JD 455 keeps rolling forward after pedal is released

[skjalggl]

Hi folks,
here comes my first ever post
I just bought myself a "new" Deere 455 - it is a 1998 model.

So far the only problem I have, is that it keeps rolling forward after I release the forward pedal.
With engine shut off:
-I have disconnected the damper that sits on the rear end of the linkage, and I have checked and verified that the bi-directional return spring inside the hydrostatic is working.
-The spring looks to be pulling equally hard&fast in both directions
-As far as I can see/hear, there is no linkage binding either.

If I try the same things with the engine ON, however:
-releasing the backwards pedal results in a quick halt (split second) - just like when the engine is off.
-releasing the forward pedal results in a very slow "return to neutral position", thereby letting the tractor travel a distance before it halts. Why is it slow now, and quick when the engine is off?

Could there some hydraulic valve or something that is causing this? It is only a problem with forward, not reverse. That has me thinking about the "directional valve-forward/reverse" that sits on top of the charge pump (see picture).
These 2 valves seem to be quite "sloppy", not resting against the free-wheeling linkage that is used to engage them. I also have 1995 model 455, and on this tractor these valves seem to be resting entirely up against the linkage (due to a large/heavy cab on the 1995 model, I have only been able to inspect the valves with a borescope).

Anyone have any suggestions?

 

[beenthere]

Do you have the service tech manual for the 455?

 

[skjalggl]

I have "Technical manual" - would that be the same?

 

[beenthere]

Yes, look at the neutral adjustment and turning the eccentric.. seems that should fix it.. I tried to get a pic of my 455 but couldn't with the fender deck on.

 

[skjalggl]

Yeah, I'm afraid I tried that already...

Also, I dont see how a badly adjusted neutral would explain why the forward pedal all of a sudden is super slow at returning to its original position when the engine is running, and then superfast when the engine is off?
My suspect has Hygard running through it, I believe..
Or am I missing something here?

 

[Kish318420]

Check the pivots that the foot pedals work on, could be that they are sticking/dragging due to corrosion/rust. There are ball bearings/supports and stacked washers (items 10,11,13,24), so that is where I would concentrate on cleaning and the PB blaster or a dry film lubricant.

 

[skjalggl]

Well, as I stated in my original post, there is no mechanical binding.
With the linkage damper removed the linkage returns fast from fully depressed forward & rearward pedal - as long as the engine is NOT running.
With the engine running, only the rearward pedal maintains a quick return.

That suggests to me that there has to be something working a force on the "hydrostatic direction/speed axle" from inside the tranny as long as the tractor is fired up.

 

[beenthere]

Maybe time to overhaul the tranny, as there maybe crud in there gumming up the works.

 

[skjalggl]

This afternoon I will try to manipulate the "directional valve-forward/reverse" while engine is running, and see if that helps.

 

[skjalggl]

This afternoon I will try to manipulate the "directional valve-forward/reverse" while engine is running, and see if that helps.

The valves seem to be OK.
Not too sure about the "Implement relief valve" though - it is the one sitting between the two directional valves.
According to JD´s part drawing, it hould have more parts than what I have...