4R70W hard 1-2 shift (already replaced accumulator springs and piston)

Messages
3
Location
Atlanta, GA
I have a 2000 Ford Mustang equipped with the 3.8L motor and an automatic transmission. The car has ~250K miles on it and both the engine and trans are original and neither has been rebuilt. The car runs great except for a harsh 1-2 shift. A while back I was driving it and the car felt like it slipped going from first to second. Ever since then it has had a hard shift going from first to second. All other gear changes are smooth. The car shifts hard enough going from first to second that it will chirp the tires if I'm over ~50% throttle. If I baby the throttle the shift isn't as hard but it is still clunky. All of my internet research led me to believe I had a broken 1-2 accumulator spring. I dropped the pan and removed the 1-2 accumulator piston only to find two intact springs and a healthy looking piston. Since I was already in there and had the parts on hand, I replaced the piston, cover, and both springs. The kit I got from CT Powertrain had a purple lower spring and a white upper spring. After I got everything back together I went on a ~30 mile test drive and the car still shifts hard going from 1-2 with no other shifting issues. If I manually force the car to shift from 1-2 using the gear selector the shift is much smoother. I looked at the output of the TPS and MAF using a scan tool and they seem to be working as intended. I even cleaned the MAF to be sure. The trans fluid is Motorcraft Mercon V and is filled to the appropriate level. I'm at a loss on what to do next, any ideas?
 
Messages
4,597
Location
Manchester, England
buy a manual or fit a manual - it will only change gear exactly when you want it to, and you can control exactly how hard or soft each change is with your foot. If you delegate the job to someone else they will do it how they want to do it regardless of what you want or what you think, but if you do it yourself you can do it just the way you like..
 
Messages
950
Location
Erie, PA
Originally Posted by Olas
buy a manual or fit a manual - it will only change gear exactly when you want it to, and you can control exactly how hard or soft each change is with your foot. If you delegate the job to someone else they will do it how they want to do it regardless of what you want or what you think, but if you do it yourself you can do it just the way you like..
?????????????? huh?
 
Messages
950
Location
Erie, PA
https://www.google.com/url?sa=i&url=https%3A%2F%2Fusermanual.wiki%2FSonnax%2FAode4R75EVactest.854772566&psig=AOvVaw2SCT1XNYexfWldb3gI_hFV&ust=1585684685343000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCKjxlY_ixOgCFQAAAAAdAAAAABAJ Here is a diagram of the valves.
 

jbar430

Thread starter
Messages
3
Location
Atlanta, GA
Quote
Did you check the resistance on the OSS sensor?
I have not - if that sensor was bad wouldn't it affect all of my shifts though? I will try and check it tonight.
Quote
Here is a diagram of the valves.
Thanks - that's really helpful.
 
Messages
5,670
Location
Fort Worth, Texas
Check for a worn Checkball, Notably the one for the Intermediate Clutch. Fordiesel69 already stated that. The checkball forces the apply fluid through a metered orifice to control shift firmness. To allow quick release of the apply fluid.....The checkball will unseat so the fluid doesn't have to exhaust solely through the orifice. The plastic balls can wear all the down 'til they pass trough the plate.....The the apply fluid is free to run through the exhaust unabated causing harsh shifts. With that said.....I do find it interesting that manually shifting the unit calms the 1-2 shift.....This could technically be because the Intermediate clutch has excessive clearance & the O/D Band coming on in manual 2nd is cushioning the apply. Or even an issue with the Intermediate Sprag/Mechanical Diode.
 
Messages
5,439
Location
Ohio
Originally Posted by Olas
buy a manual or fit a manual - it will only change gear exactly when you want it to, and you can control exactly how hard or soft each change is with your foot. If you delegate the job to someone else they will do it how they want to do it regardless of what you want or what you think, but if you do it yourself you can do it just the way you like..
Laughable!
 
Messages
5,439
Location
Ohio
When you did the accumulator work, was it's bore in good shape without any scoring? Any codes??
 
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jbar430

Thread starter
Messages
3
Location
Atlanta, GA
When I did the accumulator work I did not notice any scoring in the bore. Both springs were intact and the piston looked to be in good shape. I replaced the springs and pistons anyways since I had the parts on hand. The new piston felt like it fit just a little bit more snug. The car isn't throwing any codes but looking at the Mode 6 data it looks like my DPFE sensor is toast. I checked the voltage of the signal wire with the vac hoses disconnected and it registered around 1.2V. I went ahead and ordered a new DPFE sensor and am waiting on it to show up. I doubt that is causing the shift issue. Everything else on the car checks out ok and it runs and drives great. I also went ahead and got a new TPS even though the one on the car appears to be working ok. The trans is 20 years old and has 250K miles on it without any rebuilds, just regular fluid and filter changes. I'm not sure I'm willing to invest the time/money to get it rebuilt.
 
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