Mystery vibration at 25 mph can't be diagnosed. It's not the front end!

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jeffrey356

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I have a 1965 dart 270 w/ slant 6 and I'm getting a body shutter upon acceleration at 25 mph. The mechanics are scratching their heads. It doesn't appear to be the front end steering linkage and suspension. It's in the body or drive line. They checked the drive shaft and U joints and they seem to be okay. It's been in the shop 10 days and they can not find the source of the mystery shutter. I had the tires rotated and had alignment. All tires are at a proper psi and balanced. Does anyone have some clues to fix the problem. It Just started doing this a couple of months ago. The problem just came out of nowhere.
 
Anyone check all the engine and trans mounts?
I wouldn't rule out the ujoints unless I pulled the driveshaft and felt the pivot of each joint myself.
They can get dry and bind up without feeling loose, and 25mph is about the perfect speed to cause a shudder you can feel.
I would almost put money on it being a dry joint.

"10 days"?
What the hell?
 
Anyone check all the engine and trans mounts?
I wouldn't rule out the ujoints unless I pulled the driveshaft and felt the pivot of each joint myself.
They can get dry and bind up without feeling loose
X-2 on the engine or transmission mounts!!
 
65 has the ball and trunion front joint, right? ANY play in that will do just what you describe. ANY play.
 
Yup, I'm with Mopar Tim. The vibe on acceleration at 25 mph or so points a big, flashing red neon arrow at the ball & trunnion front U-joint. You can still get the parts to overhaul them, but it's an expensive nuisance, and finding the knowledge to do it right is even harder. Instead proceed this way.
 
Yup, I'm with Mopar Tim. The vibe on acceleration at 25 mph or so points a big, flashing red neon arrow at the ball & trunnion front U-joint. You can still get the parts to overhaul them, but it's an expensive nuisance, and finding the knowledge to do it right is even harder. Instead proceed this way.
Sounds like u joint or driveshaft.
 
Yup, I'm with Mopar Tim. The vibe on acceleration at 25 mph or so points a big, flashing red neon arrow at the ball & trunnion front U-joint. You can still get the parts to overhaul them, but it's an expensive nuisance, and finding the knowledge to do it right is even harder. Instead proceed this way.

Plum forgot about the B&T possibility, thank you.
 
Anyone check all the engine and trans mounts?
I wouldn't rule out the ujoints unless I pulled the driveshaft and felt the pivot of each joint myself.
They can get dry and bind up without feeling loose, and 25mph is about the perfect speed to cause a shudder you can feel.
I would almost put money on it being a dry joint.

"10 days"?
What the hell?
They said they pulled the drive shaft and inspected the Ujoints. I told them exactly that. Tighten all engine and trans mounts. We'll see next week.
 
I will tell them to check B&T again on Monday and definitely tie all engine and trans mounts down tight. It seems like such an easy fix, but they're very busy and probably just gave it a quick glance. This is crazy! For this problem to just come out of thin air seems to point to something came loose. I broke my back, so I can't do it myself.
 
I will tell them to check B&T again on Monday and definitely tie all engine and trans mounts down tight. It seems like such an easy fix, but they're very busy and probably just gave it a quick glance. This is crazy! For this problem to just come out of thin air seems to point to something came loose. I broke my back, so I can't do it myself.
If you ever had a Early Mopar with a BandT joint, you would know the problem just is there one day. And I bet this is your issue.
 
One quick-n-dirty diagnostic technique for a B&T U-joint is to undo the nuts holding it to the transmission output flange, install two good quality flat washers on each of the four flange studs, and reinstall the B&T over the washers. If the vibration changes at all, that is a further indication that the B&T is worn out. It's not 100% sure-fire, though, depending on the nature/pattern of wear.

the problem just is there one day

Yep. Fine on Monday, vibrating on Tuesday.
 
From all above mentioned.......

Does braking increase or decrease
Shutter?
How bout putting in neutral during vibe?
Things change?

D.
 
One quick-n-dirty diagnostic technique for a B&T U-joint is to undo the nuts holding it to the transmission output flange, install two good quality flat washers on each of the four flange studs, and reinstall the B&T over the washers. If the vibration changes at all, that is a further indication that the B&T is worn out. It's not 100% sure-fire, though, depending on the nature/pattern of wear.



Yep. Fine on Monday, vibrating on Tuesday.
I have used that method to "fix" a joint before. Sold the car, A quick flip. It moves the wear area. :lol:
 
Yup, I'm with Mopar Tim. The vibe on acceleration at 25 mph or so points a big, flashing red neon arrow at the ball & trunnion front U-joint. You can still get the parts to overhaul them, but it's an expensive nuisance, and finding the knowledge to do it right is even harder. Instead proceed this way.

I bought a 63 Fury last year and it has a similar sounding acceleration shudder which I suspected was the B+T but wasn't 100% sure so this is really good to know.I'll definitely use that method to fix the problem as opposed to trying to track down replacement parts for the B+T.Thanks for the link.
 
I worked at a CPD dealer in 1986, the Lead Tech told Me to pull in this gold 318 4WD tk. & pull the rear end cover. I did, then asked what we were looking for. 4th time in
& had a shake/vibration/shudder at speed, everything in the diff. looked perfect, clean and tight. Buttoned it up & checked for missing drum weights, etc. The Service Mgr.
told Me to take it for a ride, at certain throttle positions 40-50mph it would start bumping then bucking, at one point it shook so bad it made it hard to focus thru My specs!
The rotor rivet holding the tip was loose & it would change position at a point where the advance under certain eng. loads would let it jump to the adjacent post...........
This "shudder" could be a bunch of things, certainly prop shaft issues as well, things bind under load that seem fine in Your hands. Lesson, assume nothing & check
everything..............
 
BTW, the bumping/shuddering of a B&T is replicated in modern FWD/AWD vehicles along with tugging on the steering wheel as the (usually 3) trunnions on the frt axles
do the same thing when they start binding......................
 
BTW, the bumping/shuddering of a B&T is replicated in modern FWD/AWD vehicles along with tugging on the steering wheel as the (usually 3) trunnions on the frt axles
do the same thing when they start binding......................

Yep, because both are actually CV joints.
 
Had a '64 Chrysler limo once that shuddered right after take-off and then at expentional increasing interval speeds.
B&T unit was already changed to u-joints adn I had the axle shaft balanced already. No help.

Turned out the transmission mount was totally mush and soft by being soaked with oil over the years, which let the transmission try and "work itself around" the driveshaft centerpoint.
 
B&T joints are actually very easy to service once you know how to do it, providing the wear is in the rollers and not in the body itself.
One catch is that replacement boots are nearly completely extinct. Quick, cheap trick is to use a boot from an off-road style aftermarket shock absorber. Most 4x4 shops can hook you up with one.
Cut it to about 8 inches, and feed it through the inside of the B&T body before you assemble the joint
 
Thanks for all the information. I live in a one horse town, so I have to lean on this shop for my projects. Problem is that hardly anyone is over 30 years old and they're not used to older vehicles. I'm going in on Monday and talk to the foreman about engine & trans mount and B&T inspection. I want to make sure they understand this is the probable problem.
 
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