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Kartman01

Allis Chalmers 620 Hydro Issue

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Kartman01

I have an Allis Chalmers 620 that I am restoring and have run into an issue with the hydro system I am hopeful someone can help me with.  Prior to restoration, the hydro system worked:  drive forward and reverse, rear 3 point and front blade.  

During restoration, the transmission and hydro unit was removed cleaned and painted.  The hard lines were removed, cleaned and zinc plated.  To the best of my knowledge, the hard lines and rubber lines are reinstalled correctly.  When I started the unit for the first time, the following occurred:

- After a period of cycling the 3 point (front blade is not attached) and forward/reverse; the 3 point never would operate.  The tractor could be driven, but the operation was jerky.

- After messing with this for about 45 minutes, I drained the fluid (Dextron III) and replaced the filter (Wix 51307) - the thought being a fresh rebuild, it may be a good idea to 'flush and fill' the trans fluid

- After this, not only does the 3 point not work, but the tractor no longer has forward and reverse.  A pressure check on the charge pump confirmed zero pressure.

- I thought the pin in the charge pump that drives the impeller might have broken.  After removing the charge pump section, I was able to verify the pin had indeed broken.  After retrieving all of the pieces, a new pin was installed and the charge pump re-assembled.

- The hydro system was topped off and a new filter installed as a precaution in the event there were any metal bits in the system from the pin breaking.  System was re-primed per procedure in manual.

- After start-up and a period of 8-10 mins working both the drive and implement levers, still no operation.  A re-check of pressure yielded zero pressure.  Charge pump was removed again with the thought that perhaps the impeller pin broke again.  Impeller pin was found to be intact and in good working order.

 

So now I am completely stumped.  I thought for sure I had gotten to the bottom of the issue when I discovered the broken impeller pin.  

Does anyone on the forum have experience with the type of Sunstrand Model 90 pumps that are used on Allis Chalmers 620 tractors?  Is there something I am missing?  

If not and the pump requires a rebuild, are there recommendations for a good shop to do this work?  I do not have the equipment to test these pumps and prefer to work with a shop that can bench test the pump prior to reinstallation.

 

Thanks in advance for any help!

 

 

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Rigger9020

Are you sure the last time you assembled the charge pump it was properly orientated ?

The case is marked RH or LH to indicate input shaft rotation. The pump motor will not prime if wrong. 
 

Good Luck Mike

 

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720nut

I don't remember the gentlemans name in Canada but I had sold him a used hydro unit . anyway he had done a lot of work on these hydro's and had wrtten  a very detailed write up on them , my lack of computer skills doesn't allow me the sources to look up his write ups which I hope were not removed when he had the issues. Just my $.02

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Brettw

Perhaps also look to why, out of the clear blue, the impeller pin would be broken.  The cause of that may reveal other issues?  Unless you disassembled it during your cleaning and painting, there is no reason the charge pump should fail because some paint was added?  Just a thought to help chase this down.

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ShaunE
4 hours ago, 720nut said:

I don't remember the gentlemans name in Canada but I had sold him a used hydro unit . anyway he had done a lot of work on these hydro's and had wrtten  a very detailed write up on them , my lack of computer skills doesn't allow me the sources to look up his write ups which I hope were not removed when he had the issues. Just my $.02

It was Gill.

Here's one - https://simpletractors.com/forums/topic/60634-9020-with-low-hydro-power/?tab=comments#comment-484304

 

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ShaunE
34 minutes ago, 720nut said:

Thanks Shaun, ole memory ain't what it used to be.

Hey no worries Buddy.  

He had a great documented Sundstrand rebuild write up on Unofficial Allis but after the turmoil erupted, he deleted all his posts over there.

Wish you still had his contact info.  

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720nut
12 hours ago, ShaunE said:

Hey no worries Buddy.  

He had a great documented Sundstrand rebuild write up on Unofficial Allis but after the turmoil erupted, he deleted all his posts over there.

Wish you still had his contact info.  

Shaun I had a picture of the box and his address but apparently I've deleted it, do you remember the approximate time

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Kartman01

I finally solved the issue... I lightly pressurized the rear transaxle and it helped to clear air blockages.  It's operating perfectly now!  Thank you for all of the comments and help.

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ShaunE
23 hours ago, Kartman01 said:

I finally solved the issue... I lightly pressurized the rear transaxle and it helped to clear air blockages.  It's operating perfectly now!  Thank you for all of the comments and help.

Glad you got the system working!

It's a fine looking machine Chuck.  Glad Mike was able to provide everything you needed.  He's a good friend.

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Bird76Mojo
On 5/1/2020 at 3:39 PM, Kartman01 said:

I finally solved the issue... I lightly pressurized the rear transaxle and it helped to clear air blockages.  It's operating perfectly now!  Thank you for all of the comments and help.


