The 4L60 transmission is a popular automatic transmission known for its durability and performance. Rebuilding a 4L60 requires careful attention to detail and precision. This guide focuses on assembling the input drum and the critical 3-4 clutch pack, common areas of concern during a 4l60 Transmission Rebuild. We’ll cover key steps and considerations for a successful rebuild process.
The input drum assembly starts with arranging the friction plates in the correct order. The input sun gear, a small gear located in the drum’s center, is installed. Some sprag assemblies have a removable sun gear, while others have a fixed gear secured by a dust cover. If your sun gear is removable, install it now. Before installing friction plates, presoak them in transmission fluid for at least 15 minutes to prevent glazing during the initial load test.
Upgrading the 3-4 clutch pack often involves achieving proper clearances. A typical upgrade kit includes nine friction plates, nine steel plates, a thinner pressure plate, and a thinner snap ring. While ideally, you would replace the six stock steel plates with the nine new ones, this doesn’t always guarantee correct clearance. You’ll need to stack and measure, using a combination of thin and stock thickness steel plates and snap rings to achieve the desired clearance. The recommended clearance for firm, clean shifts is typically between .025″ and .040″. A common successful stack up is around .034″. The five small booster springs in the 3-4 clutch assembly are a point of contention. Some builders recommend removing them, while others, contradicting ATSG’s recommendation, advise installing them.
The 3-4 clutch stack assembly order is as follows:
- Backing plate (with legs facing down, clicking onto the 3-4 clutch ring)
- Friction plate
- Steel plate
- Friction plate
- Steel plate
- Continue alternating friction and steel plates, ending with a friction plate
- Top pressure apply plate
- Snap ring (using the thin apply plate and thin snap ring often requires swapping in a factory-thick friction plate to achieve the target clearance)
After assembling the 3-4 clutch pack, complete the input drum assembly. Install the washer and then the bearing onto the back of the drum, ensuring the black side of the bearing faces upwards. Use a heavy-duty tack lubricant to secure these components in place. This step is crucial for proper drum rotation and overall transmission function.
Proper assembly of the input drum and 3-4 clutch pack is vital for a successful 4L60 transmission rebuild. Achieving correct clearances in the 3-4 clutch pack ensures smooth shifting and prevents premature wear. Following these guidelines will contribute to a reliable and high-performing transmission.
