I recently had the transmission fluid changed on my 2003 Discovery II at 140k miles by a local indy LR shop (he used Mercon 3). Since having it changed, I have been experiencing hard up shifting, with the transmission holding gears too long and dropping them into the next. I assumed this was due to not enough tranny fluid being put back into the vehicle after the change. I checked the level and was able to get about a half a quart more in, and now the hard shifting is isolated between 3rd and 4th gear (always on up shift), with 3rd gear holding until around 2500 RPM before shifting, even under gentle acceleration.

Additionally, I notice a slight, momentary (maybe half a second) loss of power at about 1800 RPM, where it feels the vehicle should be shifting into 4th gear. This is very subtle and probably wouldn't be noticed unless I was scrutinizing the shifting.

Any ideas on what could be causing this or how to remedy it?

 

Any fault codes, if so what are the fault code numbers?
I would get it back to the shop and let them know the fluid was low and the tranny is not shifting right. By the way, did they change the fluid or flush the system? If they flushed it, they most likely have killed the tranny cause they shouldn't be flushed if over 70 to 80,000 miles.

 

No fault codes relating to the tranny. I will occasionally, maybe once a month, get P0134 and P0154 thrown, but they clear after a day.

I will have to double check with the mechanic to make sure he didn't flush it. I had requested a "transmission service" per the 150k maintenance checklist.

 

That is a old wive's tale and it has been proven wrong time and time again.

They used the WRONG FLUID, it takes Dexron III NOT Mercon, they MUST flush out all of the old fluid and replace it with the correct fluid at THEIR expense.
If you need to show them the owners manual, it is right in the fluids and specs section.

 

That suck, bro. Another reason most of us do it all ourselves.

 

Curious since some of the fluids say dex/merc?

For example I used valoline high milage in my tranny. It says dex/merc on the label, this fluid has worked excellent.

Valoline high milage dex/merc atf

 

why not?

 

Mercon V is "supposed" to meet both the Dexron 3 and Mercon spec. Companies also have to pay a fee for slapping those trade names on their packages, so there are some un-branded products that also claim to meet the specs.

The tranny needs to have oil and filter change just like the engine, 30K miles. This creates a disposed fluid, which on some list somewhere decreases the government rating for a vehicle. So some companies said, heck, just let it stay in there, the original owner will have sold it, warranty is over, etc. If you don't do a tranny drain and filter change so much gunk can build up that it could break loose with introduction of new fluid and cause shifting problems. But this would also happen if you had a leak and kept topping up fluid. Does not happen that often, but if confronted with that possibility, one potential solution is the machine flush of the transmission, which circulates a solvent and new fluid to flush as much of that gunk out as possible, and can even resolve some problems from the half drain done at home on high miles. You home drain and fill dos not get out the fluid stored in the torque converter. Some service operations won't change fluid in a tranny that is high miles because they don't want the liability of it. But if you had not changed the oil in the motor, you'ld still want to change it, no matter how old.

But if your tranny fluid is not red - if it is brown colored, with lots of particles (that would be the clutch disks) and if it smells like burnt coffee pot, you're probably too far gone to make much improvement.

I did my fluid on mine when I got it with almost 170K on it, no problems. My PO had touched very few things on this Disco.

 

One thing I don't state are old wives tales. Go spend as much time as I have and you will know the truth.
Most of the dealers I work with had a hard standing rule of not back flushing a high mileage tranny for a reason.

 

I too use the Dex/Merc trans fluid, however from what I understand using straight Mercon is a differnet formula than straight Dexron but the Dex/Merc is ok, I dont know why.