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Hi All, In my GMC truck 1500 Sierra, it makes an abnormal noise under the brake pedal area while pressing it. The sound comes directly from interior and its like a whistle sound and called sometime a hissing noise. The brake system functions properly and without any defects except the mentioned noise. Is it possible from the brake booster? or could be from other sources? Appreciate sharing your experience feedback in this problem. Regards, Abdulla brake gmc.xspf
Hey everybody...I just now joined the forum just to pass along a decent, easy fix for the "flexing" gas pedal in the 2014-2018 Sierras and Silverados. I stumbled across this board researching this issue that I discovered on my new (to me) 2017 Silverado Z71 5.3 that I just bought about 4 weeks ago with 788 miles (yeah, seven hundred eighty-eight!) on her. Upon starting from a stopped position (such as coming off a stop bar at a traffic signal), I was a bit bothered by what I can only describe as a "hesitation" of movement of the truck, where pressure on my right foot on the accelerator that wasn't immediately (and proportionally) resulting in matching acceleration of the vehicle. This is the same issue described in other posts on this board that has been remedied with (among other things) by placing cut pieces of paint stirring sticks behind the plastic "anchor plate" that is affixed to the firewall, and where the accelerator sensor is bolted on to. I had plenty of flex in mine, on the order of probably 1/2" to 5/8" at least where the mounting plate would flex and finally "bottom out" against the firewall before the accelerator would begin to respond to input. The fix I came up with was a pretty simple one, and I wanted to pass it along: On the black plastic mounting plate (Those of you who have researched this issue probably already are familiar with this piece I'm referring to), near the bottom where the gas pedal mounting bracket is affixed, there is an unused hole to the lower left of the pedal bracket. I used a 1/4" x 20 bolt (about 1.75" in length) with a nut and washer pre-threaded onto the bolt, and slipped another 1/4" nut on the backside of the black plastic mounting bracket (using 90 degree needle nose pliers to hold nut in place while finger-tightening bolt...this was the most tricky part). This required trimming just a little bit of the floorboard insulation (see photo below) to make it easier inserting the nut behind the plastic piece. Then I simply tightened the bolt into the nut on the back side, which results in approximately 1/2" or so of the bolt protruding through the backside of the black plastic plate and bottoming out on the firewall. The result is MUCH less flex in the lower portion of that plastic mounting plate when pushing on the accelerator. I really was skeptical of how much difference this would make, but WOW...after driving it, the difference is NIGHT and DAY! That "dead zone" where I was having to push unnaturally hard on the accelerator pedal before seeing any response from the engine is GONE! Now I can lightly push on the pedal and the response is IMMEDIATE and smooth! Attached is a picture showing the finished product (sort of helps what I've tried to describe above). I should have taken a few more pics during the procedure, but I was sort of on a roll and didn't think about taking any until I was finished. Hopefully this fix comes in handy for others of you having this same issue related to the "spongy" accelerator mounting plate. Kind of disheartening to have to fix my ~$36K truck with a $0.50 nut and bolt, but at least it fixed my issue!
Got an interesting one for the forum. After the truck (2016 GMC Sierra) has been sitting a while (usually over night or for a few hours) the pedal let's out a nice squeak. On rare occasions I can get it to do it twice in a row, but most of the time the squeak is only for the first press then is gone for all the other presses. Normal daily driving I don't hear it, it's only the first press or when I have to hit my brakes hard (ex, cut off by someone). My local dealer service department (who's treated me well and has good mechanics) looked at it and said they can't repeat it enough to truly diagnose it. Some squeaks are real quick and others last about 2 seconds. The only way I can describe it is like a relief valve letting some air out, but with a squeak. Sometimes I can hold the pedal in place after depressing and the squeak continues to let out. It's not like a metal plunger rubbing on a rubber boot as I depress the pedal, plus I would be able to make the sound every time if that were the case. Below is a video I took on two different occasions, they are looped a couple times. You'll hear what I'm talking about and see that it's gone on the second press. I did have the vacuum pump replaced due to the recall about a year ago, I noticed it after that but the dealership said the pump and vacuum is holding well the entire time, even when it squeaks. They only guess they had was to replace the brake pedal assembly or the brake booster, but admittedly said that would just be throwing parts at it. Just got the truck back today, didn't get charged for the diagnosis since they couldn't figure it out. Now I'm turning to the forum. Any idea what's going on?!?