Brake Problem, Help!

[DroptopSVT]

Ok, so my 2000 vert V6 is eating up front brakes, again (60K miles). I replaced the pads and rotors, all brand new parts...here's my new problem- a spongy break pedal. I bled all the lines and the master cylinder and I can't find a darn problem anywhere. Calipers are good as well. But, what I did notice is that when I was bleeding the brakes, I had a dip in my RPMs as I depressed the brake pedal. This happened everytime, so something tells me there's a vacuum problem somewhere. Has anyone ever come across something like this? Brake booster seems to be fine too. This is frustrating as all hell, as I think nothing is mechanically wrong with the brake system. Any advice is surely appreciated. Thanks all-

 

[SteveC]

Either you have a leaking caliper piston somewhere introducing air into the system or the master cylinder is gone bad.

If a caliper is bad it will generally wear the pad (and rotor) very unevenly.

 

[DroptopSVT]

The calipers look good, it's like the front pads haven't even touched the rotors yet! And that's with about 100 miles on the new ones. I took it to the Ford dealer today, they claim they can't find anything wrong. But, something tells me a spongy pedal isn't somthing to ignore. Anybody else have any suggestions?

 

[n0v8or]

What did you use to coat the backside of the pads to prevent vibration? I've seen too thick a coating of the gel-type compound compress when the brakes are applied, resulting in a spongy pedal feel.
How quickly did you retract the caliper pistons? Did you force the old fluid back into the master cylinder? I've seen master cylinders leak internally after a pad replacement from both these causes.
If you hold firm pressure on the pedal with the engine running, will it continue to slowly drop, or eventually firm up? A continual slow drop is a sign of a problem within the master cylinder.

 

[97v6Silver]

vacume leak... take it to teh brake shop

 

[DroptopSVT]

The brake gradually firms up when the car is running. I used a C clamp to compress the cylinders, nothing to fast though. Possibly the master is going, I'm replacing the calipers on Saturday to see if this will rectify the problem. As for a brake shop...that's where I took it before I took it to Ford today...they found a stuck caliper pin on the rear right, but that was it, fixed it and no difference. Actually, I did apply a lot of brake grease to the back of the pads now that you mention it. How common is it for that to be the problem. This good be the fix! Thanks again all-

 

[97v6Silver]

you have air in the lines if it's a soft peddle no doubt...

 

[n0v8or]

A dip in engine RPMs as long as the is pedal depressed might just be the electrical load of the brake lights on the alternator. Try pulling the brake light fuse and see if it makes a difference. If no difference, and assuming you have a vacuum-operated power brake booster, I'm in the camp with those who suspect a vacuum leak.

The too thick layer of paste is not common, but I have seen it. I've also seen the same thing happen when folks substitute fibre pad shims when the factory ones were metal. The fibre compresses slightly. Air trapped in the system is the #1 cause of a soft pedal. I would bleed them 1 more time after driving for a few days, or have them pressure bled at a shop (assuming you have not done that already).

 

[DroptopSVT]

Thanks for all the info, I may indeed bleed the system one more time. We didn't notice any leaks the first time around so I can't see where air is getting in the system. However, the problem didn't start until after I installed the new front brakes, so could this lead to bad front calipers?? I did use a lot of grease on the pads, but I doubt this is the problem. I should know more by Saturday. Thanks again everyone.

 

[97v6Silver]

riding around with no brakes is unsafe...

 

[n0v8or]

Did you disconnect any brake lines to change the pads and rotors? Ususlly it's not necessary; I just hang the caliper from a spring with a bent section of coat hanger (a low tech solution). If not, the only way for air to enter the system would be the caliper seals. If this was the cause, I would expect it to keep getting worse.

The pads only have to move less than 10 mils (0.01 inch) when braking; if you have a 10 mil thick layer of backing gel, and it compresses to 5 mils under pressure, half of your pedal travel would be used to compress paste instead of the pads against the rotors.

If the old pads were badly worn, and you had to push the piston a long way, a lot of old fluid had to travel backwards into the master cylinder. Did you remove some fluid from the reservoir first to make room for the old? Damage to master cylinders as a consequence of backflow is something I have seen often. Usually, though, you cannot get a firm pedal, even after pumping, when the master cylinder has an internal leak.

Another possibility is that the new pads are made of a softer material, so the pedal feels different (more travel between first contact and full compression force).

 

[DroptopSVT]

I didn't disconnect any lines, just used the hanger method you mentioned. The old pads weren't too bad actually, so I didn't move the pistons much at all. Once the paste is compressed a few times, won't it pretty much be out of the way after that? Would the problem continue to persist?

The new pads are Bosch ceramic pads, the exact same pads I used last time, so pad material is ruled out.

I may take the brake booster apart and adjust the rod to see if this makes a difference.

Also...once last thing I can think of...when I replaced the rears about 6 months ago, I found out pretty quickly that you have to rent a tool from a local auto parts store (Murray's in my case, for free with a deposit), to literally screw the rear pistons back in place. (I actually bent a C clamp while trying to compress the thing). I did notice that when I was turning one of the rears back in place, with each turn, I could hear air..sounded like one of the hoses. Though when I bled the brakes there were no leaks and the brake shop and Ford didn't find anything...just a thought. Thanks again.

 

[n0v8or]

The paste is resilient; that's how it dampens vibration to eliminate brake squeal. It should not permanently compress.

If anything done 6 months ago caused a problem, the problem would have surfaced then, not now.

Are the new rotors also the same brand as those that were replaced?
Do you still have an RPM drop when the pedal is depressed?
Were the pad guides were smooth and greased, and that the new pads could slide in and out freely? Sometimes the ears of pads have burrs, and one end binds in its guide. This causes one end of the pad to make contact before the other, increasing pedal travel between initial contact and full contact.

When there is air in the system, the pedal will feel as if there is a hard rubber ball between it and you foot. Plus if you pump the brakes lightly before braking, the pedal will be firm. If you don't have these 2 symptoms, I don't think there is air in the lines.

 

[DroptopSVT]

Fixed..

Finally all set on the brakes. I applied some anti-sieze compound to the caliper pins and took some of the grease off the back of the pads. Which one was causing the problem, I don't know, but I noticed a pretty big improvement when all was said and one , and I also ruled out a vacuum leak and air in the lines. Thanks for all the input-