bjornebo

A couple of weeks ago my brakes on my 97 C4S started behaving strangely. When I step on the pedal it feels like something is causing the pedal to hang-up, as though something in the pedal mechanism was hitting something. This happens before the braking action starts. Once I push past this point and the brakes start to engage, modulating the braking also feels abnormal. When I press on the pedal and braking starts (which is good...) but pressing a bit harder has no effect. Pushing harder does increase braking, but the increased braking comes on "suddenly." When I let the pedal out the increased braking stays until I have let the pedal out past the point where the "sudden" braking came on. It feels like at low braking pressures the brakes are either on or off.

My mechanic checked the pads and disks and brake fluid condition. All were in good shape. He thought that the problem was a worn out brake pressure accumulator which may have leaked internally. He replaced this, added brake fluid, and did a brake bleed. The problem persists. The brake fluid is at the proper level.

Because it feels like the pedal is hanging up on something, I pulled off the plywood cover over the pedal cluster. It didn't look like anything was amiss down there. Also, the hang-up behavior only happens when the engine is running. When it is off the pedal has quarter inch or so travel and then feels solid. So it seems unlikely to me that the problem is in the pedal mechanism itself.

As anyone here experienced anything like this? Or does anyone have any suggestions about how to diagnose this?

TIA for any help that you can offer.

George

fatmike

How old are the rubber brake hoses? Original to the car? If so, I'd consider changing them.

/

k722070

well, you've ruled out the pedal mechanism, and the mechanic has kind of ruled out the later brake system including the pump, accumulator and calipers-
the master cylinder is next.
you could either read a bunch of master cylinder threads or suggest it to the mechanic.

TheBen

How firm is your brake pedal?

pp000830

+1

pp000830

Not really related to the issue but a good idea.

I did this as a DIY job in my driveway using a pressure bleeder & braided DOT hoses. I learned something very important. If you don't have high-quality hydraulic fitting wrenches get some. Brands such as Snap-On or Craftsman. Inexpensive wrenches will flex and mutilate the fittings before they pop loose. Doesn't have to be expensive as one or two sizes are all you need and I have seen individual wrenches for sale on eBay.

Andy

bjornebo

Thanks for the input. The brakes are firm. After doing some additional digging here, I have come to the conclusion that it is probably either the master cylinder or brake booster. Between those two I hope it is the MC as a new brake booster is pretty pricy.

I will also consider replacing the brake hoses as a PM item.

nine9six

Be careful about buying Craftsman wrenches... as of late, Craftsman tools have been made in China and are not of the same quality as the Craftsman of old.

rcg412