Low Speed Shaking Diagnosis

[ECEB]

Hey Fellas,

I am having a lot of trouble figuring out the source of shaking that occurs at speeds up to about 25 mph. The truck is fine above that. In this range when it starts shaking and we put it into neutral the problem goes away. I think that is a key detail.

I have had a couple of mechanics (one being extremely good with Broncos) look and it and they are stumped. Many things have been updated and rebuilt. I had disk brakes put in the front and a lot of the components updated.

We thought it was the body rubbing against the drive shaft but lifted it up a little to get clearance and there isn't any rubbing. We also put it in 4WD and disengaged the rear driveshaft and the shaking was still there.

I was hoping you guys could help me with your expertise and experience and I could bring them ideas to evaluate against the truck which is a 73 C4 automatic half cab.

I appreciate your insights,

Tony

 

[blubuckaroo]

I'd take a ride if I were in your area.
Certainly someone will offer.

 

[68stang73]

Bent Axel?

 

[half cab]

Wheels balanced?

 

[BR549]

Not that I saying its the death wobbles, but check the track bar bushings and tires

 

[Cohammer]

I did have a 79 f100 that had an issue where it was smooth in neutral but the fly wheel was causing vibration when starting off until I changed it .

 

[66broncoCT]

Not sure how much help I'd be but if you're close by I'd be willing to take a look for you. First thing I always check with a vibration under load is u joints. When you say disengaged the rear driveshaft do you mean took it off or just put the transfer case in front wheel drive if it's twin sticked? When was the last time the bushings in the front end were done? Mine used to get a horrible death wobble from 30 to about 38 then it would be fine. There was almost no rubber left in the c bushings when I took it apart for the lift. Waiting for my new rear driveshaft to come in before I can drive it but hopefully that's gone now.

 

[ECEB]

Hey Fellas, the tires are new and the rear driveshaft was disconnected and it still had the low end shakes.

I am pretty new to all of this but the wheels/tires are also new.

66broncoCT, I am in Hartford and wouldn't mind driving out to you.

 

[DirtDonk]

What brand, model and size are the tires.
As you get more used to diagnosing this type of thing online, you'll see the need for all the little details. Even the ones that don't seem to be related.

And as we've found out many times here, "new" does not necessarily mean "good" anymore. Something to think about anyway.

Regarding it going away in neutral, what does it do when you simply let off the gas and leave it in gear?

Paul

 

[half cab]

Recent issues I had with a tire store was one wheel had to many wheel weights.

 

[ECEB]

What brand, model and size are the tires.
As you get more used to diagnosing this type of thing online, you'll see the need for all the little details. Even the ones that don't seem to be related.

And as we've found out many times here, "new" does not necessarily mean "good" anymore. Something to think about anyway.

Regarding it going away in neutral, what does it do when you simply let off the gas and leave it in gear?

Paul

So, letting off the gas in gear still will cause it to shudder.

 

[DirtDonk]

Even though a bit odd, it could still be a rear driveshaft issue. Either a pinion angle problem, or a u-joint going bad, or the CV joint centering ball needing lubrication.

Stock suspension or lifted?
Old driveshaft or new?
Did it just start doing this out of the blue, or do you remember some circumstances surrounding it's initial vibration?
Any other changes to the Bronco?

Paul