MyE28.com

Hi there

I am in the process of upgrading my e28 m5 with e34 brake calipers, discs and braided brake lines..
So i decided to drain, the whole brake fluid reservoir and brake lines...
After having done this I read that this may completely mess up the ABS system ???
Is this the case in e28 m5s?
If so how do i repair the damage?

Paniced thanks

You may have better luck posting this to the "Tech Talk" section. The M5 section doesn't get a lot of attention these days.

Bleed as you normally would after reassembling the system.

Moved to Tech Talk as per TroyArboc's suggestion. This is not something that'd be M-specific.

Sometimes, getting significant air into the system is unavoidable or inadvertent, but if you can avoid it, do not intentionally "drain" your brake fluid. There's no point in doing so, and it can lead to a whole lot more effort later, to include having air in the ABS unit. The bleeding job will not be more complete if the system is drained.

Before anyone asks "But what if the old fluid is bad?" Well, that's the major point of routine maintenance brake bleeding, which is pushing the old fluid out with fresh fluid. The second situation that calls for bleeding is replacement of parts which leads to unavoidable introduction of air.

Abaky wrote: Oct 11, 2022 4:32 PM So i decided to drain, the whole brake fluid reservoir and brake lines...

After having done this I read that this may completely mess up the ABS system ???

If so how do i repair the damage?

"Damage" is a misnomer. It will not damage anything or "completely mess up" anything. What it can do is impede function or make bleeding more frustrating. It can be difficult to correct, but it's not a terminal situation.

Pressure bleed the system. If you're left with sponginess or uneven function, bleed again. If you can, intentionally engage the ABS (some suggest a gravel road, but that can be bad for your car's appearance!) multiple times, then bleed again. At worst, you'll have to do all of this multiple times.

Did the panic stop on a dirt driveway thing to get air trapped in an ABS system out before. That was for a car that we installed ABS on that didn't have it originally. All new parts, tons of air, and it absolutely would not bleed out completely. A couple of panic stops and bleed cycles got it working perfectly.


my normal fluid flush process is to empty the master cylinder reservoir by whatever method makes sense, fill it with fresh, then bleed until the fluid runs clear on all 4 wheels. Intentionally introducing a lot of air just makes it all take a lot of extra time. Even when I have to open stuff I try to introduce as little air as I possibly can.

This time of year in the northern hemisphere the use of a slippery surface like gravel for the abs to engage can easily be replaced with a street covered in wet leaves. My abs went wild when I came home from a weekend away which had a severe thunderstorm, hail and such in my area, taking half the leaves from all the trees in late May and I was slowing down from a 1 lot length across the front of my house to pull into the driveway. Doing just over the limit where abs does not operate, maybe 5-10mph.

I never had any trouble with the ABS after brake line R+Rs. All you need to do is to keep the brake fluid above the bottom of the master cylinder reservoir. Before opening the system, I would get a couple qts of brake fluid just cuz. I 've found that jacking up the front of the car helps. IF you can't get the right rear bleeder to drip, it is airbound because there is a leak. Top off MC and start checking your work. You'll find a wet coupling. Rinse and repeat until the bleeder drips. Close it and move on to RR. That is why I like the slow ass gravity bleed. It checks your work.

Thanks
That is all very reassuring.
Will blled as usual and see how it goes...