Fubar92627

I just bought a 91 Cherokee Laredo 4.0 H.O. and every time I press on the brake I hear a buzzing sound coming from under the hood on the passenger side. Someone suggested that it could be a bad brake booster, or that it is not under the proper compression.

Any advice on how to check if it is bad/going bad/not pressurized correctly? Obviously don't want to buy, and take the time to install a new part for $225 if I can fix it instead. Thanks in advance. I know that some of you have seen every problem under the sun with you Jeeps.

freegdr

Boosters on drivers side time for some noggin pokin.

Fubar92627

Damn... Ok. Hopefully someone here that knows more than me can help me out.

Fubar92627

It has to be something related to the brakes though because the buzzing only happens when I press on the brakes, and it's almost every time I do it...

toasterknight

Could be a bearing or something in that area. Could be a vacuum issue could be nearly anything.

freegdr

Could just be vacuum/electrial related gotta push pedal and start feeling in area thats buzzing. Theres not gonna be any other wat to figure this out.

TwistedWrench

This. Does it do it when you're sitting still, or only when you're moving? Could be something as simple as a PVC valve rattling when the vacuum load changes.

And please do not take this the wrong way, it's not meant to be rude at all. But the fact that you don't know what side the booster is on(same on pretty much every car ever built) is a pretty good indication that you're just getting started on doing DIY mechanical work. I strongly suggest getting a shop manual for your XJ, or at the very least a Haynes manual, sit down and read that sucker like its the bible.

A 91 with the 4.0 is a robust vehicle, odds are the major components(engine, etc) will last you for years to come. But you're likely going to be doing a lot small repairs, all the time. Vacuum and electronic parts are going to crap out fairly often, and familiarize yourself with the basics in doing u-joints, tie rods, etc. Get a decent set of basic hand tools, and learn to love them, lol.

Everybody here will be glad to help as much as we can, don't be afraid to ask questions, or post short vids of weird noises your new Jeep makes.

Fubar92627

Whatever it is I can definitely tell that it is on the passenger side, not saying that I know it is the booster. I have already asked a buddy of mine that has a Jeep and he is the one that suggested it is the brake booster, so yeah. Not only have I spent time trying to track it, but I have had a few others listen and agree on its location.

Also, if you read earlier, I have the Chilton maual for it, but it isn't going to have info for "a buzzing sound in the engine compartment". I also know a bit about mechanic work and know at least how to check/work on u-joints.

DUH! I never thought to post a video. It may be hard to record with the engine running, but I dont have to be moving to get it to happen. The only time it happens when I don't press on the brake pedal is when I start the Jeep, it does it then too.

Thanks for the suggestion about the video!

'90Cherokee

If you have ABS it's the Bendix 9 system, google it, and it's likely the cause of the noise. I believe the pressure pump is on that side and it may be normal, don't recall how much it's supposed to cycle. If you do have ABS you may want to re-post asking about ABS cycling or something like that, may get more applicable responses. Some will scream "GET RID OF IT" while others will say it's fine as long as you keep it working. Getting rid of it properly is more than just taking stuff off. I've heard there's a lifetime warrantee on the system because it's that bad. You might be able to get free repairs, the other option is to remove it entirely as many have. Unlike most ABS systems, when this one fails it has the possibility of leaving you with almost zero braking power. Other systems just revert to non-ABS when there's a failure. I have some replacement parts for it if you find that you need something.

Fubar92627

Most helpful thing I have heard so far! I appreciate all of the info man, I'll have to follow your advice on re-posting. Scary thought about the brkes going out though. If it is ABS do I go to the Jeep dealership to get it fixed? Does it matter it I am not the original owner for that warranty?

'90Cherokee

Check with a Jeep dealer and see if they're still doing repairs on it. I think they will as long as the parts are still available. If the parts stop being available who knows, they may have to offer to buy it back or something. I believe it's any owner, much like a recall. Most of the failures will turn the light on and the brakes continue working without ABS, some failures it just stops having brakes. I bought mine from the original owner just a couple years ago. Before that he asked me to take out the ABS (I'm his mechanic) stating that it had already caused the brakes to go out a couple times unexpectedly and he was done with having it fixed. I didn't buy it at first thinking no system is designed that way so I was hesitant. Then I did some reading up on it and called him back to schedule it. I hadn't done much reading about the deletion so I just went with what I could figure out. After I bought it and joined here I found there are detailed write-ups to make it right and fairly easy. In his first accident he said he was on the brakes with both feet planted as hard as he could; it slowed some but not much according to him and his wife. I didn't really buy it till I noticed the brake pedal was bent which is pretty hard to do.