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2007 Honda 400 Rancher 4x4 ATV squealing sound when shifts into drive(TRX400FA7)


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D88F704E-9175-4D26-AA03-8E26E04E2E54.thumb.jpeg.730ff5f6d611b8623f69d3bef2f4aa15.jpegFirst time working with a Honda-Matic transmission. I didn't even know what I was getting into when I purchased this running beat up farm workhorse quad with black oil. I was thinking I could tear the cases apart and find the bad bearing, causing the random squealing noise when you put it into gear and give it gas. Upon opening the engine covers, I Learned about the Honda Matic automatic transmission and realized there's more than just an electronic shift motor going on in these quads. With my learning curve in major education mode, I'm now wondering two possible culprits to the squealing as I've torn the motor down and am staring at the Honda Matic transmission.

Two possible issues:

1. The bearing that is squealing is unfortunately inside the hondamatic unit hydraulic transmission which is apparently not serviceable? A new unit is $1,900 to replace it! Yikes!
2. The pull starter rope snapped and someone replaced with the wrong pull starter rope that eventually became severely worn out and the centrifugal lever/catch shows signs of wear from rubbing against the housing.

Thinking now the pull starter has nothing to do with a squealing that loud, so my attention is now on the Hondamatic unit, 
Has anyone gotten inside their cases to inspect the Honda Matic transmission?
There's a only 1or 2 videos out there that are not helpful for tear down and inspection.
I understand it can't be rebuilt but wondering if anyone has looked deep enough into one to clean it out from running dirty oil? Possible identify bad parts.

I refuse to believe Honda is engineeering these as completely non-serviceable?

Thinking I will try to disassemble the Hondamatic unit m. Hopefully get into it and get all the dirty oil out and replace with fresh? Any special tools needed?

Any and all thoughts/experiences with Hondamatic units would be great conversation for me..


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Automatic transmissions have been used in some All Terrain Vehicles (ATVs) for many years, but until the introduction of the Hondamatic hydraulic transmission, ATV automatic transmissions used a traditional belt drive and pulley system. The fully automatic dual-mode Hondamatic transmission featured on the 2001 Honda Fourtrax Foremanš Rubicon (TRX500) provides these features, and is compact, quiet and extremely reliable for use in agricultural, rural, and recreational applications.

The usefulness of the Hondamatic transmission is maximized when combined with the computer-controlled, dual-mode continuously variable change program or the Electric Shift Program (ESP), already in use on the Fourtrax Foreman ES (TRX450ES) and Rancher (TRX350FE/TE) ATVs. The ESP allows the operator to select higher or lower output ratios, providing precise manual control of the Hondamatic transmission.

Soichiro Honda recognized the efficiency and convenience of hydrostatic drives and incorporated the Badalini stepless transmission design into the Juno scooter in 1962. Honda engineers continued to develop their own versions of hydrostatic transmissions and incorporated them into snow blowers, lawn mowers and smaller power equipment. Honda Racing Corporation (HRCš) also applied this technology to the RC250 in 1990-'91. The RC250 was a limited-edition, works-type motocrosser that used the continuously variable transmission to maximize torque output and optimize reduction ratio selection.

In a very simplified description, the Hondamatic hydraulic transmission uses the engine to drive a hydraulic pump that forces hydraulic fluid through sequential pistons. On the other side of these pistons, the pressurized fluid enters a second set of pistons that push against an angled plate (called a swash plate). Because the cylinder body holding the pistons is splined to the output shaft, the pressure exerted on the swash plate causes the cylinder body to rotate. When the angle of the hydraulic motor swash plate is adjusted, the cylinder body (and, therefore, the output shaft) rotates faster or slower, resulting in higher or lower output drive ratios. When either of the two automatic transmission modes (D1-Maximum Performance or D2-Maximum Torque) is selected, the Engine Control Unit (ECU) continuously monitors input from six sensors to position the motor-side swash plate at the optimal ratio. Using the ESP mode, the ECU instructs the control motor to move the hydraulic motor plate to preset angles to simulate specific gear selection.


Operating Principles
The Hondamatic transmission is a hydromechanical continuously variable transmission with a fixed-volume piston pump and a variable-volume piston motor in opposition on the same shaft. As the Hondamatic is a closed circuit, any excess hydraulic fluid from the Hondamatic system is recirculated to the transmission using a separate charge pump. The Hondamatic transmission uses standard engine oil as hydraulic fluid.

