 12, 2006 12:00 PM
Location: SE PA

Re: Hydro boost issues e28 535

Post by Blue Shadow »

Do you know the correct method to fill the power fluid reservoir?

Let us know how you checked the level and when you filled it.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: Hydro boost issues e28 535

Post by Aldo525 »

In the first schematic is the procedure to top off the reservoir. It is normal a high fluid level after 15/20 "pedal pumps" until 1 cm from the top.

What you see in the ATF fluid is brake fluid or something that looks like brake fluid???....maybe a contaminated AFT was used to fill the system (water in the ATF???). Change and flush all the fluid, removing the hoses to power steering and canister, clean and/or replace the filter and add again new ATF. If the problem persist, you should be the first and the one with that unsolved mystery.

PD. Is there anyone than knows where to find the PS filter????....32411128919????....is NLA .....
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Hydro boost issues e28 535

Post by Mike W. »

Aldo525 wrote: May 18, 2023 12:24 PM In the first schematic is the procedure to top off the reservoir. It is normal a high fluid level after 15/20 "pedal pumps" until 1 cm from the top.

What you see in the ATF fluid is brake fluid or something that looks like brake fluid???....maybe a contaminated AFT was used to fill the system (water in the ATF???). Change and flush all the fluid, removing the hoses to power steering and canister, clean and/or replace the filter and add again new ATF. If the problem persist, you should be the first and the one with that unsolved mystery.

PD. Is there anyone than knows where to find the PS filter????....32411128919????....is NLA .....
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Bcrazy
Posts: 6
Joined: May 16, 2023 3:33 AM
Location: Perth

Re: Hydro boost issues e28 535

Post by Bcrazy »

Thanks Aldo, Just let you guys know, I had some success, I have a confident pedal. The issue was when I upgraded the brake hoses, I just wasn't able to bleed the system conventionally, to get all the air out. I got myself a vacuum kit and bled each line and now its good.
Has anyone upgraded to the e34 540 brakes, are they worth it? I am still not too pleased with what I have as brakes now
a2058
Posts: 38
Joined: Jun 02, 2022 12:12 PM
Location: New York, USA

Re: Hydro boost issues e28 535

Post by a2058 »

Yes, I upgraded to E32/E34 front and rear brakes. With the stock master cylinder, it took further pedal travel and push to engage like normal. I upgraded then to 750 master cylinder and all feels very normal in terms of the pedal feel and the engagement dynamics…
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