We added this special section for the GM LS4 vehicles.
This page shares the common problems that these vehicles often experience from minor nuisances to complete failures. This transmission really needs a few upgrades to allow it to reliably handle the vehicle weight and power and was plain and simple an inadequate transmission as it sits in stock form. If you are reading this page you have likely already had at least one major complaint or failure and a rebuild while several of our customers have had multiple replacements, even under 100K miles. The harsh reality is that the LS4 model transmissions only average about 60-80K miles, though we do have several customers that are around the 100K mile mark but not without issues. Most stock OE type rebuilds for this application only live for about 20-40K miles until the problems resurface. Our years of knowledge and expertise with the 4T65E transmission line have proven what works and that the LS4 models should not be treated like just another 4T65E rebuild. There are no quick easy fixes for these problems as they are inherent with the factory design and the only way to address and prevent these problems is with a quality rebuild using several improved design parts that the aftermarket world has offered. From our lineup of rebuilds we recommend our 4T65E-HPS1 base level High Performance rebuild for stock to mildly upgraded LS4 vehicles which is a much more refined and durable option that is well suited to these vehicles.
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No Forward Cold OR Hot, Neutrals at stops, Hesitation on take off:
One of the more common problems we hear about with the LS4 vehicles. The scenario.... You are driving in traffic for a while OR your car has sat for a while and is a cold startup. You put the car in Drive range and it wont move, or if driving you come up to a stop light and in heavy traffic and the light turns green and SUPRISE!!! You are holding up traffic with a car that wont go anywhere. The most common cause of this problem is a worn out inner surface of the Input clutch piston. Once the inner sealing area wears it can prevent the inner lip seal for the piston from sealing properly. You may find that revving th engine up will finally get the car to move and it will BANG into gear and this often catches you off guard! This is because the pump in the transmission is working harder and moving more fluid thus allowing the added fluid to overcome the leak which prevented the clutch from either initially applying or staying applied. From the factory the rubber lip seals that are used on the inner and outer sections of the input cluch apply piston are a Short design seal. The transmission repair service field has found that a Long style lip seal greatly helps against this problem and is what is included in aftermarket gasket and seal kits and is also what we use in our rebuilds. New seals from GM are still the short design and offer no benifit over the originals. Another area of concern that causes this is a boost valve in the valve body which is also something we upgrade and address in our rebuilds. We have had several customers report back that a fluid and filter service using Valvoline Maxlife ATF OR adding Lucas transmission additive has helped this annoying issue BUT a seal softening product is only going to band-aid the problem for so long and is not a dependable fix but may buy you a little more time.
Another scenario with this problem is the feeling that the vehicle is taking off in the wrong gear and very lazy until after a brief moment it will slam back into 1st. The hesitation on take off can be caused by a few other problems than noted above. When debris collects in the AFL (Actuator Feed Limit) valve bore in the channel plate this can cause the valve to be stuck intermittently which can block the fluid feed to the 1-2/3-4 shift solenoid. Another problem we see is the channel plate casting can wear in the area the 4th steel plates engage and dig grooves into the metal so this could cause 4th clutch to stick on until jarred loose and essentially give you a 4-1 downshift, or even a 4-N-1 downshift if the input clutch is not holding due to the problems noted above so it can be a combination of things going on. The 2nd clutch drum is also prone to wear and the steel plates could get momentarily stuck in the drum which would give a 2-1 downshift bump right at take-off. These are often problems that are intermittent and can be difficult to replicate during test drives. No codes will set in the computer from these problems.
Tach bounces up and down a few hundered rpm while cruising:
Another common problem / concern of this transmission and more pronounced with added engine power or higher mileage. This generally happens when the valve body has excess wear in the TCC regulated apply valve area but also has other causes. Excessive fluid leakage in this area of the valve body causes TCC apply pressure loss and can lead to uncontrollable TCC operation which causes the engine rpm to bounce up and down a bit. This problem is noticed most after driving a while and speeds over 50 mph and in 4th gear. There are other causes to this problem that can be from a hard and shrunken TCC regulated apply valve end plug o-ring, worn or shrunken teflon seals on the input shaft, a bad o-ring on the input shaft that seals in the torque converter, or even a faulty torque converter clutch. A dirty MAF sensor can also have effect on this condition and should also be inspected.
Due to the nature of the LS4 vehicles since they have DOD (Displacement On Demand) or also called AFM (Active Fuel Management) there is a lot cycling between 4cyl and 8cyl mode and the torque converter clutch can take a lot of stress as it constantly slips to retain smooth operation on the engine side. These transmissions also use the 258mm style torque converter which are known for warped TCC apply pistons caused by too much apply pressure- related to issues noted above- and torque converter lockup shudder, chatter, or flaring are the result right before failure. Once the TCC clutch lining degrades you have a metal apply piston riding against the metal cover or the torque converter (flexplate side) and then the metal debris starts to rapidly accumulate.