Upon engagement by the centrifugal clutch, the engine turns the transmission's pump-side outer body, causing the fixed-angle pump-side swash plate within to rotate, sequentially stroking the pump side pistons. This action draws low-pressure fluid into the pistons, which discharge high-pressure fluid (corresponding to the input torque). The fluid is distributed to the high-pressure circuit by the distributor valve on the pump side. The distributor valve on the motor side opens and feeds the high-pressure fluid to the pistons on the motor side for the suction stroke. Each distributor valve is eccentrically synchronized to the rotation of its respective swash plate, ensuring that fluid is transferred at the proper time. The amount of fluid discharged depends on the angle of the motor-side swash plate. The greater the slant, the farther the pistons move and the more fluid they transfer. This additional volume transfer makes the motor side less efficient, resulting in a differential based on the volume transferred. As the motor-side pistons travel down the slope of the motor side swash plate, the fluid pressure is drawn through the pistons and rotates the motor-side cylinder body (which houses the pistons). As the cylinder is splined to the output shaft, the output shaft also rotates, transferring power to the drive train.

When the motor-side swash plate is perpendicular to the pump axis, the pistons do not stroke (therefore, oil is not discharged). In this condition, oil cannot flow between the pump and the motor and the motor is hydraulically locked (1:1 gear ratio). An overdrive is achieved by adjusting the swash plate to an angle beyond perpendicularity to the pump axis, creating a drive ratio of 1:0.84.

As the pistons begin their travel back up the motor-side swash plate, they begin their discharge stroke. The hydraulic fluid is transferred back through the motor-side distributor valve and into the low-pressure circuit of the body. The fluid then passes through the pump-side distributor valve, where it is timed to the suction stroke of the pump pistons.

Distributor Valves
The hydraulic fluid is transferred between the pump and motor piston chambers by the sprue-type distributor valves arranged radially around the shaft. The pump-side and motor-side distributor valves are eccentrically arranged on the shaft and are aligned to time the transfer of low-pressure and high-pressure fluid in tune with the direction and inclination of the pump and motor swash plates. As the cylinder rotates, the eccentrically arranged valves slide in and out of the cylinder body, opening and closing the paths in the body.

Compression Braking and Pressure Control
During normal running, the check valve in the pump-side cylinder feeds hydraulic fluid into the low-pressure circuit. The check valve is open when the hydraulic pressure in the low-pressure circuit drops below a specified level and, upon achieving the proper pressure, closes to prevent backflow. Under engine compression braking conditions (where the rotational force comes from the wheels), the motor side becomes a pump (driven by the input shaft) and the pump side becomes an hydraulic motor. In this situation, the high- and low-pressure circuits in the Hondamatic body are reversed. The Hondamatic transmission uses a separate check valve to feed hydraulic fluid to the engine braking low-pressure circuit.

Pressure control valves vent excessive high-pressure fluid into the low-pressure circuit during both normal running and compression braking conditions.


Torque Amplification
The input reaction force torque from the engine is transmitted to the pistons that are fixed within the rotating cylinder. This force is then transferred through the cylinder to the shaft (mechanical power train). When the ratio is 1:1 and the motor side swash plate exerts no reactive force against the motor cylinder, the input torque is transferred directly to output torque with no amplification. When the angle of the swash plate is increased, the reaction force increases, amplifying the output torque. The total output torque is the sum of the input reaction force torque and hydraulic output torque.

Shift Mechanism
As previously discussed, the output shaft speed is controlled by the angle of the motor-side swash plate. The position of this swash plate is determined by the ECU, which uses various pieces of information to send commands to the control motor that moves the swash plate arm. The signals used to determine optimal Hondamatic output are:

Throttle opening (throttle sensor)
Vehicle velocity (speed sensor)
Engine speed (rpm) (ignition pulse generator)
Hondamatic motor-swash-plate angle (angle sensor)
Gear position (gear position switch)
Control mode and map (mode/map switch)

In the fully automatic modes (non-ESP), the ECU is continuously monitoring these signals. When a change in motor swash plate is deemed necessary, the ECU sends a signal to the control motor, which moves the ball screw (attached to the swash plate arm) via reduction gears. There are two rider-selectable automatic modes: D1-Maximum Performance and D2-Maximum Torque. The D1 mode emphasizes higher engine horsepower output for riding performance, while the D2 mode maximizes torque output performance. Within these rider-selectable modes, there is a choice of standard output ratios (Drive) or lower output ratios (Low) using the automobile-like shift lever. Reverse can also be selected using this gear lever which engages a reverse gear located in the subtransmission.

