PowerTrain Pro: Automatic Transmission

Sponsored By: 


Search Autoparts/Motorage/Powertrain-pro-automatic-transmission/

Third Clutch Burn Out

Wednesday, April 1, 2015 - 07:00
Print Article

It is not unusual for a 2000-2004 Honda or Acura vehicle using a 5 speed 3 shaft style automatic transmission to come in to the shop with the third clutches destroyed (figure 1). Many times rotational damage of the piston, return spring and spring retainer accompanies the third clutch burn out (figures 2, 3 and 4).

Motor Age Magazine Want more ? Enjoy a free subscription to Motor Age magazine to get the latest news in service repair. Click here to start you subscription today.

 Get more in-depth transmission knowledge with ATSG Manuals at 30% less!


The main shaft, counter shaft and secondary shafts are each supported by their own bearings secured in the main case cover (figure 5). Overtime, vibration combined with torque causes these bearings to wear into the case allowing for unwanted shaft side play. Stationary hydraulic feed pipes in the end cover that fit into these shafts run hard against the rotating bushings inside the shafts (figure 6). The wear caused by shaft side play not only damages feed pipe sealing capabilities dropping clutch pressure (4th & 5th clutch main shaft, 3rd clutch counter shaft, 2nd clutch secondary shaft), damage can also extend to the sealing rings on the front of the main shaft. When this happens to the main shaft, the rings to cut into the regulator valve body compromising converter pressure. In fact one symptom this causes that rebuilder Max Deese in Chicago experienced is a sudden stall while waiting at a stop light.

It is understandable how the third clutch can burn out due to a pressure loss caused by worn feed pipe bushings, but the rotational damage? Jesse Zacarias of Elec-Tran discovered a computer strategy which briefly pulses the third clutches on and off during a forced 4-2 downshift. Factory manuals show this clutch being pulsed on and off during an engagement from Park to Drive without mentioning the 4-2 shift strategy. The purpose of this brief pulse of the clutch is to assist in a smooth shift transition. After 80k miles or so when shaft alignment begins to be compromised, this forced 4-2 downshift becomes a problem. The third clutches are being applied (albeit briefly) during high rpm conditions with less pressure control resulting in clutch burn out with rotational damage.  

When rebuilding this transmission it is imperative to restore shaft alignment along with shaft bushing and tube wear otherwise repeat failure is imminent. Companies like Slauson Transmission parts recondition these cases so that bearing pocket wear is a thing of the past. Bushing tool kits are available in the aftermarket to remove and replace shaft bushings. Honda clutches and fluid are a must with the exception of Raybestos’ GPX® friction plates (figure 7). It is very compatible to Honda fluid and due to its unique friction material and special grooved patterns. This tends to provide cooler operating temperatures and endurance of this clutch pack which is especially suited to the demands placed on this particular assembly. In fact they have announced a new friction they call the HT plate which is totally different in material and grooving. This newly added HT plate emerged from continued studies they originally conducted with groove designs to see what impact it had on durability and performance with the GPX plate. The fluid flow dynamics with this new plate’s unique groove patterns and friction materials (figure 8), is expected to positively impact durability, performance and clutch drag reduction. Starting with several Toyota transmissions (U660, A750 and A760), these frictions will also find its way into some Ford and GM units as well.

Article Categorization
Article Details
Sponsored By: 


< Previous
Next >
blog comments powered by Disqus