48RE No Overdrive

[JohnHaggerty]

I'll try this again based on what I learned on my eariler post.



A guy at work has an 04 with a 48RE. When he was almost one quart over on fluid the overdrive wouldn't lock up. He drained to the proper level and all seems fine. Was it that simple or might there be something else going on?



Thanks!

 

[RDeFayette]

Direct out of the service manual:

DIAGNOSIS AND TESTING

DIAGNOSIS AND TESTING - EFFECTS OF

INCORRECT FLUID LEVEL

A low fluid level allows the pump to take in air

along with the fluid. Air in the fluid will cause fluid

pressures to be low and develop slower than normal.

If the transmission is overfilled, the gears churn the

fluid into foam. This aerates the fluid and causing

the same conditions occurring with a low level. In

either case, air bubbles cause fluid overheating, oxidation

and varnish buildup which interferes with

valve and clutch operation. Foaming also causes fluid

expansion which can result in fluid overflow from the

transmission vent or fill tube. Fluid overflow can easily

be mistaken for a leak if inspection is not careful.



So yes it "COULD" 'cause the TC not to look up. IT "COULD" be that simple.

Over drive doesn't lock up, the TC does.

Just pay attention to what the trans is telling you.

If it's not talking everything should be fine.

If you starts to talk (act strange/different) better be listening!

Same cause and affect as home with the other half.

If she's nto yellin' at ya alls well, if she is and you ignore her it's gonna cost ya.

Got it?

 

[cerberusiam]

Based on my experiences, no. A quart over full will have no consequences. I typically run 1-2 quarts over the full mark with the trans up to operating temp.



If the trans gets to the point where the fluid is getting aereated you will almost always see a leak under the truck. The vent on the pump and the case will normally puke fluid in these cases. If they don't, the fluid is not getting churned.



The supply for the lockup and OD solenoids is the same as the clutch apply. If all the gears are working correctly and no obvious slipping, its doubtful and solenoid operation is going to be effected. In the same vein, getting the fluid aereated enough to feel the difference is quite hard. The fluid pickup is towards the bottom of the sump where the heavier non aereated fluid is going to be anyway. Also, once it goes thry the pump the bulk of the air is going to removed anyway.



As for something else wrong, that is entirely possible. Was it actually OD that was not engaging or was it the lockup solenoid? Typical source of intermittent OD engagement is going to be the governor solenoid and transducer, barring a mechanical failure. If he has many miles without changing these 2 items then they are the first item to address. In the BEST of circumstances about 40k is all they are good for. Close to or over that, replacement time.

 

[maineman78]

Ok hoping for an answer or help orsomething.. 48re trans line had a leak lost fluid while doing 70 w cruise cntrl down the hwy... babied it a mile to exit filled trans fluid shop had put a compression fitting on the line which loosened up.. tight that up no leak fluid filled no i guess no tc lock up in 3rd or od.. ive changed fluid, filter, od lock solenoid, gov press sol and sensor, and output vs sensor and still nothing.. it was working fine till then... i dont really tow or drive hard just norm driving really.. ive done a myst switch will lock tc in 1/2 but not 3rd or od... no codes when scanned... what do i check or do next...

 

[cerberusiam]

Valve body or TC, could be either or both. VB is easier to replace but the TC is probably the problem. The lack of fluid likely slipped the ltuch and messed up the lockup. You can feel it is 1 and 2 because of the gear reduction but it slips in the other gears from the TQ. Is it manual 1 and 2 it locks in or will in lock with the shifter in D? If that is the case and lockup feels solid in 1 and 2 something in the VB is physically not letting the lockup apply even with a mystery switch.