Brakes lock for split second over 50 MPH?

SKIMAN

MEMBER
2003 JEEP GRAND CHEROKEE
4.7L
V8
2WD
AUTOMATIC
165,000 MILES

When driving over 50 MPH, the brakes lock up for a split second and then release. I am unsure if the brakes are locking or if the transmission is failing to shift into a higher gear. It only seems to occur over 50 MPH. It doesn't seem to matter whether I am actively accelerating or coasting. I did put an OBD ll on it (while parked but it doesn't show any saved codes) and I am guessing I may need to have it hooked up while driving and catch it in the act.

I am leaning toward an issue with the transmission, but I am having a hard time finding anyone with this particular symptom. I realize most issues show up in the lower gears as those are worn faster than the higher ones but is there a way to test it?

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,254 POSTS

Hi,

Based on your description, I don't feel it is brake-related, but anything is possible. On the other hand, it could be something related to the overdrive circuit.

I agree with you about live data being used to identify what is happening. Also, you may want to consider having the can-bus scanned for codes.

CAN stands for controller area network. Basically, all the different modules are tied together via a few wires. This type of scan will retrieve codes regardless of the module storing them. In this case, it could be in the transmission control module, ABS module, and so on.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Let me know if that is something you could do or have done.

Take care,

Joe

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Sunday, January 29th, 2023 AT 2:45 PM

SKIMAN

MEMBER
4 POSTS

Thanks for the response. Interesting that you mentioned the overdrive circuit because there seems to be some lag with the OD light illuminating and/or turning off. I've noticed this issue for some time now but it was only a couple of seconds of lag and didn't appear to affect the operation of overdrive, so I didn't give it much thought. However, now when I engage/disengage OD (e.G. While going uphill), the RPMs will actually rev higher for a few seconds instead of lower when I put the vehicle back into overdrive. I will take my foot off the gas at this point to allow the RPMs to drop before giving it gas again. Now, I don't know if this is related to the sudden screeching of the tires at higher speeds or if this confirms a definite issue with the transmission, but I am planning to replace the In/output speed sensors. I don't plan on throwing money at the issue by replacing parts but this is a simple replacement and inexpensive, so I figured it's worth a shot.

The only way I can check the Can bus is through a garage or dealership. I don't know anybody with the software/equipment to do this.

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Sunday, January 29th, 2023 AT 8:37 PM

JACOBANDNICKOLAS

MECHANIC
108,254 POSTS

Hi,

It does sound like it may be transmission related. By chance, is your scan tool a live data tool? If it is, connect it and go for a ride to see if anything shows up.

Also, let me know about the speed sensors. I'm interested in knowing.

Take care,

Joe

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Monday, January 30th, 2023 AT 4:01 PM

SKIMAN

MEMBER
4 POSTS

It is a live tool. I will plug it in and hopefully it will log some codes.

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Monday, January 30th, 2023 AT 5:56 PM

JACOBANDNICKOLAS

MECHANIC
108,254 POSTS

Hi,

Great. Let me know what you find. If nothing shows up, we may need to get a different scan tool, but if it is transmission related, it should work.

Take care,

joe