When the operator selects the ESP feature, the UP and DOWN buttons on the handlebar switch are enabled. When the appropriate button is pressed, the ECU commands the control motor to move the swash plate to the next higher or lower preset position.

The Hondamatic transmission is the first continuously variable transmission of its kind. Housed within a compact, fully sealed assembly, it uses the principles of hydrostatic drive, mechanical power transfer and modern electronic controls to create a unique hydromechanic drive. Unlike traditional belt drives, the Hondamatic is quiet, maintenance-free, rugged, impervious to external contaminants and features true engine braking.

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What makes you think it's a squeal from inside the cases ? Did you find any metal shavings or dust in the cases when you stripped it ?

Could it be an engine mount squealing ? Exhaust rubbing ?  Something like that..

I'd be really doubtful that anything inside there could be making a squealing, and under throttle, without there being signs of wear, and probably heat.


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Exact conditions when I purchased it:

bad battery

only pull started.

Started up, a bit rough on idle, but otherwise is decent running order, put it into fwd and no sounds, put it into reverse, no sounds, fwd again and the squealing started with gas and forward motion between 3-8mph. It was unique enough and alarming enough that I figured it was a bad transmission bearing, like a bearing freezing and the shaft was rotating in the bearing. so I just decided to investigate for something obvious with that much noise. Found the previous owner probably hasn't changed the oil recently as the entire protective pan and drain plug were caked in with debris and dried stuff(Took me good 30-45 min to clear it out and find the drain plug). Oil didn't register on the dip stick, but did have oil in it. Was very black, but not burnt smelling or dirty with shavings. Just looked like it wasn't changed in a long time. When pulling the piston and cylinder, I expected worse, but the piston rings had obvious wear and carbon build up on the exhaust side of the piston rings and oil rings, but nothing was seized.

All good questions to ask, but I'm very sure it wasn't a brake rotor, CV joint, or wheel bearing.

Ive been studying the posting by MECH(thank you) on the design and operation. Makes me think that with this design, Honda knows the robustness of it, however the design uses the engine oil as the Hydraulic fluid for the Hondamatic unit. I would think this would be a concern for  exactly my situation with lack of engine oil maintenance. However, the last section reads:

" the Hondamatic is quiet, maintenance-free, rugged, impervious to external contaminants"

So I'm not sure exactly how they keep it "impervious to external contaminants" if it's in the engine oil? I'm guessing they must be referring to other transmission belt transmission type technologies?

Anyhow, all good thoughts, I still have to get the Hondamatic transmission out of the cases and look further/closer at it. I'll post my findings.

if anyone has any diagnostic info aside from what's in the manual, I would appreciate the suggestions.

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  • 4 weeks later...

I may have found a problem.

Most cranks I've worked on, the bearings are an interference fit, so the crank must be pulled into the bearing with a crank puller, or the bearing installed into the case and the crank is pulled into the bearing, etc.

I've found upon inspection before splitting my cases that my crank actually spins freely inside of the roller bearing, could this be the problem?

Does anyone know the tolerance or clearance of the Roller Bearing to Crank?

I should have the cases split for further inspection this weekend and will advise what I learn...

See video clip attached.



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It does seem a bit loose, but I doubt that oil soaked part is going to make a squeak.

So when you say it went into forwards and was quiet then reverse and it was quiet and then forward and it made the squeak..  Do you think it was the shifting that changed something, or was it just a matter of time needed for the squeak to start ?

It's really important to diagnose things before we pull them apart, because we can't do any tests or find the technique that will repeatedly and predictably cause the issue once they are apart. If we don't know the technique to repeatedly get the issue to manifest, then we can't test things after the repair to be confident we have fixed it. We might have just temporarily cured the symptom without fixing the problem.. 

If I was you Mat, I'd be putting it back together and riding it and testing it till I'd found the problem. I definitely wouldn't be splitting the cases. Oily parts don't squeak. Squeaks that appear within a certain speed range only, don't sound like anything from inside the engine to me..

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  • 2 months later...


Oil Drain plug and skid plate was packed in with dirt and mud/debris.

Wondering if the engine oil was changed at all?

