700R4/4L60/4L60E Tips

 To

Prevent 3-4 Clutch Failures

Part 1

    The 3-4 Clutch is a busy, hard worked clutch that needs all the help we can give it. The pump stator has one of the most important jobs and that is to hold the shaft steady while the input drum assy is turning, anywhere from idle to 5500 rpm (stock vehicles). The front and rear stator bushing are extremely important and probably the most overlooked bushings in this transmission during repairs or rebuilds. These bushings must hold the input shaft steady so that 4 small sealing rings can deliver the oil pressure needed to apply and release the clutches in the input drum assy. Let’s start with the front stator bushing as seen below. I prefer to use a 350C front stator bushing, on big shaft (84 up) front stator assy due to the added support it gives as seen in the photo below.

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    The rear stator bushing often overlooked, because of old habits die-hard. In the past GM transmissions have not been known to have much problems other than maybe drainback, with stator bushings (photo below). A few parts suppliers are selling a wider bushing for the rear & is recommended if it’s available in your area. Always check in inside bore of the stator where the rings ride. Nothing short of perfect is allowed.

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    Now, We go & add Teflon Scarf Sealing rings (early model units), which are expected to seal in almost any condition. Then we find out scarf cut rings don’t work that well after all in this area after all. When using solid teflon rings tolerances must be held much tighter than with scarf cut rings. The quality of the rings is just as important and is left to the builders preference, because everybody has their own opinion on what parts are the best. My preference is to use GM Oem rings part # 8667235, they are a little pricey and are sold in bags of 10 (photo below).

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    The aluminum stator assy itself is famous for being warped on the avg .008 to .012 on the good looking stators. warpage is common right around the boost valve area and pressure regulator area. Always take a small cut on the stator assy to prevent cross leaks & loss of boost pressure in this area (photo below).

 

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    Those of you that like to press out the steel stator to try and save a pump, remember to machine the stator after you change it to insure it is going to run straight. Don’t trust your eyes on this one! If the stator is not in perfect, it causes premature stator bushing wear & eventually will takeout the teflon rings on the input shaft causing clutch failures in the input drum assy. Always take a small cut on the stator assy!

 

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    Let’s move on to the input drum itself. Air check the drum assy (photo below) upon teardown or inspection with clutch packs still assembled. Apply aprox 70 psi in the 3-4 clutch apply hole (between the 3rd and 4th seal ring as shown in the photo below.

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    Apply a small amount of ATF fluid and look for any leakage in the area indicated by the seal pick in the photo below. It’s best to do this upon teardown to save time because everything needs to be in the drum. You will be surprised by how much leakage that some drums will have here. I have not found a reliable way to salvage a drum that leaks in this area.

Part 2 (New)

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