Need help identifying if this is indeed an E28 M5 or even BMW part?

[DiseaseWithNoCure]

I have been working on a 4 year E28 M5 revival and have had a weird backfire issue develop at a certain repeatable RPM that I can’t seem to work out...but that’s not what this post will be about.

Armed with that backstory, I finally caved and took it to a local’ish (90+ miles away) specialist (or maybe more appropriately “specialist”) who tested everything under the sun — and too could not get the issue addressed.

Moving on, upon pickup he handed me this part (photo below) and said “he found this lying on a frame rail but can’t identify where or what it goes to...but is definitely something BMW”.

https://ibb.co/LC3J3pG

Having four years of lift calisthenics and tear down experience on this car — I did not identify it whatsoever and frankly disagree...BUT here goes — can anyone say with certainty yes/no if this indeed could be from an E28 M5?

To me it appears more like a piece from a Harbor Freight tool but I have to ask...but I’ve been wrong once (maybe twice :-D) before in life...

(Thread soon to be started on the issue at hand - thanks in advance)

[vinceg101]

You are not alone.
I found one of these little suckers in my M535i that I never could identify nor trace where it came from.
At the time I swore it came from the the brake system hydraulics but that was discredited. It obviously wasn't that important since I never put it back in and hasn't been missed in the subsequent years.
I still have this in a drawer in my tool chest.

[DiseaseWithNoCure]

Holy crap.

This is like finding out I have a long-lost sibling or something - I’m in total disbelief that you even included a photo hah!

Well...guess it IS a BMW part — now hopefully someone can identify that location or part number and we’ll really be set!

[dsmith]

Broken tstat internals?

[austin8753]

Broken tstat internals?

sorta looks like the internals of the auxiliary thermostat, found on US spec e30s.

[Preyupy]

It looks more like a one way valve or blow off valve but I don't recognize it. What is the diameter? Neither picture gives any kind of reference as to size.

[M5BB]

I've totally rebuilt a couple S38 and M88's and have never seen that in or on an engine.
Some other parts of my M5 have never been apart so can't positively say it didn't come out of car.

It does look like a valve of some kind.
I have totally rebuilt my master and hydro boost and never saw that their either.

I'll send to a friend mechanic that has worked on BMW's all his life and see what he thinks?

Gary

[jdb]

This was many years ago:
I do believe I have seen that part laying on the floor under a car that just had a accumulator (cannon ball ) replaced.
Most likely fell out of the DS regulator.

Jeff

[Machtig]

The part in question is part of the brake servo unit (p/n 34331156925 ) forward hose nipple. Based on realoem.com I do not believe it is available separately from the servo unit.

[vinceg101]

I KNEW I wasn't crazy that this didn't come from the brake & hydraulic system.
I've been running years without it with nary an issue. I wonder if it's worth pulling this out and installing it back in.

[Machtig]

I'm not completely up to speed on what that servo unit does, but I would wager that spring part helps maintain pressure in the system if the engine stalls or something? Or maybe limits pressure?

[Aldo525]

I KNEW I wasn't crazy that this didn't come from the brake & hydraulic system.
I've been running years without it with nary an issue. I wonder if it's worth pulling this out and installing it back in.

That part is a "check valve" on the low pressure side, where the oil flows into the reservoir.

Not having it in place means that probably every time the brake is pressed, there is a return vacuum (oil) from the reservoir to the booster, but it shouldn't be a serious problem since you have been able to function without that valve for so long.

[vinceg101]

Not having it in place means that probably every time the brake is pressed, there is a return vacuum (oil) from the reservoir to the booster, but it shouldn't be a serious problem since you have been able to function without that valve for so long.

Other than making a potential mess by disconnecting the hose and pulling the nipple out, it's simple enough to do. It serves a purpose (how much remains to be debated).
Thanks for the ATE diagram.