frustrated over bounce

[blumule]

.Bear with me as I describe my situation and what I have tried so far.the problem is a front end bounce at exactly 43 or 44 mph.this is a speed related bounce every time at same speed whether I'm cruising, coasting or the engine completely turned off.ive researched every component and tried everything I can think of to no avail.ivegoogled and posted here as well.ive eliminated tires, wheels as ihave switched and swapped numerous combinations.driveshaft balanced twice because you cant trust anybodys work anymore.replaced u joints with spicer brand twice. Replaced front and rear driveshaft yokes.numerous axles, wheel bearings, body bushings and all new suspension bushings.frontend alighned and axles cold bent to spec after disc brake swap.tires road force balanced twice.the truck tracks and drives straight and smooth otherwise.ive gone over this a hundred times in my head so someone agree with me that a vibration or wobble or bounce has to be the result of a rotating object that is not balanced or out of round.what on gods green earth is left to rotate on these trucks other than what I have already described. Could it just be freaking harmonics from some unnatural twist or bend in the frame? I love my truck and will send 50 bucks to the first person to diagnose correctly my problem.there really ain't nothing left to try.send me your suggestions.I'm serious about the 50 bucks. oh yeah its a 69 2 wheel drive straight gear short bed.

[tnlprt]

Do you have a lift kit on the truck
If so check the Brackets for any cracks
My bronco had a wobble around the same speed the cross arm bracket was cracked at a bolt hole
Are all the rivets tight for the trailing arm brackets
Do you have a steering stabilizer
Are the pitman arm splines in good shape



When you have the problem try gently swerving from side to side and see if the problem changes

The wrong toe in will cause a shimmy at certain speeds (google sprint cars and see for yourself)

[iwhodat]

I had the wobble/bounce at 60 mph. My buddy drove on the side of me and saw my passenger side wheel hopping when I got to 60 mph. I replaced the front shocks and my issue went away. Good luck, man!

[blumule]

rivets are tight as much as I can tell. ive gone over everthing suspension wise.no cracks or breaks anywhere. the shocks are fairly new . they are a Monroe brand and seem to be doing their job per the push test.As far as pitman arm, I had to grab the donor arm from same 75 model I got the axles from for disc swap.They were both manual steering trucks but the pitman from my 69 didn't line up with the steering linkage.This is a 2 wheel drive truck.i will check it again for slip. I cant really see how a pitman arm could cause my front end to feel bouncy.

[cep62]

after disc brake swap.tires road force balanced twice

Did it do it before the brake swap ? out of round rotor?

Did you try different front wheels and tires?

[tnlprt]

ive gone over this a hundred times in my head so someone agree with me that a vibration or wobble or bounce has to be the result of a rotating object that is not balanced or out of round.

Which one of the three is it

You want to check your shocks to see if they are working properly

Drive down a fairly rough or bumpy road for 10 minutes
Then grab ahold of the shocks and see if they are all warm and around the same temperature

[crazyhorse]

Mr Blue I'm sorry you are having this trouble.
I hope you find it soon.
Below is some suggestions you can try.
Please be careful and make sure the truck is safe to work around.
1-If you put it in neutral and slowly rev the engine to the 43 mph rpms, is it smooth through out the rev?
2-Jack up the rear end , both rear tires off ground, put in high gear, start engine and rev it to 43 mph , is it smooth?
3-You can remove the drive shaft and "rotate " the drive shaft 1/2 round .
4-Jack up the front wheel off the ground, using a piece of yellow tire chalk , spin the wheel and hold the chalk very lite to the spinning tire tread and slowly let the chalk mark the entire tread area.
If the tire is round , the chalk will mark the tire evenly all the way around the tire.
If the tire is NOT round , the chalk will not mark the tire in the low places and mark it heavier in the high places.
5-You can mark the side wall while the tire is spinning and if the tire & wheel is straight the chalk will mark the tire evenly all way around the tire.
6-While the tire is spinning , look at the tire closely to see if you can tell if it wobbles or is out of round.

Good luck.

[blumule]

En gine runs smooth in nuetral and with rear tires off the ground.rotors are perfect true, according to my runout gauge.tires also seem visually round.no high or low spots.ive swapped tires and wheels from other trucks. I don't think its my shocks because it happens only at the same speed every time.never below or above the 43,44 mph. Its awesomely consistant.ive also narrowed it to the front end somewhere.heres my theory and see what y'all think.today's balancing procedure is always hub centric mounting while older cars and trucks were lug centric Balanced.I called around and nobody had the ability to mount my tires and balance them the way their mounted on by truck which is lug centric.could this be the reason at a certain speed the tire wheel combo is overcome by a slight out of round condition caused by the way it was balanced?

[crazyhorse]

Mr Blu, you may be on the right trac .
When you raise the front wheels off the ground and spin the tire, does it look to be round?
When you spin the tire, line it up with something with your eye, this way you can tell if it is round or wobbling .
When you look at the wheels , does all the wheels have the same amount of weights?

Can you find a shop in your area that can speed balance your front tires while on the truck?

[blumule]

ive called every tire shop in the phone book. no one does that anymore .I understand there is an adapter plate tire shops can purchase that mounts to todays balance machines that will allow lug centric balancing.they claim theres not a high enough demand to justify purchasing it.one thing I have discovered though is that todays tire shop are nothing but a rip off pure and simple.Most of the emplyees have no idea what to do unless a machine tells them.there just isn't many old school tire shops around anymore.ill figure this out eventually,but have to admit its been a frustrating experience. I keep asking myself if its not wheels and tires what else would cause a frontend to shake like this at a certain speed? im stumped.all components seem tight underneath.i even thought of tieing myself under truck while wifey takes her for a spin.

[Kurt Combs]

I have done this type search myself for many years on a '72 F-250. Changed tires, wheels, engine, transmission, rebuilt frontend, bushing on leaf springs and I still have a "bounce" above 66 miles an hour. This type of problem is almost impossible to fix. I suggest you look at things like body and engine mounts and the like, not spinning parts. Good luck.

[crazyhorse]

One would "think" if you rotated the tires/wheels, it would at least cause a change in the bouncing.
Can it be in the transmission or drive line?
When it is bouncing, if you put it in 2nd gear, and run 43 mph, will it still bounce at 43 mph?
If you are going down hill , put transmission in neutral, turn engine off, does it still bounce at 43?

[blumule]

yes I remember you curt. I think we share the same problem. Did you ever resolve yours? And yes to crazyhorse. 43 mph it appears, coasting, in neutral or even with the engine turned off.problem is I cant mimick it with the rear tires elevated.even if it was body mounts wouldn't there still need to be a rotational imbalance to cause the body to shake? I swear it feels like a out of round tire,but it does it with other tire wheel combos.the tires on here now have been road force balanced twice.i don't know of a way to spin the front wheels fast enough to achieve the right speed.eyeballing them with a block in front of them show no high spots in the tire.

[crazyhorse]

Mr Blu, it you run 43 mph in 2nd gear ( with a 3 speed transmission) does it still bounce?

[Hedgebilly580]

What about kingpins. I remember when I was young my dad had a motor home that did the same exact thing after he spent $1400 on new tires and countless weekends trying to fix the problem it turned out to be the kingpins he replaced them and it never happened again