intermittantly not shifting into 4th

[Handyman]

First post here( I think, found out I had a log in here already) so far a nice site. Anyway, I will be picking up my 1st diesel, '99 F-250, and the owner( a fellow co-worker and honest guy) has informed me the gremlin he thought was fixed has reared it's head once again. He says the tranny will not shift into 4th gear...and it does it intermittantly, doesn't matter if it's hot, towing, driving in the city, etc...it just will not shift into fourth, He says it will not shift when it's real cold though. He has an early DP tuner on it and talked to the guys there and they say they can reflash the ECU with an updated software load(please chime in if this could fix it). He also said that the guy he bought it from installed a switch that will engage the Torque converter when he let off the throttle( called it the "poor man's jake brake) when going down hill...He's taken it to a few shops in the area and they are stumpedas to what it could be. To me it sounds like an electrical issue and I keep wondering if that switch to engage the TC may be the culprit ot contributing factor. He's flushed the tranny fluid and sees no signs of the tranny failing.. no metal flakes or excessive amounts of particulate matter...any help or suggestions would be greatly appreicated...

 

[BJS]

I'd find out what has been done or replaced in an attempt to eliminate the gremlin before you start doing anything.

based on the "will not shift when it's real cold" leads me to believe that what you are experiencing is normal as the torque converter will not lock up until the temp sensor (integrated into the solenoid body) sees warm enough temperatures from the trans fluid. This is often mistaken for the transmission not shifting into the higher gear since the toque converter locking will bring the rpms down roughly 500. This should not happen when the temps are above 70°F if memory serves me right. torque converter lockup is easily determined by hitting the gas hard and if the rpm's jump up then you're unlocked if they slowly climb in proportion to speed then it's locked.

Provided the above does not apply then there are 2 places I would start troubleshooting. 1st is the valve body though any competent trans shop should have started here and clean it very very good, while you're cleaning it it wouldn't be a bad time to start the modification train with a good shift kit like the transgo tugger kit which will essentially rebuild the valve body at the same time. The second place I would start looking is the solenoid body, given that it is an intermittent problem you're just going to be replacing it and you can get pretty good ones for just over $100.

 

[rammertide07]

I'd find out what has been done or replaced in an attempt to eliminate the gremlin before you start doing anything.

based on the "will not shift when it's real cold" leads me to believe that what you are experiencing is normal as the torque converter will not lock up until the temp sensor (integrated into the solenoid body) sees warm enough temperatures from the trans fluid. This is often mistaken for the transmission not shifting into the higher gear since the toque converter locking will bring the rpms down roughly 500. This should not happen when the temps are above 70°F if memory serves me right. torque converter lockup is easily determined by hitting the gas hard and if the rpm's jump up then you're unlocked if they slowly climb in proportion to speed then it's locked.

Provided the above does not apply then there are 2 places I would start troubleshooting. 1st is the valve body though any competent trans shop should have started here and clean it very very good, while you're cleaning it it wouldn't be a bad time to start the modification train with a good shift kit like the transgo tugger kit which will essentially rebuild the valve body at the same time. The second place I would start looking is the solenoid body, given that it is an intermittent problem you're just going to be replacing it and you can get pretty good ones for just over $100.

x2 + an aftermarket torque converter

 

[Handyman]

I will look into that...I'm going to assume the 7.3's have a tranny/oil cooler....which line is it that goes from the tranny to the cooler?? I did a complete flush on a Benz tranny that had a tranny cooler and I unhooked the line that ran from the tranny to the oil cooler andpumped all the crap out of it... did that a few times and the tranny worked 1000x's better.....is this a method I can use on this truck?? and what is the tranny fluid capacity??

 

[DaveBen]

If you look at the SDD Technical Articles WIKI section, in the TOP BLUE LINE above you will find tranny flush articles. Give that a try.

Dave

 

[Handyman]

that link is coming up as a way to make your AC colder.....

 

[DaveBen]

Click on Articles and you should see the articles listed. I just tried it.

Dave

 

[Handyman]

ah..Thank you...sounds pretty flippin' easy