Solved: sudden deterioration in ride quality

[Cees Klumper]

Appreciate any pointers here. Two days ago, I hit someone from behind, at about 20 mph. Lucky for me mostly, the vehicle I hit had a very beefy trailer hitch, one of those square tube receivers, that spared them any damage, and 'only' bent my front bumper out of shape. We concluded no need to exchange insurance info, and went our separate ways. For me, that was a 2-3 mile ride home. I did have to reset the inrertia/fuel cutoff switch, as the bump had tripped that.
All seemed fine, as usual. Only at the very end of my trip home, I started to notice the ride felt a lot more jittery than before, I was feeling every bump and crack in the pavement and it seemed to be coming from the rear. It was so noticeable that I even thought I was riding on a flat tire.
But no, tires properly and evenly inflated. Checked the shocks (front and rear newly installed 9 months ago) - all seem good, bouncing nicely. Checked the body mounts, torsion bars, rear leaf springs, front springs, all other suspension components I can get my hands on - nothing seems off, loose, bent or anything.
I thought I might be imagining things, but on my first trip yesterday, it was again so noticeable that, again, I pulled over to check for a flat rear tire - that's how bad it feels. Before, this truck was buttery smooth.
This morning, I pushed with my foot on the top of the rear tires, 'inward', and noticed distinct movement/play and a clear clunking sound. Not good, could this be the cause? But why so sudden, and how could this at all be related to my fender bender? Seems impossible? Coincidence? Anyways, took the wheels and brake drums off and there was end to end play on the axle shafts of about 1.5 mm. Not a lot, but who knows, if the rear wheels can move sideways, maybe this explains the jittery feeling over bad surface? I then checked the differential fluid level, for the first time since getting this truck, about 1 year ago. 450 ml too low. Hmm, not good either (no leaks though, so how did that happen?). After topping up and test driving again, the side to side play in the rear wheels seems gone, but the ride is still as harsh as before. The truck has 235,000 miles and likely the original differential and bearings, not sure.
I still need to double-check front wheels/suspension/bearings, and the rear wheel bearings. But there are no grinding noises when driving, on smooth surfaces it rides just fine and quiet. It's only on not-so-great surfaces that the ride has suddenly become really jarry and bad. Vibrations at low speed that weren't there before, on bad road surfaces. It feels as if all suspension rubber was replaced with super hard polyurethane race stuff - in the rear.
Any tips appreciated! Bad rear wheel bearings? Slightly bent front frame rail on the side that got the most impact (I hit the hitch slightly off center). Frame seems fine, eyeballing it, and the impact was not THAT major (ordered a new bumper). Have not taken it on the highway yet. Could the rear shocks have gone bad from having been extended super-quickly as I hit my target and no doubt the truck flipped up at the rear? Seems unlikely, but then what explains this?
Many thanks for any pointers, I am at a bit of a loss.

 

[MikeG]

A teeny bit of endplay (side to side) is normal for an axle in a c-clip rear end. However, rocking (tipping the top in as the bottom comes out, and vice versa) is not and probably a wheel bearing about to go.

If it's a wheel bearing, then most likely coincidence with the fender-bender. When they go.... they go. If it is a bearing get it replaced before it sends parts into the oil and the diff bearings.

Just some thoughts.

 

[Cees Klumper]

Thanks Mike - definitely will be checking and most likely replacing the bearings, cheap insurance if nothing else.
All other thoughts welcome! This is really bugging me, I love this truck!

 

[Cees Klumper]

Update - I checked all shock absorbers and they appear to function fine. I checked the rear wheel bearings, there appears to be 0 play in them - there's only the 1.5 mm left-to-right movement in the axles. Checked the condition of all 4 springs - seem fine. Standing on the bumpers making the car go up and down - seems fine, no strange noises, nothing. All body mounts seem fine. I checked the front wheel bearings and both had a small amount of play - adjusted that out so they're tight again. I even checked the transmission mount because I figured if, maybe through the fender-bender, it had gotten detached, then going over rough surface might make the transmission (and engine) 'jump' and cause harsh vibrations, but it seems fine. Motor mounts appear solid. Checked tire pressure, all close to 33-34 psi. Nothing appears to be touching the cab that isn't supposed to.

