Brake pedal hard, no power assist?

[Hoffbrohaus]

I just bought my car and the guy said "That's the way they are" with a 735i MC & Booster. From what I have read on the forum that's not true. The pedal is hard all the time and requires a lot of force to stop. My friend that drove it says there is no power assist.

My cruise control also doesn't work, doesn't this run off of the booster or at least use vacuum somehow? The car is running rich as well, strong smell of gas in the exhaust, not sure if related but again maybe a related vacuum issue?

I just don't think it's the booster or MC since those are newly replaced, so what could it be?

[E30_fiend]

You either have a gigantic vacuum leak at the booster or your booster is bad.

As for the cruise control, it doesn't have anything to do with the master or booster but it does have to do with the brake light switch. Make sure yours is adjusted correctly. The cruise not working can also be attributed to a faulty or missing clutch switch. Both aforementioned switches are mounted on the pedal box assembly under the driver's knee bolster.


Taylor

[Hoffbrohaus]

Thanks I'll update the thread once I track the problems down. 1st I need to address my leaking oil pan :(

[AndrewBird]

There is a check valve at the booster. Make sure it isn't installed backwards (not sure it can be) and that it is functioning correctly (flow in only one direction).

[Hoffbrohaus]

I think the vacuum is ok I read somewhere if you pump the pedal before turning on, then with your foot on the pedal start the car and the pedal should drop slightly. Which it did.

So I decided to really test the brakes and found abs isn't working. Took it to a parking lot got up to speed a few times and hit the brakes as hard as I could, never engaged. My abs light comes on in the acc position and turns off after ignition. Like it is supposed to. Reading all the threads on abs it looks like it may be the abs cpu? Should I check anything else before replacing this? If the relay was done the light would stay on. Same with any wheel sensors. Could non working abs also lead to my issues with the hard pedal?

Oh yea one other thing. The check light for the brakes comes on whenever I start the car and then goes out when I press the brakes. I didn't think anything about it but thought I should mention it.

[AndrewBird]

When you were testing the brakes, were you ale to get at least one wheel to lock up? The ABS won't engage until there is a wheel locked.

The brake check control is a normal thing. Nothing wrong with it.

[Hoffbrohaus]

I couldn't get a wheel to lock because even standing on the breaks would bring me to a slow stop. But that's interesting, abs may be fine once I figure out what the overall problem is. I think I will find some gravel for the next troubleshooting step. I'll see if all 4 wheels are breaking and maybe the slip on gravel will engage abs.

[Hoffbrohaus]

I found a dirt lot and tried it out. Sure enough abs works. Fun rally car too :) I'll have to get it on a rack and check each caliper I guess. At least I can cross off one possibility.

[Hoffbrohaus]

If I want to check vacuum pressure related to the booster where should I check it & what should it be?

I figured check before & after the check valve. The Bentley manual says to take the valve out and blow through it too. Can I check something on/after the booster? And again what should the vacuum pressure be?

btw, the PO put in cross drilled rotors, SS lines, new calipers (not sure what kind), along with the 735i MC & Booster.

[Hoffbrohaus]

Update in case it helps anyone in the future.
Checked booster by pumping brakes with car off, then with foot on the pedal turn car on. Pedal drops slightly, booster working. check.

Hooked up vacuum gauge to intake with car running, vacuum close to 20, according to Bentley that is good (15-22). But noticed when you press the brakes vacuum drops to 15-17. Which may be normal since the booster is pulling vacuum.

Flushed brakes completely, checked pads & rotors, roughed up in case of glazing. No better.

So I ordered a vacuum booster from a fellow r3vster. Last night in preparation for its arrival I pulled out the master cylinder. Low & behold there was no o-ring between the MC & booster. As the Bentley manual says: "A faulty O-ring can be the source of a vacuum leak, causing a reduction in braking performance or an erratic idle speed." I would say no o-ring = vacuum leak = poor braking performance. Thanks PO ;D

Ran down to o'rielly and picked up an o-ring, will re-install tonight but I'm pretty sure that's it!

[Hoffbrohaus]

Nope. Didn't do it. Will replace pads just in case. Then booster.

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