Issue Summary:
- A 1995-2000 Hummer H1 enters the shop with an unexplained transmission-fluid loss, venting from the transfer case or transmission fluid contaminating the air filter.
- 1999-and-up Ford vehicles with the AX4S transaxle may exhibit a short delay followed by a bang when engaging any forward range.
- Ford vehicles equipped with the AX4N/4F50N transaxle may exhibit a short delay followed by a bang when engaging any forward range.
- After overhaul, Ford vehicles equipped with the AX4S, AX4N or 4F50N may exhibit a complaint of no third gear.
Before or after overhaul, a 1995- to 2000-model Hummer H1 enters the shop with an unexplained transmission-fluid loss, venting from the transfer case or transmission fluid contaminating the air filter.
One cause may be that the oil cooler in the transfer case has a crack and is leaking ATF into the transfer case.
Hummer uses a cooler inside the NV242HD transfer case. The cooler tube is prone to cracking, which will allow pressurized fluid from the transmission cooler to leak into the transfer case. Once this begins occurring, the transfer case will become overfilled and, depending on the severity of the crack, fluid may vent from the transfer case, or the fluid can make its way into the air cleaner, contaminating the air filter and leaking near the right-front tire. It is also possible for the fluid pressure to push out the rear seal. Damage also may occur to the transmission if its fluid level becomes too low.
In 2001 Hummer introduced an updated cooler with a revised support bracket and additional mounting tabs to restrict movement and eliminate cracking of the cooler. This revised cooler has a blue identification stripe on one of the external fittings.
Refer to Figure 1 for cooler location in the transfer case.
Figure 2 shows the location where the cooler tube may crack.
Figure 3 shows the revised transfer-case cooler.
Figure 4 is a routing diagram for the transfer-case cooler, hoses and cooler lines.
Install the updated cooler.
- AMG Hummer part # for revised transfer-case cooler . . . . . . 6011652
1999-and-up Ford vehicles equipped with the AX4S transaxle may exhibit a short delay followed by a bang when engaging any forward range.
The cause may be a leak in the lube circuit, which is now fed directly from pump output, through an 0.089-inch orifice in the main spacer plate (Figure 5).
This leak may be from a broken O-ring on the lube pipe where it fits into the case or a crack in the brazed area where it feeds the support (Figure 6), or a damaged orange lube seal in the support (Figure 7).
A leak in the lube circuit may cause low overall line pressure; when the PCM detects that forward has not been engaged, it will elevate line pressure, causing the bang when forward finally engages.
Ensure that the lube-pipe O-ring and the brazed area of the pipe are in good condition, and make sure that the orange seal in the support is in good condition.
Ford vehicles equipped with the AX4N/4F50N transaxle may exhibit a short delay followed by a bang when engaging any forward range.
The cause may be a worn 1/2-clutch accumulator pin and piston causing a slow engagement into drive. This slow engagement will cause the PCM to elevate line pressure, which causes the harsh shift/bang on engagement. Refer to Figure 8 for the identification of the 1/2-clutch accumulator pin and piston.
Figure 9 shows a cross-sectional view of the hydraulic circuit for the 1/2-clutch accumulator.
Ensure that the accumulator pin and piston have a snug fit; replace as necessary.
After over-haul, Ford vehicles equipped with the AX4S, AX4N or 4F50N may exhibit a complaint of no third gear.
The cause may be that during overhaul the direct-clutch bonded piston was replaced and the apply ring was not transferred to the new piston. As the cross-sectional view in Figure 10 shows, when the apply ring is left off, the direct-clutch piston will not contact the direct-clutch bottom steel.
Ensure that the apply ring is assembled onto the direct-clutch piston (Figure 11).
June 2009 Issue
Volume 26, No. 6
- AMG Hummer H1, 1995-2000: Mysterious transmission-fluid loss
- Ford AX4S, 1999 & Up: Neutral-to-drive delay/bang
- Ford AX4N/4F50N: Neutral-to-drive delay/bang
- Ford AX4S, AX4N, 4F50N: No third gear