390HST no reverse

Ernie Alabama · Oct 23, 2011

New guy here, I'll get around to introducing myself in a bit.
I have a FamTrac 390HST with 300 hours on it. I've had zero problems other than a plugged fuel filter.
I used a boom pole to lift an 1,100 pound engine into my boat. Hung out 8 feet, the 3PH didn't quite have the umph to lift it, but it supported the weight just fine when the lift bleed was locked and the load lifted with a chain hoist.
The tractor sat a couple of days with the load hung while I fabbed the motor mounts.
So yesterday, I left to pick up some parts, and my nephew Jason unlocked the bleed off and dropped the chains and moved the tractor while I was gone. He only went forward 50 feet or so, and noticed nothing unusual.
So, I get back and figured I'd pull the tractor back to the boat and load all the cribbing into the bucket so we could work on the exhaust and wiring without tripping over a bunch of lumber.
I fired it up. Jason had not idled it down before shutting it off and the tractor lurched forward a few inches, but then had no creep.
I pushed on the reverse pedal and nothing. I looked down and the reverse pedal was all the way down and the forward pedal seems higher than normal.
I reached down and pulled up on the reverse pedal and the tractor moved forward a bit, so I pulled up on the forward pedal and was relieved to find that the tractor backed up.
The cam sector is centered and since it appears to be mounted on a square shaft, I can assume it hasn't moved. The linkage rod that appears to center the pedal height is tight and looks undamaged.
Can someone point me in the right direction?

Ernie Alabama · Oct 23, 2011

I took the tractor out back and moved 4 or 5 yards of dirt with the FEL and pushed all hydraulic functions to limit several times. I pushed the trans a bit as well. No change.
Pulling up on the forward pedal while backing up is all fine and dandy until you forget about that pine tree and hit it with a back tire.

mljenkins · Oct 23, 2011

Per the service manual your problem could be either the forward/reverse linkage from the pedal to valve is damaged or your reverse relief valve could be damaged. Since you said you can get it to go in reverse by pulling up on the pedal it may not be the relief valve and instead the linkage. You could try adjusting the neutral position position of the pedals if both pedals seem to be in the wrong spots for forward/reverse motion.

Shoot me an e-mail matt at mljenkins dot com and I can send you the powertrain section of the service manual for the 390 HST referring to the HST transmission.

It's strange that holding the amount of weight would have caused that problem. That is why I am wondering if it could be a relief valve or something that was damaged as the weight sat there and left pressure on the hydraulic system. Unless the problem is unrelated to holding the weight.

trac · Oct 23, 2011

Problem is in the cam, that has twisted under the pedals. It is the one with the small roller bearings on it. We had quite a few of them years ago do it. Replace the cam, adjust the pedals back even and good to go. I've got 2 in stock if you can't find them. If you force the pedals down in high range, the cam will twist.

Ernie Alabama · Oct 23, 2011

Thanks. I'll check it out.....
I see the cam you mention. I'll pull it off in a bit, though I see no signs of damage. You do mean the cam that has an adjustable mounting point that can be raised and lowered on a short threaded rod with an eye on the top and 2 nuts on the bottom?
Thanks a lot for taking the time to answer.

Ernie

Ernie Alabama · Oct 23, 2011

I pulled the cam assembly and see no sign of twisting from looking at the welds. I sprayed to bearings with some PB Blaster and they are running free now. Here's a picture of each side of the assembly. Do you see damage?

trac · Oct 25, 2011

It only takes a small amount of twist to throw off reverse. Try reinstalling and adjust the nuts to raise the cam. I always replaced them when they did it. The manufacture wouldn't admit to a problem with them, but always paid the warranty, when issued. I sold many 390's and I believe they all twisted. Replaced the cam on all of them. It corrected the problem.

Ernie Alabama · Oct 25, 2011

I put the cam back on today. raising it up about 3/16 set the pedals at the same height. I have full range in both forward and reverse though one of the return springs seems about an 1/8 too long. Not stretched out, just too long.
I'll order another cam and keep it on hand.
Thanks, guy!