4L60E Repair Guide - Home            



If you are reading this, there is a good chance that your transmission has no reverse, drives in 1st, does not drive in 2nd, drives in 3rd, and has no drive in OD.  There is likely no MIL or “Check Engine” warning lamp on, but there may be a light and an error code for a general transmission performance problem.  The transmission engages in DRIVE normally with no delay, may have a slight pump whine/howl at idle in park/neutral.  If that is why you are reading this, it's likely your transmission has slipped a hub on reaction sun shell.  For a fairly thorough repair of the problem, plan on about $250 in parts and three-five full days duration of repair.  I've been through this a handful of times.  The last time, I decided to do it (with the cooperation of the owner) on jacks and stands, with no air tools or special tools, and with no assistance.  This is the manner in which a typical vehicle owner would perform the repair.  Standard Flat Rate for the removal, repair, and installation in a Blazer/Jimmy with 4WD is 19.4 hours in a worst case scenario and in a fully equipped shop.  This method required more than 32 hours, not counting chasing parts and supplies.  Needless to say, I wouldn't be very profitable this way, but a learning experience is almost always worth the journey. 

This information is not intended to supplant or supercede that which is published in commonly available service manuals.  It is merely anecdotal information presented to clarify the procedures and directions found in published manuals and instructions.  Anyone undertaking a transmission repair is strongly urged to acquire a thorough repair manual and review it fully.   Most of the images contained within the pages are thumbnailed and can be viewed in a larger format by simply clicking them.  While by no means complete, this will hopefully familiarize readers enough to have a general understanding of the procedures involved. 


Having an adequate selection of good hand tools is all that is necessary.  A transmission jack, floor jack, and four secure jack stands are a requirement.  Without the necessary hoisting and holding equipment, this type of repair should not even be considered.  If you have an assistant, you may be able to wrestle the transmission out without a jack, but it is far safer and easier with an appropriate jack.  I cannot even imagine trying to install the transmission otherwise.

The only potentially “special” tools necessary will be a long extension bar or enough shorter extensions to reach 20" to 30" up and over the transmission.  A good quality T-45 Torx bit and driver are essential - Ideally it will be a Torx Plus bit, but a good quality Torx will work if used carefully.  A flexible-head ratchet will be very useful, but not absolutely necessary.  A torque wrench calibrated to at least 55 ft/lb will be necessary.  A band clamp of at least 9" in diameter (or an improvised series of large hose clamps) will be very helpful for pump assembly.   A magnetic pick-up tool will be useful.  An oil suction gun is not absolutely necessary, but will make the job cleaner and easier. 

Additionally, having a good vehicle service manual AND a transmission repair manual (like an ATSG, Helms, or Motor/AllData manual) for the vehicle and transmission at hand is strongly advised.  The minimal cost of a repair reference will more than pay for itself in potential problems avoided.  If you must choose between the two, the transmission manual will be the better investment.

You will need a sturdy workbench to perform the transmission repairs.  The work area should be kept as clean and dust-free as possible, since contaminants in the transmission hydraulics, bearings, and seals will reduce the longevity of your repairs.

You will need a good supply of towels, rags, or wipes to clean and dry parts.  Avoid use of any granular absorbents (such as OilDri or cat litter) since the clay dust created by these products will adhere to the oily transmission parts and ruin your repair as quickly as throwing a handful of sand into the oil pan.  Disposable paper towels are actually good for this, since they tend to leave very little lint behind, and any lint which does remain is soft, non-abrasive, and is easily trapped by the filter.

Good lighting under the vehicle will be essential.

A large oil catch pan will be necessary to contain the oil drained from the transmission (and transfer case on 4WD models) while under the vehicle. Newspapers will be used to protect the work surface and absorb oil which will drain out of the transmission as parts are removed.  They can also be used under the vehicle to absorb drips and leakage without creating harmful dust.

A small jar of TransGel or petroleum jelly (Vaseline or equivalent) will be necessary to assemble the transmission.  At least one quart of the appropriate clean transmission oil should be available for coating seals and contact parts as they are assembled, and to pre-soak any new clutch plates which are installed.  A new transmission filter and at least twelve additional quarts of the appropriate transmission oil (currently Dexron III) will be necessary.  If the vehicle is AWD or 4WD, two liters of GM AutoTrak II (P/N 12378508) oil will be required.


At a minimum, the hard parts necessary will include a replacement reaction sun shell, a pump bushing, a new transmission filter, and a seal kit.  This repair can usually be completed successfully with only those parts.  However, given the time and effort required to remove the transmission and disassemble it, additional parts which will enhance the reliability of the transmission are worth considering.  The reaction sun shell problem is so common that the aftermarket has offered a replacement unit which is substantially thicker and stronger than the factory units.  The cost differential is usually only a few dollars for the heavier shell, so unless the repair is being performed in a dealership or factory repair facility required to use original parts, the replacement GM shell should not even be considered an option. 

After the reaction sun shell, the next common weakness found in these transmissions used under heavier loads is the 3-4 clutch assembly.  Stock transmissions may have five or six clutch plates and the necessary compliment of clutch steels (discs) required to make the assembly the proper thickness. Later factory versions and aftermarket heavy duty kits provide up to nine clutch plates and steels, greatly improving the holding capacity of the clutch assembly.  The relatively reasonable cost of a new set of plates and steels is probably worth the expense if the vehicle is used for towing, hauling, or other heavy-duty or high-performance use, the heavy-duty 3-4 clutch pack is advisable.  These have additional plates and steels and provide superior clamping at the same pressure for greater power throughput. 
A commonly available arrangement is the Raybestos "Z-Pack" seven-disc clutch kit, as well as many others.

If the transmission has near or over 100,000 miles, or has been used for heavy hauling or towing, an assortment of other clutch plates, clutch steels, thrust bearings, a separator plate and gaskets, pump vanes, a replacement band, and thrust washers and bushings should be available.  If any slippage in second had occurred prior to the failure, the band should likely be replaced. 

As an upgrade for higher RPM applications, roller thrust bearings are available to replace the plain thrust washers found in several locations throughout the assembly.  Additionally, a high RPM pump is available for continuous use over 5,500 engine RPM. 

The forward sprag can also be a wear item, and should be available.  At a minimum, the existing forward sprag should be disassembled and inspected closely for roller and race damage.  If the transmission is subjected to heavy use, an upgraded, full-complement roller forward sprag is strongly advised.

There are upgraded apply pistons for the forward clutch and 3-4 clutch within the input drum assembly, along with the necessary revised spring retainer.

There is a later model factory change from a four-pinion gear planetary set to a five-pinion planetary set at standard ratios, and this gear set is markedly more robust than the four pinion assemblies. 
If the vehicle application is a lighter weight, higher performance type, a lower ratio 1-2 planetary gear set is available to decrease the first gear ratio from 3.06:1 to 2.66:1 for improved acceleration.   These units also have five pinion gears as opposed to the original four pinion design of the transmission. 

If the torque converter has high mileage, has experienced heavy use, or if the transmission has excessive contamination from damaged or worn parts, it may be better to replace it with a new or factory remanufactured unit.  

If these parts have to be ordered and delivered after disassembly, there will be additional down time. 

Your time and financial constraints, and willingness to perform repairs again will bear on whether you decide to replace additional parts.  Some transmissions at over 120,000 miles appear almost new, and some appear to be prehistoric at only 40,000 miles.