Wheel hop at 45

[KATOOM]

If the hop is so bad that you are not comfortable driving at highway speeds then jack the rear axle off the ground and have a trustworthy friend sit in the cab with the engine running and the transmission in gear while you watch from outside looking for anything moving more than it should.

 

[Mark31]

Log, I've been rumbling this around in my marginally functional grey matter. My number one suspect is a busted belt. Inflate the tires to max, jack up the beast and put a block almost touching the tread and turn the tire slowly, looking for where it hits the tire. Look for a slight pooch 6-8 inches long just off center. Put on some gloves (in case a wire belt is busted and is barely sticking through) and give them a "soft handed" rub. If you don't find anything, pull the wheels off and, with the truck resting on GOOD jackstands, (my peculiar self likes a board under if on concrete and over so I don't have metal to metal) and slowly accelerate to 45 mph. Let it run a few minutes and check out the U joints and especially the carrier bearing with an IR gun. I've seen and read on here some "doozies" about them. Don't forget--you are looking for things that go bad sitting. The last tidbit: I had a flywheel "cleaned up" when I replaced the clutch in a C60 Chev and the marsupial that did it didn't have it properly mounted and cut it one sided. Vibration!! Replaced flywheel. Hope you find it today so you can start off with a Happy New Year!

 

[Loghead]

Good thoughts Mark.
On the flywheel: I ran the engine up to a bit above 2500 - loaded and unloaded. I detected not a hint of imbalance under the hood; so I'm comfortably certain that all is well in the bellhousing and the transmission.
That's a good thing, since it would be a major pain to pull everything out to fix anything in that area. I do need to adjust the transfer case shift linkage; 4H is right at the back of the gate. I'd prefer to reach the detent a bit before the end of the gate.

 

[Joe Mc]

Although you already checked the engine and detected not a hint of imbalance... when there's a load on the engine there's a bit of a difference as to what's going on internally versus without a load and since you switched from Auto to Std the difference in weight from flex-plate/converter to flywheel/clutch-pack could be a consideration. More so, since it was sitting for 6 mos +/-, it might be worth checking out the vibration damper. If memory serves me, there's the inner and outer hubs which are bonded together by "rubber" there should be an alignment mark (a scribe line along the center going across both hubs) if the line isn't "lined-up" the rubber has failed and will no longer "effectively dampen" vibration changes. The other thing to look for (there might not be a scribed alignment mark) is just the condition of the rubber, IE: if it looks smooth, not cracked or bulged out (front or back sides - check with a mirror and flashlight) then it "should" be OK. However, if the hubs aren't aligned (even 1/32nd"), rubber is not smooth, is cracked and/or excessively bulged out it "could" provide unloaded dampening "but" everything changes with a load... Something else to look at. sorry, but you never know...

Not saying to go out and get a new damper or anything, but if it doesn't check out good this could be the gremlin. On mine at around 160k or so I found the damper rubber was cracked, brittle, bulged and (I'm almost certain) the scribe line was off by about an 1/8th", and there was no real indicator of imbalance at all. "But", when I installed the Fluidampr (at the time about $425 from Summit, Geno's now has them for 98.5 - 02 and 03 - 05 for $435 and for the 94 - 98's for $488) I immediately noticed the engine idled smoother and seemed to run quieter = a miracle.

Also, as mentioned by others here, when you have it up on 4 stands and can safely run it up to the speed where you're experiencing vibrations look at the propeller shaft carrier bearing. If, when at the speed where you've experienced vibration everything "seems" OK, remember there's no load on anything, try running it up and/or down in 5 mph increments. And "make certain" the universals are clocked/synced/aligned correctly from pinion thru to X-fer case flange. As for tires/wheels, if you've ever worked on bicycle tire/wheels and had to adjust the spokes to get the wobble out, when your tires are spinning look at the rim/wheel lips (inside & outside) for any slight variations - this is best observed while idling in gear - perhaps in your case 1st gear.

I hope you find whatever it is soon and it doesn't cost you a "BRAZILLION" dollars to rectify.

 

[Bamtech1]

Someone earlier mentioned brake drums.

I haven’t confirmed it yet, but I experienced a severe hop in the rear the other day that just HAS to be rear brake.

The truck has been sitting for months with only short trips to the body shop, junkyard etc. during this time I did the rear brakes, new shoes and cylinders, turned drums.
On Friday I drove it to work for the first time and then decided to go after some parts. After about a 30 mile interstate run with no issues, no vibration I smelled hot brakes when I got out. Investigated and saw that the Torklift camper tiedown was pushing on the e-brake cable.
So, after a half hour or so I got back in the truck to go home and the vibe at 45 or so was awful. Backed off the e-brake cable and took backroads home, it eased up as it cooled. I suspect I’ll need to redo the left rear.

Think you had a brake stuck?

 

[Joe Mc]

Bam, I tried so many different things before I finally converted to rear discs to quell the whole rear drum hop when brakes were applied. Here's a few: New drums, shoes, GMC 3500 (I think they were 3500) wheel cylinders - didn't help, had the "new" drums true-cut - a little better, finally what reduced it the most, and almost to an un-noticeable level, was to fit the shoes to the drums. What a time consuming PIA job that was... I did one drum shoe combo at a time, remove drum & shoes, place them in the drum as they would be when installed. What you're trying to end up with is about 0.020" on one of the shoe heels "and" for the shoe to be perfectly against the drum = top to bottom/side to side, so the only part of the shoe material touching the drum is a little in the center, which will wear-in quickly. Obviously you can only do one shoe at a time. I also sanded a slight chamfer/angle across the material on each heel = about ½" up towards the center and only 1/32" into the edge of the heel, to help prevent chatter and promote flat wear-in. This fitting to the drum was accomplished by placing round (maybe ⅛" dia.) piece of steel stock away from where there was to much gap between drum shoe and crank on the shoe frame with a c-clamp where the gap was noticed to reduce the gap. If there was gap on both ends you'd take two c-clamps and crank on them to "flatten out" the gap. Like I said "a time consuming PIA". This helped the best of anything I ever did, but there was still that little hint when the brakes were applied - come to think of it more noticeable between 35 - 50 than at lower or higher speeds.

