suncoast V/B downshift problem

[231jasonS]

I recently had a Suncoast valve body installed with a torque converter in my 06 48re.



At 30 MPH when held at this MPH for about 100 yards the tranns will downshift to 2nd and then back to 3rd and then back to 2nd. It will do this until i speed up or slow down. Its as if the tranns cant decide which gear to be in.



I reset the TPS, no change. Cleared the memory in the computer(disconnected batterys) then rest the TPS again and problem is still there.



Suncoast told me they suspected the TPS needed to be re-set, but that did nothing.



Ill call them back on Monday, but anyone else have any ideas?

 

[PBax]

its the transmission actuator. 05+ trucks have actuators controlling shifts instead of kickdown cables.



What power mods do you have on the truck? this problem is most noticeable when using programmers... but still occurs using modules on some trucks... not all. On totally stock power, the transmission should shift fine... if not, pursue that issue with Suncoast. This problem shows up with aftermarket transmission parts because the transmission is much tighter and more efficient.....

 

[231jasonS]

the only mod thus far is the AFE.



It shifts great, very firm and much faster. Much less boost drop between shifts and the converter is much tighter. The problem is only when cruising at 30+-2 MPH. It seems to be "hunting" for the gear. (between 2nd and 3rd)



Ive triple checked the fluid level and its fine. Temps are normal, maybee 10-15 cooler.

the truck only has 6700 miles.



What to do now?

 

[redfuelrules]

The aftermarket transmission in my 05was doing the same thing, especially on the 1-2 shift & it was driving me crazy. It might not be the throttle actuator thing. Do you know what kind of internal pressures your transmission is running? Maybe at idle, cruising, and at WOT? I talked to a well known transmission builder & we figured out that the transmission wasn't building the kind of pressures that it should. I installed a new valve body on Thursday. Now it shifts great!

 

[RobertP]

its a govenor pressure v. s throttle valve pressure problem and thats the bottom line. both have mechanicle and electricle fixes.

 

[231jasonS]

Ok with that being said what is the best way to determine what the next step is.



I know very little about auto tranns. I can R&R just about anything, but i haven't diagnosed any tranns problems.

 

[redfuelrules]

Ok with that being said what is the best way to determine what the next step is.



I know very little about auto tranns. I can R&R just about anything, but i haven't diagnosed any tranns problems.

With my new valve body, my transmission runs 85 psi at idle, 175 at wide open throttle. I can't recall what it runs cruising down the road.



Suncoast might be able to help you R&R over the phone as well. I have a used Suncoast converter & they were very helpful when I called them with questions regarding their flywheel, converter bolts, etc.



My new valve body was built by Goerend Bros. Dave is also great to talk to. I couldn't be happier with my new valve body.



Good luck correcting your transmission problem.

Ben

 

[231jasonS]

how did you measure the PSI?

(R&R=remove and replace, the easy stuff-figureing which parts to change offers the challenge)

 

[redfuelrules]

Second 1/8" plug from the front, passenger side. Use a 200 psi or higher gauge with at least 6 feet of tubing. I taped my gauge to the passenger window. The gauge will only show pressure when the transmission is in a forward gear. I read the pressure at idle and at wot parked, with the brake on and the transfer case in neutral. I then went for a short gauge to read cruising psi and confirm wot.



I bought a guage with the necessary tubing and fittings from Napa for 40 or 50 bucks.



Knowing the pressures might help Suncoast figure out what's going on inside your transmission/

 

[231jasonS]

ok, thanks. Ill try to talk to suncoast in the AM

 

[231jasonS]

well i checked the pressures and at idle its about 80 PSI, at cruise in lock up its about 120 PSI and at WOT it was about 145-165. When the problem occurs the pressure drops to about 80 PSI.



I also noticed i could not seem to recreate the problem in tow/haul mode, but did not have much time to try it out. Will test again on friday. I need to find someone with a good scan tool that has 06 software to see what the computer sees as far as the pressure.



Suncoast said "Sounds like a computer glitch" which was a weak attempt at a diagnosis.