FJ 60 Vibrating at higher speeds - Help

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Have you checked your rear drums?
I've had the rear axle up on stands and spun the rear wheels, mainly checking for signs of wheel bearing fatigue. There were no nasty noises coming from either the bearings or the rear drums. I had the rear wheels off when I removed the axles and had a good look at the drums but I didn't actually take them off. There's no difference to the vibration when the brakes are being applied or not so I figure the brakes are ok (but obviously I might be wrong!)
 
I’m fairly certain this is not the cause of your issue, but, changing the body mounts made a tremendous difference in how much vibration made it into the cabin.

My vibration was in the rear differential. I had some old damage to one of the leaf spring hangers and over time it allowed the rear axle to walk back and forth which destroyed the pinion bearings. The first thing I changed was the body mounts. Didn’t fix it, however, the difference was very noticeable.

Fixing the leaf spring hanger and replacing the suspension made a big improvement, but ultimately I had to install new differentials and the issue completely resolved itself.
How big a job is it to replace the body mounts?
 
I've had the rear axle up on stands and spun the rear wheels, mainly checking for signs of wheel bearing fatigue. There were no nasty noises coming from either the bearings or the rear drums. I had the rear wheels off when I removed the axles and had a good look at the drums but I didn't actually take them off. There's no difference to the vibration when the brakes are being applied or not so I figure the brakes are ok (but obviously I might be wrong!)
I chased a vibration on mine that ended up being warped drums. Easy enough to do a gross check by jacking up the wheel, giving it a spin and watching/listening for the wheel to come to a stop without grabbing anywhere.
 
Dried mud in the inner side of wheels?
Isolate the symptom - rear / front axle / driveshafts / in-gear coasting / out-of-gear coasting / leaf-spring pins frozen or lubed?
Can you tell me more about the leaf-spring pins please? Are they supposed to be able to move (i.e. not be “frozen”?).
 
Can you tell me more about the leaf-spring pins please? Are they supposed to be able to move (i.e. not be “frozen”?).
Well there are greasable shackle pins and the bushings allow movement where the leaf spring wraps around the pin.
 
How big a job is it to replace the body mounts?
I did it in an afternoon. It’s not too difficult but it’s labor intensive. Lots of squats and crawling around on the ground and dealing with rust. Just think things through before you start lifting the body. You don’t want to bend the pinch welds or drop it on your hands while you’re installing new bushings.
 
A vibration on mine ended up being misfiring cylinders. My spark plug wires were just loose enough it didn't start to misfire until I got up to speed. Easy fix. Tightened the wires down on the spark plugs. Just giving another possible avenue to check out.
 
I did it in an afternoon. It’s not too difficult but it’s labor intensive. Lots of squats and crawling around on the ground and dealing with rust. Just think things through before you start lifting the body. You don’t want to bend the pinch welds or drop it on your hands while you’re installing new bushings.
Do you have to remove all the old bushings, then lift the entire body or is it possible to remove and replace one by one?
 
Do you have to remove all the old bushings, then lift the entire body or is it possible to remove and replace one by one?
You do one side at a time. Front to back. One at a time. Remove all the locking nuts so they’re all loose. Then lift the front and remove the bushings and replace. Then move to the center. Then the rear. Repeat on the other side.

Pay attention to where you apply lifting pressure on the body. You don’t want to bend it. I used a length of 2x4 to distribute the weight along the pinch welds at the bottom. I bent it slightly in one spot but it’s not bad.

It’s not that bad a job really. I would do it before I install a lift. It will be easier if the truck is closer to the ground.
 
Which body mounts did you replace yours with? How do you like them?
I used the kit from 4crawler. High quality polyurethane. I think it was about $265 for everything.
 
I used the kit from 4crawler. High quality polyurethane. I think it was about $265 for everything.
I chased a vibration on mine that ended up being warped drums. Easy enough to do a gross check by jacking up the wheel, giving it a spin and watching/listening for the wheel to come to a stop without grabbing anywhere.
I’ve had another go at doing this and paid close attention to this. Last time I was very focused on the wheel bearings. This time I notice that one wheel does have a bit of drag and doesn’t spin out as freely as the other, but I find it hard to imagine it’s the source of the terrible vibration. I guess it could be much worse when the weight of the truck is on it? How bad was the grabbing on yours? Could your wheel still spin?
 
I’ve had another go at doing this and paid close attention to this. Last time I was very focused on the wheel bearings. This time I notice that one wheel does have a bit of drag and doesn’t spin out as freely as the other, but I find it hard to imagine it’s the source of the terrible vibration. I guess it could be much worse when the weight of the truck is on it? How bad was the grabbing on yours? Could your wheel still spin?
My wheels spun, but there were consistent spots that the drum dragged pretty strongly as it turned, indicating the drums were pretty warped. I had them turned and it actually got worse (shop screwed up), so I ordered new drums and had them turned before installing (better shop this time). That cleared it up. I was honestly surprised that that fixed the vibration.

Backstory: I rebuilt the rear drums and replaced both wheel cylinders a while back. Immediately after that work, I started experiencing the common drum brakes overtightening issue. It took me several months of trying different things to prevent the over adjustment, so I was pretty certain the drums were warped at this point.
 
Does the vibration happen at the speed regardless of power applied or in neutral?
 
Does Autozone or similar loan NVH (noise, vibration, harshness) analyzers? If you could narrow down the frequency of the vibration it would go a long way to figuring it out. Wheels will vibrate a lot differently than driveline.
 
Does the vibration happen at the speed regardless of power applied or in neutral?

Does the vibration happen at the speed regardless of power applied or in neutral?
Regardless. It always happens. Doesn’t matter if it’s in gear or neutral, engine on or engine off, touching the brakes or not touching them. It’s strong enough to shake the whole car.
 
Check for play in your u joints.
The rear prop shaft is currently out of the car so those 2 UJs are not the problem. The vibration and noise is still there if I roll the car with the freewheel hubs open, so it’s not the front UJ either. Using the same logic I’ve eliminated the diffs too.
 

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