Transmission Thud (1 Viewer)

[Cougar]

I have been searching for any information on this to no avail. I have a '98 100 series and sometimes when finished coming to a complete stop the transmission with thud ever so slightly. It only seems to happen when stopping a little quickly and the tranny almost "catches" up and thuds into place? Maybe the gears are catching? When you stop nice and slow it doesn't seems to happen. I am going to do the "normal" checking of fluid, but would appreciate any thoughts.

 

[Mark SR.]

I have been searching for any information on this to no avail. I have a '98 100 series and sometimes when finished coming to a complete stop the transmission with thud ever so slightly. It only seems to happen when stopping a little quickly and the tranny almost "catches" up and thuds into place? Maybe the gears are catching? When you stop nice and slow it doesn't seems to happen. I am going to do the "normal" checking of fluid, but would appreciate any thoughts.

I'd say the three most important things to do when trying to diagnose the dreaded "transmission thud" are search, search, and search.

-Mark

 

[Mark SR.]

Cougar,

Look first at driveshaft lube.
This has been discussed in great detail recently.
Try searching thump, thud, or clunk.
-Mark

 

[NMuzj100]

try "thunk" too!

 

[Tinkerer]

I have been searching for any information on this to no avail. I have a '98 100 series and sometimes when finished coming to a complete stop the transmission with thud ever so slightly. It only seems to happen when stopping a little quickly and the tranny almost "catches" up and thuds into place? Maybe the gears are catching? When you stop nice and slow it doesn't seems to happen. I am going to do the "normal" checking of fluid, but would appreciate any thoughts.

My '99 exhibits an occasional tranny clunk when slowing to a stop, as vehicle speed drops and gears downshift from 2nd to 1rst. It's a hard 2-1 downshift. At 110 k miles on original (factory) trans fluid, it may be related to fluid condition.

(This is not the same issue as the infamous rear driveshaft thud upon starting to roll, which is related to the driveshaft slip joint lube condition. THAT condition was resolved on my '99 by using moly type grease and pumping the joint over-full of grease, until grease observed coming out past the seals, per FSM.)

 

[NeilC]

grease your shaft. There is just no way to put that without sounding dirty.

 

[chief88]

I do remember some discussion on this recently (of course couldn't find it) but - I thought the consensus was that greasing the driveshaft slipjoint too much was a bad thing due to the pressure build-up and potential for driveline "binding"?? I have this problem, and lubed the u-joints and slipjoint - but definitely stopped short of "over-filling" as Tinkerer describes. I've got 120K on my '99 and I've never personally done this maintenance. Should I try a few more "pumps" to see if the "thud" goes away - or is there agreement that I can "over-fill" until grease seeps out past the seals?

 

[ShottsUZJ100]

Lube your tube!

 

[Tinkerer]

I do remember some discussion on this recently (of course couldn't find it) but - I thought the consensus was that greasing the driveshaft slipjoint too much was a bad thing due to the pressure build-up and potential for driveline "binding"?? I have this problem, and lubed the u-joints and slipjoint - but definitely stopped short of "over-filling" as Tinkerer describes. I've got 120K on my '99 and I've never personally done this maintenance. Should I try a few more "pumps" to see if the "thud" goes away - or is there agreement that I can "over-fill" until grease seeps out past the seals?

Remember - this thread started about the clunk when slowing down to a stop (caused by tranny 2-1 downshift in my experience), NOT the thud when starting to roll (caused by driveshaft slip joint).



But, about the driveshaft slip joint:

FSM says to grease it until grease is observed coming out past seal.

I read about the potential grease pressure & resulting axial load concerns too, and did not overgrease either, for a long time. Finally took the slip joint apart to see why it was thudding, and found nothing apparent wrong. After cleaning and lightly regreasing with non-moly grease, the thud disappeared for a while, then returned. Eureka! Must be stiction! Moly is good for reducing stiction, so I tried moly grease, and also followed the FSM instructions to overgrease until grease flows past seal. Now the thud is completely gone, has not returned for ~15k miles.

On the residual axial force in the driveshaft: I noticed that there was residual force in the assy when I first took it apart, due to air pressure! Apparently the slip joint seal works really well...maybe TOO well. So the shaft assy will have residual axial force whether slip joint is overgreased or not...I bet the thrust bearing in the tranny (and thrust bearing function in rearend input) are designed to take a fair amount of thrust, based on this observation.

 

[NeilC]

Lube your tube!

How about slick your stick?

