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| Here is a procedure that we
use to decide if a transmission is worthy of repairing the TCC regulator
system, rather than doing an overhaul. We hook up the scanner and prepare
for a road test. 1st we scan the DTCs and see if P1870 is present which
will verify the cause of the customers "harsh 1-2 shift when hot"
complaint. P1870 is a Transmission Component Slipping code, but most of
the time the component slipping on the 1995-up vehicles it is the TCC
doing the slipping. 1997-up seems to be the worst, as they have the carbon
woven ECCC clutch material that is very durable, BUT does NOT have the
holding capacity of the older paper linings. One the test drive carry a
pencil and paper. Write down the TFT and the TCC slip RPM at different
temps. Example:
TFT 155 TCC Enable ON TCC Slip 7 TCC Duty Cycle 45% TPS 22% MPH 40 This is OK and Proves the TCC clutch can still apply and hold. Now heat it on up and monitor the slip speed: TFT 175 TCC Enable ON TCC Slip 0 TCC Duty Cycle 45% TPS 22% MPH 40 Now this is the trick, just as you see, or feel the TCC go to Enable ON, crowd the TPS just enough to strain the TCC apply, but not enough to make the TCC Enable go to OFF. Many times once the TFT reaches 175-200 the TCC will not apply at all during a slight crowd just as the TCC command on, but will if you ease the TCC apply torque. And if you continue to maintain a steady slight crowd the TCC will slip 200-350 RPMs till the vehicle reaches a speed that you have to back out of the crowd, and at that point, the TCC will apply and the TCC slip will go to 0. This is during the crowd: TFT 180 TCC Enable ON TCC Slip 320 TCC Duty Cycle 90% TPS 39% MPH 42 And if you lift the TPS a little: TFT 180 TCC Enable ON TCC Slip 0 TCC DUty Cycle 85% TPS 20% MPH 65 All of the reading above are made up from memory, but if the TCC clutch applies and them falls off during the higher TFTs, then I feel it is a great candidate for a repair, rather than an overhaul. Another wonderful data item to monitor is the TCC Duty Cycle. Just keep in mind the HIGHER the duty Cycle the MORE the VCM is TRYING to stop slipage. The lower the TCC DUty Cycle the more the VCM want to see TCC slip. Now of course there are many other factors that have to be considered, in making the decision about just pulling the valve body and repairing the TCC Regulator lineup, verses doing a complete overhaul. Mileage, PSI readings, what the transmission looks like inside the filter, and what the customer wants to do, are important factors. I let them make the decision. Of course what we recommend many times is what the customer chooses. Since we went to testing the TCC in the manner above, we have had great success with the repairs. Never try a valve body pull and TCC Regulator repair on a transmission that the TCC doesn't lockup and have no TCC slip, when the TFT is below 140. It is usually going to take an overhaul,converter, and possibly a pump. There is always a chance of a P1870 being caused by a failed TCC apply solenoid, or TCC PWM solenoid, but this is not a common condition. Lastly the valve body repairs I'm referring to is either a Sonnax 77754-03K (1995-1997) and 77754-04K (1998-2001), or installing a inner pump spring. The inner pump spring should be used with caution on a badly worn valve body, as the worn valve body can cause an extreme loss of AFL oil to exhaust, and cause delayed or no 4th gear, not to mention reduced transmission life and performance. What we have done in our shop is IF the transmission is being overhauled and it has no history of a P1870, we install the inner pump spring to preserve the valve body. But, IF the transmission has a store history or current P1870, we ream the valve body and install the Sonnax repair. We have installed many inner pump springs on P1870 and corrected the condition, but I'm convinced that this method should be used cautiously. With the P1870 DTC becoming as common as burnt 3-4s on the 1988 4L60Es, I think we will all find it a profitable fix. |
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