96-98 4R70w re-rebuild - TCCoA Forums
 
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post #1 of 2 (permalink) Old 04-07-2015, 07:24 PM Thread Starter
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Arrow 96-98 4R70w re-rebuild

Back in August, I built a transmission to be installed in a 1996 F-150 truck with a 5.0L V8.
The transmission core was originally from a 1998 V6 Mustang and had been previously rebuilt with the incorrect valve body gaskets.
I rebuilt it, with the correct gaskets and did some upgrades so the truck could be used to tow a boat.

The vehicle owner called me in October saying it was installed and was slipping. I drove 2 hrs to his house to assess what was happening.
On the test drive the transmission would slip briefly when taking off from a dead stop but did NOT slip once the vehicle gained speed.
The transmission up shifted and down shifted normally.
Originally, I suspected the torque converter slipping or the low/reverse one way clutch was not holding.
We agreed he would take the transmission out again and I would fix it for him.
Fast forward to the end of January and the vehicle owner called me saying he had hurt is back and was not able to remove the transmission himself.
He said the transmission had lost 3rd gear and was slipping in 1st and 2nd. I Towed the truck to my house to evaluate what had happened.
With the transmission removed and torn apart, I found the plastic thrust washer on the pump was melted, the forward clutches were burned and the direct clutches were burned.












NO other damage was found.... no cut seals, no damaged teflon rings or sealing rings, no damaged gaskets in the valve body, no stuck valves, front pump was good visually and had proper clearance a feeler gauge.
I happen to stumble across an old TSB from Ford in one of my ATSG manuals;

**Complaint; After rebuild, the vehicle displays a slip and/or chatter in forward ranges when you are accelerating from a stop, Reverse is OK.
All sealing rings, bushings, seals and forward clutch drum are known to be good.

Cause; The cause may be a partially clogged shift solenoid #2, which will stroke the 3-4 shift valve far enough to exhaust some of the forward clutch oil.

Correction; Install 2 pressure gauges to check the line pressure and forward clutch pressure. With the transmission in Drive both gauges should read the same and should be 55-75 psi. If forward clutch pressure is lower than line pressure and all internal parts are known to be good, replace the shift solenoid.
**

This described exactly what was happening!

A new shift solenoid was ordered and installed. I fully rebuilt the transmission again, new seals, new gaskets, new clutches and I replaced the low/reverse one way clutch and installed new front pump gears, for good measure.
Once I had all the parts assembled, I figure out why the plastic thrust washer had melted. What I found was the end play measurement was right on the threshold. I suspect, while my measurement was correct, the thrust washer that was used may have been on the thicker side of normal and caused too little clearance.



My measurement came out being 1.585" which is supposed to be correct for the Red thrust washer, but when I assembled the front pump on the trans case it was too tight. I dug through me bag of spare parts and found a OEM natural thrust washer that was on the thicker side of normal and assembled the pump on the case with that washer and it came out perfect.... so lesson learned, the chart is not always correct.

With the transmission built and ready to install, I had a few other issues to deal with.... First 3 of the 6 bell housing bolts were missing, as in never installed from the previous install. I was able to find 3 spares I had from a core transmission. Second, the passenger side bell housing alignment pin/dowel was missing, again I was able to find a spare and install it. You can see in the picture of the alignment pin below where somebody had installed the transmission with out the dowel installed and chewed up the bell housing plate.




Third, the nuts that bolt to the transmission mount to the transmission cross member had been replace with with wheel lug nuts that had been cross threaded on. I robbed a good mount from a core transmission. With those issues resolved, I flushed the transmission cooler and installed the transmission.





Test drive the vehicle and confirm it has all gears, no slipping and shifts correctly. Hook my pressure gauges, as the TSB mentions, and confirm correct pressures.

While I had the truck, the owner complained of the truck running poorly and would randomly mis-fire. First thing I found was the vacuum hose to the HVAC blend servo was deteriorated. I repaired that with a new piece of hose.



The second thing I found was the base ignition timing was set incorrectly.
I marked the balancer, pulled the spout connector and set base ignition timing to 12* BTDC. The truck ran much better and seemed to have more power. I also found the coolant temp was reading too cold (174 degrees) which is not hot enough to get the PCM to switch from closed to open loop.
I offered to replace the thermostat, but the owner declined. Owner of the truck picked it up last week and claims its running and shifting better than ever.

I rebuild AOD/AODE/4R70W/4R75E transmissions....Check out my Facebook page: https://www.facebook.com/pages/North...48414635312478
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post #2 of 2 (permalink) Old 04-08-2015, 08:01 AM
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i love these sort of posts. great detail and in the end all is well. nice work.
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