Yet Another Transmission Thread - 48re shift issues and more

[deathbysnoosnoo]

I've been tracking some issues with my '07 with a 48re. Hopefully the usual experts will poke their heads in here and chime in.

Basics

• Bought in '13 and PO stated the transmission was a Suncoast. Visually it is the original case so if anything the PO upgraded internals. TC is gray, not orange like some however I’ve seen sites that sell SunCoast TC’s that look identical to mine so I’m not sure if this is an old model or newer. I have a picture if it'll help
• DNJ governor pressure solenoid
  
• Believe it has a shift kit/modified valve body based on firm shifts
  
• Front and rear bands adjusted. Lots of adjustment left
  
• Fluid and filter changed a couple thousand miles ago. My sense of smell is broken but I was told the fluid smelled burnt before changing
• A little bit of material on the magnet, about a 1/4" thick. Rest of the bottom of the pan was pretty clean

Issues/Complaints

• 2-3 / 3-2 clunk. Most notable when the engine/trans warms up. All u-joints appear original but are tight from front to back
  

• When TC locks at 52 mph the engine seems to bog down - noticeable drop in RPM (don’t have the exact amount but will get that info). I want to say it feels like it slips based on the lack of horsepower it has right after it shifts but not knowing how a truck should shift I may be off on this. Under more throttle it locks up at 60-62 and it doesn’t dog down and sounds more normal
• Sometimes the shift from OD to lock is short when on the throttle. Ex: Climbing a grade in the mountains and it'll go, from a dead stop, 1, 2, 3, OD then quickly into lockup

• Trans runs 190-196 degrees on hot days. Hot as in >=96 degrees and AC on. This occurs once I get off the freeway and hit 3-4 lights before reaching my destination. Understood increased temps in stop and go traffic are the norm but 190+ measured from the in-pan sensor seems excessive. All cooling components on front of truck were inspected months ago when radiator was replaced

• Sometimes TC locks up in 3rd under light acceleration and deceleration. Usually the pattern is 1, 2, 3-lock, 3, Lock where the last two are really quick and unnatural and the bogging issue mentioned above occurs

• P1740 code shows up sometimes. All I’ve ever found from day one on this is “it’s normal for an aftermarket TC”. With all of the problems I have I question if that is true in my scenario

I would like to get to the bottom of this issue - determine what the issue is and is this something I should tackle myself or take to someone. I'm willing to tear into it as I've done a lot of work on this myself (injectors, installed a newer and shorter lift, AC repair) but transmissions are something I've never touched.

 

[cerberusiam]

Sounds pretty normal for a tall tire truck with a tight converter.

The clunk seems to be more in line with t-case wear, or, center support bearing worn (if it is a long bed).

 

[deathbysnoosnoo]

Sounds pretty normal for a tall tire truck with a tight converter.

The clunk seems to be more in line with t-case wear, or, center support bearing worn (if it is a long bed).

Thanks for the reply, Cerb. It is a short bed. What is a good way to verify the amount of play in the transfer case? What is an acceptable amount?

 

[cerberusiam]

By hand and see if there is much slack, pretty subjective what will make a clunk though. Slip yoke slack and movement on the t-case housing is another area. With the enhanced pressures and firmer shifts ANY slack has the potential for more noise.

 

[deathbysnoosnoo]

By hand and see if there is much slack, pretty subjective what will make a clunk though. Slip yoke slack and movement on the t-case housing is another area. With the enhanced pressures and firmer shifts ANY slack has the potential for more noise.

So it can be done with the transmission in park and wheels on the ground?

 

[cerberusiam]

So it can be done with the transmission in park and wheels on the ground?

That will bind it up if there is any slope. Leave in park and get the rear wheels off the ground to look for slack works better.

 

[deathbysnoosnoo]

Update: U-joints are fine. No unexpected movement.

I've noticed that when slowing down I see the edge says I'm in 2nd but I'm actually in 3rd. I can manually drop it down and feel it grab second. That explains the sluggishness I've had when taking corners, etc. It's fine during the 2-3 shift when accelerating.

Is the only cause for this a bad governor solenoid?

My 2-3 / 3-2 clunk may be caused from the sonnax accumulator causing 2-3 over-run. Is the fix for this just not using the sonnax and going back to stock?

 

[cerberusiam]

Have you replaced the gov pressure transducer lately? It sounds more like it is bad and just giving false info. Might be time to try the BD transducer and see if that helps.

Have you advanced the TTVA motor a tooth or 2?

The accumulator just cushions the shifts under high TQ, IE upshift under power.

 

[deathbysnoosnoo]

I bought the truck 3 year ago and it had a DNJ components gov pressure solenoid already in it. I do not know how long it has been in there though. Even if I have the upgraded one they do still go bad is that correct?

I also do not know if the TTVA has been advanced. Is there an easy way to tell if I pull if off the transmission?

I may be confusing terms here - accumulator and servo. I came up with the 2-3 / 3-2 over-run thought from here - http://www.cumminsforum.com/forum/3rd-gen-powertrain/1728593-48re-slips-then-hard-shift-3-4-a.html. I would say that's what my shift feels like. Whichever one you can see exposed when the pan is dropped is the sonnax part I have in my truck.

 

[cerberusiam]

As a rule the GM type solenoids don't ever go bad, even the OD solenoid is not that bad, the OE gov housing is a bigger issue. The transducer being the same crappy OR piece causes more issues than anything, it will start drifting readings after 20k and make a precision setup act weird. The sloppy stock stuff doesn't make as much difference but they shift weird anyway at times. Changing the OE transducer every 25-30k when you do a fluid exchange solves most of the problems.

The 2-3 and 3-2 shift are done with the front servo, the OD shift is controlled by computer and a separate 3-4 accumulator that should have been fixed with the rebuild. The OD shift circuit doe snot normally effect the 1-2-3 shifts as they are all hydraulic not electronic.

As usual on CF they got out into the weeds with totally baseless recs on stiff that doesn't matter. You have to sift that detritus with a fine filter to find anything partly useful at times.

If your shift issues are 2-3 and 3-2 then it is the front servo and gov pressure that will impact it for the most part. If you just have a clunk and no problems with shuttle under low throttle opening or weird 2-3 shifting then it is likely in the gov pressure and TTVA settings. An advanced TTVA setting will cause a clunk on the downshift coming to a stop, it doesn't really hurt anything and the benefit is less shuttle on acceleration. A clunk on a 2-3 shift could be something worn in the drive train or just an extra firm shift point, it is hard to tell exactly what you are feeling. It is entirely possible the PO advanced the TTVA motor to compensate for the crappy OE setup.

There is a cover on the bottom of the TTVA motor where it sits on the TV shift of the trans. If that looks like it has been messed with it has probably has. Factory has nice smooth clamps on the tangs with no marks, usually you see evidence of plier marks or chisels on the tangs if they have been modified.

 

[akhappyjack]

Is the intermediate band adjusted correctly tighten to 72 inch pounds back off 2 turns? I set back mine off 1.5 turns if the band to loose or stretched will cause a flare going into 3rd and a clunk on 3-2 downshift just a thought

 

[deathbysnoosnoo]

The band has been adjusted twice because i thought this may have been the problrm. i will adjust it again and test drive.

i checked the ttva and i cannot see any evidence of it being tampered with.