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Chris
Chris, Shop Foreman
Category: Jeep
Satisfied Customers: 3172
Experience:  Jeep Certified Master Tech
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I can be driving at up to 70 MPH and without warning it

Customer Question

I can be driving at up to 70 MPH and without warning it feels like my Jeep slams on the brakes then immediately resumes. Meanwhile, my face nearly hits the steering wheel. I was out of my home town when it happened so I took it to the Jeep dealer. It was Saturday and all they were doing was service. The person at the service desk said it sounded like a caliper and to take it to the tire dealer. The tire dealer took off the wheels and said they could find nothing wrong with the brakes. NOW WHAT?????
JA: How old are the tires? And have they been a problem in the past?
Customer: The tires are 3 days old.
JA: What is the model/year of your Jeep?
Customer: 2004 Jeep Grand Cherokee LTD
JA: Are you fixing your Grand Cherokee yourself? What have you tried so far?
Customer: I'm not fixing it. I need a hint. The Jeep dealer didn't know and the tire dealer didn't know. Les Schwab also does brakes.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I'm an old lady and would not know what to ask
Submitted: 26 days ago.
Category: Jeep
Expert:  Jared D replied 26 days ago.

Rather than a brake issue I would be more suspicious of a transmission issue. The brakes can't really apply themselves- they don't work that way. The transmission can however lock up internally and make it feel like the brakes are on if it is starting to fail. The 4wd transfer case could as well.

How often does it do this?

Customer: replied 26 days ago.
It did it 5 times in a 45 mile trip
Expert:  Jared D replied 26 days ago.

It's an automatic transmission, correct?

Customer: replied 26 days ago.
Customer: replied 26 days ago.
My grandson took it to a car parts store & plugged it into a diagnostic machine. That didn't show anything.
Customer: replied 26 days ago.
Jared, are you still there?
Expert:  Jared D replied 26 days ago.

Sorry!

I got pulled out into the shop for a bit there.

I think there is something failing in the transmission, transfer case or differential. Since there was no check engine light set, I would say it's likely a mechanical issue.

I think the best bet is to have a transmission shop or drivetrain shop check it out. I'm willing to bet that whichever parts is failing likely has metal chunks or shavings in the fluid.