Brake Issue

[gtyates]

I am having an unusual brake issue on my '97 Explorer. It has the OHV engine. So far I have replaced all brake pads, flushed system 3 times, replaced master cylinder due to sinking pedal when stopped, and replaced brake booster due to vacuum leak. The problem I am having is a "spongy" pedal, but only when braking from highway speeds to slow down for traffic. In downtown stop and go traffic pedal is firm, and once I get slowed down for traffic from highway speeds pedal is firm, but while slowing down is when I get a spongy feeling to the pedal. Truck always stops, and does not seem to be taking any longer distance to stop, just the spongy feel to the pedal. Any ideas??

 

[Dilbert5]

When you replaced the master cylinder, how did you bleed the brakes? Did you vaccum, pressure, gravity, bench?

 

[gtyates]

The shop that worked on it did what they called a power bleed. I am not a mechanic, so please forgive my lack of full knowledge. This is such an odd problem, and I do not want to keep replacing parts if I do not need to. I have never had a vehicle have this type of issue before. And this particular shop has always done my work for me, including brake jobs on other vehicles, and have never had an issue before because of their work. I can tell you the fluid was completely flushed and replaced with all new as part of the work performed.

 

[Dilbert5]

I would take it back and talk to them about it, I am sure that they would not have a issue discussing your concerns considering that you are a repeat customer.

 

[gtyates]

Some more info as I try to resolve the braking issue. When I press the brake pedal, not only is it a little spongy (though better after last power flush), but the RPM's do an unusual thing. As I take my foot off the gas pedal to move the brake pedal, the rpm's drop, as they should, to around 800-900, then the raise to 1100-1200 as I am pressing the brake pedal, then drop down to 750 as I am stopping, sometimes a little lower until I stop. Also, when I am parking the vehicle, such as in a parking space or in my garage, the rpm's will really drop to 400-500 range as I turn the steering wheel. Once I straighten up, the rpm's will raise back close to 750 as they should. I do notice driving around town when turning the wheels and stopped at a traffic light, the rpm's will also drop. And the steering is not as smooth as I prefer, but not overly jumpy either. All of this together makes me wonder if this is really a braking issue, or something else. I have no CEL or any other light on. MAF is about 3 years old. I cleaned the IAC a couple of months ago, though it was not particularly dirty when I cleaned it. I am stumped!! Just to remind, it is a '97 4x4 with OHV engine, 134k miles. Any help/ideas appreciated before I just start replacing various misc. parts.

 

[Dilbert5]

Spongy brakes are normally air in the system, the fact that it improved after the last power flush confirms this. How long has it been since the last tuneup?

 

[gtyates]

Tune-up was done about 20k ago. New plugs, new fuel filter, the usual. Also, upper intake gaskets have been replaced due to vacuum leak. I was thinking air in brakes line as well, but the dropping rpm's make me wonder. Thanks very much for your input so far

 

[Dilbert5]

Slight changes in the idle speed are not anything to worry about. If the engine is running well I would not be to concerned. As far as the brakes, I would suggest having them bled again, ask them what they are using to bled the abs unit. I suspect that air got into the abs when they replaced the master cyl. It sounds like they got some of the air out with the last bleed,

And you are welcome.