Wheel hop at 45

[Loghead]

My truck has been sitting for six months or so. I finally took it for a drive a few days ago and had severe wheel hop at 45mph.

The reason the truck sat for so long was my swapping the auto trans for a 5 speed - all while working full time and framing a house 200 miles from home on weekends - which helps explain why it took so long.

I used the flywheel / clutch for a 5600; the engine runs smooth as ever - nothing seems to be out of balance there.

So there are some - okay, many - factors that will need to be sorted out.

First, the front was up on jack stands the entire time - flat spots in rear tires? Further, the rear shocks have seen better days. Could they, having been sitting more compressed for all that time, leaked and are now making the problem worse?

Second, the swap itself required the rear driveshaft be longer/front driveshaft shorter. The shop that made up the new shaft has a good reputation. I've used shortened and rebalanced shafts from them before; drove fast enough to break the sound barrier with no drive line vibrations.
I did jack up the rear end and run it in 5th to 45mph with no discernible vibration, for what it's worth.

Third, the front end is in sore need of an alignment. The toe setting is so bad you can see it.
I had wondered if driving with the front so far out to lunch could cause this, but I had run the truck this way for short trips before the transmission swap - a mile to get fuel, ten miles round trip for inspection - without any wheel hop. I had been using it mostly for plowing my own driveway, which is why I let it go that way. Pushing snow at 10 mph rarely gets scary.
So I'll be fixing the front end no matter what.

I don't have lots of time on my hands these days, so any thoughts would be appreciated.

 

[JR]

How Severe would you rate it? Tires would be easy to eliminate by either having them balanced or swapping front to rear and see if the vibration changes corners.
Is the driveshaft still a 2 piece? Installed correctly (in phase).
If you have access to a go pro or something similar it is an invaluable tool to use for diagnosing problems like this. Secure it to the underside and go for a drive.

 

[PBJ2500CTD]

I agree with JR. Flat spotting usually resolves as the tires heat up. Moving the tires from front to back would seem to be the easiest first step. I would also recommend checking the tires for an out of round condition or slight bulging which may indicate tread or cord separation. It could be a simple combination of a wheel weight taking a hike and poor shock absorbers as you mentioned.

 

[Loghead]

How Severe would you rate it? Tires would be easy to eliminate by either having them balanced or swapping front to rear and see if the vibration changes corners.
Is the driveshaft still a 2 piece? Installed correctly (in phase).
If you have access to a go pro or something similar it is an invaluable tool to use for diagnosing problems like this. Secure it to the underside and go for a drive.

The vibration is so bad that it's not merely annoying; it's scary.

The driveshaft was and is one piece.

There's a crazy kid at work who makes mountain bike videos for GoPro.
He'd probably hang by his tail under the truck just for the thrill.

Back in the old days the truck profile was easy to find - mine's a 2500 regular cab 4x4 / Yoostahbee Auto. No serious go-fast mods. It's got a 3rd gen track bar installed and a Redhead steering box, both a big improvement even with the front end like it is.

 

[PBJ2500CTD]

Just throwing some thoughts out here:
Do the manual transmissions require a pilot bearing in the crank; could the transmission input shaft be bent? However, if there was no vibration when you had the rear end jacked up and run at 45 MPH, probably not an issue.
Another check would be to jack up the rear end, following all safety and security procedures, then run it at 45 again. Carefully take a piece of chalk (or other marking device) and slowly approach the drive shaft until it initially makes contact. If it is out of round it will make contact on a small portion of the arc of the tube.

 

[JR]

It definitely sounds like something in the driveline is amiss.
More of a feel in the steering wheel or seat of the pants?
Cross member bracket in good condition and tight?
What's the history on the new transmission?

The gro pro is sounding like a good idea minus the hanging off the bottom of the truck part.
It could eliminate a lot of guesswork.

 

[Loghead]

The pilot bushing is in the flywheel hub.
The transmission is a rebuild by a guy - well spoken of - in eastern PA. He installed a new 1 3/8 input shaft so I doubt that it's bent.He also installed a 5th gear retainer fix. It doesn't seem to make any weird noises under power or anything - pretty smooth really and I have to say the thing pulls like a team of mules when I get it into 4th gear; I've got 4:10's in the axles so the lower gears probably won't really impress me until I get a heavy load on and start pulling.
I kind of doubt it's the transmission.
I re-used the transfer case; installing new bearings and so forth when I swapped in the 29 spline input gear. I didn't replace the chain; It seemed fairly snug and I've never done any serious off-roading with the truck. Most often 4wd is used for plowing snow and that's about it; I rarely push it too hard when plowing - only enough weight in the bed to balance the weight of the plow. (I'd rather break traction now and then instead of breaking driveline parts)
I'll have to double check the transmission to crossmember fasteners- as far as I remember, they're okay.
I'm inclined to have someone observe the rear wheels while on the jack at 45; there was nothing "high frequency" about the shaking I've described as "wheel hop".
I took another look at the rear shocks after my last post. They look worse than terrible and could very well be the root of the problem - or at least contributing to it.

 

[PBJ2500CTD]

I'd do the chalk indicator test to the tires and rims. A good shock may dampen the wheel hop, not fix it.

 

[Joe Mc]

I’m thinking tires too. I’m with Bruce on checking with chaulk both tires and rims.

