Akerman tracked excavator goes forward and backward but doesn't turn left or right

[mbreg7]

Does anyone have any ideas on what would make an Akerman H12BLC lose its ability to turn left or right? It goes forward and backward with full power but doesn't turn. This model uses a forward pedal and a separate reverse pedal, and a hand lever moves left/right to control left or right steering. When the hand lever is engaged, it slows down like it wants to engage in a turn but doesn't actually turn.

A mechanic took apart the left/right steering control and we looked it over, and everything seemed to look fine - its basically just a big heavy chunk of steel with very simple valve mechanisms and about 7 control lines.

In terms of activities leading up to this problem, it was working fine until a track came off about 800 foot up a driveway in a woodland clearing. I got the track back on and drove it back down the 800' drive to where I park it. The track had about 8" too much slack, so I tensioned it to specs (165mm from track to center of roller). Then went to drive it and in less than 10' realized it wasn't turning. I checked out the tension and saw that I had compressed the idler spring, so released all the pressure on the spring (about the same amount of slack I had before tensioning it), but still had the issue with the excavator not turning right or left.

Any thoughts on cause/resolution? Any ideas are appreciated!

- Mike

 

[mike944]

I have an H10blc, I assume it works the same.

it's normal for it to slow down when the steering control is moved left or right, But, that's a completely unrelated electrical function.

I can't see how it's possibly related to the track coming off on you.

Did you try a pivot-in-place turn? I.e. Push the stick left or right, and push down both travel pedals at the same time?

Try lifting one track in the air, push the steering stick in that direction, and push the forward pedal. The track in the air should not turn. The way the steering works on that machine is that the steering stick causes one of the tracks to stop turning, while the other one keeps going.

Good luck

 

[mbreg7]

I have an H10blc, I assume it works the same.

it's normal for it to slow down when the steering control is moved left or right, But, that's a completely unrelated electrical function.

I can't see how it's possibly related to the track coming off on you.

Did you try a pivot-in-place turn? I.e. Push the stick left or right, and push down both travel pedals at the same time?

Try lifting one track in the air, push the steering stick in that direction, and push the forward pedal. The track in the air should not turn. The way the steering works on that machine is that the steering stick causes one of the tracks to stop turning, while the other one keeps going.

Good luck

Yes, I tried contra-rotating left and right (pivot-in-place), both pedals down with steering stick left or right, but it still doesn't turn.

When I lift up one side and try to just hold the steering stick for just the raised side to turn, the side on the ground still tries to turn at the same speed.

My mechanic put pressure gauges inline between the steering control and the manifold/spools, and we tried each combination of Forward, Fwd R, Fwd L, Back, Back R, Back L. We got pressure as expected for all the right combinations which makes it look like the steering control is working and control pressure is appropriate going to the high pressure travel valves. So I'm baffled at what could be the issue.

Controls Direction
Fwd Fwd right Fwd left Back Back Right Back left
Line pressures
Left Motor:
Fwd Left 800psi 800psi 0 0 0 0
Back Left 0 0 0 600 0 600
Right motor
Back Right 0 0 0 800 800 0
Fwd Right 800 0 550 0 0 0

 

[mbreg7]

Ok, looks like my chart of pressure readings lost its column formatting after posting. Here's an image of the chart:

 

[mike944]

Yeah, it looks like your control pressures are correct. That makes this even more puzzling.

What happens when you try to do a contra-rotating turn, in both directions?

So, what else is further down the line? The valves themselves, hoses to the swivel joint, swivel joint, hoses to the motors (and brake packs)

Assuming there's only 1 way a hose can go bad, and that's a leak, I'd say it's got to be the valves themselves, or the swivel joint. Maybe your valves have gotten hung up on dirt particles? Then check your swivel joint. From looking at the cross-section in my parts manual, I suppose it's possible that it could start to come apart, shift and start to connect passageways together. It's a long shot, but that's a really puzzling problem

 

[mbreg7]

Yeah, it looks like your control pressures are correct. That makes this even more puzzling.

What happens when you try to do a contra-rotating turn, in both directions?

