47rh overdrive cruising speed problems

12vfleet

12vfleet

beCummin broke
Joined
Aug 15, 2010
Messages
616
The transmission has a single disk billet tc, valvebody, and a billet input. Shifts fine up into overdrive with no problems. However after so long of cruising around 70-75 mph on the interstate all of a sudden it will shift down into 3rd for some damn reason and then when I give it some throttle will shift right back into overdrive. I have a manual lockup switch and this happens with the 47rh locked up. Anybody know why this is happening?
 
Sounds like either a bad connection coming loose, or a failing lock-up solenoid.
 
Why would a failing lockup solenoid cause it to completely shift down into third? It only does this from 70-75 mph is what I don't get. If I am goin 75+ its fine, same if im doin 65-69. The whole truck is about to get alot of garage time due to a short bed swap this winter.
 
When it kicks down take your foot and pull up on the brake pedal see if it shifts back into o/d. I have had several misadjusted brake switches cause it to kick out of o/d
 
The failing (overheating) lock-up solenoid shorts out the power supply to both solenoids and causes the overdrive solenoid to deactivate momentarily.

I can't inspect your truck/tranny over the internet so i can only guess and throw out possible scenarios.

TPS as listed above usually the culprit when it drops in and out of lock-up intermittently.

Dropping clear down the third with the lock-up switch engaged tells me something is haywire with the lock-up solenoid.

By the way, do you have a jumper wire in place of the transmission relay under the hood?
 
OK that makes sense then. I think the only wire under the hood would be the wire for the lockup switch running to the passenger side computer box. Unless thats what your talking about. Thanks for the info Big Blue.
 
Anybody know where to get a decent price on a tps? I'm guessing that they are around $200 everywhere probably with my luck.
 
it replaces the tps and only cost about 13bucks. Not trying to be a D@#$ but search pot mod or potention meter and it should come up. All the parts are at Radio Shack.
 
pot mod

gmcz71502 said:
it replaces the tps and only cost about 13bucks. Not trying to be a D@#$ but search pot mod or potention meter and it should come up. All the parts are at Radio Shack.
Click to expand...

What am I missing here? Are you suggesting replacing the TPS with a manual Potentiometer with a knob?
 
You set it at what speed you want OD to engage and that's the speed it will always engage. I still haven't installed mine I have od hooked to a old fashion dimmer in my 1st gen. Mine has been sitting in the truck for a month.
 
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