How did you go about this, and what PSI did you use?

I'm having trouble with my 720 not wanting to climb inclines, it feels like the hydro is weak, but I just had the system open. I had to remove the hydro cooler and filter for about 2 weeks while I installed a rear pto, and went through the entire rear brake system and drop boxes.

The tractor drove and operated perfectly before all of my work, so I'm thinking the hydro needs primed. It has a new WIX filter and the fluid has maybe 2 hours on it but is a year old or so.

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midnightpumpkin
8 hours ago, Bird76Mojo said:


How did you go about this, and what PSI did you use?

I'm having trouble with my 720 not wanting to climb inclines, it feels like the hydro is weak, but I just had the system open. I had to remove the hydro cooler and filter for about 2 weeks while I installed a rear pto, and went through the entire rear brake system and drop boxes.

The tractor drove and operated perfectly before all of my work, so I'm thinking the hydro needs primed. It has a new WIX filter and the fluid has maybe 2 hours on it but is a year old or so.

Sounds to me like slipping drive belts.

John U

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Bird76Mojo
16 minutes ago, midnightpumpkin said:

Sounds to me like slipping drive belts.

John U

It very well could be. The drive belts seem pretty old.

What a nightmare it'll be to replace them though! I just finished installing all of the repainted tins around the hydro cooler, the rear pto, etc.. I think pulling the engine would be the easiest route to replace the belts if they need it.. ?

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Talntedmrgreen
1 hour ago, Bird76Mojo said:

It very well could be. The drive belts seem pretty old.

What a nightmare it'll be to replace them though! I just finished installing all of the repainted tins around the hydro cooler, the rear pto, etc.. I think pulling the engine would be the easiest route to replace the belts if they need it.. ?

No no!  Replacing the belts is pretty simple.  I tie back the clutch pedal with a ratchet strap to the front axle.  Then unbolt the oil cooler and tip it up and out of the way to the RH side of the tractor. 

Unbolt the rear pto shaft and then wiggle the belts off the pulleys using the slack from the disengaged clutch.  Removing the spark plugs can help, as rotating the crankshaft pulleys aids in rolling the belts off.  

I do concur, slipping belts is a primary cause of “weak hydro”.  Were the pulleys painted by chance?

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Bird76Mojo
14 hours ago, Talntedmrgreen said:

No no!  Replacing the belts is pretty simple.  I tie back the clutch pedal with a ratchet strap to the front axle.  Then unbolt the oil cooler and tip it up and out of the way to the RH side of the tractor. 

Unbolt the rear pto shaft and then wiggle the belts off the pulleys using the slack from the disengaged clutch.  Removing the spark plugs can help, as rotating the crankshaft pulleys aids in rolling the belts off.  

I do concur, slipping belts is a primary cause of “weak hydro”.  Were the pulleys painted by chance?

I didn't paint the pulleys, but after work today, I had a few hours to diagnose the issue. Turns out the belts were very loose. I have no idea how the tractor plowed successfully last year. The previous owner had the clutch free-play and the belt tension set up all wrong. As well as the little bracket that keeps the belts from jumping off. Once I set the tension and free-play, the little bracket was hitting the rear pto splined yoke, which spooked me pretty bad when I started it up. O.o

I set the large spring to the factory recommended height, and adjusted the clutch free-play to factory specs and the tractor now climbs any hill I point it at. One of which is about a 40-45 degree angle. dOd

During the diagnosis I did find another issue though. The tractor has always crept forward a little. I found a missing bushing on the hydro lever in the tunnel. Part #24 in most online "speed control" diagrams. Simplicity part # 2172949  -  So I'll have to locate one of those somehow. Or attempt to fabricate one. My parts tractor may have one to spare though... Fingers crossed!

THANKS FOR THE HELP EVERYONE!!!  I'm stoked and ready to hook up the front and rear blade and start scraping the brush in my wooded backyard. Gotta get both sets of wheel weights mounted back up first though..

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Talntedmrgreen

Its very common for guys to make those bushings.  Nylon, brass, even fuel line all work well for next to no expense at the hardware store and some slight fitting work. 

If that wasn't caught in the restoration work, then I would recommend looking at the other bushing locations known to fail.  The rear PTO shaft has two at the coupler. 

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Bird76Mojo
6 hours ago, Talntedmrgreen said:

Its very common for guys to make those bushings.  Nylon, brass, even fuel line all work well for next to no expense at the hardware store and some slight fitting work. 

If that wasn't caught in the restoration work, then I would recommend looking at the other bushing locations known to fail.  The rear PTO shaft has two at the coupler. 


I wouldn't call what I do "restoration work" but more like "pretty'ing up"  lol

I just installed the rear pto shaft and clutch, and I made sure the bushings were all good. I had to swap them in to another splined yoke because it had tighter splines. I had to press them out using sockets and the vise.

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