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4T65E HD Upgrade Kit

Transmission & Drivetrain - 4T65E HD Upgrade Kit
Transmission & Drivetrain - 4T65E HD Upgrade Kit

The stock differential in the non-HD version of the 4T65E is small and weak. By upgrading the L36 non HD differential you strengthen the weakest part of your transmission. This is a must for people drag racing with increased power output and/or drag radial/drag slick racing tires. The kit comes with a stock HD differential(from a supercharged car) so you won’t have to worry about it failing in the same manner that the clutch type units do. The kit includes a HD differential, HD differential cover, and a HD passenger side axle. The axle is shipped complete so no special tools are required and install time is quicker than our competitor’s kit.

Complete with:

  • ZZP stage 1 HD passenger axle
  • HD differential cover
  • HD differential
  • Torrington bearing

IF your NA (not supercharged) car comes with the 3.05 final drive differential, this kit will change your final drive to 3.29. This is an upgrade for an NA car, however the PCM should be adjusted so the speedometer and shift points are correct. Common cars that come with the 3.05 final drive diff are all NA and Impala, Monte Carlo, Bonneville, and Park Ave.

To install this in a 4t60 transmission a 4t65e ring gear would be required. Does not fit on H-Body cars (Park Avenue, LeSabre, etc) as they require a longer axle. 

Transmission & Drivetrain - 4T65E HD Upgrade Kit
Transmission & Drivetrain - 4T65E HD Upgrade Kit
Customer Reviews
4.0 Based on 4 Reviews
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Frank T.
United States United States
Thanks ZZPerformance

Everything I have ever needed for my car with quick service you guys are the best.

United States United States

I just have to say,I have a GXP Grand Prix 2008, has the HD... Still broke. I’m about to have to drop the subframe and rebuild the engine and I’m throwing around the idea of mating it with a North Star transmission. Far superior in about every way from this HD.... Maybe for the 3.8s I guess but the HD version still won’t handle that much torque...they’ll break drag racing with slicks.

Patrick J.
4T65e Upgrade Kit

The parts appear to be of a very high quality! I would like to have received the necessary gaskets though!

Gerbilkill G.
4t65e HD Upgrade Kit

Great product . came together like buttcheeks, lol . less the 5 hours and I am rollin HD. Thanx ZZP.