Help with coasting vibration
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Help with coasting vibration
I have a '78 F150 4x4 with 4 speed, NP435 with NP205 transfer case. I have installed larger 33" tires about 5K miles ago. Truck has been running awesome, then suddenly, there was a terrible vibration when coasting. No vibration when under load (accelerating). Truck shakes badly side to side. There was nothing noticeable before this happened. I've done some searching, and people were all over the board. Spline bearings, U-joints, flywheel bolts, driveshaft center support, etc. I'm not very good at diagnosing driveline problems. Can anyone with experience give me an idea of how to efficiently troubleshoot this? Exact steps to take? I have shop manual on disc and Haynes, but it would be nice to know which to check out first, second, etc. and what to look for. Thanks in advance.
Postmaster
Joined: Jan 2013
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From: Panama City
And if I remember correct this truck doesnt have a driveshaft center bearing
Moderator & parts slinger
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From: S/W Missouri, Polk county
X2 on insp the rear d/s u joint straps or u-bolts nuts.
Insp the rear axle u bolts themselves for being tight, broken and or loose..
Insp the rear tires for a side wall bulge from cord separation.
Lug nuts tight? Wheel bearings good?
Swap the tires (rear to front) and see if the vibration and side to side play goes with it.
Insp the rear axle u bolts themselves for being tight, broken and or loose..
Insp the rear tires for a side wall bulge from cord separation.
Lug nuts tight? Wheel bearings good?
Swap the tires (rear to front) and see if the vibration and side to side play goes with it.
Hotshot
Joined: Feb 2004
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From: The Shenandoah Valley
A worn U-joint at one end of the driveshaft will let the driveshaft swing like a jump rope when not loaded as in a gentle coast down .... but will tend to self center under load like when power is applied or you gear down really low to assist with braking. Under such loads the cross's journals are forced to opposite sides of the bearing cups, they'll self center even after the rollers are powder. When not loaded, like in a coasting situation, they are not forced to self center, they will then "flop" and swing the driveshaft like a jump rope.
I'ld check U-joints really close.
I'ld check U-joints really close.
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I had/have the same problem. While on the gas or brake it rode smooth but coasting it shimmied. I jacked up my front end and could wobble my front tires the bearings were so bad. Should have them all back on and back on the road today. So I'll let you if that fixes mine.
My C bushings and radius bushings look bad too, but I'm not changing those just yet. Waiting to when I do my lift kit.
My C bushings and radius bushings look bad too, but I'm not changing those just yet. Waiting to when I do my lift kit.
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From: Pa.
yes .. Wherever there is a yoke or 2 drive shafts coming together check to see if the U-joint has slop by placing one hand on each side of the driveline with the suspect u-joint in the middle .. Try and twist it .. if you can't move it then it is good .. If you can move it then replace it ..
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From: US/Baja border
In neutral with parking brake on, wheels chocked
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From: S/W Missouri, Polk county
You need to take the "load" off the drive line to ck the "play" in the u joints. So yes in neutral and chock the wheels or parked against a curb with the e brake on.
Grab the d/s and the yoke and see if there is any play (movement/twist) in the end caps. Try to push it up and down also. You should have 0 play or free twist.
Grab the d/s and the yoke and see if there is any play (movement/twist) in the end caps. Try to push it up and down also. You should have 0 play or free twist.
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Thanks again for the replies. I put the truck in neutral, chocked up tires, and twisted at the joint. I'm hoping that's the problem, as there was a lot of play. Hopefully I can get to replace it this weekend. I will post to confirm that was the problem if it works.
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From: S/W Missouri, Polk county
Make sure you phase mark the d/s and slip yoke with a marker (sharpie) or paint marker.
Usually you only disconnect the lower end (remove the 2 lower small u joints around the u joint caps) and compress the d/s into the slip joint and then pop it out the lower yoke. Then slip it out the upper slip joint to work on it on the work bench.
You want to get the d/s and slip yoke back in the same "line" or back in "phase".
Also lube the slip yoke collar, there should be a grease zert on the end cap, if not lube it by hand.
Usually you only disconnect the lower end (remove the 2 lower small u joints around the u joint caps) and compress the d/s into the slip joint and then pop it out the lower yoke. Then slip it out the upper slip joint to work on it on the work bench.
You want to get the d/s and slip yoke back in the same "line" or back in "phase".
Also lube the slip yoke collar, there should be a grease zert on the end cap, if not lube it by hand.
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