A440F auto transmission "thud" when letting off gas

[Super77]

For the few years I've owned my truck, it's made an occasional transmission "thud" when letting off the gas, typically after climbing or accelerating. It seems to be a hard 1-2 or 2-3 upshift. I initially suspected the kick down cable, but reading here, that seems to apply to the opposite situation: delayed downshift. No problem with those. I can somewhat control it by feathering the gas at the right moment. I get a similar noise when shifting into R from a cold start, although I run a high start idle, so that might be related.

Any thoughts on what might be causing this? I'm about to do a Rodney flush and install a tranny cooler, so I'm hoping to address any other maintenance issues.

 

[Shes Mad]

I'd start with u joints. See if you have play there, or possible clunking in the rear axle.

Then motor and trans mounts. Any one of those that have separated from the rubber will cause a nice clunk when getting off power. Try power braking and see if you have engine movement out of the ordinary, or clunking.

 

[Cruiserdrew]

It's wear on the transmission output shaft. 62s are particularly susceptible to this. Read up on McNamara gears. You need one.

 

[SteveH]

How many miles on the tranny?

 

[Super77]

How many miles on the tranny?

Just a bit over 200K.

 

[3_puppies]

as @Cruiserdrew stated above it is a good chance the output splines.
you can remove the PTO cover and see the gear and check for play.

 

[Super77]

as @Cruiserdrew stated above it is a good chance the output splines.
you can remove the PTO cover and see the gear and check for play.

I was just about to ask how to check for wear. I know how to check the U-joints. Can anyone provide more detail on removing the PTO cover? First time for me working on this part of the truck.

 

[Living in the Past]

PTO cover is on the left side of the T case. Held on with six bolts. If your is like my 1990 spare T/T it will have a PTO gear and a spacer. The splines are not visible. If it has a PT0 gear hold that and try to move the input gear with the T case in neutral. The movement between the gears should show how much wear on the output shaft where the input gear rides. This also depends on how tight the nut on the back is. If it is really tight might not be able to check the wear by just wiggling the gears by hand. I've tried this on a FJ62.

 

[Devils Paw 80]

It's wear on the transmission output shaft. 62s are particularly susceptible to this. Read up on McNamara gears. You need one.

Not necessarily. Mine has always done this in my 14 years of ownership, both before and after McNamara gear. And, my output shaft wasn't actually very worn when inspected. I think it may in some cases just be internal transmission wear.

 

[dffj6288]

Rodney flush you disconnect the oil cooler return line right the one on passenger side of radiator?

 

[Randy88FJ62]

I still get this clunk with my DIY McNamara installed. Not as harsh as the one you are describing. Makes me want to check the trans mounts!

 

[SteveH]

Various automatics will bang or thud if you let off the gas just as the transmission completes an upshift. This is just due to the way it was programmed or the internal design - not really a defect. A harsh cold engagement into reverse is just more typical of an older, tired transmission.

 

[DirtRoads]

Various automatics will bang or thud if you let off the gas just as the transmission completes an upshift. This is just due to the way it was programmed or the internal design - not really a defect. A harsh cold engagement into reverse is just more typical of an older, tired transmission.

My trans shifted a lot more smoothly after installing a new kickdown cable. I can only assume it was because the old cable would stick and hold the line pressure too high for a smooth shift.

 

[lechnito]

I vote that you take a look at your kickdown cable.

When mine went bad recently at just a bit over 200k, it caused my trans to be "stuck" in a low gear. This definitely resulted in some thuds on deceleration and some inappropriately high RPM driving. I've also experienced a thud when I tightened the kickdown cable down too much.

The kickdown cable is connected to a lever inside the trans that controls how much ATF gets pumped through the valve plate. When you push the throttle, the butterfly switch on the throttle body pulls the kickdown which mechanically relays the position of your throttle back to the pump. Over time, the wire inside the cable can get corroded, which impedes or entirely prevents the trans pump lever from pulling the wire back when you stop pushing the throttle.

Hit me up if you want some tips for replacing the cable without dropping your trans.

 

[ColoCruiserJeff]

Old thread, but thought I'd reply as I just picked up a '91 FJ80 with 315k and it does this exact thing. From letting off the gas there is a thunk. The front driveshaft will rotate by hand a good bit and I'm not sure how much play is acceptable in the drivetrain. I'll definitely check and change fluids all around...and read about the gears you all mentioned.

 

[lechnito]

@ColoCruiserJeff, don't forget to check out the kickdown cable.

 

[ColoCruiserJeff]

I'm not sure what to "look-for" in regards to the cable...it is present and accounted for

As far as adjustments go - Im gonna have to search those out.

One thing to mention is that the thunk goes away completely whenever I engage the center differential lock and test drive it. Definitely scares me that the tranny/t-case are all needing to be rebuilt.

 

[SteveH]

My brother had a bearing fail in the transfer case of his '94 LC and it caused the rear of the transmission to leak suddenly and dramatically. But, one of the symptoms before the leak was a 'thud' when he let off the gas.

Might be worth draining the xfer case and checking the magnet to see if it's clean or covered with shavings.

 

[Michael Hanson]

HI, I totally rebuilt my transfer case with Toyota parts, wasn't cheap, and it made no difference in the clang which it's had since I bought it. Keeping the drive shafts lubed up helps our cruiser. Mike

 

[pithicus]

Mine used to clunk rather than thud. Did it for years without issue. Eventually replaced the trans and transfer case and it went away,
Not sure what would happen if the spline stripped. No drive or reverse I suppose.