So, what else is further down the line? The valves themselves, hoses to the swivel joint, swivel joint, hoses to the motors (and brake packs)

Assuming there's only 1 way a hose can go bad, and that's a leak, I'd say it's got to be the valves themselves, or the swivel joint. Maybe your valves have gotten hung up on dirt particles? Then check your swivel joint. From looking at the cross-section in my parts manual, I suppose it's possible that it could start to come apart, shift and start to connect passageways together. It's a long shot, but that's a really puzzling problem

If I do a contra-rotation turn, in either direction, it doesn't go anywhere.

Basically, it looks like from the schematic that the pump pressure goes to the forward and reverse pedals, then to the steering control, forward in the front of the control, reverse to the rear of the control. So forward pedal + right turn control sends servo pressure down VF (V=Venstre or left, so left forward) control line, back + right turn control sends servo pressure down HB control line (H=hojre or right, so right back). Forward + back + right control sends servo pressure down VF and HB to contra-rotate. And same for left, there's HF and VB lines.

The lines go in pairs to two valves, VF and VB to a valve marked VB (left back) which is to the left track motor, and HF and HB to a valve marked HF (right forward) to the right track motor.

From there, there's 4 high pressure lines to the center passage, 2 for right motor and 2 for left motor, along with servo pressure to release the track brakes.

So its possible that there could be some kind of gasket failure in the center passage, but it would require 2 separate and non-connected failures for it to go both forward and backward without turning to either side, and without losing pressure by going right back up the return lines. I've heard that usually center passage seal failures result in loss of forward/back power which isn't happening.

All this makes me wonder what else could possible happen? Is there some kind of connection between the 2 valves for left and right track motors, maybe something to equalize power that connects them that failed? Or is there something to do with the electric switch on the steering control that slows down the machine for turns - is it slowing it down to much to make any turns? Or something else? Very puzzling!

 

[uffex]

God day mbreg7
The Akerman H12b machine has a in line valve mounted beneath the central joint, if this sticks in the activated position it will prevent track steering. I will check out if I still have any illustrations, if you drop me a mail via the forum I will try to find these.
Unlike modern excavators these do steer without raising the undercarriage.
Kind regards
Uffex

 

[uffex]

Akerman H12B

View attachment AKERSchematicH12b.pdf

Good day once more found the schematic see item 6a
KR
Uffex

 

[mbreg7]

View attachment 139398

Good day once more found the schematic see item 6a
KR
Uffex

Thanks very much Uffex for that schematic.

I saw something kind of like this in an Akerman EC420 manual but my H12b parts manual didn't have this level of detail. It looks like 6a might be related to the track brake. I thought that any action from a pedal with or without steering control movement would send servo pressure to activate a piston and compress the springs to release the track brakes (apparently they're activated until there's a pedal movement to release them). The 420 manual describes the track brakes as "only intended to act as a parking brake". Since I'm able to go forward and backward with full power it leads me to think that the track brakes are releasing properly.

Does this control perform a track brake function or something else? I would think that once the control lines select the right 3 way position in the left and right track motor valves and high pressure is sent down either the forward or backward left track hoses and/or forward or backward right track hoses to the track motors that the excavator's speed and direction is controlled by the amount of pressure in those high pressure lines. Is this control somehow affecting that at the trackmotor?

thanks!
Mike

 

[lantraxco]

6a puts both track motors in series when shifted. Indeed may be your problem since in that state no matter what you do if you send any oil down to them they will drive in lock step. Signal appears to come from valve 14a, is that a solenoid valve? Some kind of straight travel, or high speed setup?

 

[mbreg7]

6a puts both track motors in series when shifted. Indeed may be your problem since in that state no matter what you do if you send any oil down to them they will drive in lock step. Signal appears to come from valve 14a, is that a solenoid valve? Some kind of straight travel, or high speed setup?

Thanks very much for that explanation, that's really helpful. I didn't realize that was indicating that a signal from 14a would put both track motors in series! It sounds like this could very well be the answer if I can figure out what/where that solenoid is.

 

[lantraxco]

Well, that's what the schematic symbols seem to indicate... oddly enough it looks like the default is for the pressure to be high from 14a until it is activated so the default is series? Not sure I'm reading that right. I'm wondering if activating the left/right hand lever doesn't activate 14a to unhitch the motors...? Anybody got the electrical schematic, might shed some light on things?

