HD21B crawler dozer
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=169320
Printed Date: 17 May 2025 at 7:41pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: HD21B crawler dozer
Posted By: Charles O
Subject: HD21B crawler dozer
Date Posted: 21 Mar 2020 at 7:47pm
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Hi there, I have a HD21B crawler dozer around a 1978ish it moves forward and reverse just fine in all gears. Pushes real well but it says no transmission pressure on the gauge and does not turn left or right. I’ve changed steering pump but it does not seem to be getting oil there from the rear of the machine. Is there something in the trans that builds the pressure to feed the steering pump thank you
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Replies:
Posted By: Charles O
Date Posted: 21 Mar 2020 at 8:07pm
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The old allis chalmers dozer however the rest is in good shape. About 85% undercarriage runs great pushes like nothing so I would like to repair its illness and get pushing again. I thank you for all the help I can get
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Posted By: DMiller
Date Posted: 22 Mar 2020 at 8:21am
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Before you fry if have not already, that steering pump I would be pulling ALL the screen fittings and cleaning them. If a New pump failed to deliver oil it likely has no source to suck from.
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Posted By: gemdozer
Date Posted: 22 Mar 2020 at 8:39am
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You need to change or cleaning the strainer filter and after working 5hours check again the strainer could still have brake metal in
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Posted By: Charles O
Date Posted: 22 Mar 2020 at 9:03pm
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I put new pump, new screens new filters and new oil. Blew out lines best I could. Would trans pump put oil pressure to fill line. With everything new thought steering pump should pull but not sure if there’s a prime in there. I also filled tube on top of pump to give it a start with new oil. Thank you for reply
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Posted By: DMiller
Date Posted: 23 Mar 2020 at 6:57am
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These are PDP or positive displacement pumps, either pull a suction and draw oil or don't or does not have oil to draw. The trans pump on my own smaller unit takes scavenge suction off the main sump to feed to a second sump to draw on and also supply the steering suction. As this is likely a Power Shift or Torque coupled trans the system is functional enough to feed oil to that so the suction level for the steering pump should be supplied. The big concern of these is that suction is ABOVE the oil level where ANY significant air inleakage on the suction side will stop it from drawing oil. Another issue does it have Splined coupling or the slotted and two pin coupling? Can be either, the spline coupling are notorious for stripping enough will not stay engaged and the two fingered version being similar if not same as Detroit Diesel fuel pump drive shear at any significant resistance.
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Posted By: Charles O
Date Posted: 23 Mar 2020 at 10:42pm
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I agree, I’m going to pull trans pump and check it out. I have no real pressure coming to the test port before the filter. It does go through the cooler first. Is it possible cooler is plugged? Maybe I should pull that and make sure it will flow threw there as well. I appreciate the insight thank you
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Posted By: DMiller
Date Posted: 24 Mar 2020 at 3:49am
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If the pump has pressure will flow thru the cooler or howl to beat hell. Need to determine if the pump is sucking air, every connection has to be sealed on the suction filter side. If the trans is shifting and functional I do not think you have a trans pump failure.
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Posted By: Charles O
Date Posted: 24 Mar 2020 at 7:16am
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Ok. Thank you. I’ll check all connections and keep you posted.
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Posted By: Charles O
Date Posted: 14 Apr 2020 at 10:56pm
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I have checked all hoses lines etc. No leaks or anything like that. I have no trans pressure on the gauge but I thought I would try engaging pto while it’s warming up. By doing that it allows it to steer but if it warms up before I do this it won’t. I put another gauge on trans and it read same as original gauge. Says it has no trans pressure but by engaging pto it steers fine and moves forward and reverse fine. Not sure why I would not have trans pressure. I did some pushing with it and it never even slowed down. Thought it might when it reads 0. So I’m a bit confused. Any thoughts
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