So this is nifty, the best explanation of how the brake/pilot parts of the pump work have come from the patent that JD filed, that makes more sense, its a closed circuit system, So the issue seems to be super low pressure. Now the brake pump that's installed looks nothing like any of the new/used ones on the market (matches the parts book) this one is a little strange. I'm going to go and get a data tag photo and see just what's going on. Whereas it was pissing brake fluid into the front axle and the rear axle brakes were wasted, I'm starting to wonder if they turned the pressure down so its just enough to run the pilot functions. More exploring and fun.
Well it seems the pump is an Oilgear AT139444 and was used on the E and G models 544/644 so it looks legit but it looks a lot different that all the other pumps out there. Guys will go ahead and do some pressure tests on it this weekend. I've developed a theory! The brake seals were pissing fluid into the front diff, so they lowered the pressure on the brake / pilot pump so it was just good enough to run the pilot functions and give a tiny bit of braking. That or the pump is out of adjustment or totally screwed
Check the accumulators for charge pressure, set the pressures to spec, probably be just fine. (crossing greasy fingers for you)
Just as a hunch, the accumulators are either flat or there isn't enough pressure to make them go. with the engine running, hitting one pedal makes the other jump, engine off there isn't any of that. If the pump exploded and sent junk downstream, judging by the debris found in and around the o-rings it might be a good thing to pull the accumulators and clean them. Looking at the book if I recall they're 400 psi charged, nothing too serious. Don't have nitrogen but do have argon in the shop. the more I think of it the more I bet they should be pulled out and cleaned or rebuilt, I can see them being filled with trash.
Don't know about that specific model but on John Deere they are usually welded
Heya, the parts manual shows a whole pile of parts for the accumulator, seals, checkvalves and the like. Looks possibly like snap rings.
Probably floating piston style then rather than bladder, they need periodic recharging as they are never perfectly sealed even new.
Yeah, I was thinking that, I'm not sure if they have the charging type valve on the bottom or if that's an add-on picture just shows a drain on the bottom. Service book showed a valve assembly
well, no such luck, sitting at idle, the pump is putting out 450 psi with a bit of vibration on the gauge needle, there's one screw that looks like the typical lock screw pressure adjuster, loosen and add a couple turns, no change on the output pressure. spin the screw back to the starting spot and lock it down again. hmmm curious. This pump may need an overhaul, what's it cost for a pump overhaul? I'm thinking a local hydraulic shop that works with oilgear pumps can give us an estimate on the repair.
Before you yank the pump, try capping the lines, one at a time, the first I would try is the one going to the pressure reducing manifold, not sure of all the functions, has a pressure reducing valve, three solenoid valves, tank line? If the pressure doesn't come up, try capping the accumulator outlets one at a time, see if the pressure doesn't jump up. Might wanna back the pump down a few turns before you start, in case you do get a pressure spike. Or put a flow/pressure meter on the pump outlet and test it properly.
Actually tried that when testing the brakes with the wheels in the air, capped the pilot circuit line. tested the brake lines with a porta power and it held pressure. The pump looks pretty easy to remove, just need some hose line caps or even an assortment of rubber lab corks
Good golly I left a thread hanging!! So applied a pressure gauge to the pilot /brake pump 350 psi max, enough to run the pilot controls but barely anything for brakes, spec says 2000 ish psi. Pulled the pump out and sent it off to a 'Hydraulic Repair shop' well they called back a few days later, pump can't be fixed and needs to be replaced. Okay, so I go and pick it up and its in a hundred pieces, assembly isn't included in the free inspection.. Well it takes me a day to figure out how the regulator assembly goes. It was like CSI, match up all the scratches and wear marks to get the pressure regulator back in good nick. But the pump is toast.. Well down at the bottom of the spinning pump barrel is a UHMW bearing, its disloged and has some damage on it as it was floating around the middle of the barrel. This allowed the cylinder to cock sideways, scoring the top cover just a whisker. I ordered every part and seal available from JD and set to work.
So there's a swash plate, it has two connecting rod bearing looking parts, the low pressure side looks like a delrin shell the high pressure side has a steel insert with a UHMW overlay on it. This overlay is badly damaged. but nothing on either side is scored. I cleaned off the overlay with careful scraping and find that the large UHMW bearing from the bottom of the pump has the same thickness, soak it in acetone to degrease it, rough up the tin backing on the bearing material, find the right size socket, apply superglue to the bearing shell and glue the insert in place, securing around the socket with a hose clamp. A little careful trimming of the insert and a new high side bearing shell has been created. Pistons all look good, snug fit, no burrs. The cover is the non repairable part, a solid .002 groove between high and low side and the pump is a little rounded off. I opted to dust off my cast iron surface plate, glue down some sandpaper and set to lapping in the proper figure 8 pattern. With about 20 or 30 cycles the groove started to fade, I switched from 180 to 320 grit paper for another 20 cycles, ending up with a nice looking cover.
