HD 4 Main Pressure Relief
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Construction and other equipment
Forum Description: everything else with orange (or yellow) paint
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=115730
Printed Date: 19 Jul 2025 at 4:28pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: HD 4 Main Pressure Relief
Posted By: johnP
Subject: HD 4 Main Pressure Relief
Date Posted: 05 Dec 2015 at 2:53pm
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Hello all, I have a HD4 that had really slow hydraulics so I pulled main relief and found it had come apart, like the setting screw come unthreaded. So I fixed the threads a little and put it back together and now my pressure is too high. Where can I test main pressure to set the relief back up to 1750 like it should be. Thanks for any help John
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Replies:
Posted By: pinball
Date Posted: 05 Dec 2015 at 10:35pm
| Why do you think the pressure is to hi. Dozer or bucket loader. norm |
Posted By: johnP
Date Posted: 06 Dec 2015 at 3:41pm
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When I got it together I blew a hose right away. I would like to check it anyway since I had no idea how much to load the spring in the relief. 
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Posted By: pinball
Date Posted: 06 Dec 2015 at 5:04pm
| On my h4 crawler I have two ports to the outside of the control block. You could put a guage in there. Its for an auxillary equipment. One is the power lift and other is the return. I would first back your set screw back out to lower the pressure as much as you can. Install your guage and crank it but don't start it. It will build pressure up when turning. Not sure where but I suspect at a low pressure. If it keeps building pressure then your relief valve spring is probably broke. Your hose could have been ready to leak anyway. If you don't have a guage then back the screw out. Look in your reservoir and crank it. you should see a lot of oil movement coming back from the relief valve. That should tell you the relief valve is recirculating the oil. If you do then start your crawler and see how your bucket raises. I would say on mine from the ground to fully raised position it probably takes 6/7 seconds. May just take trial and error to get it adjusted. Hope this helps. |
Posted By: johnP
Date Posted: 06 Dec 2015 at 7:12pm
| Well what happened was I lowered lift cylinder till it lifted machine and stroked out and blew the hose. So maybe I should be looking at the relief on that circuit also? The hoses aren't the best either but its not a working machine. The spring looked fine when I put it back together. I'm still not sure where to tap in and take a reading, I almost want to drill and tap a hole in the end cap on the valvebank. |
Posted By: pinball
Date Posted: 06 Dec 2015 at 7:28pm
| Theres is two covers on my box in the front. Top one is easy to take off. I suspect you have another port on your control block. Those blocks are plugged since there not in use. They are for auxillary equipment such as a scarifier, back hoe, etc. You should be able to remove one of those plugs and put a guage on it. Mine has 4 ports on it. Two are plugged and not in use. The other 3 ports are for lift, tilt and a scarifier. I have had my assembly off to replace some o rings. I think when I was reading the manual they only made 3 and 4 ports assemblys so you should have one not being used to put a guage on. Course I could be wrong. Norm |
Posted By: johnP
Date Posted: 08 Dec 2015 at 6:19pm
| Your 100% right norm, mine has quick couplers on the far right of bank. I Picked up a fitting and will test when I get a couple more hoses changed. |