Long sliding shifts:
This problem is one that most 4T65E transmissions experience sooner or later. The factory design didnt allow enough compensation for wear- so the result is normally poor shift feel and long or lazy shifts, especially the 1-2 shift which leads to eventual failure. The 2nd clutch clearance from the factory is set very loose and as wear occurs this will grow and make the shift feel worse. General wear inside the transmission also causes apply pressure to drop with age so these two problems add up and this is one area that does not need to be short handed on pressure. The factory TCM (Transmission Control Module) has a very aggressive line pressure setting for the 1-2 shift to help accomodate the high engine output but can only do so much. Often times if the transmission has low mileage and is in good internal condition you can upgrade the factory 1-2 and 2-3 accumulator parts with ones from a Transgo Shift Kit and this is a good aid to help get clutches to apply when they should. A shift kit does not make up for excessive clutch clearances but does speed up the time the clutch will apply.
Complete Loss of movement any range, Possible whine noise:
Likely the most common problem that we see often with these models is complete loss of movement after driving and wont move in any shifter range. Shutting the engine off for a short period of time and restarting may allow it to move again but only for a very short distance. Typically the source of this is a plugged filter due to torque converter and/or torque converter clutch failure and the debris finds its way to the pan and gets sucked up into the filter. Dropping the lower pan for inspecition often shows heavy amounts of either a gray metal flake or dark colored debris. If you remove the filter and cut it open you will find the debris trapped in there also. Replacing just the torque converter is a short term fix at best so we do not recommand it. The debris is throughout the transmission and a complete rebuild with a few upgrades is the only way to fix this problem and keep it from coming back.
Grinding or Crunching noises, Loss of movement:
This is a problem that is not as common to see on these vehicles but enough that it should be mentioned. The final drive (differential) in these transmissions serves two functions. First- it is the final drive gear ratio of the transmission and final section of geartrain to transmit power to the axles. Second- it serves as the differential by means of spider gears connecting the left and right side axle. The differential section of the final drive is rarely at fault as these vehiclese use the HD (Heavy Duty) style differential, but the final drive section has been found to shred itself and cause loud grinding or crunching noises followed by loss of movement. Dropping the lower pan will reviel shards and chunks of metal from the gear teeth being chewed up and broken off. The fluid return drain hole for the final drive section drains straight to the lower pan near the magnet and end of the filter so it will be very easy to see the damage that ends up in the pan.
The LS4 vehicles from the factory came with dark or black colored final drive gears. We have no preferrence on using these and honestly have seen more of these to fail over the years than the traditional silver gears. If they appear in good condition when disassembling the transmission then they should be OK to keep using. Sometimes we see chunks missing out of gears but were not making any noise- and in this case we replace the final drive assembly. The ring gear teeth should be closely inspected as well as we have seen them fracture but not break.
The LS4 transmissions from the factory have an Internal Ring Gear with the designation "V8" etched on the inside that faces the forward drum. These reportedly have a special heat treating process, but again we don't have a preferrence and use them if they are in good condition but should be closely inspected for cracked or fractured teeth.
Engine Coolant inside the transmission:
Not a problem we see often on these vehicles but one that needs to be made aware. While the cause is often blamed to be the radiator and/or internal cooler failing and leaking- this can also be causes from excessive metal debris from a failing torque converter. It will act as a constant abbrasive on the cooler passages and can eventually wear a hole through and cause an internal leak. By the time the problem occurs you blame the cooler for causing the transmission to fail but it could have been a failing torque converter and large amount of fine metal debris flowing through the system that caused the cooler to fail.
ANY time we see excessive amounts of debris in the fluid or know the torque converter failued with an LS4 equipped vehicle we replace the factory cooler (radiator) and will not try to flush or reuse the original.
High Transmission Fluid Temps:
This is a concern for all LS4 powered vehicles and some are simply worse than others. It is very common to see the transmission fluid temps once fully warmed up to sit at 200-225 degrees F and can shoot up even higher in heavy traffic or long drives in hot summer weather. This is not ideal for fluid life or seal life. We prefer to see the fluid temps around 180 on average. Installing an auxiliary cooler in-line with the radiator cooler is a great way to help drop the high temps down. Completely bypassing the radiator cooler with an adequate sized external cooler is another option and a very popular one especially if you need to replace your radiator cooler due to contamination. We offer several options to help keep transmission temps under control.
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