drive line vibe decelerating on highway down hill only. hj47 (1 Viewer)

[calen]

Hi all, feel like this is thing ive read about this before but couldn't find anything about it. if its been discussed id love a link so ive got a low mild vibration at highway speed 95-100kmh going downhill when i let off the gas. if i accelerate again it goes away. if I let it idle/engine break, it goes away. it just vibes in the little slack driveline window. i could if i wanted, ride the window and keep it vibrating. its making my pinion weep oil. Its got a brand new, sticker on, split case. took the shaft off and pulled yoke, no play in u joints, no play in slip yoke. checked pinion angle, dead on, bolts all tight, flanges in phase (yokes lined up right?) There is play about .25" when rotating the output flange while tranny in gear. theres a little more then that at the flange of the diff. feel like that is normal? I would love any insight. thanks.

 

[mattressking]

Your flanges can have rotational play but not up/down or side/side so no it’s not correct and causing your decel vibration. Your pinion bearing is worn and you could temporarily tighten to zero play but the lash is out of spec and will perpetually worsen over time until you pull the diff and service bearings and reset lash.

 

[calen]

Your flanges can have rotational play but not up/down or side/side so no it’s not correct and causing your decel vibration. Your pinion bearing is worn and you could temporarily tighten to zero play but the lash is out of spec and will perpetually worsen over time until you pull the diff and service bearings and reset lash.

hahaha if it was moving a quarter inch side to side/up down, there'd be a'ellova lot more vibes on the highway!, probably would have a drive shaft poking through my floor by now definitely zero play. that is not the issue.

 

[peesalot]

Balance & slip spline wear. Get some old school drum brake axle grease, almost like cold butter, pack the slip splines, take her out and do a test, I bet that vib is gone at first and slowly comes back. easy test. give the u-joint a squirt with gun to be sure they are full. The pinion weep has not occured with my driveline vib which has been present for decades at 42 to 47 decel on offramps as you describe. Might want to check pinion bearing as mentioned with dline off, you can tighten but usually the bearing will start to get ratchety when doing so.

 

[calen]

Balance & slip spline wear. Get some old school drum brake axle grease, almost like cold butter, pack the slip splines, take her out and do a test, I bet that vib is gone at first and slowly comes back. easy test. give the u-joint a squirt with gun to be sure they are full. The pinion weep has not occured with my driveline vib which has been present for decades at 42 to 47 decel on offramps as you describe. Might want to check pinion bearing as mentioned with dline off, you can tighten but usually the bearing will start to get ratchety when doing so.

hmmmm, i mean there is no play in the slip splines. its well greased as well. again, U-joints were all tested with the shaft completely off, zero play. what am i looking for in checking the pinion bearing? it has no side to side play at all. just the slack pick up rotationally, which i believe is normal. is there a type of rotational play that might be indicative of something? like it has two stages of play. like if its rotated to full stop and then i rotate the other way, its "stepped" like two tiny stages of resistance before stopping, if that makes sense. like two gears fully locking up.

 

[mattressking]

hahaha if it was moving a quarter inch side to side/up down, there'd be a'ellova lot more vibes on the highway!, probably would have a drive shaft poking through my floor by now definitely zero play. that is not the issue.

I get that but in multiple trucks I've experienced the exact symptoms and pinion preload/play is the fault. Radial play is driven by the ring to pinion gear tolerance which is setup off the truck. If there is a lot of play then it can cause clunking as there is a delay in gear mesh between forward/reverse and coast.

If you truly know what you're inspecting and confirmed ruling it out - then look at engine/trans mounts because that's the majority of movement in the driveline.

 

[peesalot]

I hear what you are saying, I tried alot of fixes, cv, shimming rear pinion, had 3 diff drivelines all with stock fj40 slip, all vibed, its a combo of pinion angle, tcase flange angle, driveline balance, and slip spline. I have achieved = angles on rear diff flange and tcase flange guess what, same vibe. That said my 40 is SOA, the tcase & diff flange do not match, I do not run a cv, stock fj40 dline with modified yokes for clearance at droop, it vibes and spits ujoint grease out and cooks the rear diff pinion seals. Mine is not a dd tho.

 

[WildernessRimFab]

pinion preload/play is the fault

I'm with @mattressking.
Rear pinion is loose. This happened to my truck a while back shortly after I bought it.

Get a new pinion seal and stake nut to limp it along until you can rebuild the rear 3rd member.

 

[pb4ugo]

The pinion is supposed to have some rotational play. It's the spiders loading and unloading against the inside of the carrier. You say the driveshaft angles are good. Did you measure them. Did this vibration just start?

 

[calen]

I get that but in multiple trucks I've experienced the exact symptoms and pinion preload/play is the fault. Radial play is driven by the ring to pinion gear tolerance which is setup off the truck. If there is a lot of play then it can cause clunking as there is a delay in gear mesh between forward/reverse and coast.

If you truly know what you're inspecting and confirmed ruling it out - then look at engine/trans mounts because that's the majority of movement in the driveline.

no no, that was what I was looking for Id definitely know it was the problem if there was side to side movement, which there isn't any. so yes, very curious about how to know its the ring to pinion gear tolerance? is there something i can feel? or is it a "its seems to be nothing else so its gotta be that" thing? and can only be truly diagnosed by re preloading the pinion? I had a leaky pinion seal about a year ago, and replaced by just making sure the pinion nut went back on the same exact amount of threads and was staked back in the same spot.