![]() GM also designed the transmission with the wrong 3rd clutch clearance - the transmissions are out of GM spec even when new - had to manufacture parts to fix that. Crazy chain drive inside the transmission. Lots of special tools required for the GM transmission. 3 piece valve body with the oil pump integrated and 10? solenoids is very complicated to put together. I spent 8+ hours cleaning out the GM valvebody with a tiny little paintbrush in a parts washer to get rid of the metal "paste" that was spread out through the transmission. Clean is good - a clean transmission is much easier to rebuild. No bands to deal with, and the cartridge filter seems to keep the fluid very clean. Once you remove the valve body and the 6 oil pump bolts everything comes out easy, in simple to understand assemblies. The 68RFE is vastly easier to work on than either of those. Note it starts flickering just as we get to 16psi from 15psi.Click to expand.So far i've rebuilt a VW DSG and a GM 4T65E in my garage. The green line is attached to the TCM pressure switch wire. The graph shows line pressure in the 230psi range with a leakage into the OD circuit (orange) of about 16psi. It was then possible to replicate every run after that while the transmission was hot. To our surprise on only the fourth test the problem began rearing its head. Each time the transmission temperature would climb somewhat and we would continue repeating the tests until it was at least 200 degrees Fahrenheit in the transmission. To keep all equal, we held the truck at 2000RPM, 3rd gear, put between 200-240 wheel horsepower of load on it and held that for 1 minute intervals with brief cooldown periods in between. To best replicate the fault, we observed the conditions that caused a P0871 to set in a late model truck (that already had the anodized valve body) and recreated those on the dyno. Our sensors are wired into a high speed data logger that is also tapped into engine/TCM sensors. Analog gauges with rubber hose are far too inaccurate for this type of testing and length of rubber hose acts as an accumulator or buffer to the readings. Here we have modified a transmission oil pan to accept bulkhead fittings, installed pressure transducers (sensors) and connected very small nylon lines to the valve body to get accurate and fast response pressure readings. 1-The Solenoid Shift Valve (SSV) and 2-The Valve Body Separator Plate. This means by the time you're setting P0871s, you've already been dragging the OD clutches.Ĭertainly there could be minor leaks from many areas, but our exhaustive testing shows there are only two areas we need to concentrate on to correct this leak. Our experimentation shows this switch triggers at 16PSI, this just so happens to be right around the pressure required to apply the OD clutches (air check this if you don't believe us). This code is triggered when the pressure switch in the solenoid pack detects pressure in the circuit when it shouldn't be. Leaks into the OD circuit will cause the annoying P0871 code (set in 2nd or 3rd gear) but are also partially responsible for the burnt OD clutches we see on a daily basis. The caveat of increased line pressure is increased cross leaks, so it is important for us to correct these leaks when making a performance transmission. We, like most others, increase line pressure in our 68RFE transmissions to increase clutch holding capability. The most common cross leak observed with 68RFE transmissions is leakage into the overdrive (OD) hydraulic circuit this is in fact the only chronic cross leak area we see on 68RFEs. It is tribal knowledge among transmission builders that valve bores need to be inspected or vacuum checked and repaired and that flat surfaces need flat sanding to reduce cross leaks, but this "old wisdom" does not always result in a "fix" for newer transmissions. One of those is cross leaks in the valve body. Part One: The Valve BodyĪlthough cited as the weak link in the 2007 to present 6.7 Ram trucks, the 68RFE transmission can be a decent unit if you can correct some of its shortcomings.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |