Just got a 98 2500 quad cab auto trans cummins. The motor runs great but I'm not crazy about the way the trans shifts. The truck was a trade in to a dealer that maintained the truck since new. They rebuilt the trans 20K miles ago.

The trans seems to start out in 2nd, then quickly shifts into first, then shifts back into second fine. Then it hangs in second until the revs hit nearly 2300 or until I back way off the throttle, then it shifts into third and fourth almost immediately. Also, if I accelerate very slowly, it seems to shudder a few times for a second before it gets going. I also am having a problem with the heater control - I get temp control, but I only get air out of the defroster. The vacuum line to the firewall is pulling vacuum, the the control doesn't work.

Is there a connection? Does the trans have a vacuum modulator like GMs do? If so, could a vacuum problem be causing the shifting problem?

Is this kind of shifting problem common? Any fixes I can try?

Appreciate any comments and/or advice.

Thanks...Steve.

 

sounds like a problem in the valvbody or the pressure control cable needs to be adjusted

 

That's a 47RE. It could be the TV cable. Th eGovenor Pressure solenoid and sensor are notorious problems and some junk could have messed them up. A shop with a reall scanner should be able to diagnose this as by watching the pressure that the sensor and solnoid are seeing.

 

It's not one of the cheapos but does real time data logging. Will it be able to pull the trans trouble codes? If so, I'll get after it tonight. Is the ODB-II connection under the dash like on most cars?

I've done some searching and believe that I have the Chrysler code definitions, just wasn't sure if the trans computer was standard ODB-II.

Thanks for the help.

Steve.

 

Yes the scanner port is under the dash on the drivers side.....closer to the trans hump IIRC. My buddy pulled the codes out of mine with my trans dumped and it threw a gov pressure code....if it has real time data logging you might be able to take it for a spin and see what it says but I don't know whats normal and what isn't. I know my trans guy took mine out for a spin and because of the readings knew the sensor and solenoid were bad because of the readings.

I pulled this reply off of DR from member Tim Holt:

The solonoid is a pulse design, that means it shuttles the valve in it at a very rapid on/off. The signal can be read with a osilliscope and thats how it controls GOV pressure.Over time the bore and valve wears and lets the fluid to bypass rather than being controlled. It takes very little wear for the fluid to bypass and lock the valve from equalizing pressures. The sensor also fails because of the pulsed fluid pounding on the litttle pressure pad and tiny little circuit board. The computer needs to see the pressure that its commanding the solonoid to make. It can make little adjustments to the solonoid PWM (pulse width modulation) signal and can, to a point, compensate for the solonoid wear.

On a data scanner there is a desired pressure and a actual pressure that can be read from the scanner and these need to read within one PSI of each other. If the actual pressure starts getting erratic then shift problems occur. When the actual pressure gets fixed or locked then wrong gear starts or no shift will happen. This can happen when either the solonoid or sensor fails. The best idea is to replace them both instead of just one.

The Dodge solonoid uses a sliding valve and the GM version of the aftermarket replacement uses a pintle design. The pintle version is a lot less victim to debris, fast failure due to the lack of fluid changes and high pressure.

These components do not control line pressure and does nothing for shift quality. They only control when the shift valves are stroked. The main VB is still a 727 design and needs a govenor to work. Instead of a mechanical govenor, a computer generated one is used. This has the advantage of a much shorter OD housing for 4X4s, but created other problems that the list is long.

If your having a sliding second gear, then likely the front band is way out of adjustment due to the band lining being worn too thin. At this point a band replacement and a general refresh job is reccommended. Do it before the band goes to metal to metal contact with the drum and more expensive parts need to be replaced


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Another post from Tim:

If you can get a scanner to look at the live data from the computer, not just read trouble codes, you can look at the desired Gov pressure and the actual pressure. They should read within one pound of each other. If not, replace those components.

