Hondamatic Headaches TRX400FA Rancher Automatic Slipping

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TRX400FA Transmission SwitchA customer of ours recently brought in a really nice 2005 Honda Rancher TRX400FA Automatic that had been swamped in a deep mud hole by his wife. After they managed to pull it free from the muddy abyss, it stopped pulling forward or reverse in both auto or electric shift mode. The quad would lurch a little, and make a terrible sound that was similar to what you might expect to hear from a stripped spline, spinning within a clutch hub. Not a sound any owner wants to hear!

Honda TRX400FA Rancher AT

I’ve read cases online where other Rancher owners had experienced similar symptoms. In several of those cases the local Honda dealer immediately told them repair costs would be over $2,500 in order to split the cases and replace the Hondamatic transmission. Those machines ended up getting sold or parted-out, rather than repaired. I can’t help but wonder how many quads like this have been misdiagnosed and parted-out needlessly?

When this Foreman was brought to my shop, we found that water had made its way into the crankcase. This was made clearly evident by the chocolatey foam on the dipstick. After draining and flushing the crankcase several times using a mixture of clean oil and Marvel Mystery Oil, we were confident the water was out of the system, and changed the oil and filter.

We tested the machine, and initially thought that the contaminated oil was the culprit. However, when the engine reached full operating temperature the slipping and horrible sound returned. After cooling, the symptoms would again subside temporarily.

Proper oil pressure is instrumental in the proper function of the Hondamatic transmission, and affects operation in both automatic and manual shift modes. We hooked up a pressure tester to see where we were at.

According to factory specs, at 80°C (176°F) oil pressure should be 18 psi @ 1,400 rpm, and 85 psi @ 4,000 rpm

The machine that we were working on barely made 18 psi throughout the entire rpm range. We decided with the customer’s consent, to replace the oil pump, and relief valve (inside the front cover), as well as the smaller set relief valves and springs (located on the outside of the cover under the socket head set screws.) While clearances were within tolerance within the pump, there was some mild scoring. For less than $150 in parts we changed all the major oil system components and o-rings. While we had things apart we checked out the clutch and verified that it was within spec and not damaged, as well as the one way bearing which was also good.

The only thing left now was to put the front crankcase back together and see if we’d solved the oil pressure issue, and what effect it had on our transmission. Was there any internal leakage within the transmission?

I’m happy to say that our pressure tester confirmed that the lubrication issue was solved, and a long test ride in the southern sun on a 95° day, proved that the transmission was no longer slipping or grinding, even when hot. Our customer was happy too! He was planning on parting the machine out if it needed to have the cases split.

Hopefully, this post will find someone out there before they decide to scrap their Rancher without first checking the oil pressure. Maybe their story will have a happy ending too?

Enjoy the ride!

Big Len


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Big Len

It all started with homemade minibikes, and then a little green Kawasaki 90! I was hooked! I've been riding and repairing dirt bikes, motorcycles (Harleys for the last 10 years), and atv's for about 40 years now, and I don't plan on stopping if I can help it! I hope you enjoy this rider's ramblin's - enjoy the ride! [Read More About Big Len Here]

2 thoughts on “Hondamatic Headaches TRX400FA Rancher Automatic Slipping”

  1. I have the same exact issue with a 420 hondamatic that my son swamped in a creek. Flushing oil multiple times and adding high quality oil and new filter didn’t fix it. It will move slightly forward and reverse but acts like clutch is slipping or something. Could you point me to some instructions to replace the pump and other parts you describe? Sure would be sweet if I can avoid parting out a nice machine. Thanks.

  2. Hi i have a 2006 honda rancher 400at and a rubicon 500 and i have never seen a case like this i have only seen when they go into limp mode. Limp mode acts quite similar to what you are saying but you are stuck in the third gear position (even though they dont technically have gears)

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