strange brake noise
 

I am not sure if I can accurately describe this, but here goes...

my brakes work fine with no noises, except right after I have to back up for some reason. When I do back up, the brakes are real spongy. After I start back forward and hit the brakes for that first time, they will make a loud click noise and the pedal is still spongy. Sometimes it's just one or more fronts, some times it's the rear too. After that, they are back to normal firmness with no noises until I have to reverse again.

It is aggravating and embarrassing. I cannot figure out where the noise and sponginess is coming from. They have been bled and flushed several times.

Any ideas?

Have your looked very closely at your Caliper Mounting points? Maybe cracked or Pin Cracked. Sounds dangerous though. Especially if the Caliper goes flinging everywhere at Highway speeds.

what is most likely the problem are loose wheel bearings,
This situation to be fully diagnosed includes removal of the hubs, to inspect the lower seating area of the inner wheel bearings.
You will probably find that the inner wheel bearings are loose on the seating area, thus allowing the hub to also move when the bearings are adjusted per the book with a lite pressure being able to move the washer under the nut.
That said dont try to make the bearing preload tighter to take up the slack, just adjust them and get used to the way things work with the additional play in the hubs.
The only way to fix this is the replace the wheel bearings and the spindles.
I suspect that the spindle metal isnt as hard as it could have been , as i have seen many spindles with worn inner seating areas

Thank you for the replies.

Some more info: I have had all 4 calipers off to inspect. Everything seems fine there. I have also inspected the bearings to the extent that there is minimal play in them.

What is strange, is the lack of brake pedal in reverse. It feels like all the fluid is out of the calipers when in reverse, needing one good pump to get them back up when starting forward. The sound is like the pistons are being forced out quickly and slamming into the pads.

Is there some kind of check-valve in there somewhere that could be leaking back when going backwards or could it be something with the ABS?

It does not feel unsafe, as I am not going that fast when reversing and that is the only time I am having issue.

Thanks again.

Chris

it seems like the brakes are independent of wich direction you are going. so it would almost have to deal with somewhere around where the tires are, something with the calipers or something, not really an electronic issue. when did you last have the calipers and bearing inspected? you said you have had them off but when was that? maybe something went wrong since then?

yep, that's why I am baffled. I pulled the calipers and inspected the bearings a few months ago, when I noticed the sound. I had not messed with anything previously that I could have screwed up to create this.

While taking a potty break :cool:, I developed a new hypothesis: with this only occuring when moving in reverse, the stopping power will be directed towards the rear brakes and calipers. Now, there is no evidence that the rear rotors (or front for that matter) have been replaced. Is it possible that the rear rotors (and possible fronts too) are thin to the point that it feels the brakes are spongy when they are the ones responsible for slowing or stopping the cars momentum, and the sound is the pads reseating? I am also wondering if the parking brake has something to do with the sound.

I am going to stop and buy something to measure the thickness of my calipers tonight and I will post back. Incidentaly, anyone know off the top of their head what the thickness range is for front and rear rotors?

SmileWavy

just pull the hubs and inspect the spindles for wear, if worn then the wheels will push the pads away from the rotors when you change direction, this a common thing with worn parts.

ah, that makes sense. New spindles sound expensive. :(

You can always go good used and warranted by 928 Intl.

Check your ABS sensors and make sure they are clean. I have a simular problem with my 86.5 for some reason when in reverse the ABS will cycle very quickly.... only happens in reverse and gives me simular experience. I'm planning on doing my torque tube soon and will dig into it at that time.

are you getting a soft peddal and click noises when you apply the brake?

We are also on our 86. Especially when just starting up and backing up. Have it on jackstands now. Noticed that left rear brake isn't even holding to resist transmission (was running car in gear on stands during fluid change).

I think there is air in the system, maybe originally caught in the antilock unit after carefully doing a 4 caliper rebuild. Will bleed brakes well and report back.

Get soft pedal and a brake clunk from front, usually left. Also matters how steering wheel is turned. Might have a brake line with internal collapse, but not sure I understand why its doing what its doing.

Bearings will be next after the bleed.

good luck!

I checked the bearings last night and they were a little loose - faint click when I pull on the tire (forget if it was 9 and 3 or 12 and 6). The other suspension parts were nice and tight (that's what she said). Looked to tighten but they were snug. They are now added to the list.

I bled the brakes again, but no change. I read about getting air in the ABS, and not being able to get it out. This may be something we have to live with. :(

what did the spindle inspection show??

The pedal pulses and you can feel the pump activate then it stops. It only happens on the initial push of the pedal. I am theorizing that there is some crud around one of my rear sensors that triggers the ABS.

the spindles looked fine, I made sure the bearings were adjusted properly, and I cleaned the ABS sensors. There was some improvement, but it's still not perfect.

could just be a crap load of air in the system. may try another flush.

What are you all using from brake fluid. I'm currently using Castrol Low Moisture (or something like that).

I use the blue racing stuff available from the major 928 suppliers.

when bleeding/flushing the system, are you starting with the right rear, the left rear, then right front, then left front?

is the master cylinder original equipment, or has it been replaced/rebuilt since the car was built in '86....? (something to think about >>>> how old is your stuff????)

--Russ

I have considered using the blue or gold racing fluid, not b/c I race but just to make it easier when flushing the system.

yes, I started at the furthest point and worked my way up to the master cylinder, which is original.

I don't/wouldn't race mine either, but the purchase was convenient. when I first flushed my system, it was a real shock to see all that black/goooey fluid come oozing out--probably had never been changed since the car was built.

keep searching.....:)

--Russ

I haven't taken a potty break since 1967 when I was 2 years old, been taking a dump ever since. http://forums.pelicanparts.com/support/smileys/lol2.gif

You're amongst friends, no need to be so formal.

Bleeding by itself had no effect on the spongy brake pedal on my 79. Flushing out the old brake fluid is what finally cured it.