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AC D12

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=131418
Printed Date: 23 May 2025 at 5:10pm
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Topic: AC D12

Posted By: RAR45110
Subject: AC D12
Date Posted: 16 Nov 2016 at 7:34am

Hello,

I have a 1959 AC D12 that was restored by someone else. It has a traction booster installed. I cannot make the implement rams retract. I have gone through the operating and maintenance manuals and have adjusted all the A, B, C, and D screws and adjusted the linkage rod. I have set the traction booster screw into the housing to eliminate the traction booster. I have no implement installed on the arms. I disconnected one of the hydraulic hoses to one of the cylinders and the oil leaked out, causing the implement arms to lower. When I replaced the hose and started the engine, the rams slowly extended again and would not go down. By going through the maintenance manual, I have determined that the most likely problem is that the hold valve (1 in the diagram) is stuck closed. Before I remove the holding positioning valve body, which contains the hold valve, I would like to know if there is anything else that could be wrong or is there another way to free the valve?

Thank you in advance for your help,

Robert Read

Replies:

Posted By: PaulB
Date Posted: 16 Nov 2016 at 7:56am

If it is a late model (Series III) the traction booster valve is generally stuck.

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If it was fun to pull in LOW gear, I could have a John Deere.
Real pullers don't have speed limits.
If you can't make it GO... make it SHINY

Posted By: RAR45110
Date Posted: 16 Nov 2016 at 9:20am

Thank you for your input. My D12 is an early one, lower than 2000 serial #

Posted By: Larry in NC
Date Posted: 16 Nov 2016 at 10:09am

Your D12 without the live lift option has the same hydraulic pump as a CA. If you cannot get it to lift, you may have to remove the pump and start cleaning and making sure nothing is stuck. It sounds like you have gone through the process of playing with the adjustments. There are recent forum postings that show what other members have had to do to get CA's working.

Posted By: RAR45110
Date Posted: 16 Nov 2016 at 6:42pm

I am new to AC, this spring. Thank you for the information regarding the CA.

Bob

Posted By: Larry in NC
Date Posted: 16 Nov 2016 at 6:52pm

Since you are new to the tractor, you do have to have the PTO engaged for the lift to work.

Posted By: LeonR2013
Date Posted: 16 Nov 2016 at 7:16pm

I believe he said he had a lowering problem, not lifting.

Posted By: Larry in NC
Date Posted: 16 Nov 2016 at 7:23pm

You are correct.

Posted By: RAR45110
Date Posted: 16 Nov 2016 at 8:08pm

Gentlemen,

The lift arms will raise, but will not drop. I have done the adjustments in the manual. I believe I have traced the problem to the hold ball check being stuck. However, I do not want to take anything apart if I do not have to. One person said to attach a long pipe to one lift arm and pull down with the lift control down. Presumably this will put pressure on the hold ball check and unseat it. I was just trying to find out if anyone had this problem and knew how to fix it without disassembling the holding positioning valve.

Thanks,

Bob

Posted By: Tracy Martin TN
Date Posted: 16 Nov 2016 at 8:12pm

Have you tried pushing them down? If pushing will not work, the hold valve is stuck. Could be rust ,debris, or broken spring. If they will go down with valve in lower position, the packing is too tight.

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No greater gift than healthy grandkids!

Posted By: RAR45110
Date Posted: 20 Nov 2016 at 6:40am

Thanks to all for your help. I have decided to take the hold valve off and rework it to unstick it since this seems to be the most likely problem. Thanks again,

Bob

Posted By: DrAllis
Date Posted: 20 Nov 2016 at 7:11am

Before doing that, I'd screw in "D" 100% all the way inward and then see how the lift/lower lever reacts. If the pump is constantly pumping (because of a stuck control plunger) the hold valve doesn't stop the pumps oil flow from raising the load. The pump must not be pumping for the hold valve to be able to release trapped oil from the lift cylinders.

Posted By: PaulB
Date Posted: 20 Nov 2016 at 9:27am

Now that I know you have the early CA type pump, if all else fails the is a "LOWERING VALVE" inside of the pump control that may be stuck. You can get at this valve by removing the rear cover off of the pump. Get ahold of a service manual and it will have a clear picture of those valves. It will be easy to unstick if that is the problem.

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If it was fun to pull in LOW gear, I could have a John Deere.
Real pullers don't have speed limits.
If you can't make it GO... make it SHINY

Posted By: Dave Richards (WV)
Date Posted: 20 Nov 2016 at 5:34pm

Not sure what you guys call the hold valve. On mine the traction booster valve was stuck and I got the same result.

Posted By: RAR45110
Date Posted: 22 Nov 2016 at 3:33pm

Thanks to DR. Allis, Paul and Dave for the suggestions. I have a maintenance manual and will look this up tonight.

Thanks again,

Bob

Posted By: Eldon (WA)
Date Posted: 22 Nov 2016 at 9:09pm

It has been awhile since I had mine, but I think I just unhooked the rod and rotated the shaft by hand and mine dropped...never missed having the rod on there.

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