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Tranny need a tune?

dodge123

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dodge123 Enthusiast

dodge123

Posted
Posted

Lately the transmission seems like it slips a little bit when shifting from 3-4 and even 2-3 when under moderate acceleration. It revs up to about 3500 rpm in the 3-4 shift when accelerating onto the highway. I was told when I bought the truck last January that the tranny was replaced recently with a remaned unit. Ive put 20k on it so far this year. Could it simply need a tune or should I have a dealer run a diagnosis on it? The shifts dont feel as rough as I would like. I like to feel the truck bang into each gear so to speak.

 

I changed to fluid and filter about 6000 miles ago and use dex 3 non-synthetic and keep the level full or a bit above. I did run it below the low mark on the dipstick for a couple hundred miles one week though. I also scratched the bore a bit in the tranny where the filter seal fits into upon removal of the old one. I made sure to lightly sand the scratch with emery cloth to take off the rough edges and I wiped the bore clean to remove any aluminum particles. The new seal fit tight and covered the scratch anyway.

nbuchanan Enthusiast

nbuchanan

Posted
Posted

Put it in tow/haul mode and see if it does the same thing. It should shift nice and firm with that on, if not then there is probably a problem. My transmission has always "slipped" a little between gears, but thats how they work these days for "comfort".

yukon25008.1 Senior Enthusiast

yukon25008.1

Posted
Posted

Thats a pretty stupid comment! " if it slips its done"

Any transmission can be only 1 qaurt low on fluid and slip..

wavery Enthusiast

wavery

Posted
Posted

Just a tip..... NEVER run the ATF above full, hot. It won't cause slipping but it can blow seals out.

 

Your comment, "It revs up to about 3500 rpm in the 3-4 shift when accelerating onto the highway." doesn't tell us much. What is important is the RPM before the shift compared to the RPM during the shift. 3500RPM would be pretty normal while accelerating onto the highway. If you said that it started the shift at 3500RPM and went to 4,000RPM before settling @ 2500RPM after the shift, that would indicate a problem.

 

If the trans is slipping, either your clutches are shot or you are loosing oil pressure somewhere. Sucking air around the filter seal will cause a loss of pressure, so will a bad pump or pump seal. If the trans were sludged up, I might suspect valves sticking in the valve body but that doesn't sound likely.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

Thats a pretty stupid comment! " if it slips its done"

Any transmission can be only 1 qaurt low on fluid and slip..

 

 

well thank you very much ,you must feel better now ,

 

i guess i didnt explain the whole gd process for you as to why i said that ,

 

got spell check ???

dodge123 Enthusiast

dodge123

Posted
  • Author
Posted

I havent driven the truck today to pay attention to exactly how the rpms look but, I do have a fluid leak from the pan gasket. I had the leak when I bought the truck and after I changed the fluid and gasket it became worse. I suspect I had the wrong torque numbers and I havent wanted to waste money by doing the job over again right away. I dont remember how the tranny shifted before I serviced it.

 

I have put 20,000 miles on the truck since I bought it.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Just a tip..... NEVER run the ATF above full, hot. It won't cause slipping but it can blow seals out.

 

Your comment, "It revs up to about 3500 rpm in the 3-4 shift when accelerating onto the highway." doesn't tell us much. What is important is the RPM before the shift compared to the RPM during the shift. 3500RPM would be pretty normal while accelerating onto the highway. If you said that it started the shift at 3500RPM and went to 4,000RPM before settling @ 2500RPM after the shift, that would indicate a problem.

 

If the trans is slipping, either your clutches are shot or you are loosing oil pressure somewhere. Sucking air around the filter seal will cause a loss of pressure, so will a bad pump or pump seal. If the trans were sludged up, I might suspect valves sticking in the valve body but that doesn't sound likely.

 

 

I fail to see how running the trans fluid a bit over full can "blow seals out". My experience is almost completely with the older Chrysler 3 speed auto trans, but, the principles are the same. Too much oil does not mean too much pressure. About the only thing I can see it doing is maybe aeration, but, you would need to have double the fluid inside the trans have that happen and that would not blow a seal. I would think that you would also have fluid running out of the vent at that level as well.

I am not saying it is safe or good advice to run more fluid than recommended, just never agreed with the "too much oil will blow seals" argument.

wavery Enthusiast

wavery

Posted
Posted

It's not like it's going to "Blow-out" the seals from over pressurizing. Too much ATF can cause foaming. Foaming can cause hot spots and can damage the seals...... The seals get hard and leak.... thus the "Blow-out" comment. When a seal leaks, we usually say that the seal is "Blown".

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

It's not like it's going to "Blow-out" the seals from over pressurizing. Too much ATF can cause foaming. Foaming can cause hot spots and can damage the seals...... The seals get hard and leak.... thus the "Blow-out" comment. When a seal leaks, we usually say that the seal is "Blown".

 

 

i am sorry but the hot spot thing is new to me ,explain that ,i was a tranny guy for a few yrs and that wasnt mentioned once in any of the GM courses i took,,not saying its BS ,just learning

wavery Enthusiast

wavery

Posted
Posted

When you get foaming, you get some super-heated air passing through the system instead of solid oil that has absorbed the BTUs. Just like air getting into the engine cooling system. Doesn't usually hurt hard parts but can overheat the seals. At least that's what I was taught in college.

uh6tdrvr Enthusiast

uh6tdrvr

Posted
Posted

No professional knowledge on this but the two times i have transmissions rebuilt both said dont EVER over fill the tranny. When i bought my 09, they too some fluid out because it was over the full line and when i had the pump seal replaced a couple moths ago he pulled some fluid after he over filled it.

Two completely different trans shops and two different dealers in different states.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

No professional knowledge on this but the two times i have transmissions rebuilt both said dont EVER over fill the tranny. When i bought my 09, they too some fluid out because it was over the full line and when i had the pump seal replaced a couple moths ago he pulled some fluid after he over filled it.

Two completely different trans shops and two different dealers in different states.

 

 

overfilling is obviously dumb ,,

 

i like gms dipsticks the best with full cold and hot levels ,either ford or dodge have full hot only which is ghey !!!lol

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