BX2350/BX24 Abrupt Reverse Stop

[MoreCowbell]

I know there have been a lot of posts about the BX2350/BX24 abrupt reverse stop issue, but I don't think there has been a discussion about which specific part(s) were modified in the the current BX line to fix that.



Looking at the transmission part numbers and diagrams, both the old and new BX HSTs share the same part numbers for the vast majority of the transmission. When looking at the assembly for the HST pump and motor (labeled 060 and 100 in the diagram), those bear different part numbers. The Messicks site shows that the old pump and motor part numbers have been replaced by the new ones. It would seem that if the modifications to either of these was indeed the fix, someone replacing these in a BX2350/BX24 would see the issue resolved. Has anyone experienced that?

Both the pump and motor apparently work with the "Port Block Cover" casting (labeled D013) which houses a couple of relief valves that also have different numbers between old and new. However, I doubt the relief valves are the cause of the problem.

Anyway, I'm just curious as to whether anyone has identified the actual replacement part(s) that would resolve the issue. My understanding is that Kubota has not released this information. I assume they did not want to invite warranty claims if the issue was fixable with a part or two (these parts are rather pricey).

 

[oldnslo]

I doubt the rotating group(s) would make much difference. My best guess is the neutral lever/fork or as Kubota calls it "shaft" which is item 030 on the page labeled HST 2. I suspect this lever/fork forces the tranny to neutral which causes the abrupt stop. On most HST the operator can feather the controls to achieve a smooth stop. On these BX's the feathering is next to impossible.

In my BX1850D the p/n is K2581-14530
On a BX 1860 the p/n is K2651-14520

 

[MoreCowbell]

I thought about it some more and I think you are right that the pump and motor are most likely not the cause given the way those units work.

However, I'm not sure the neutral lever is the cause either. As a test, I backed up a hill, kept it in gear and moved the pedal to neutral. It rolled down the hill pretty easily. I then pointed the tractor uphil and did the same thing, but the wheels were locked in place - preventing the tractor from rolling backwards. The pedal was positioned in neutral both ways.



The image above was taken from a BX23 hydraulic schematic someone posted here (thank you to whoever that was). I could not find one for our series, but I think they are very similar. Here is what I think may happening. When neutralizing the pedal while still moving, the motor is acting like a pump. For the motor to keep turning, it needs to bleed off the pressure it is building up. The pump will not pass that fluid since the swashplate is in neutral position. The checkvalve will not pass fluid in that direction, and the relief valve only passes fluid under very high pressure.

The only thing left to allow fluid movement is the flow restrictor (I pointed to one with a red arrow). Maybe for our BX series, there is a flow restrictor in the forward circuit but not the reverse circuit?

 

[oldnslo]

Here is the schematic from my WSM for my 1850. Not sure which direction is forward and which is reverse. It does show only one orifice. Not sure if this orifice is part of the relief or not. Interesting thought on this being the cushion but would allow a small free wheeling effect. Yes when stopping the motor turns into a pump and if the oil has no place to go to you stop.

 

[CHDinCT]

The part number that fixed my BX1850 was a BX1860

 

[BXpanded]

I believe the actual fix is in the linkage and the hydraulic damper on the foot control. The 50 series slowed the return from the forward position only. The 60 series slows it from both forward and rearward positions.

There are lots of different parts in the linkage. I would guess they would retro-fit.

BTW, I find the longer it's been since the pedal pivot was greased, the less abrupt the stop.

 

[MoreCowbell]

Here is the schematic from my WSM for my 1850... It does show only one orifice.

First of all, thanks for posting that schematic. I was looking for that for a while. Secondly, I can't believe I guessed right! Now I'm really thinking that the absence of that orifice that is the problem.

I was hoping this orifice was built into the relief valve assembly, but I looked at the part numbers between the xx50 and xx60, and the relief valves on the HST are the same between the two series - so there is no change in those parts, and apparently they would not be where the fix was. It may be cast into the cover for the HST. That part is about $550.00. If that is true, it looks like I'll be living the problem for a long time.

The part number that fixed my BX1850 was a BX1860

Chris, what part from the xx60 line did they install for you to fix it?

Thanks.

 

[like2wheel]

Chris, what part from the xx60 line did they install for you to fix it?

Thanks.

I think he meant they installed a new tractor under his butt.

Not very helpful, & certainly more expensive than the hst cover...

 

[MoreCowbell]

I think he meant they installed a new tractor under his butt.

Rats. I got my hopes up thinking he found the holy grail.

 

[oldnslo]

I believe the actual fix is in the linkage and the hydraulic damper on the foot control. The 50 series slowed the return from the forward position only. The 60 series slows it from both forward and rearward positions.

There are lots of different parts in the linkage. I would guess they would retro-fit.

BTW, I find the longer it's been since the pedal pivot was greased, the less abrupt the stop.

Actually the damper controls in both directions on both models. And no the **60 series damper does not help on the **50 series. Yes the linkage is different from the **50 to the **60 series.