Brakes seem sluggish to apply when panic braking???

[brutpwr]

Any reason the brakes on my 99 Tahoe (GMT 400) are slow to apply if try slamming on the brakes hard and as quickly as possible? Brakes completely fine under normal brake loads pedal feels normal but if you try just slamming on the pedal quickly and firmly you get a hard pedal that seems to go down slowly before getting full braking. Probably lasts less than 1/2 second but you can use full leg force and it does not seem to go down any quicker. Needless to say it seems a bit dangerous you can't get full force right away. No ABS or any codes. Bad or defective booster? I just replaced this about a year back don't recall for sure but I think it was an A/C Delco from Pep Boys. I can practically get a leg cramp trying to push down the pedal quicker. Truck slows immediately but not with full force til the pedal travels furthur down which like I said takes almost a 1/2 second. Is this the quick take up or the ABS acting up? Tahoe will engage the ABS on the front wheels just not like "right now"...

 

[redfishsc]

I have the same problem on a 99 C1500 Suburban. However I do not have this problem on my 99 K 1500 Suburban. Both have the same brake system.

I put a new master cylinder on the C 1500 hoping that the master cylinder was just mushy. With a truck off, it did not build pressure as much as the other truck did, trying to get a firm pedal. So I assumed it needed a new master cylinder. Unfortunately that didn't seem to change a thing.


I had the brakes bled at a local shop that uses the scan tool to cycle the ABS to purge the air out of the lines, and that actually did make a big difference for a month or two, but now but now they're mushy again.

You can hear an audible hiss when you do a panic stop. I honestly cannot tell if it is the brake booster or the master cylinder, it does not sound like air hissing out of a small hole.


One thing you definitely need to do though, is rule out rear drum adjustment. Poorly adjusted rear drums can cause the same feeling. If you haven't done it lately, pull the rear drums off, remove the little star adjuster, clean it up with some brake clean. Then put it back together with some caliper Glide. Adjust them nice and tight, take it for a drive.

 

[Supercharged111]

Rear brakes out of adjustment will cause this.

 

[brutpwr]

Ok I'll check the rear brakes. I recall having a hissing sound for a little while a short time after I installed the master cylinder. I think it only made the sound if you pushed the pedal down real quick like when you panic brake but it no longer makes that sound anymore. Maybe that was a sign something is a miss with the booster. I tested the pedal a bit over the weekend and I did notice I can apply the brakes faster if I don't slam my foot on the pedal. But either way your still moving 20 to 40 feet at highway speeds before you get full braking which could lead to an accident. I'm leaning towards a defective brake booster but will check the rear brakes first.

Jason