Late shift from 1st to 2nd

[rammertide07]

Buddy of mine has an 04 Sierra Z71. He called me and asked me for my input. He said his tansmission shifts late from 1st to 2nd...about 4000rpm. He's had the truck for about 6 months and this is not normally what it does. He said all other shifts are fine. I'm thinking along the lines of maybe a filter needs to be changed (maybe not if rest of the gears are shifting fine?) or valve body.

Also, the fluid in it has been changed since he has had it (except the filter) and the current fluid level is full and does not smell burnt.

 

[Molson02536]

Buddy of mine has an 04 Sierra Z71. He called me and asked me for my input. He said his tansmission shifts late from 1st to 2nd...about 4000rpm. He's had the truck for about 6 months and this is not normally what it does. He said all other shifts are fine. I'm thinking along the lines of maybe a filter needs to be changed (maybe not if rest of the gears are shifting fine?) or valve body.

Also, the fluid in it has been changed since he has had it (except the filter) and the current fluid level is full and does not smell burnt.

Start with the simple and Check TPS for smooth and linear electrical response over the entire range of motion. If not, replace.

Other area would be leak in the 2nd gear apply circuit (servo assembly or 1-2 accumulator). Doublecheck by using the pressure gauge on the pressure test port and watch for a big drop when the PCM commands 2nd gear. Worst case, poor line pressure rise.

IF its only at WOT, the 1-2 accumulator piston cracked or stuck cocked in the bore. Check the yellow spring inside the accum housing for breakage. Also, if the accumulator housing walls are scored, the housing must be replaced. Easy fix in the pan.

Hope this helps and keep s posted.
Molson02536

 

[rammertide07]

Start with the simple and Check TPS for smooth and linear electrical response over the entire range of motion. If not, replace. Where does he test at and what voltage should be seen?

Other area would be leak in the 2nd gear apply circuit (servo assembly or 1-2 accumulator)Where is that?. Doublecheck by using the pressure gauge on the pressure test portWhere is it and how much pressure should be seen? Should he just put the rear end on jack stands and run it like that through the gears or does there need to be a load on the drive line? Is it a NPT thread test port?..Just use a liquid pressure gauge? and watch for a big drop when the PCM commands 2nd gear. Worst case, poor line pressure rise.Worst case?..what would that mean?

IF its only at WOT, the 1-2 accumulator piston cracked or stuck cocked in the bore. Check the yellow spring inside the accum housing for breakage. Also, if the accumulator housing walls are scored, the housing must be replaced. Easy fix in the pan.

Hope this helps and keep s posted.
Molson02536

Thanks for the informative response. Sorry for all of the questions, but neither of us know the specifics of this transmission. I know my transmission pretty good by being on the forums and learning. Is there any of the above mentioned inspections viewable via OBD2 port?

 

[Molson02536]

Thanks for the informative response. Sorry for all of the questions, but neither of us know the specifics of this transmission. I know my transmission pretty good by being on the forums and learning. Is there any of the above mentioned inspections viewable via OBD2 port?

There maybe a transmission code stored in your data but and the TPS my not show up as a code unless its not sending out any readings at all.

Start with the TPS (Throttle Position Sensor) to make sure that it has a smooth and linear electrical response over the entire range of motion. If not, replace.

Keep us posted.
Molson02536