 

[fest3er]

Rear drums could cause a *really* bad hop if they've a spot the shoes can stick to. I was getting a bad hop anywhere from 20-75 until I replaced the shoes and broke them in.

If the hop's in the rear, you should see the end of the bed bouncing via the rearview mirror (and maybe the side mirrors). If it's the front, the rear-view mirror should be fairly steady.

 

[Loghead]

If you guys think one of these Dodges can be a miserable thing to work on, try a Tacoma.
That's what I've been stuck on most of the day, replacing the front axle actuator. Of course the most fun was taking out the steering rack to do the job I actually had to do. Frozen bolts, a grinder and a chisel got involved. Ugly
Sheeezsh.

I took a minute to check the transmission mount and I did find a loose nut at the mount to crossmember connection. Even if that's not the cause of the greater problem it's not good.
That's what happens when I work in too much of a hurry.

In addition to actually tightening the loose mount, I'll install new rear shocks and pull at least one drum to see if there's a rusty patch from having sat so long.

I'll set the toe angle too.

Tires have plenty of tread but I bought them while Dubya was in his second term. They may be ready for the deep six.

 

[Joe Mc]

LOL!!! I hear you on foreign autos. Yesterday I replaced the sera belt tensioner on the "wifey mobile" (01 Volvo XC-70), which was held on by only 2 bolts... Of course which to gain space to just get to I had to remove the power steering pump. Once the 2 bolts were out I couldn't get the blasted part out until I removed the right front wheel and fish it out from the bottom. Installation, as always, reverse removal process. "Then" getting the derp belt laced in proper order, the best part was trying to get my hand on the ratchet to move the tensioner so the belt could be forced onto the last pulley

To the truck. I totally forgot about the rear drum possibility (I converted to discs many years back) very well could be the issue or contributing factor. A loose trans mount and the tires being ancient for sure could all be contributors - tires more importantly are a safety issue. Hope things work out for you.

 

[KATOOM]

There is a signature hop you'll find some members complain about that takes place between 40-45 mph, described as like the rear tires are egg shaped for a moment, can be slight or more severe, can be overpowered by simply driving through the 5 mph window, doesnt happen with any amount of weight in the bed, etc...

Over the years there's been many ideas and concepts to what the heck is going on and why this strange hop can occur in only some trucks. Well I had the hop many many years ago and it went away completely with a brand new set of TOYO M/T's. Recently I got rid of those old TOYO's and replaced them with some Cooper ST MAXX's.....and.....immediately I've started to randomly experience the egg shape hop again on some roads.

Is it the tires?...I say absolutely yes. Why?...not completely sure because they balance but maybe they're not as "perfectly" balanced as they could be or maybe there's something to the stiffness of compound of the tire in relation to the suspension stiffness and geometry which gives just the right combo for this almost rhythmic movement.

 

[fest3er]

More than likely you have a wheel that is out of true. One of mine has 'hopped' at 38-44 MPH since the day I got the truck. Only when the weights are brandy new does it not hop; but the 'bounce' starts not long after. Good, stiff shocks will hide the problem; lower pressure might also.

 

[Mark31]

I had a '74 D200 Dodge 2wd with 950x16.5 tires. The ONLY way the tires could be balanced was on the truck with a strobe light balancer. It would be slick as glass for about a year, then rotate and rebalance. The rear end felt like it was jumping up and down like a pogo stick "balanced" any other way. I bet you couldn't find a man and machine this side of Bangkok who could do that now

 

[Joe Mc]

Mark, I agree with on-vehicle tire/wheel balancing and haven't seen a shop that did this in decades (at least 4). I've never seen a shop with a strobe wheel balancing system. I searched for the past 40 minutes or so trying to find a shop near me with "on-vehicle" balancing - to no avail.

 

[crabman]

Lots of water under the bridge since I saw one of those strobe light tire balancer!

 

[BigPapa]

A vibration appearing at 45mph that goes away at higher speed and appears again at 70mph typically indicates an “out of round” condition caused by a bent rim, separated belts, or just a bad tire. You never said how long the truck sat or when it was parked. If it was parked during very warm temps and has sat into very cold temps, the flat spotting could take a very long drive to work out.

As far as there being more weight on the rear compressing the shocks, jacking the front will not change the weight distribution unless you loaded the bed. Shocks will not CAUSE a vibration, at any rate. They may allow more vibration but won’t cause it.

-Scott

 

[Loghead]

A vibration appearing at 45mph that goes away at higher speed and appears again at 70mph typically indicates an “out of round” condition caused by a bent rim, separated belts, or just a bad tire. You never said how long the truck sat or when it was parked. If it was parked during very warm temps and has sat into very cold temps, the flat spotting could take a very long drive to work out.

As far as there being more weight on the rear compressing the shocks, jacking the front will not change the weight distribution unless you loaded the bed. Shocks will not CAUSE a vibration, at any rate. They may allow more vibration but won’t cause it.

-Scott

I don't know what speed the vibration stops because I'm too chicken to try and find out. 45 is scary enough.
The truck was parked for a little over six months - June until December - with temps in the mid 90's down to single digits.
I ordered new shocks and the truck won't see the road until they're installed. At that point I might dare to find out when the vibration stops, since the truck should be at least controllable.

 

[Ozymandias]

Tire too, will go away within 50mi.
But good shocks are a must too.