Found black oil/low on oil, suspected internal bearings was the cause of the squeal with low oil condition.
I split the cases and found excessive clearance between both roller crank bearing and the standard crank bearing's outer race and the engine cases, but otherwise all other internal bearings were surprisingly in good shape. My main concern for the Hondamatic were relieved when it was in great shape with no visible wear, or grinding noises, the ball screw was in great shape with smooth operation and motion, no abnormal noises. Wahoo!

Since the 2005-08 TRX400FA AT is aircooled, it's kind of a unique animal in the Honda history it's surprisingly closest to the Rubicon 500 AT.

It was difficult to hunt down the original OEM roller crank bearing and standard bearing, but I found them and replaced them while I was in there.

I've reassmbled it now put it all back together.

I am working from both a TRX420 Rancher 420 manual shift repair manual and a Rubicon 500 Hondamatic repair manual because there was no Rancher 400 AT User's Manual saved to our QuadCrazy resources.

I'm noticing slight differences between the models and need advice.

Upon first start, the Hondamatic needs to go through an intial setting. This will programmatically set the ECU to recognize each of the system sensor's base setting for operation since they were all unplugged pulling the motor. Most notably are the Hondamatic Angle Sensor(senses the hydraulic awash plate angle that is equivalent to changing gears in a traditional transmission) and the Carb's Throttle Position Sensor.

I assembled my Angle sensor according to the manual preload instructions but they didn't clearly explain how much angle to preload the sensor to, so I don't believe I preloaded it as required. I am now working through troubleshooting these first initial settings and sensors. When removing the carb, Throttle Position sensor stays in place, but removing the throttle cable will require re-doing the intial setting.... no problems here.

So on first start, Idled immediately and smoothly...great motor!

so then test drive it first before going through the initial setting (and potentially having incorrectly installed the Angle Sensor).

If you don't do this initial setting, the machine will start up with no problem, but my experience with a potentially incorrectly installed Angle sensor was it will stay stuck in high gear and if shifted into reverse.

Additionally, it will have super-rough knocking if shifted into Reverse and anything more than idle will worsen the knock to motor dying on you.
You are stuck in high gear and not able not able to shift regardless of mode., or button you push. There is also no noise heard from the shift motor at all during any of these steps.

Question: can anyone confirm the diagnostic functions and settings are the same between Rancher's and Rubicon models of the same yars?
They appear to be identical, but looking for a confirmation.

Does anyone have screen shots of the Rancher TRX400FA AT users manual they can send?

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Aha! They are slightly different. Thanks Mech for sending!

The ESP switch has to be set to Auto for the initial sequence. 

Additionally, the Angle Sensor preload installation instructions image was very clear in this 400 manual and really unclear in the other 500 manuals.

Great to know I installed the sensor wrong.


So this maybe my last update to this thread... and solving the squealing problem..

During the rebuild, forgot to mention that I used new bearings and to ensure snug fit, I firmed up the gap between the roller bearing outer race and case with Loctite 609.

Got it all back together, and still had initial setting issues... 

I just removed the angle sensor and set the preload correctly to the angle sensor, and it was like a new machine!

The ECM now recognized the Hondamatic swashplate position and allowed for the shift position. That immediately allowed the shift motor to work, now I can hear the shift motor operating, and immediately there was no more reverse stalling and idling issues.

It's running awesome! 

I took a few hot laps around the neighborhood for the first time on a Hondamatic and I could use the AutoShift and switch over to the ESP selectable shift.

The Hondamatic is pretty amazing for it's design and torque transfer to the wheels.

Also, take into consideration that this is smooth for a machine that was ran down to black oil and low oil at 16,000 miles on it. 

I had also replaced the pull start assembly as the other old one was junk. 

No bearing squealing on drive, neutral or reverse, not a sound on launch, easy shifts from D-N-R, runs full speed, fast and smooth and punchy.

I see that i still need to remove the back wheels to complete the initial setting.


My hunch is that the outer race press fit area of the roller bearing side of the crank bearings started spinning inside the case after the oil got low and dirty enough? 

The old bearings rolled smoothly during disassembly and inspection, but I noticed an odd shimmer/polish to the bearing press fit area between the outer race and the case half?

I can't be sure, but wondering if the engine was so low on oil it somehow slightly started building friction on the rollers and started spinning the roller bearing's outer race in the case half itself?

I'm happy to have went through the whole motor to confirm all was good.

And it's an awesome machine now!

Cheers Mech! Thanks for your contribution and foresight to this thread!


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