sprayking

Hey everyone absolultely great site alot of stuff on here. I have a 95 burb K2500 7.4 and its been great for a couple of years. I have changed the trans fluid before but just used the regular oem stock fluid when I bought the vehicle but the other day I had a mechanic buddy drop the pan and change the Trans Filter and all the oil to Royal Purple synthetic, He drove it just around the block when he was done just to make sure the pan didnt leak and said it shifted hard but never drove it before that. When I got in i noticed it shifted REALLY hard up and down shifting, SES engine light on, and to me it sounded like it was whining when around 1700-1800 RPMs ?? What gives? Should I have stuck with regular oil? Somebody else told me that these older chevy trannies like to stick with the oil they have been using and not to switch it up and other people have told me that switching to a synthetic should have made it shift smoother? I am way confused and taking it back to my buddy tomorrow and drive it around with him to show him what I hear/see. Anyways any help would be appreciated. THX.

sprayking

any tranny pros out there?.....

Zed 71

It sounds like they did not perform a transmission flush and subsequently only ~1/3 of the fluid was changed. So now you have ~2/3 of regular tranny fluid mixed with ~1/3 Royal Purple. Not sure if those two fluids can be mixed...

slw210

Perfectly safe to mix and perfectly safe to switch.
Sounds like the trans guy messed something up.

A little more info on the truck and transmission would help.

TransDr2759

It's very safe to switch to Synthetic ATF ! He most likely cracked one of the shift solenoids in the back of the valve body when either removing or re-installing the trans pan. It's kinda tight in the back of the 4L80E and I always remove the mount bolts and lift up the trans. at the back. You'll prob. see shift solenoid code when you scan it, which means it's probably cracked. Good Luck

DCSCO

I have the same year, model and engine. Please let me know what you find.

sprayking

the truck is a burban k2500 7.4, 4l80e trans, Yes I took it to a tranny shop today and the code its throwin is a 43, which is a knock sensor. When I had the tranny serviced I also had the starter replaced and the knock sensor is right in front of the starter. The tranny guy said its probably that sensor which makes the engine change timing and the tranny have high pressure which would make it shift hard and clunky. So they are changing out the knock sensor and see what happens. If not the guy said the filter could be installed wrong or the o ring installed wrong which is letting air in the tranny. so hopefully I can get this worked out. thanks guys..

Zed 71

I wasn't questioning the switch to synthetic, just the amount of fluid left over and the compatibility of the fluids at those amounts. Good to know they are fully compatible and thanks for the info.

Good to hear the code was just an issue with the knock sensor. Still not convinced it would make is shift hard and clunky. I could see it being a soleniod/valve body issue since it is a little difficult to get the pan off (at least on the 4l60e NNBS).

Good luck and let us know how it goes.

sprayking

Well I got the burb back today from the tranny shop. It was the knock sensor, My buddy installed the starter and must have damaged the knock sensor some way or it coincidentally went out at the same time as the starter. Anyways 150 bucks later the burb is shifting the way it should now and installed a new knock sensor with a new pigtail harness and runs the way it should. so the knock sensor CAN mess with the tranny being that it changes the timing which in turn pumps up the trannys pressure which made it shift like crap. Well anyways just another thing down the road....NEXT is to change out the rotors and pads up front to Powerstop drilled and slotted rotors and pads. Got em today in the mail And while im down there I should install some new shocks also. Well I will keep you guys informed.....