Hey guys!

So, ever since I purchased this R53, the brakes have given me the same issue. When I first bought it, the whole pedal was very stiff and it was hard to brake. However, after weeks of just slamming on the brakes, it seemed to get a lot better. Now, I mean "a lot better" but by no means "good". The pedal was always stiff and hard but it just wasn't as stiff. The past 2 months, the pedal has seemed to randomly go stiff and it's pretty hard to stop quickly. Now, the first 1/3 of the pedal is ok, but the rest is really stiff.

I've pondered and pondered the issue and it just seems to always go back to the booster. I've never seen one go bad. One of the things that makes me hesitate is while reading on the forums, people who have issues with the booster seems to always mention this "hissing" sound associated with the booster, but I have no types of sounds like this.

I'm running ceramic pads with drilled and slotted rotors. It should stop on a dime.

Any thoughts?

 

Very stiff pedal sound like the booster is not doing the job of assisting. I suggest you compare the pedal stiffness with engine off vs running. When off it should feel rock hard. With you foot on the pedal and start the engine the pedal will sink slightly, and the pedal would feel softer.

I suggest checking the vacuum supply to the booster first. Evidently there is a check valve:

 

[QUOTE=pnwR53S;4343773]Very stiff pedal sound like the booster is not doing the job of assisting. I suggest you compare the pedal stiffness with engine off vs running. When off it should feel rock hard. With you foot on the pedal and start the engine the pedal will sink slightly, and the pedal would feel softer.

I suggest checking the vacuum supply to the booster first. Evidently there is a check valve:


To be honest, this seems like much more of the culprit than anything! Being as I'm not having a leak, nor is the booster giving me any noises or other problems, it would seem to be a blockage.

I'm going to tackle this issue today.

Do you think I could just get any generic vacuum line at an auto parts store? I have to get this fixed to day as it's really unsafe. I'll get the proper part at a later date.

 

[QUOTE=romero.riche;4343940]Did you perform the tests that I suggested? It is a definite check if you are not getting vacuum.

If so then do the next check, disconnect the vacuum line from the booster and check to see if there is very strong suction when the engine is idling. You should seek experienced help if you don't feel comfortable working on cars.

I will not use any other hoses except the proper replacements for this. It is possible the check valve in yours failed (see above diagram and link to read up on it). I think the function of the check valve is to maintain the brake booster chamber in vacuum when the SC engine's vacuum line turns pressure line.

 

[QUOTE=pnwR53S;4343981]I'm sorry for not mentioning the test. Yes, I did perform it and it responded exactly as you said.

So I took off the vacuum line and it really doesn't to seem very strong at all. I don't have anything to compare it to, but it's definitely not a strong vacuum.

Now, I did notice a hissing sound, so I investigated. I followed the line, it goes through a small wall where the intake filter is, then goes down into the engine. I was able to disconnect the hose before it dipped down into the engine (i think the SC) and it's still not a strong vacuum there. Also, with the car on, I can tell the hissing sound isn't coming from that specific line. However, I'm undecided if it's a hissing sound or just the engine. The closer I put my ear, the more it blends in to the sound of the engine. Below is a video that records the audio pretty well.

youtu.be/UcDxhHbq9yw

I really think this is a vacuum issue now. Any thoughts on diagnosing vacuum issues?

 

[QUOTE=romero.riche;4344038]I think when engine is at idle there is about 15 PSI of vacuum, as my photo here attests.



Since in your tests the foot pedal turns softer and went down a bit when engine is started that likely means you are getting good vacuum at the booster. Very likely the check valve is stuck open - becomes a two way street. I suggest you focus on that.

 

If I have not mistaken, the purpose of the check valve is to allow the vacuum in the brake booster when the engine intake has no vacuum - that is whenever the engine is under boost.

To trace where the hissing sound originates, get a length (3-4 feet) of soft hose and use it as acoustic stethoscope. One end to your ear and the other aim at the suspect area. Be careful with anything that turns on the engine.

BTW, 15 PSI is about the pressure of a badly underinflated tire from neglect.

 

[QUOTE=pnwR53S;4344052]So, I checked the check valve. It was only allowing air one way.

Where would I hook up the gauge at to test the vacuum? Should I expect this pressure right at the inlet to the booster? I could disconnect the hose at test it before the booster.

15 psi is pretty low, so maybe I'm getting that to the booster. The check valve is good. Maybe this is just a booster issue after all.

The main symptom I'm experiencing is that the last 3/4 of the brake pedal range is very stiff. Also, if I'm coming to a light, and I press the pedal a few times instead of just one consecutive press, the pedal will completely stiffen up by the third press.

My issue is definitely not a "leak" in the sense there's no pressure in the pedal. It's that it's just too stiff. I suspect the car was sitting for a long time before I purchased it.

Would a vacuum leak cause stiffness?

 

It is possible you booster has a small leak. It is also possible the check valve is intermittent. You have to try to be more resourceful in your troubleshooting, as the problem may not be clearly black or white. If it were me, I will figure out how I can test the booster for leak. A small leak can disguise it as OK in the test that you performed.

 

Yeah, I agree. Yet, at this point, I think I'm just going to replace the booster and vacuum line to be safe. I'll get a new booster in this week and replace it on Saturday. I rather just be safe. 12-13 hour work days, don't allow for much time.

I need to find some good material on how to properly bench bleed that master cylinder.

That'll be one more issue checked off the list:
-strange oil leak that appears under the oil pan opposite to the tranny
-hard steering
-p1242 code after SC service

 

BTW, I love your project post! Really great stuff on there. I loved the idea of putting in a boost gauge and found the same one on amazon warehouse deals and just got it. I'm going to do a little more research before going with the alta mount, but, honestly, the few extra dollars is probably way worth it. Did you end up liking the Alta mount?

 

UPDATE

It did end up being the brake booster. I just found a $50 used booster and MC. We'll see how long they last....

Thanks!

 

Thanks for the update. I wonder what cause the leak. I have always thought if brake fluid leak from the master cylinder if a piston seal is bad etc might be the cause. Brake fluid attack the rubber diaphragm. Or may simply be too many brake strokes.

 

Yeah, in my experience, it's not usually the brake booster. Yet, I know something was fishy because I wasn't losing pressure and my MC was new. I did notice that the vacuum line with the check valve seemed to be broken, or had some integrity issues. It wasn't completely broken. I just tried to temporarily seal it up but made no difference. At least I'm pretty familiar with my braking system now!

It's stopping so well now! It is about time for new pads and rotors all the way around. They never last too long with the way I drive...