Question about brake shutter

[2K6TBSS]

Hey all,
In my 99 Denali I am getting some brake shutter (feels like ABS is kicking in), but only when the temp is coldish. I only notice this when the vehicle is cold, and the temp is in the 60s or lower. When the brakes warm up, they work fine.

I have replaced the rotors/pads with no luck. I then tried to bleed the brakes, but the fluid looked good, and found no air in the lines.

Does anyone else have this issue, or know what the resolution would be?

 

[grimm]

There could be air in the ABS system. If you bleed the brakes, that part has to be bled as well (either by manually engaging the ABS system while bleeding or using a scan tool to engage the ABS, again while you are bleeding). If that's not the issue, you could try replacing the ABS sensors, or looking at the calipers, to see if the piston is malfunctioning. You can check your wheel cylinders in the back as well.

 

[2K6TBSS]

I haven't bled the ABS system yet. My only question about that would be why would it only happen when the brakes are cold? I would guess that air in any of the brakes lines (or ABS system) would show this problem more consistently. Now that I am seeing 90+ temps during the day, I have not had a single issue. When I was down in Capitola last weekend the temps were in the 60s and I was getting brake shutter for about the first 5 mins of driving.

I will look into the ABS bleeding though.

 

[grimm]

Yeah, those were just some things to consider. As for the change in performance when its hot/cold : Metal Expands when hot. As such, something may be out of adjustment to the point that it cannot function properly until heated up. I know that's not much help, but its worth considering. Look over your entire brake system including your ABS system.

Does this happen when you apply heavy pedal force? Does it only happen with light pressure? Does it actually feel like the ABS is engaging or does it feel different? I know you said it only happens when cold, but are there any other conditions that could help pinpoint the problem? Either way, good luck.

 

[2K6TBSS]

It does feel like the ABS is engaging when I hit the brakes. I have noticed that it doesn't really matter about the speed I am traveling, just the temp. However, I have noticed it's more dramatic when going slow (below 30 MPH). When you apply pressure to the brakes, light or heavy the pedal feels like its falling away from you (like when the ABS is activated).

As of right now that is all the information I can provide, as I have only had the vehicle for about 1.5 months, so I haven't really experienced a lot of "colder" temps to make this happen. I just know that it happened every morning when I was in Capitola (colder weather), and it happened 3 or 4 times when I was driving in the am around my house (around 60ish temps) in the morning.

 

[grimm]

I would definitely look into the ABS system again : sensors, actuators, etc.

You might also check for any pinhole leaks in your brake lines or hard lines, as those can swell when warm, masking the problem under moderate braking conditions. Also check fittings and connections around the master cylinder. Something is definitely not normal; your brakes shouldn't be doing that. Anyways, I hope you figure it out, good luck... from a fellow Bay Area guy.

 

[2K6TBSS]

Thanks bro! I will start looking into the stuff asap!