 

[mbreg7]

Well, that's what the schematic symbols seem to indicate... oddly enough it looks like the default is for the pressure to be high from 14a until it is activated so the default is series? Not sure I'm reading that right. I'm wondering if activating the left/right hand lever doesn't activate 14a to unhitch the motors...? Anybody got the electrical schematic, might shed some light on things?

According to another person commenting on this topic:
"No speed sensor in this circuit, no electrics at all in the undercarriage. On the other side the speed is almost the same both up & downhill. The switch in the hand lever are supposed to shift 6a to parallel mode (low-speed), to make it possible to steer. 1d is the servo-pump, and 2d the servo relief valve."

 

[mbreg7]

Here's the electrical schematic for the H12b:

 

[lantraxco]

Too small to read sadly, but that's sounding right, when you activate the turn lever it closes one pump flow off at the valve for that side, right or left, so you get one pump flow to the 6a valve, which slows the machine by half. If the 6a valve is not shifting though then both motors still drive together, no turning.

Need to locate the 14a valve I think and start there, test light or meter, see what you've got, then if you don't have power when the turn lever is moved, work your way back through the schematic, relay, switch on the steering lever, and the power supply to that. Could be nothing more than a blown fuse or broken wire. If you are getting power to the solenoid coil (I'm assuming it's a solenoid, can you find the connection in the electrical schematic?) then there may be a hydraulic issue like a stuck spool in the 6a valve.

I don't know anything about Ackerman but it's possible there's a manual override switch or pressure switches that would shift the 6a valve into low speed also for climbing slopes? Is there a low/high travel switch in the cab?

 

[uffex]

Good day Mike
The meaning of this valve was to provide high speed tracking, the flow passed into one transport motor and then on to the second. Actually this gave a slight bias to one side in high speed but double the pump flow. The valve should knock out when you make a turn then one pump serves one side and the remaining pump serves the other = low speed.
The philosophy was to prevent operators making turns in high speed (not good for the tracks).
In answer to your question no this valve has nothing to do with transport brakes these are released via the transport pedal 65 bars of pressure.
If you study the central joint you will see a small connection at the base cabin side, this si the activation of the in-series valve.
Before you do any thing more try selecting low speed on the dash and then try turning the tracks, let me know and I will try to help more.
PS 14a is on the end of the main valve chest
Kind regards
Uffex

 

[ben46a]

I've seen cats that wouldn't turn when the swivel manifold seals were gone internally, allowing oil to bypass.

 

[uffex]

Good day again
Not to sure if I have the correct model and it is some twenty years ago, however if you have a control lever to the left side which is used for steering the tracks then take the panel from the side (Three screws). Beneath the control you will find a micro switch this is the item that knocks out high speed. It is a crude device prone to this issue, I'm sure once you locate it the function will be clear and easy to check out.
KR
Uffex

 

[mbreg7]

Thanks Uffex and Lantraxco for the ideas about 6a and 14a, and the hand lever switching to parallel mode, I hadn't thought about a possible electrical problem previously.

I checked the panel today and saw a blown fuse and replaced it and was able to turn again! ..briefly, then was unable to turn again even though the fuse didn't blow again. So maybe an issue with the wire, switch or valve/solenoid.

I scoured the schematics and wiring diagrams in my H12b parts manual and an H16 manual but didn't see anything in them other than the speed select switches. Looking at the machine, I can see the switch on the steering lever, the speed switch on the panel, and a valve/solenoid on the high pressure valve manifold, which has the 2 travel spools along with 6 other spools. Here's a picture of the valve/solenoid there. I didn't get time today to do any testing on it but will next time I'm out there. Also, here's a picture from the bottom of the center passage.

 

[lantraxco]

That sure looks like the right solenoid valve. I think you're definitely on the right track, since you got it to turn for a while!

Just gotta figure out if you have bad coil, bad wire, bad switch, or bad connection I think. Did you try locking the speed switch on the panel in low? May be the same circuit but if the steering lever switch were bad the panel switch may override it? Probably the same wiring from some junction point though.

Cheers, Lanway