Fun With Transmissions - October/November - 2016

The A5HF1: What’s It All About?

The A5HF1 has been on the road for some time now and there really isn’t a lot of tech info available for it. This unit appears in 2006–up Hyundai and 2006–up Kia models (figure 1). The transmission may look familiar because it closely resembles the F5A51 found in Mitsubishi vehicles.

In this edition of Fun with Transmissions, we’ll check out the A5HF1 and what features make it unique. We’ll also get the lowdown on special tools and procedures for an efficient and profitable repair. Start with a look at the clutch and band application chart (figure 2).

The A5HF1, while similar looking to the F5A51, has many upgraded components. They include:

  • more direct planet pinion gears (from 3 to 4)
  • more OD planet pinion gears (from 3 to 4)
  • larger reduction band apply piston
  • higher capacity torque converter

The A5HF1 uses seven solenoids to control transmission shifts (figures 3A & 3B). The shift solenoids actually control the different apply components in the unit (figure 4). These solenoids work exactly as the 604 solenoids have since 1989.

Unlike its predecessors, the A5HF1 has a variable force solenoid (VFS) to control line pressure. In the past, the F5 and the F4 series transmissions used a fixed line pressure.

But unlike traditional pressure control solenoids, the VFS solenoid doesn’t control line pressure rise. Rather, the VFS in the A5HF1 could be called a pressure reduction solenoid. When the vehicle gets up to speed in 3rd, 4th, and 5th gears, the VFS solenoid will drop line pressure. The result is the all-important reduction in fuel consumption.

This transmission is also the only unit we’ve seen with a “dam” and cooler pipe for the VFS solenoid. The dam acts as a bucket and the orificed tube sprays cooling oil directly onto the solenoid.

Rebuild Tips

ATRA’s management spoke to a major hard parts supplier about what he’s selling for the A5HF1. According to that supplier, “The units are holding up well on hard parts. In the last eight months, we’ve sold 51 pump bodies; the gears are breaking apart and sometimes they break the crescent as well. We’ve sold 10 stators, 19 OD planets, 11 rear planets, 11 UD drums, 13 reverse drums, and 4 valve bodies.”

The supplier did add that the reason for the high number of pumps is that it’s the same body whether it’s a 4-speed Mitsubishi or a 5-speed Hyundai.

The front pump alignment is very critical in this unit because it isn’t a self-aligning pump. There are a couple different ways to align the pump: with a special tool and without.

Without Alignment Tool

The pump-to-converter housing and the stator support half-to-main case is practically an interference fit. This means you can use the two to align the pump (figures 5a and b).

Here are the steps:

  1. Assemble the pump body to the stator, leaving the bolts loose.
  2. Secure the pump to the main case (figure 6).
  3. Bolt the converter housing to the main case (figure 7).
  4. Tighten the bolts, securing the pump body to the stator support through the center of the case (figure 8).
  5. Disassemble the case halves and remove the pump from the main case.
  6. Torque the stator to pump body bolts to 90-110 lb-inches (10.0– 12.5 Nm).

With Alignment Tool

  1. Assemble the pump and stator, leaving the bolts loose.
  2. Install the Sonnax alignment tool into the pump (figure 9) and torque the bolts to 90–110 lb-inches (10.0– 12.5 Nm).

The special tool indexes from the inner diameter of the stator and pump bushing for a solid pump alignment. As you can see, using the special tool does have its advantages.

The Unacceptable Method

Never use the torque converter as an alignment tool (figure 10)! If you’ve been using this method without issues such as noise and broken gears, you’re very lucky.

There’s nothing holding the internal components of the torque converter in alignment (figures 11A, 11B and 11C). The converter clutch has no alignment to the cover because it rides on the impeller, which is splined to the input shaft. The stator has no alignment because it’s riding on the stator splines.

Bottom line: Never use this method to align pumps.

Direct Planetary Gearset

The direct planetary gear set is a part of the driven transfer shaft assembly. The direct planet in the A5HF1 has four pinions; the F5A51 has only three. You must take this shaft apart for inspection and cleaning during the rebuild process. If it looks familiar, that’s because the Ford FNR5 and the Toyota U250 have the same style transfer shaft/planetary gearset.

Once you’ve removed the 50mm nut (the largest socket in your box), the shaft parts press apart, much like its Ford and Toyota counterparts (figure 12).

After you’ve cleaned, inspected and replaced any parts necessary, you’ll reverse the pressing order.

The last step is to torque the very large nut. You’ll do this during the final transmission assembly, after you’ve added the parking pawl assembly to the case. Now you can engage the park mechanism and hold the case (figure 13) to torque the nut to 125 lb-ft (170 Nm). Much easier than attempting to hold the shaft outside the case.

One More Special Tool

The low/reverse clutch return spring can be a challenge without the special tool. The factory uses tool MD99957 (figure 14).

We put together our own special tools out of some extra parts we had laying around the shop. We used a piece of steel bar stock from another tool we made. To adapt it to this unit, just drill a couple holes to match the case. The ring gear is from a 604 and it fits the job perfectly (figure 15 and 16).

You’ve seen this unit before and now you should have a better understanding of what it’s all about. As long as you use the correct tools and use practical methods, you should be able to keep on having fun with transmissions!