Pinpointing slippage - TCCoA Forums
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post #1 of 4 (permalink) Old 05-14-2015, 01:28 PM Thread Starter
Join Date: Apr 2005
Location: Vancouver, WA
Age: 35
Posts: 3
Pinpointing slippage

I've about given up troubleshooting this on my own, and this forum seemingly being having the most 4r70w discussion, I hope some others may be able to suggest some areas to look.

History: A long time back I picked up a engine/4r70w combo from a 2003 3.8L mustang. It supposedly had 13k miles, and it lookd like it. I used the transmission before my 302 and sold the engine. Fluid and pan looked clean. Not knowing much about cars at the time, everything seemed good after install, with a Baumann TCS. Eventually I found I had a small issue with converter lockup in between 40-45mph and closed throttle. My "fix" was to give a 10-15% pressure boost at closed throttle, but set to 20% just for a little safety margin. It was my daily driver for years and seemed to work great. When I had 3.55 gears in the car, the 1-2 shift would fishtail and require little throttle to gain control again. I went down to 3.08s for the better economy and safer WOT.

The last few years the car has been a project, and I've made some engine changes, reinstalled the 3.55 gears, installed a PI Stallion 9.5" single-disc lockup converter (for higher shifts rather than use the stock 12" converter), and performed the jmod. I was hoping the converter change would fix my odd lockup issue at closed throttle and lower pressures (stock tune from Baumann), but the lockup issue persisted. I found that the car was stalling really high and occasionally I'd floor it at 20mph, rpms would shoot up agove 5k, but the car wouldn't accelerate very quickly. The car feels like it's way down on power, but only because it isn't getting to the wheels. Tires aren't spinning - I actually am having a hard time breaking the tires loose right now, with the smaller, higher stall converter.

Today and details/items tested:
I reviewed datalogs from last weekend, and datalogs from years ago. Datalogging was pulling using a Moates Quarterhorse and Binary Editor/EA. RPMs and mpg readings are acurate. WOT slippage numbers are below:

PI 9.5" 3000 stall converter slippage:
4000rpms: 36%
4500rpms: 30%
5000rpms: 23%
5500rpms: 17%
6000rpms: 13%

Stock v6 12" ~2200 stall converter slippage (years ago):
3000rpms 26%
3500rpms 17%
4000rpms 14%
4500rpms 12%
5000rpms 10%

Slippage is the same in 1st and 2nd gear. It doesn't seem to change at all with fluid temperature (80F ot 200F). Transmission gets hot very fast with the PI converter - up to 200 degrees within about 10 minutes of continuoos driving, some with lockup, from cold (I'm working on adding a larger cooler).

Last year I pulled the transmission apart and installed a 7-tooth output shaft. The pan was clean and the clutches looked great. I replaced the tail shaft seals, some parts of the valve body (since they came in the kit that I needed a single gasket from), the new-looking accumulator piston(s?), everything torqued to spec/pattern with a snapontechwrench, pump was reused and looked like new. Basically the internals LOOKED great, but I'm not an expert on diagnosing these things.

Last night I got pressure tests done on the EPC and line pressure ports. Hooked up to pressure transducers, I was able to datalog pressures at different engine loads. They were within 3psi of my OTC pressure gauge, hooked up to a tee.

1-2psi EPC
40psi line forward
63psi line reverse

100psi EPC (100psi transducer maxed out)
200-210psi line forward
290psi line reverse

I cut the EPC wire and no change in behavior except it runs at max pressure. I ran a ground directly to the car battery, to the solenoid and TCS grounds, no change in behavior. These tests were betwen 100-160 degrees Fahrenheit fluid temperature.

If needed, I will work on moving my pressure testing equipment to other ports, but since I have what appears to be fluid delivery issues in 1st gear, 2nd gear, and lockup in 4th, I don't think looking at any specific clutch pressures will tell anything further unless both the direct and forward clutches are low on pressure.

I'd think that the problem lies in the hydraulics going to the converter - maybe pressure, maybe volume. I have no idea what could control this though.

Motor peaks around 400ftlbs crank at 4200rpms an tapers off to ~320ftlbs at 6k.

Anyone have ideas on what I can try next? From what I understand, I should be seeing under 10% slippage once I get a bit past stall of the converter. I'm tempted to just swap out the valve body and see if one of the many things it controls will resolve this issue.
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post #2 of 4 (permalink) Old 05-14-2015, 05:46 PM
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Why not log with the converter locked in 2nd gear to reduce the number of variables? Or are you not convinced the converter holds while it's locked?

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post #3 of 4 (permalink) Old 05-14-2015, 06:16 PM Thread Starter
Join Date: Apr 2005
Location: Vancouver, WA
Age: 35
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Originally Posted by theterminator93 View Post
Why not log with the converter locked in 2nd gear to reduce the number of variables? Or are you not convinced the converter holds while it's locked?
That's actually the second suggestion I've had today on that. I'll give it a try.

I don't fully trust the hoses I'm using to attach the pressure transducers, so I haven't wanted to drive further/on the highway. I have no reason not to trust them though as they didn't seem to leak a drop on the half dozen loops I made around the neighborhood last night, but it's still tight down there near the pan and larger exhaust pipes. Exhaust temperatures have me worried and I don't want to remove the hoses and wiring harnesses until I know there isn't any more other data I should grab from the EPC or line pressure ports. It took some ridiculous 5 hours to get this stuff hooked up this week, mostly due to exhaust (lack of) clearances and the work involved in removing and reinstalling it.
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post #4 of 4 (permalink) Old 05-15-2015, 11:56 AM Thread Starter
Join Date: Apr 2005
Location: Vancouver, WA
Age: 35
Posts: 3
Dan with silverfox suggested I should be able to hold WOT with my single-clutch Pi converter. I'm going to give it a try tonight, and datalog what I can.

Does anyone have some slippage numbers of a correctly-functioning transmission/converter? All I can find are slippage numbers from discussions about reaching the end of the drag strip (3rd gear, near redline), not anything in between (at stall speed, 1000rpms past stall, 2000rpms past stall, etc). I figure a lot of people are under 500hp/tq, so most data should be loosely relatable.

I understand the 10% slippage at 5k on the 12" converter may be "normal" at the end of a track, but what about all the other rpms below that?
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