Automatic Transmission Problems :)

[twood]

Hi all, I'm working on getting to the bottom of an issue I'm having and wondering if anyone has any experience with what I'm feeling.

The issue is as follows: On a hill, in drive, the car rolls backwards, very fast on steeper hills. I understand this isn't uncommon for auto trans, but the speed at which it rolls is concerning. Occasionally, there will be a clunk if I stop hard on a hill. Additionally, when coming to a complete stop, or when I let off the brakes when rolling through a stop at slow speeds, there is a slight clunk that I can feel in the gear shifter.

I'm much more concerned about the speed at which it rolls backwards, as it feels almost like it's in neutral.



I have done a stall speed test, which didn't seem to indicate any issues, no DTCs, no shuddering or slipping from the torque converter when driving or accelerating from a stop. Gear shifts are all smooth. I drained and filled the oil pan and the oil looked as fresh as it could be. Also checked the idle RPMs on a hill and on the flat and it stayed at a consistent 600RPM in drive. Even when I brought it up to 1000RPM on the hill, it still rolled back at an abnormal rate.



It's a 2000 SR5 3.4 4x4 with the A340F, but the previous owner had the transmission replaced with a used unit back in 2022. The truck is from Colorado, so it isn't the CA spec; however, the transmission was replaced with a unit from CA. The new (used) transmission is from a 99' SR5 which I am gonna guess is a CA model. This has made me question whether or not I'm getting an accurate reading from the dipstick, but I can't seem to read it anyways for the life of me so I'm less concerned about that as I already drained and filled it to the correct level. It's currently equipped with an external cooler as well.


I am inclined to believe that there is a blockage on either the filter, or the internal solenoids/ valve body. I will probably drop the oil pan in the near future and see if there's anything obvious internally, and probably change the filter while I'm at it.

Does anyone have any experience/input on what could possibly be going on?

 

[jgue467]

I am confused - if you can't read the dipstick how do you know its at the correct level?

These trans won't "clunk" unless they have air in the trans lines.

Have you greased the driveshaft? Those 'clunk' on fast stops when not greased well.

 

[3bears]

I dont remember that there was a difference in a state or ca auto tranny, guess I could be wrong. Years back I had to replace a pan on a 2000, and there was not a question as to what style.

if you cant read the dipstick you need to learn how or why not...wrong dipstick etc

 

[twood]

I am confused - if you can't read the dipstick how do you know its at the correct level?

These trans won't "clunk" unless they have air in the trans lines.

Have you greased the driveshaft? Those 'clunk' on fast stops when not greased well.

I ended up getting some XG-8 lubricant for the slip yoke over the weekend which fixed the clunk issue. I guess I assumed the clunk and the quick rollback were related and overlooked the obvious that it was the driveshaft.

I also dropped the trans pan last night and replaced the filter/ tested the solenoids while I was in there. The magnets were pretty clean and there didn't seem to be anything of concern. Then filled it back to the proper level with some Maxlife (I was having a hard time with the dipstick because it is pretty kinked and picks up a lot of oil from the sides of the tube when I pull it out, but my technique got better and I'm confident it is at the correct level when hot and after cycling through all the shift positions).

The car still rolls back pretty aggressively on a hill when letting off the brake, but I have to assume it's because it's got 33s and even the 4.3 gears arent enough to hold them in place. I havent seen anyone else bring this up anywhere on the internet which is why I am concerned there is something going on inside the transmission, but for now I'll just have to continue using the e-brake on the steeper hills.

 

[AuSeeker]

I ended up getting some XG-8 lubricant for the slip yoke over the weekend which fixed the clunk issue. I guess I assumed the clunk and the quick rollback were related and overlooked the obvious that it was the driveshaft.

I also dropped the trans pan last night and replaced the filter/ tested the solenoids while I was in there. The magnets were pretty clean and there didn't seem to be anything of concern. Then filled it back to the proper level with some Maxlife (I was having a hard time with the dipstick because it is pretty kinked and picks up a lot of oil from the sides of the tube when I pull it out, but my technique got better and I'm confident it is at the correct level when hot and after cycling through all the shift positions).

The car still rolls back pretty aggressively on a hill when letting off the brake, but I have to assume it's because it's got 33s and even the 4.3 gears arent enough to hold them in place. I havent seen anyone else bring this up anywhere on the internet which is why I am concerned there is something going on inside the transmission, but for now I'll just have to continue using the e-brake on the steeper hills.

When it's rolling back on hills, you haven't given us an idea of how steep a grade you're talking about, no automatic transmission will hold on a grade that is too steep, the weight of the entire vehicle is just too much when the grade gets too steep.

 

[twood]

Hard to estimate the exact grade of the hill, but I would say roughly 10 percent. At this grade, the truck would almost fall backwards as if it were a manual and the clutch was in, but its an automatic...

I ended up taking a second look today just to see if I was missing anything obvious. Turns out the external trans cooler that was installed by the previous owner was plumbed backwards, so the send line was at the top, and return at the bottom. I swapped them, and the issue seems to have resolved itself. Must've been trapped air since it never could purge it all through the system.

 

[phattyduck]

The car still rolls back pretty aggressively on a hill when letting off the brake, but I have to assume it's because it's got 33s and even the 4.3 gears arent enough to hold them in place. I havent seen anyone else bring this up anywhere on the internet which is why I am concerned there is something going on inside the transmission, but for now I'll just have to continue using the e-brake on the steeper hills.

Though your situation has improved, you can and should use two feet when driving offroad in steep situations. Gas it up until you get 'on the converter' (maybe 1300-1500rpm) then release the brake to avoid any backwards motion on steep hills. Obviously, in daily driving situations this shouldn't be needed (and you SHOULDN'T be two foot driving on the street).

-Charlie