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Grinding Vibrating Jittering something under breaking

XJiggy

NAXJA Forum User
Location
Cleveland
Well i just finished my header install this weekend and have a new 2.25 in exhaust with a flowmaster super 40 muffler.
So as it goes with my jeep I am on to the next problem.
I first noticed whatever is goen on about a week ago while driving in the snow in four wheel drive. under hard breaking there is a grinding noise accompanied by a vibe.

At first i figgured that it was just the tires sliding and then grabbing again becase pavement was still visible in some spots. However This weekend the roads were completely clear and i was taking the jeep out to test the new header and exhaust.

I got up to about 40 and then hit the breaks hard (all in 2 wheel drive by the way) . Once the nose of the car started to dip the Vibe and grinding noise kicked in. When I let off of the breaks it stopped. Under normal and even medium breaking conditions there is no grinding noise or vibe. Rather it seems to be only under breaking hard enough to dip the nose.

I cant tell if it is located in the front or rear of the car. I checked the drive shafts for excessive play but there was none at all. Everything seems to be in order up in the front suspension, so my guess would be towards something with the breaks or axle. I havent looked at the shoes in a long time and am not sure what shpae they are in but i will do that this weeknd.

Any Ideas what is going on??
 
no i dont have an sye and the drive shaft is not too old either...I am also leaning more towatds the drums but to be sure ill have to check it out this weekend
 
I had the same exact thing happen to me when my crossmember was a bit bent, i guess it caused the rear driveline angles to a be slightly off. My point is the suggestion above about removing the rear driveshaft is a good one. I am gonna bet its that since i had the same problem, it would feel and sound like loud grinding.

pete
 
alright well im gona pull the drums before i start taken the drive shaft apart cause that sounds like a much bigger job then just pullen the drum off
 
alright new developments...While driving on a rough road today i hit a bump and heard a scraping sound. Maybe this goes along with the noise and grinding when the nose dipps??

Also my suspension is extremely crappy...completely stock. sagging terribly. old shocks. its sucks so that may have somethen to do with it
 
Here is a long shot..

It could also be the motor mounts. I had a similar problem and found my driver side motor mount to be completely seperated. The other was ok, however it was a little cracked and on the way out. Once I replaced them everything was all better.

Mine is a 1990 Jeep XJ...

Andrew
 
Well i did not check out the rear drums this weekend because of the sub zero temps and my garage was full of crap.

However I discovered that the grinding happens whenever the car gets off axis. If I make a hard turn and the car rolls to one side then it will make the grinding sound...If I hit a bump real quick then the nose will dip adn ther will be a grinding sound...If I break hard and the nose dips then something drinds.

What is going on? It drives fine so i guess ill know if something breaks? haha thats terrible planning but i have no idea.

o I dont think its the motor mounts because if it was wouldnt the torque from heavy acceleration cause some extreme twisting and that sound would insue, but that is not the case
 
Sounds more suspension related like you are getting tire rub in your fender wells. Could also be your u joints binding from the change in driveline geometry. Check your wheel wells for rub marks, if you see damage to the wells or tires, then you have found your culprit.
 
yea i still havent looked at the drums but i am pretty confident that it is not them, and my reasoning is this... if I slam on the breaks in the snow the tires will lock up and there will be no grinding, however if i get on the breaks on dry pavement and the nose dips then there is a grinding noise comming from somewhere. I believe that it is located right under the center consol so tranny but i cant be sure.

how can i check to see if the u-joints are worn. I got under there and shook the drive shaft but there was zero play and everything looked good so....:(
 
Check to see if the frt driveshaft is hitting the exhaust pipe under hard braking , had this happen to an 89 once.
 
check your exhaust hangars (one on the crossmember before the cat, one after the muffler to the frame, one by the right leaf shackle), check along the exhaust pipe for burnished or scraped non-rusty areas. Trouble spots to check are next to the shackle, where the exhaust goes over the crossmember, and right next to the rear pinion/diff housing where the pipe goes over the axle. I've had all of those spots come loose and collide under various conditions.
 
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