I started on the pump itself, hitting it with sharpie on the flat face and giving one quick lap showed the surface to be curved by .0015 someplace just under .002 I figured this surface doesn't matter much for overall height as its held by the pump springs and pressure. I started with lapping, grabbing it as close to the surface plate as possible and going slow to keep it square, When I was done, a light coat of oil and the pump would lift the pump cover if touched together.
So of course everyone has a hydraulic pump tester right? Certainly!! I obtained a yellow hydraulic tank, a couple hoses and a hydraulic needle valve, the application of some hydraulic rated black electrical tape to secure the hydraulic tank (fitted with optional screen cut from a paint filter) and using a copper tubing sleeve from a 1/2 inch pipe to make a snug fit over the 5/8 input shaft splines before clamped securely in the test bench jaws. A block of vibration absorbing wood and steel shim were clamped beneath the pump flange. Gauge and needle valve fitted before filling the tank and running a few cycles to bleed out the air. Then with the test bench running at 400 rpm start adjusting the pressure screw to give 2000 psi on the gauge while flowing maybe a half ounce per second. Adjusting the flow saw the pressure stay dead on and there was a very limited flow from the case drain line.
Well we now have pressure for certain but lets inspect the accumulators as they don't seem to be doing anyting, we have brakes with the engine running and nothing with the engine off. Pulled the accumulators and carefully checked for pressure, nothing, not even a whiff. Turns out an accumulator is nothing to write home about, a steel tube with a snap ring groove in each end, gas fitting on one side, hydraulic on the other and a piston in the middle. Tore it all apart and saw some minor grooves and scoring, could see it but not feel it. Bore was round and true so I dragged out a 3 stone engine hone and started, just like honing a 4 inch cylinder bore, again worked it until the scratches were gone then let my brain do its thing. A 200 grit cylinder hone stone is meant for bedding piston rings not o-rings and teflon backer rings, I went down the line to 400 grit, removing all the scratches and rinsing with diesel all the while, cup and bucket technique, making sure to hone completely from end to end. Filted my honing fluid with my favorite blue shop rag and then wrapped a green scotch brite pad around the hone all the way and set to polishing. With about 20 minutes more polishing on each accumulator I reached a point where a scotch pad wasn't removing any more material and there was just a hint of a crosshatch. I though about the pressures, 2000 psi and that the o-rings must take a beating!! but no, properly charged the o-rings only see a few psi as the piston drifts up and down, balanced between the nitrogen and hydraulic oil. Good enough, nice smooth, clean bore. All new seals for both accumulators were ordered from Deere. Deere uses a really wacky fill adapter, its a 1/2 inch 13 thread with something having a plunger to hit the button down at the bottom of the bore. Can't have just the standard tire valve.. I needed a good piece of stock, found a 20mm metric bolt about 60mm long, tossed it in the lathe and started turning. Once I got the adapter from 1/2 13 to .303 32 done, I thought it should have a hex, so I drilled out a random nut and pressed it onto the adapter, giving it a quick mig weld. I opted to add an O-ring cause why not. For the center 'pin' I took an 8 penny finish nail, welded and turned a bead about 1/4 inch up from the accumulator end, bored the hole to a close fit for the minor diameter then drilled a relief for the bead. Peened the end with a punch to make the floating pin captive.
final step was fitting a valve and gauge, One of the guys scored a loaner nitrogen tank but no regulator, so just opted for the crack-n-fill method, add a little juice till it hits the suggested, 500 or 600 and close the tank, withdraw the valve and presto, holds the charge spot on, reinsert the 1/2 inch shorty bolt in the hole and now Tiny has 30 or so brake applications with the engine off from each pedal! To see something funny, open the axle brake bleeder and hit the brakes, the column reaches about 30 feet or more!
Nice work. Like your improvised solutions.
+1. Always nice to see someone "making things work", a little lateral thinknig is all that's required. I enjoyed reading that
+2. Great job !
Thanks, I don't mind replacing parts when they need it, but sometimes a little refitting of parts is all that's needed, I don't think the 1 inch thick cover plate will ever miss that .002 nor will the pump, may be a closer fit than factory with a careful precison lapping. I would think a hydraulic repair shop would have the ability but perhaps they just don't have the skillset anymore.
There is no craftsmanship anymore. It's all about replacement parts and expedient repairs.
Thanks! My though was nothing to lose beyond a $100 seal kit, getting the oil out of the uhmw bearing was the hardest part. Lapping is a bit of art and just needs some patience.
The “patience” part of your last statement I think is the problem, Along with the fact if they messed with it that much and it didn’t work they would be out the time and couldnt charge you for it. Plus they probably wouldn’t warrantee something put back together like that and be worried that it would come back and bite them in the arse. I think you did a great job resolving your problem and it should last you a long time, great job!
I suppose that swapping in a warrantied part shifts the blame away from the installer if the new part experiences infant mortality, versus owning it all if they rebuild a part and it fails again for whatever reason. Allows them to swap out seasoned machinists and mechanics with experience hand fitting parts with wrench turners and screwdriver holders.