RESOLVED - violent acceleration

[LorenzoGarbanzo]

On the highway doing about 65 today, I needed to pass a car. Punched it up to 75 but it shook violently from the rear up to speed. It felt like I'd describe wheel hop when accelerating from a stop and was a bit concerning. Have I broken a driveshaft or axle?

 

[donalds]

I'd start with balancing the tires

 

[Rick]

I would also check the U-joints.

 

[94Eddie]

On the highway doing about 65 today, I needed to pass a car. Punched it up to 75 but it shook violently from the rear up to speed. It felt like I'd describe wheel hop when accelerating from a stop and was a bit concerning. Have I broken a driveshaft or axle?

Is the shaking something that came on suddenly or has been building over time?

 

[LorenzoGarbanzo]

Is the shaking something that came on suddenly or has been building over time?

Suddenly. I drove about 200 miles straight today and it started in the last 15 or so.

 

[94Eddie]

Suddenly. I drove about 200 miles straight today and it started in the last 15 or so.

It could be a wheel weight(s) came off, U-joint came apart and lost some bearings etc. The first thing I would check is the U-joints. Sometimes it is hard to tell if they are bad. Jack up the rear wheels so it can spin easily and this makes finding a problem easier. Look for where wheel weights could have come off. There might be fresh mark indications. Also, while the rear wheels are up spin them and listen for anything odd sounding.

 

[LorenzoGarbanzo]

One wheel does appear to be missing a weight on the front. The shake did not present in the steering wheel so I felt that ruled it out but plan to get that fixed at my next rotation anyway.

The interesting thing I noticed is that the rubber bushing that attaches the drivershaft center support bearing is completely deteriorated and the driveshaft is easy to move around inside that bearing's bracket. U-joints & CVs checked out OK from a visual / hand test. Looks like I'm heading to the driveshaft shop this week.

 

[Rick]

The interesting thing I noticed is that the rubber bushing that attaches the drivershaft center support bearing is completely deteriorated and the driveshaft is easy to move around inside that bearing's bracket.

That will do it.

 

[LorenzoGarbanzo]

Fixing the driveshaft in this truck has been difficult, the supply chain is truly hurting because of covid and non-serviceable parts (WHY, FORD??) are a problem. I do have one shop who claims they can build me one this week so I have my order in. It will be completely serviceable with stronger parts than stock. If they come through and the install goes well, I'll definitely post a recommendation on here.

My usual mechanic found one through his sources, but it was about $1000, said ford discontinued it and there's no aftermarket replacement for the 4.0/2wd combination. The local driveshaft guy refused to replace the bearing, said it was non-serviceable. Everything in junkyards has a bad bearing or was destroyed by a forklift.

I found advice on the forum & FB group with recommendations for a couple of companies, but they couldn't get one at the moment. I read the threads about replacing the center bearing on here but we have a non-replaceable univeral joint that's shot as well so I might as well replace the entire unit.

 

[LorenzoGarbanzo]

Finally got the replacement driveshaft this week and installed it today. All's well again, the truck rides smoother, the vibration is gone, and a bump when shifting I had learned to ignore has been resolved as well.

Anyone who finds this, keep in mind that Ford has discontinued the part, covid is still disrupting the supply chain, and some aftermarket suppliers can no longer make or get this part. I was able to purchase from driveshaftpro in California, they were extremely professional, built the part quickly, and shipped out quickly with pretty good packaging. Their quote beat any other prices I got at the time of purchase, with free shipping.

Things to note, the u-joints and center support bearing are now replaceable on the new part, and it has some excellent looking spicer u-joints installed. It seems balanced well so far, and fit into the truck perfectly. Here's the link -- Driveshaftpro.com --> this is the part for our trucks, you may need to adjust configuration depending on what you drive.