 

[Bamtech1]

BlahblahblahREAR DISCSblahblahblahetc...
That’s how I read it!

 

[Joe Mc]

Bam, good one. Not really bla, bla, though, I just had enough of messing with the drums and the hipity hopity upon brake application (think I converted in like 2010). Just trying to share what worked for me on fitting the shoes to the drums.

 

[Loghead]

Someone earlier mentioned brake drums.

I haven’t confirmed it yet, but I experienced a severe hop in the rear the other day that just HAS to be rear brake.

The truck has been sitting for months with only short trips to the body shop, junkyard etc. during this time I did the rear brakes, new shoes and cylinders, turned drums.
On Friday I drove it to work for the first time and then decided to go after some parts. After about a 30 mile interstate run with no issues, no vibration I smelled hot brakes when I got out. Investigated and saw that the Torklift camper tiedown was pushing on the e-brake cable.
So, after a half hour or so I got back in the truck to go home and the vibe at 45 or so was awful. Backed off the e-brake cable and took backroads home, it eased up as it cooled. I suspect I’ll need to redo the left rear.

Think you had a brake stuck?

Well B'tech, I jacked up the rear and ran it up to 45 on the speedometer without any discernible vibration. I let it idle down (in 5th) , the speedometer was 15 - 20, got out of the truck and went aft to check it out.
No really alarming sounds other than 5th gear being a bit rattly - I've heard they do that so I'll keep my fingers crossed on that score.

Rear discs...
I almost put an 11.5 AAM out of a Chevy under my truck; somewhat stronger than the Dana 70 (but nowhere near as strong as a Dana 80)
with disc brakes as a bonus.
Turns out there are lots of junkyard experts who count 14 bolts and say "11.5" automatically when it could be a 10.5 like the one I got.
Luckily I was able to get my money back.
A cab and chassis Dana 80 with 4:10's and a Sure Grip made its way from craigslist to my garage soon after. Massive DRUM brakes

 

[BigPapa]

What did you ever find out?

-Scott

 

[Ozymandias]

I still vote for the tyres, having a flat spot after months at the same place.

 

[Loghead]

What did you ever find out?

-Scott

Between working ten to twelve hour days and keeping the house in the mountains project moving I haven't had time to do much work on the truck.
It will push snow off my driveway as it is so it hasn't got the "HAIR ON FIRE" urgency it would otherwise.
I'll keep you guys posted.

 

[Seabee]

Since everything else has been mentioned, are you sure it is not stuck in four wheel drive and that is causing your vibrations at higher speed? Try spinning the front drive shaft by hand to make sure that it is not engaged.

 

[Loghead]

Since everything else has been mentioned, are you sure it is not stuck in four wheel drive and that is causing your vibrations at higher speed? Try spinning the front drive shaft by hand to make sure that it is not engaged.

I have a cable axle engagement setup - in place of the stock vacuum setup. After my first venture out on the road I noticed the cable was pulled into or near the "axle engaged" position.
After reminding myself of what a dummy I must be and disengaging the axle, I took it for another spin.
Same thing, so I doubt that's the issue, but I'll certainly double check just to be sure.
Thanks

 

[Loghead]

I replaced the rear shocks and the steering damper. I adjusted the toe angle and tightened the transmission mount.
There was no wheel hop at any speed.
Getting the truck in and out of my garage is a headache- otherwise I would have taken it for a spin after each repair.
Thanks for your interest and input guys.

 

[Joe Mc]

Do you think it was the rear shocks?

 

[KATOOM]

and tightened the transmission mount

I'm interested in this... Because unbeknownst to many, shocks are NOT there to stop tire wobble. They're only there to dampen movement from road conditions.
A loose transmission mount will allow the transmission housing the move uncontrolled up and down which will definitely be felt in the cab.
So my question to Loghead is, how loose was the mount that you tightened up? Did you visually notice movement before tightening?

 

[Joe Mc]

I'm interested in this... Because unbeknownst to many, shocks are NOT there to stop tire wobble. They're only there to dampen movement from road conditions.

Understood, but shocks should also "dampen" slight tire wackiness of course until shock is spent. Just saying. Tire "wobble" due to bent wheel etc. shock won't address that. Interested also in how loose the trans mount was and were bolts loose at trans, or cross-member, or both?

 

[Loghead]

Do you think it was the rear shocks?

The shocks were rusty and crusty with oil leaking out, so whether the long period sitting in one spot with the front jacked up put a flat spot in a tire, or miserable road conditions induced a hop that was uncontrolled, those shocks weren't doing much but adding weight.

I had to cut them both out with a Sawzall and cutoff grinder - oh what fun.
Only the studs/nuts at the mount to crossmember were not fully tight.
I believe I'll need to replace the transmission mount fairly soon; one of the studs seems to be stripped.

 

[Joe Mc]

Sounds like fun. Glad you're rolling smoothly. Since shocks were so rusty you might want to check rear spring hangers out. They seem to catch all the s_ _t that comes off the rear tires...