48RE Problem!

[MLamb]

I don't want to alarm everyone but thought I would get this out to see if anyone has had a similar problem.



Symptom - Under hard acceleration and after shifting from 1st to 2nd the transmission appears to slip (high revs, loss of acceleration). When I back off on the throttle it shifts fine. I can't seem to make it happen every time and it happens with or without a load. Date of manufacture is 01/03.



Diagnosis - Dropped it off at the dealer today and just got the call I was dreading "... there definitely is a problem and we are still investigating".



I am hoping its nothing more than a chip/program/sensor deal but worried nonetheless... I'll keep the board posted but I'm interested in hearing any theories some of you may have (other than: "shoulda gotta 6 pack!!!")



Thanks

Mark (aka DockHigh)

 

[MLamb]

Picked it up from the dealer yesterday. They said they were able to duplicate the problem but saw no error codes. They adjusted the throttle linkage and added oil and told a skeptical me that it was good to go. I must have checked the oil 5 times before bringing it in so I knew that part of the 'repair' had no merit. Sure enough, its still doing the same thing. Must check and see how much extra transmission oil I have now. .

 

[Steve M]

If it's after a hard acceleration and then you have to let up alittle for traffic or whatever reason after it shifts to second. My 47RE does the same thing. If it's the same thing... It feels like it gets real confused about which gear to be in. If I maintain throttle pressure whether it's light or heavy, it does ok but if I have to let up on the throttle right after a 1-2 shift, it does it's strange shifting thing whatever it's doing. I don't know if it goes back to 1st for a split second or third and back to second before it straightens back out but it is doing something it shouldn't do. If I'm towing our 5th wheel, it does fine and doesn't slip at all. I've decided not to worry about it.

 

[MLamb]

No Steve, its definitely a slip. I understand the issue you are describing and its not that. Imagine putting the throttle to the mat and happily accelerating through the gears and someone throws the gear shift into neutral... that's my problem. It only happens when going into the high tension area of the accelerator pedal -you know that area at the top of the travel where the spring gets a little stiffer, some call it the kick down. Even then, its not all the time. .

 

[Bill Stockard]

MLamb,



Since you are in Dallas and if I were you, I would contact TDR member "inarush76" the local DTT installer and a very good, honest automatic transmission man. I would pay him to diagnose the problem. If there is a problem, you'll know what it is when you go back the the dealer.



Bill

 

[sag2]

MLamb

When it "slips", does the RPM increase on the tach, or are you already up on the governor? The 03's seem to derate the fuel more than prior engines, and it might be derating it as it makes the shift. The 47's do it to save the transmission under heavy torque loads, but I assumed the 48's were stronger and they could change the fueling a tad richer than the 47 equipped trucks. Also a mis adjusted kickdown (TV) cable can cause a slip on the shift.

I know of one technician in Nebraska that replaced a transmission on warranty for a "slip" at WOT, and after it didn't change they checked the TV adjustment, and that was it. Expensive mistake!

 

[mr plow]

sound familiar...

i too had this problem. it appeared in my second transmission. The tech then adjusted the hell out of the kickdown cable and made it even worse. Long story short, i hade the cable returned to normal, and problem has almost dissapeared. I am having my original transmission rebuilt and it will be reinstalled shortly. I think its an electronic hiccup. These trucks have all kinds of hiccups, too many electronics.....



i still love it, and it has never let me down, no matter what.



Oren.





Waiting for my x-monitor and edge box on order... .....

 

[MLamb]

Sag2, Mr Plow



The RPMS hit high shortly after the shift into 2nd. I would gues it happens around 2200.



Sounds like kickdown cable is suspect on a few at least. This is good information guys, thank you.

 

[inarush76]

48RE

Did the dealer drive it with a gauge on the front servo and line pressure? Did they note line pressure? Is the WOT shift at 2200 as mentioned? If it is, that is too soon. I wonder what procedure was used when adjusting the TV cable? How does the 1-2 shift feel? It needs to be established if the problem is second gear letting go or if it is a slip on the 2-3 shift. Is reverse OK? Obviously more diagnosis is in order. Mark PM or email me your phone number and I'll see if I can help further. What little my wife allows me to drive our new one :{ I know my wide open shifts are a bit above 3K. I haven't done that but a couple of times since it is still real low miles.

I have noticed that the 1-2 is a bit drawn out and the 2-3 seems to have a good bit of overlap. I have the DTT stuff ordered and I'll fix that soon! I hope my wife doesn't mind WOT 1-2 rubber!Oo.

James

 

[MLamb]

Mystery Solved

Well, after much work by myself and the delear, the problem is now solved. I finally had to take the transmission tech out for a drive to demonstrate the problem while he watched the computer. There were no codes but he did see some transmission pressure readings that appeared to be out of whack. He told me the transmission will disengage rather than self destruct if certain readings are not correct. Initially he thought it could be a warped valve body that was not allowing free movement of all the parts but it ended up being a governor pressure sensor.



So if the computer knows enough to disengage the transmission due to abnormal pressure readings, why wouldn't it spit out an error code?