2017 Grand Cherokee TrailHawk: brake issue? - JeepForum.com
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post #1 of 17 Old 04-03-2020, 06:51 AM Thread Starter
2017GChTH
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2017 Grand Cherokee TrailHawk: brake issue?

Hi all,

I was just wondering if this is an issue and that I need to have it check out. Every time when I am about to start my car I notice that it's hard to suppress my brake paddle (like when you pump your brakes a few times when the car is off). I'm able to start the car up just fine and once it starts the brake paddle is back to normal. I was wondering if anyone notice this issue and the possible cause of it? If there are any questions, feel free to ask. Thanks!

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post #2 of 17 Old 04-03-2020, 09:19 AM
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Have you ever had to control a vehicle that has stalled but is still moving? No power= no power brakes. I think that is all it is....tho, I am by no means a mechanic
I have the same jeep--I'll pay close attention next time I'm in it just to check.

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post #3 of 17 Old 04-03-2020, 10:03 AM
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Thats a classic sign of a booster or vacuum leak problem, often the booster check valve (a relatively inexpensive part). After turning the Jeep off, the booster should have enough vacuum reserve for a few pedal pushes, eventually losing the vacuum reserve and vacuum assist, so the pedal feels hard. So something is draining off the booser vacuum.

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post #4 of 17 Old 04-03-2020, 11:31 AM Thread Starter
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Nope, everything works just fine once the car start.
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post #5 of 17 Old 04-03-2020, 11:33 AM Thread Starter
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Thanks, ColdCase. I assume I would need to take my jeep in?
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post #6 of 17 Old 04-03-2020, 12:44 PM
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If its under warranty I would. If not, you could look for a vacuum leak first and perhaps try changing the booster check valve, if you feel comfortable doing that. The valve is on the booster end of the brake vacuum hose.

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Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #7 of 17 Old 04-03-2020, 02:05 PM Thread Starter
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changing the booster check valve doesn't seem hard (I youtube it), but I can't find where it's located on the jeep...
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post #8 of 17 Old 04-03-2020, 02:27 PM Thread Starter
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Look like it's behind the plastic shield where the brake fluid is at... Had to remove it to see the valve that's connected to the booster.
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post #9 of 17 Old 04-03-2020, 05:09 PM
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Am i missing something? after a tap, the brake pedal is always harder to depress until the jeep is started....

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1997 GC Limited Beach Buggy (Deceased....RIP)
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post #10 of 17 Old 04-03-2020, 05:55 PM
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It should take three taps or so, if everything is working at high efficiency. It may pump up a bit, feel different as the vacuum reserve used, but will not get full hard until the vacuum reserve is used up. Vacuum can leak over time, which diminishes the reserve.

Instead of replacing parts, if you have a vacuum pump/gauge you could troubleshoot a bit. Some will blow through the check valve, it should only allow air one way. I'm not sure if the 2017 is subject to the booster recal, this is where the booster rusts out and leaks vacuum.

A quick way to check the booster:

- With the engine not running, pump the brake pedal several times to remove any vacuum from inside the booster.
- On the last push of the brake pedal, hold moderate pressure on the brake pedal. Don’t push like you are panic stopping, but simply hold pressure like you are sitting at a red light.
- With your foot still on the brake pedal, start the engine and pay attention to what happens to the brake pedal. One of two things is probably going to happen:

1) If the pedal drops slightly, that means that the booster diaphragms are working correctly as the engine starts to create vacuum and the diaphragms are physically holding. At this point, it can be assumed the booster is working correctly.

2) If the pedal does not move at all, that says that the booster does not have the ability to hold the necessary vacuum inside or the two-way valve internal of the booster is not functioning properly
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post #11 of 17 Old 04-03-2020, 07:13 PM
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that's what i'm saying ...the op states "(like when you pump your brakes a few times when the car is off)"...then he sez after start up everything is normal. I think he's chasing a problem that doesn't exist...

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post #12 of 17 Old 04-03-2020, 10:02 PM
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What the OP is saying that he comes out to a hard brake pedal in the AM without pumping the brakes (but it is hard as if he had pumped the brakes).


If it under warranty then he/she should take it in.
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post #13 of 17 Old 04-04-2020, 06:33 AM
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Ok...was beginning to wonder if i had a problem also....cabin fever...

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post #14 of 17 Old 04-04-2020, 09:00 AM Thread Starter
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ceb1: you are correct
Coldcase: I did the test you mention and it look like my booster diaphragms are working correctly. I must have a small leak somewhere... probably just need to replace the valve.
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post #15 of 17 Old 04-04-2020, 09:44 AM
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Quote:
Originally Posted by Homer1 View Post
Ok...was beginning to wonder if i had a problem also....cabin fever...
As long as it isn't COVID fever...
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