420c Hydraulic Control

General help and support for your Lindeman through 2010 John Deere crawler
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Spratley
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Joined: Wed Feb 13, 2019 1:42 am

420c Hydraulic Control

Post by Spratley » Wed Feb 13, 2019 7:42 pm

I've got a 1957 420C. It's got a Holt blade with tilt and a rear 3pt arms and PTO. My issue is with the rear 3pt arms not staying up.

When the hydraulic hoses are disconnected from the control valve and the crawler is running, hydraulic fluid pours out of both outlets of the 3pt arm's control valve, so I think the check valve must not be working, although when I inspect it, it seems fine and the spring seems in good shape. It's the single stage type of check valve.

With the crawler shut off, I cannot raise the rear 3pt arm by force when the controls are not engaged. However, if I bungee the control lever open, I can lift the arms by hand and as long as the control level remains bungeed the hydraulic cylinder will hold the arms up. Therefore, I don't think it's a problem with the hydraulic cylinder, but with the control valve.

The other hydraulics work good. The front blade will not drop if left up. I've pulled the top relief valve off and pulled out the check valve to inspect it, but that's as far as I've gone so far. Next I think I'm doing to swap the hoses and see if that allows me to raise the rear 3pt arms with the hydraulics... Then I guess I'll take apart the control valve assembly and see if there's some kind of obstruction that's creating too much pressure for the check valves? I don't know... maybe the linkage just needs to be adjusted? Any advice or experience with this would be appreciated. Thank you.
Last edited by Spratley on Thu Feb 14, 2019 12:13 pm, edited 1 time in total.

Jim B
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Re: 420c Hydraulic Control

Post by Jim B » Thu Feb 14, 2019 7:18 am

Welcome to the forum.

With some more info and better understanding of what you have, folks here will help you work through this. Your photos do not show. This site has a dedicated photo server where you store a copy to post. You can read about it on the Messageboard Q&A and Announcements forum. You need to contact Lavoy at postmaster@jdcrawlers.com to get set up to use the site's dedicated photo server. Do you know you can access the John Deere parts catalogs on line if you don't have a hard copy? The parts pages may help you point to the components you have and are talking about. The on line catalogs are at https://jdparts.deere.com/servlet/com.d ... nguage=19 . Enter 420 as the model. When you get the drop down for models with 420 in them, select the 420 tractor (PC505). This manual includes the 420 and 430 wheel tractors as well as the crawlers so read the headers and have your serial number at hand as well.

Do you have a service manual? It can be a help with trouble shooting and repairs. If not Lavoy can help you out with that as well. This is his website and his business, parts and service for these crawlers, supports this site for us to use. Check things out and post back. A word of advice, don't start tearing things apart without some more diagnosis.
.

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Lavoy
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Re: 420c Hydraulic Control

Post by Lavoy » Thu Feb 14, 2019 9:41 am

I think we have a terminology issue as well. PTO stands for Power Take Off, which is the power shaft on the back of the crawler for running implements. 3PT is the hitch on the back for lifting mounted implements, I believe this is what you are talking about?
Lavoy
Parts and restoration for antique and late model John Deere crawlers.
Owner and moderator www.jdcrawlers.com

Spratley
MC crawler
MC crawler
Posts: 3
Joined: Wed Feb 13, 2019 1:42 am

Re: 420c Hydraulic Control

Post by Spratley » Thu Feb 14, 2019 12:17 pm

Yeah. I edited my post to fix the terminology and removed the picture, as they were not showing.

Jim B
350 crawler
350 crawler
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Joined: Sun Nov 05, 2017 11:36 am
Location: western Maine

Re: 420c Hydraulic Control

Post by Jim B » Thu Feb 14, 2019 1:16 pm

Can you ID the control valve(s)? Is the valving the shown in the 420 parts catalog? Given you say it is a Holt blade with tilt, it is hard for me to tell how it is plumbed up and if the JD valves were used. Hopefully someone else will know just what you have, but for me you are going to have to get set up with Lavoy and post some photos of valves and plumbing for me to see. It would sound like you either have a valve for 3 functions (lift, tilt, and 3PT) or a two function valve for the blade and a single function for the 3PT. Is it using the cam pump or a different pump?

Spratley
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Re: 420c Hydraulic Control

Post by Spratley » Thu Feb 14, 2019 2:32 pm

Yeah, it's a triple remote control valve assembly. Similar to the double remote control valve assembly as show on page 55-52 in my parts book, except made of of 6 housings (part no. M3331T) instead of 4. The check valve though, is not the 2 stage one (part no. AT10471T), but the other one shown. It all runs off of the front camshaft pump.

Jim B
350 crawler
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Joined: Sun Nov 05, 2017 11:36 am
Location: western Maine

Re: 420c Hydraulic Control

Post by Jim B » Thu Feb 14, 2019 6:35 pm

So it is using the "standard" JD valve; two spools to run one cylinder, 3 pairs of valve sections. What is the condition of your control handle and linkage? I had to rebuild my 430 valve handle and the rods. Excess play was letting the spools shift a bit and the blade would settle, I could stop it by moving the handle slightly and holding it. If the centering springs on the spools are weak or broken the spools can move off center slightly and could have a drifting symptom as they could be cracking the check valves open. If you work the handle gently can you stop the drift? Unhook the handle rods and try moving just the spools to see if they are firmly held centered by the centering springs. Just wondering - do you have the service manual (SM2019) as well as a parts catalog? Mine shows and gives a good description of how the valve works.

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