Brake puzzle, new to the e24

[potshot]

I recently acquired a 1982 633 after about 10 years with e30s. When I first got it steering was impossible and brakes were about the same. I learned that it had hydroboost, saw that the fluid was very low and refilled and exercised the steering and brake pedal and everything has been fine with short local trips for a couple months.

Two questions;
1. Driving home from my first 40 mile highway trip about a week ago, I had to make a panic stop and successfully avoided a collision, although I locked up the brakes and put flats on the front tires. First dumb question; would this car not have anti-lock brakes?

2. Front tires replaced and on a local BMW club outing with significant stop and go traffic for about an hour+ and then traveling down a local highway at about 60mph, I lost brakes completely. Thankfully I had the room for an e-brake stop. My pedal went to the floor, and I did have a whiff of hot brake fluid, but I saw no obvious leaks and the brake reservoir was at a good level. After getting it towed home then going inside for some lunch, I was going to ease the car into the garage only to find that the brakes are pumped up, feel decent and stop the car (at least at low speed in front of my house). What's up with that?

I see there's a brake accumulator test I can do, and I plan on doing that but now I'm looking at my HB reservoir and I see that it's about half full. Clearly there's some sort of leak there, but should I fill that up some before I start my test? How much? Obviously I'll need to locate that leak but would like to sort the brake operations first.

I figure if it's the accumulator I'm supposed to replace the filter in there as well, but I'm not sure if a bad filter would cause problems on its own.

Any thoughts on this, other than I got lucky two weekends in a row? lol. Be gentle, I'm not a mechanic but have enough experience wrenching to get me by. Any advice is appreciated!

[Ralph in Socal]

Welcome to the madness. 82 did not have antilock brakes. That started in 85

82 is also the changeover year from Series 1 to Series 2. By saying you have a hydrobooster, it tells me the brake system is Series 2. Hydroboost is known for leaking and we have a known rebuilder of these units. JCS is a member here and he is very well versed in the e24 systems

Loosing the pedal after spirited driving or hot brakes is an indication of old brake fluid that has absorbed moisture. Basically causes water vapor in the calipers. Vapor goes back in solution after cooling down so you're left scratching your head. BMW recommends brake fluid replacement every 2 years

Use DOT 4 fluid to flush the system out but that may not be sufficient. The calipers corrode internally from the moisture in the fluid and may need to be rebuilt to get all the moisture out.

Hydrobooster works from the Power Steering pump. Specific procedure to check reservoir level. With engine off, pump brakes continuously until brake pedal is solidly firm. That empties the brake bomb (accumulator). Level in reservoir should be 10 mm from top. Good luck

Ralph

[plip1953]

As well as the above, which I agree with, I think you might do well to suspect the operation of the master cylinder insofar as the seals might be passing fluid, especially when temps under the bonnet get pretty hot.

[potshot]

Thanks,

I'll definitely flush and replace with good fluid. I'm betting that's good advice on the master cylinder, I'll probably just replace it while I'm going through things.

I appreciate the coaching

[86_6series]

+1 on the master.

[potshot]

Thanks again for the advice. I suppose I'll need to identify the master since I've been reading the the series 1 masters can be rebuilt, but the series 2 not so much. Does that sound accurate?

[Ralph in Socal]

Thanks again for the advice. I suppose I'll need to identify the master since I've been reading the the series 1 masters can be rebuilt, but the series 2 not so much. Does that sound accurate?

That's just that start of the differences. Series 1 brake calipers are 4 pot up front but the upper and lower chambers are separate. The Series 1 master uses the front piston to feed the upper chambers of the front calipers and the rear piston feeds the front caliper lower chambers along with the rear brake calipers

Series 1 is a complicated system while Series 2 is straight forward. I have never seen the Hydro Booster used for Series 1 brakes. Doesn't mean it wasn't done, I've just never seen it.

Ralph

[GRNSHRK]

If I may, I would like to add a bit I learned from another board member

it is true that the series I M/C's can be rebuilt, because they have a retaining ring holding the seals and whatnot in place

But from what I was told, the later series II M/C's are sealed and therefore cannot be dissembled

I can vouch for the fact that series I versions can be taken apart, I cannot speak for the latter

[bobbit4447]

I am in the process of dismantling the MC on my Series 2 and also questioning if they are repairable. The issue for me there is a pin, locating the stage 2 plunger assembly. How do I get this out ? From what I see the bore is OK , seals are available, so I want to repair if possible. TIA

[bpoliakoff]

If you don't want to go new, look up WhitePost Restorations. IIRC they sleeve the cylinder in stainless and do a total rebuild.