Yet, driving 20-30 MPH over less-than-perfect street surfaces still creates vibrations, as if driving on flat tires. It did not do this a week ago. I am completely at a loss, it makes no sense . Before I order new rear shocks, just to rule out what seems the most obvious potential cause (KYB gas-adjust that go for $70 the pair on Amazon) just wanted to see if anyone has any thoughts.

 

[SenorNoob]

Any possibility that you flat-spotted the rear tires? With no weight back there they skid easily under heavy braking.

 

[Cees Klumper]

Thanks for that, will check it. Although one of my frustrations was that, at the time of the accident, I slammed on the brakes but they seemed to hardly work. I thought there was enough time to stop, but the brakes did not function normally, and for sure did not lock up in the rear (it does have ABS on the rear). My wife, who was in the truck with me, afterwards commented she thought it was strange that I barely applied the brakes.

 

[Cees Klumper]

Update - I replaced the rear shocks, no change.
My latest theory is that the cab 'slid' forward due to the sudden impact on the frame it sits on. Although the body mounts appear ok, it is possible that the whole cabin moved forward and now either some of the through-bolts for the body mounts are touching the cab/frame, and transmitting vibrations from the chassis straight through to the cab, OR because of the different position of the cab vis-a-vis the chassis, the cab is now touching some part of the frame/suspension somewhere, and doing the same thing (transmitting vibrations to the metal of the cab, when that is supposed to be isolated from those vibrations by the rubber mounts).
I understand loosening the cab mounts can be a major hassle, but at this point I think that's my best bet, to see if I can 're-position' the cab on the chassis?

 

[Roert42]

Do you feel excessive vibration while the truck is stopped? Put it in neutral and rev it bit.

Does it drive straight?

Do you hear any new noises? Windows open, driver side/passenger side closed to isolate noise?

 

[Cees Klumper]

Thanks - no vibrations when car is stopped - or driving on smooth surfaces for that matter. Nothing in the drivetrain. No sounds/creaks, car drives straight.
It really feels like road surface uneveness/bumps etc are transmitted straight to the cab, despite good new shocks, springs and other suspension components.
It reminds me 100% of when once I installed polyurethane bushings in my other car's rear trailing arms-to-body attachment points, in place of the factory softer rubber bushings, to improve handling. I took one ride around the block and immediately swapped the old rubber bushings back in, due to how very harsh the ride had become, just from those two poly bushings. I was amazed.
I am usually pretty good at diagnosing these kinds of issues, and my best bet right now really is some unwanted metal-to-metal contact, somewhere in the suspension/frame-to-body connections, as a result of the fender-bender that stopped the frame, while the cab body (and my wife and I in it) kept moving forward just a little bit, due to the rubber bushings, and now the body just doesn't sit on the frame quite the way Ford intended.

 

[Roert42]

I'm inclined to agree that something is touching something else it shouldn't be. Now for the hard part....

 

[Cees Klumper]

So the problem has been solved: today I loosened all 10 body mount bolts (what a job that was). The very first one 'jumped' about 3 mm when I started loosening it, that's how much tension was on it. So I loosened all eight a couple turns, went for a drive, and re-tightened all of them - problem completely gone, no more jarring/vibrating. The ultimate test was the glovebox door - since this started two weeks ago, it would almost constantly rattle while driving. Now that has stopped also.

What this does mean to me, is that if anyone is ever in even a minor fender bender, or bought one that ever was, chances are they don't ride as smooth as they should. If I had sold mine without addressing this (took me about 8 hours today, believe it or not, and half my toolbox scattered across the driveway, I had to take both seats out, remove the protective plate that shields the gas tank, loosen the gas tank straps so I could nudge the tank over so I could get a wrench onto one of the 21 mm nuts, and so on and so forth) then the next owner probably never would be the wiser. In fact, had this been my first Bronco II / Ranger, and it had this problem, I would have just attributed it to "well it's a truck, what can you expect" as also it was not all THAT unbearable - just annoying, IF you know how this truck is supposed to drive. So not that I recommend spending 8 hours just to check whether this is something that is 'off' in your truck, but I would not be surprised if there are quite a few out there that could drive so much better.

Thanks for all the tips - this was driving me nuts and spoiled my enjoyment of driving around in this Bronco II, now the fun is back.

 

[RobbieD]

Interesting. Thank you for the update.