4R70W FWD clutch troubles

4R70W FWD clutch troubles

Joined: April 28th, 2009, 8:30 pm

April 28th, 2009, 8:34 pm #1

I have a 4R70W in a 04 Crown Vic Police car. I removed the tranny to do a rebuild b/c it was whining bad. I replaced the converter and pump, all clutches and some bearings. When I installed the tranny in the car it did fine for 10-15 miles then it neutrals out 1st gear. At a stop sign, give it gas it revs then BAM it goes. I hooked a pressure guage to the Line tap and when it has the concern it will drop from 150ish PSI to 90ish PSI and the FWD tap pressure from 90 ish to close the 0 then back and it goes. Has anyone seen any concerns with this transmission and parts related to the forward clutch? Thanks
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sILVERFOX
sILVERFOX

April 30th, 2009, 7:39 pm #2

Was that pressure at the FWD tap or Main?
What is the main saying?

Did you replace any electronics or sensors?
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Joined: April 28th, 2009, 8:30 pm

May 15th, 2009, 6:29 pm #3

By main you mean the line pressure tap. I need to go back and recheck my numbers but I think the line pressure falls to near 50 and the forward pressure falls to 0 and then when it engages it comes back to 60. Also when driving down the road in 4th gear around 55-60mph and let of the gas it bucks and engine brakes like its going into 3rd gear. I have my scan tool hooked up and the PCM is commanding 4th, but it being an 04 I can look at the Trans_Rat PID to see what the actual ratio is, but when it acts up the RPMs will raise and the car slows due to engine braking.

This is my theroy on the engine braking. We took it apart and the O/D band was destroyed and the reverse drum was scored bad, replaced both parts and installed a SONNAX servo pin b/c we thought it has to do with a worn case bore, BUT what I think is somehow the transmission is appling the FWD clutch, direct clutch and O/D band all at once and the O/D band is the weakest link. All help is welcomed. I have had reports of cracked cases to bad PCM's and RF interfernce from a bad alternator. This car is running me in circles. THANKS!!!!!
Last edited by Silver91Hatch on May 15th, 2009, 6:33 pm, edited 1 time in total.
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Joined: March 29th, 2009, 7:43 pm

May 15th, 2009, 7:11 pm #4

Fwd pressure drop and hard engagement sounds like you cut a seal in the forward clutch or the sealing rings have worn a groove the drum. When this trans shifts from 3 to 4 the fwd clutches come off and the o/d band comes on. If your not getting a lock up on the upshift then the forwards must be coming off. If you get a lock up on the downshift then the forward clutch is coming on before the band comes off. If you suspect a worn servo bore then go to a small servo piston with sleeve. Also update the accumulators to molded design. What happens when your in o/d and hit the o/d button. Does it go into 3rd without bind up?
Mac
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Joined: April 28th, 2009, 8:30 pm

May 18th, 2009, 12:26 pm #5

The pressure drop doesn't happen during first engagement. Say you start the car up in the morning, drive it around town, after its good and hot, you come to a stop light. When the light turns green you lightly touch the throttle, that is when it drops pressure, then instantly reapplies all pressure. With the engine reving and the trans basically in nuetral it will apply the FWD clutch and BAM, it hits hard. I have replaced the pump, sealing rings and the FWD drum/input shaft assembly. The seals on the FWD piston have been replaced twice suspecting a nicked or cut seal, no luck there. I don't exactly remember what happened when I hit the O/D button, under normal driving conditions(not acting up) it all works spot on. This is driving me up a wall...

New pump
Converter
Known good valve body (drove great for 100 miles then reappered)
All clutches
All piston seal
O/D band
Sonnax O/D pin
O/D servo
Reverse servo and cover
All have been replaced during rebuild...
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silverfox
silverfox

May 18th, 2009, 7:26 pm #6

how about a new EPC?
Short in the harness, grounding out and fooling the noids?
Mechanical diode locking up due to failure?
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Joined: April 28th, 2009, 8:30 pm

May 18th, 2009, 7:48 pm #7

Vehicle harness has been disassembled and checked(from bulkhead to connector on firewall). I haven't tried a new EPC, but I will look into it. Will the OWC/ Mech Diode cause both concerns?? I spun and checked it, it sounded good, but I'm still dropping FWD clutch pressure when it neutrals out I think, haven't rechecked but its coming. Are you talking about a short in the internal harness/blukhead or external. BTW I have no codes. Have you seen any case failures?? This is a police car and it takes a lot of abuse, I have talked to many people about this concern and I have gotten different theroy's from a broken/cracked case to a bad PCM and everything in between(not saying that anyone is wrong, just waying my options to see what my next plan of attack is). Thanks all
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Joined: March 29th, 2009, 7:43 pm

May 18th, 2009, 11:58 pm #8

Haven't had this in the 4R70W but is common problem in AXODE. The FWD piston splits in the outer seal grove. If you remove the seal and put a screwdriver in the seal slot and twist it you will see the slot open.You will have to go all the way around the piston to find it. This neutral condition will only occur if you complete the shift into O/D so the fwd clutches come off. Then when you stop the piston opens and the FWD clutches won't come back on utile the piston closes up. While it's trying to do that the FWD apply pressure will drop to or near 0 psi. This is more likely to be the problem if you have an aluminum or a riveted steel piston. Sorry you have to go back inside to check it.
Mac
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Joined: April 28th, 2009, 8:30 pm

May 19th, 2009, 8:02 pm #9

Thats sounds very possible, its an aluminum piston. Come to think of it, the nuetraling mostly happens after a long run in O/D. It might also be my 3-4-3 shuffle b/c the piston is cocked and keeping the FWD clutch applied slighty. I will let you know... Thanks!
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Joined: April 28th, 2009, 8:30 pm

May 26th, 2009, 6:08 pm #10

Got it out and all apart, on the bench. I can't see anything wrong with anything. Piston looks good, seals are ok. This is driving me nuts!!
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