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Senior Member
'68 - Case 155, '73 - 646a
2,020 Posts
Discussion Starter · #1 ·
My $.02 and editorial, your mileage may vary.

My premise is that IF there are ANY bubbles in your hydraulic tank when you are running the tractor you have an air leak in the suction line / pump somewhere.. If your system is TIGHT there will be NO - ZERO bubbles in your hydraulic tank.

I have a '73 - 646 that has THIS pump in it:
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There is a steel line 'directly attached' to the pump. There is NO compression fitting or any kind of threads on the line or at the pump. it just looks like a steel line stuffed into the Aluminum pump housing.
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IMO its very hard to get a GOOD picture of the pump, but that's the back of the pump in the middle with the suction line running diagonally down to the right. (and YES, those ARE 1/4 grade 8 bolts in my steering gear. I can torque the ever loving $%^# out of them AND also get them loose someday in the future as compared to 'allen' keyed set screws.. The light colored stuff is anti seize grease applied all through that shaft, key and gear joint).

While I was pulling and reinstalling the tank, oil cooler and suction lines, I noticed that the connection of this line to the pump is NOT solid, it moves and turns. Which on the one hand is nice for aligning it. BUT how can you seal that connection? Either there is a O ring in there or a seal. (the service manuals give NO information. This is always pictured as the pump's rear casting with the suction pipe attached.)

Either way, whatever is supposed to seal that joint, its 40+ years old and checking this area after I put oil in the tank shows that there was a small oil leak. (Blue paper shop towels are fantastic leak indicators. Because they change color when 'wet' you can wrap one around the pipe, and YEP that is a leak....)

My process to refill - restart the hydro system, because I have had the rear end off, the tank off, the oil cooler off, all of the loader cylinders and lines off.. I wanted to check, clean and flush the pump and the motor. So, I put oil in the tank until 1/2 to 3/4 full and started the engine.. I ran the Hydro motor with transmission in neutral to make sure it was cycling oil.

The new 15W-40 oil in my tank looked like it would make great BEER, the foaming "head" on it was really nice.. The longer I let the tractor sit and run, the MORE the oil foamed in the tank.

IMO even thought the tank if full of oil and the suction line is flooded with oil, with a leak RIGHT at the entry to the pump it is GOING TO SUCK AIR.. At 80 degrees outside, the air is lower 'viscosity' than the 15w oil, so the pump is going to suck as much of it in as the leak will allow.

and to PROVE that, here is my repair method. (I was not about to pull the pump at this stage because I am trying to get this up and running and out of the shop where its been since June 25th.)

After thinking about this for a while, IMO this joint is fairly low pressure - low suction. So RTV should be able to seal this. AND rtv will give me some flexibility that this joint is supposed to have. Therefore, I bought a new tube of mid grade RTV that is supposed to tolerate oil and I basically smeared it all around the exterior of this joint. I built up a fillet of RTV between the suction line and the pump housing.

I had drained the Hydro system before I started this so there hopefully would be no oil in the system. I used my oil vacuum to suck as much oil out of the tank and the suction line as possible.. On this 646 the tank outlet is right below the cap, so I stuffed the vacuum hose down the suction line and sucked as much oil back out of there as possible.

I cleaned the area around the pump and suction line with shop towels and also wiped it down with a shop towel soaked in acetone to make sure I got the oil off the pump and the pipe. Applying RTV all of the way around that pipe was interesting. Part of that joint I had to put the RTV on my finger and then smear it on to the joint.. The back side is a challenge to get to or to see.. I used an inspection mirror to see that was going on back there..but I did work a liberal coating of RTV all of the way around the joint. Not pretty, but thats what the covers are for? And this is kind of a proof of concept... (Thats my excuse and I'm sticking with it..)

'course the instructions for the RTV say to wait 24 hours after you apply it before you expose it to oil.. Being the compliant child I let it setup for 24 hours..

BUT, now my Hydraulic tank has ZERO bubbles in it when I run the tractor - loader or 3 point..

So if you have a 1970's 646, 646B, 446, etc with one of these style of pumps with the pipe 'stuck' into it.. You might consider spending $5 on a tube of RTV and clean and seal that joint.. Just in case.. Again, my $.02..

1,351 Posts
You are right, that pipe is just somehow stuck in there. And they do get lose and pulled out.

Nice job on the fix. I hope it holds. I know you will be checking.

I think a lot of people are sucking air and unaware. Old or loose hose connections can cause the same thing.

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29 Posts
I had that style pump on a 75 446. I had the same thing happen to me and I tried RTV and didn't have much luck with it holding long term. I ended up replacing the pump because I had that steel pipe came loose several times and I got tired of cleaning up an oil mess. The new pump has a threaded fitting with an o-ring boss style fitting. That was the fix for my problem.

Senior Member
'68 - Case 155, '73 - 646a
2,020 Posts
Discussion Starter · #4 ·
Finally got into the tractor and pulled out the old pump, more of less threw it aside, but since this came up again, I did a little Dissection on the pump.

Here is the OEM standard pump from a 1973 646A, this is the Borg Warner pump that has the really long curved suction inlet:

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The Gray - black silicone -rtv is what I troweled on in an attempt to seal the joint. (it kind of worked.. )

I scraped the silicone off and the input pipe literally fell on the floor.. Here is the input port, I have not touched this or cleaned it or anything.

There is NO O-ring, or seal or sealing compound in this assembly that I can find:
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And the pipe - tube that fits inside there, the end that fits into the pump looks like this:

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There are no o-ring grooves or anything on that tube, it looks like they might have attempted to roll or swedge the tube into the pump..

But once this tube joint gets touched or disturbed its going to leak. IMHO is you have reason to get into the tractor far enough to pull the engine. Replace this .<BLEEP>..... Thing...

Personally I used a Dynamic Fluid Components GP-F20-12-P-C. which is a .73 Cu inch displacement, but I'm splitting that for power steering. A .61 Cu Inch displacement GP-F20-10-P-C would be a closer replacement for a 646A..

Here is pictures of that pump in my 646A:

Along with the pump, I added a PTO valve and the comments are trying describe that.. Write up on the TCV as a PTO is here:
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