 

[Cougar]

Cougar,

Look first at driveshaft lube.
This has been discussed in great detail recently.
Try searching thump, thud, or clunk.
-Mark

Thanks everyone. I forget sometimes that "base" terms like thud, clunk or thump is not only OK, but necessary when explaining and searching for stuff.

https://forum.ih8mud.com/showthread.php?t=22649

 

[Tinkerer]

I have been searching for any information on this to no avail. I have a '98 100 series and sometimes when finished coming to a complete stop the transmission with thud ever so slightly. It only seems to happen when stopping a little quickly and the tranny almost "catches" up and thuds into place? Maybe the gears are catching? When you stop nice and slow it doesn't seems to happen. I am going to do the "normal" checking of fluid, but would appreciate any thoughts.

FWIW, now confirmed on my '99 LX:

The slight "thud" or "clunk" in tranny, when slowing to a stop, was indeed a hard 2-1 downshift, apparently related to high mileage original factory trans fluid at 110k miles.

After complete trans fluid changeout (all 12+ quarts), the hard 2-1 downshift is completely gone. All other shifts are also smoother. Tranny is nice & smooth all the way around now.



(And the moly grease fill in the rear driveshaft slip joint is still keeping that other thud source happy and thudless. No thuds anywhere now.)

 

[bamachem]

Anyone else notice this? This just showed up on my 2007 after swapping from Toyota WS to Amsoil Low-Viscosity ATL.

 

[OregonLC]

bamachem, did this ever get resolved?

 

[bamachem]

Nope.

Only happens after a "quick, hard stop". Not an emergency stop, but more than just slowing down.

It's almost like the transmission is trying to downshift but doesn't get to 1st before the wheels stop moving. At that point, it's like it's not in gear at all. You can let off the brake and it won't move. You can give it gas and it will rev. It's like it's in Neutral. After anywhere from 1 or 2, and sometimes upwards of 4-5 seconds, it will SLAM into first. Hard. If you don't have your foot on the brake, it will give you whiplash.

Amsoil swears that the fluid is correct. They sent me some bottles to get a sample and send to them for verification. I will most likely be taking it to Mr. T for a checkup this week. My initial visit last week to ask about it and see if they've seen anything like it yeilded "it's the driveshaft. you need to grease it". I insisted that I knew what that felt like as I owned a 2000 LC for 5+ years. This was different. They were insistent that this was the cause. Said as the front dipped, air was getting trapped in the slip yoke and it was releasing all at once causing the "JOLT".

I tried to explain that the transmission felt like it was in neutral, and got the "you should try the grease first".

I did. Didn't fix it, just like I thought. I put a half-tube of Amsoil Syn Grease in it. TONS of old grease came out.

I'm going to have to make an appointment and get them to go for a ride w/ me. I can reproduce it sometimes, but I mostly can predict it right before it happens by the feel of the downshift than being able to reproduce it on every hard stop.

 

[OregonLC]

you don't think the slosh of the hard stop is temporarily starving it for fluid do you?

 

[alaskacruiser]

(Deleted)

 

[bamachem]

Odd if it is. I don't have the dipstick, but I followed the FSM procedure for getting up to temp (checked w/ IR gun after driving) and removing overflow plug and fill plug. Topped off fluid at exactly the right temp range. Maybe it's a little low? Sounds like you might be on to something. Hard stop = all the fluid at the front of the pan, and if low, the pickup runs dry.... Hmmmmm.... I have a half-quart or so left over. I think I'll add that tomorrow and see if it gets better or stays the same.

 

[OregonLC]

Odd if it is. I don't have the dipstick, but I followed the FSM procedure for getting up to temp (checked w/ IR gun after driving) and removing overflow plug and fill plug. Topped off fluid at exactly the right temp range. Maybe it's a little low? Sounds like you might be on to something. Hard stop = all the fluid at the front of the pan, and if low, the pickup runs dry.... Hmmmmm.... I have a half-quart or so left over. I think I'll add that tomorrow and see if it gets better or stays the same.

perhaps air was trapped in the system immediately after the flush giving an erroneous high reading?

while we're on the topic, what is the point of checking the ATF running and hot? i'm having a hard time understanding why there wouldn't be a valid check for cold/off.

 

[bamachem]

perhaps air was trapped in the system immediately after the flush giving an erroneous high reading?

while we're on the topic, what is the point of checking the ATF running and hot? i'm having a hard time understanding why there wouldn't be a valid check for cold/off.

You guys are BRILLIANT and I'm the moron.

Seriously.

You peeked a question that I had to find the answer to. In my haste to get the job done, I neglected to fully read and COMPREHEND the FSM/Bulletin Procedure as outlined here. Yes, I am the moron who checked the fluid level in his A750F transmission at the right temperature, but with the engine OFF.

I know better! I know to ALWAYS check fluid with engine warm and running! I'm kicking myself in the ASS for this!

Anyway, I now know exactly what the issue is and how to fix it - leave it running and top off the fluid.

THANKS for being a sounding board for diagnosis!

$50 also says that the same thing was wrong w/ the original poster's transmission - quart low or so - and by changing the fluid, the proper amount was replaced.