 

My code reader/data logger found no error codes. Took it for a ride and TPS, Temp and RPM seem OK. No visible holes in TPS output - seems continuous.

Can the solenoids/ pressure sensors go south and the computer not throw a code?

I'm stumped.

Any advice/help appreciated.

Thanks...Steve.

 

Have you adjusted the TV cable? If not have it set so with the pedal at full throttle you have about a 1/16" of play in the throttle valve arm.

 

Fooled around with it a bit - 1/8" slack and tight - no change. Trans still seems like it starts out in second for 1 sec, downshifts to first, shifts to second and hangs there. It won't shift to third unless I back off for a few seconds, then it will shift to third and fourth very quickly. Once in fourth, it won't downshift under 50 mph.

Trans doesn't seem to be slipping and the shifts are OK..when they happen. Computer is still showing no codes.

Already checked all the obvious stuff like shifting linkage and fluid level. Fluid is nice and pink and no burnt smell. Trans sent by dealer to local shop for rebuild 20K miles ago. No transferrable warranty of course.

Any advice greatly appreciated.

Thanks...Steve.

 

Okay....it's got to be a valve in the valve body and my guess is the TV valve. Do you know if a shift kit was installed when it was rebuilt? I had a problem with skipped shifts after my rebuild. What happened was the line pressure was increased and the PCM has minimal programming in it so it was stroking the shift valves but because the line pressure was increased with the shift kit it was actually stroking the 2 and 3 shift valve so under normal driving mine would shift 1-3-OD-LU. Under very light throttle and full throttle it would shift 1-2-3-OD-LU. Now my builder and I were discussing this issue and Tim Holt told me about a little experiment he was doing to cure this problem. The cure was to trim .040" off the stem of the TV valve. This spread out my shifts and kept them from stacking. I still have the stack shift with a bit heavier foot but during normal driving it's gone. I am not a big fan of the Trans-Go shift kits for this reason now. I have been talking with Karl at Redline Diesel and he builds his own Valvebodies and he is not a fan of the Trans-go kits either. I think you are having a VB issue where a valve is bleeding off pressure and causing the issues. The valve might be bad or it wore out the passage and is leaking past. I would give Karl a call and run it past him. Swapping a VB isn't to hard and can be done in the driveway as long as you keep things clean or you can have a local shop do it. Redline Diesel: (330) 624-7000

 

Turns out my trans wasn't hanging at the 2-3 shift, it was hanging at the 3-OD shift. My 1-2 shift was very short and kinda slushy and I missed it. When I manually shifted the trans and did some RPM-speed tests, I was able to figure out what was happening.

I tried adjusting the TV cable by giving it a little more slack. Interesting change. Before, when the TV cable was within 1/16 inch of snug, the 1-2 shift was at 1,700, the 2-3 shift was about 2,000 and the motor would hang around 2,300 until I let off, then would shift into OD and lock up within a couple of seconds.

Now, with about 1/4" slack in the TV cable, the motor shifts at about 2,400 on 1-2 and 2-3 and will hang for about 5 seconds at 2,500 (sounds like it's on the governor) until it shifts into OD, but it will shift into OD now, just not quickly.

Sounds like I'm on the right track but it also seems like too much change - and the wrong ones - for an over-slack TV cable. I figured an overslack cable would cause the trans to shift at lower RPMs, not higher ones. I'm at the weekend house and 120 miles from home so I'm a little leery of adjusting too much further.

Does all this make sense? Should I try even more slack?

Also, I noticed that my trans fluid seems a little overfilled. Like by about 3/4 inch. However, the trans dipstick isn't a good fit and seems to be bottoming out on the pan so I'm not sure if it's measuring accurately, or sitting too low. Could an overfill condition be causing shushy shifts and a reluctant OD?

Also, I checked with the trans shop that did the rebuild for the dealer for the prior owner. They did not do any mods to the trans - stock TC and VB.

Thanks for all your help. I appreciate it.

Steve.