The 34 clutch is a busy, hard working clutch that needs all the help we can give it. One of the first things we can do to keep the 34 clutch working properly is to replace the stator support bushings. The stator support has one of the most important jobs: to hold the input shaft steady while the input drum assembly is turning, anywhere from idle to 5500 RPM (stock vehicles).
The front and rear stator support bushings 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 the four small sealing rings can deliver the oil pressure needed to apply and release the clutches in the input drum.
Let's start with the front stator support bushing: I prefer to use a 350C front stator support bushing, on large-shaft stator support assemblies, due to the added support it provides (figure 1).
The rear stator support bushing is often overlooked. In the past, GM transmissions haven't had many problems caused by stator support bushings, other than maybe drainback. A few parts suppliers are selling a wider rear stator support bushing; this is a great bushing to use, if it's available in your area.
Always check inside bore of the stator support where the rings ride. Allow nothing short of perfect.
These units use Teflon, scarf-cut sealing rings (early model units), which are expected to seal in almost any conditions. Then we find out scarf-cut rings don't work that well 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 builder's preference because everybody has his or her own opinion on which 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 (figure 2).
The stator support assembly is famous for warping by as much as 0.008" to 0.012" on the good looking supports. Warping is common around the boost valve area and pressure regulator area. Always take a small cut on the stator support assembly to prevent cross leaks and loss of boost pressure in this area (figure 3). Also make sure that the pump and stator support bolts are not too long after machining the support. You may need to use washers to make up the difference, or use shorter bolts.
Those of you who like to press out the steel stator support to try and save a pump, remember to machine the stator support after you change it to make sure it's going to run straight. Don't trust your eyes on this one! If the stator support isn't installed perfectly, it'll cause premature stator support bushing wear and will eventually take out the Teflon rings on the input shaft, causing clutch failures in the input drum assembly.
Let's move on to the input drum itself: Air check the drum assembly upon teardown or inspection, with clutch packs still assembled. Apply about 70 PSI in the 34 clutch apply hole, between the 3rd and 4th sealing ring (figure 4).
Apply a small amount of ATF and look for any leaks in the area indicated (figure 5). It's best to do this upon teardown to save time, because everything needs to be in the drum. You'll be surprised by how much some drums will leak. I haven't found a reliable way to salvage a drum that leaks in this area. If your drum leaks badly, throw it away and get another one.
These are just a few of the measures you can take to reduce 3-4 clutch failure. In later articles, we'll cover other procedure that'll add life to your work .