G1900 HST question

lugbolt

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Equipment
ZG127S-54
Oct 15, 2015
4,877
1,610
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Mid, South, USA
Backing up about a year. G1900, later production, 54". Runs awesome. Had zero issues with it last year other than running out of fuel on the last mowing. I get almost 19 hours on a tank of fuel. Anyway, I refilled it, finished the last mowing of the season, then pulled the deck, sharpened the blades, replaced gearbox fluid & cleaned the breather, replaced air filter, both fuel filters, engine oil and it's filter, bled fuel system, replaced HST fluid and filter (Super UDT2) and just checked it over. Finished by removing the rear fender and hood, and giving everything a good washing with the then new Yamaha power washer.

It sat all winter, from November through March. Out in a storage building with no heat or a/c.

Fired it up this last March to move a small trailer. Little sluggish at first but it cleared up nicely, as expected after sitting, and it was about 45 degrees that day. I let it run about a minute or so at just off idle speed, so about 2000 RPM give or take (no tach obviously). Get on it, raise the deck, hit HST pedal to go forward and it sits still. After a few seconds it makes a lot of noise and then finally takes off. Finished what I was doing, parked it in the shop and let it sit overnight. Came back out the next morning to check the HST fluid thinking maybe it was a little low from last year's service. Nope. If anything it is a shade high, but maybe 1/16" over the high line on the level gauge. Nothing worth being concerned with, IMO. April comes around and I have to start mowing onions. Same deal. Starts fine, HST is non existent and after maybe 30 seconds to a minute, it will make noise and take off-although noisy. Revving the engine helps make things start happening sooner. Shut engine off, even hot, and restart after a minute, same thing. Like it loses it's prime. Something else I noticed is that when I go to raise the mowing deck, the HST will slow down. If I hold it in the raised position, the HST will get real noisy and eventually stop working. When this happens, it freewheels as if you were to move a release lever, will head down the hill like in neutral. Also noticed that there is some residue near the HST fill cap on the back of the transaxle. HST fan is in perfect condition; as are both U-joints as I bought it with failed joints a few years ago.

I do not see any signs of any kind of external leakage, no spots, and when the fender was off last year, there were some dry clippings around the top but nothing indicating any fluid leakage.

y'all got any ideas? Mowing season is finally done-and it got a workout this year. Mowed twice a week for 2 months due to a really wet summer, so I didn't have any time-nor a spare mower-to do anything with it. The HST screen is clean-I cleaned it last year and again about midway through this season, both times did not find one speck of metal or dirt or anything else on it. It was also spotless when I got the mower.
 

100 td

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Equipment
B21TLB (B21, TL421 & BT751) Toyota SDK4 T116 Bobcat
Aug 29, 2015
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ɹǝpunuʍop
Mowing season is finally done-and it got a workout this year.
So you have continued to use it and it has worked flawlessly, has it continued to be "primeless" when starting up?
This has never happened before you did the fluid change?
Are you definitely using the correct hst filter? If the micron rating is to fine it will limit prime and also probable hold an air pocket in the filter, which then creates cavitation/starvation on starting.
Personally I would replace the filter, also check for double gasket. If there is a slight imperfection on filter fit or gasket seal, you would get similar symptoms.
YMMV
 

100 td

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B21TLB (B21, TL421 & BT751) Toyota SDK4 T116 Bobcat
Aug 29, 2015
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Do you have a service manual showing the hydraulic and HST fluid circuit?
 

100 td

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B21TLB (B21, TL421 & BT751) Toyota SDK4 T116 Bobcat
Aug 29, 2015
1,776
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ɹǝpunuʍop
Just had a look at the parts diagram for your machine, I expect you have a suction leak going to the charge pump. So this will be caused by either the 2 orings at the HST screen, or on the oring at the other end of that pipe at the charge pump itself. (I would replace all 3 orings) It could still be caused by the hydraulic filter if the HST charge draws from the filter directly, hard to tell from parts diagrams. You have been in both of these locations.
Good luck, hoping for an easy fix.
 

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,877
1,610
113
Mid, South, USA
update: Fixed.

Been cold, grass ain't growing, so I put a little time into it. Long story short, it was a leak on the suction side of the charge pump. There are several steel pipes that run from the HST to this and to that. The charge pump (on the back of the HST) has two pipes. One runs from the pump to the hydrualic block for the deck lift, and the other runs down to the left side of the tractor, has a screen on it. Screen was perfect. Both O-rings on the screen were perfect. The O-ring on the top, where the pipe enters the charge pump, was perfect. I honestly found nothing wrong so I started to re-assemble it. Upon reassembly I noticed that the suction pipe, where it goes into the top of the charge pump, well that pipe has a rubber lined clamp that holds it to another pipe. The clamp was loose when I took the thing apart and I gave it no thought. So what I found was that the charge suction pipe was kind of off center in the bore of the charge pump because the pipe's clamp was not installed properly. It's not a real tight fit so it's easy to happen. This allowed the charge pump to pull air into it, which aerated the oil and caused the whole problem. Reinstalled the clamp and centered the pipe, works great again.

Also, with there being a little bit of an air leak on the suction side, I think the HST would bleed down overnight which would explain why it would freewheel after it set for a while.

Charge pump can't be removed without removing the transaxle and then splitting it in it's different sections. But it CAN be removed if you ever so slightly grind away a tiny bit of material on the top of the differential case; so that the pump will slide back JUST far enough to clear the shaft. Worth mentioning if anyone ever has to work on one of these.

Glad it's fixed. I was actually considering buying a new Z125/54" and this cheap fix just saved me about $6000. Now, if it'll just stay unbroken for a while.....
 

D2Cat

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L305DT, B7100HST, TG1860, TG1860D, L4240
Mar 27, 2014
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40 miles south of Kansas City
Lugbolt, there's not much that is more rewarding then getting something working that has been frustration you for a while, and at little cost!

That machine may run for years.
 

100 td

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Equipment
B21TLB (B21, TL421 & BT751) Toyota SDK4 T116 Bobcat
Aug 29, 2015
1,776
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ɹǝpunuʍop
Glad it's fixed. I was actually considering buying a new Z125/54" and this cheap fix just saved me about $6000. Now, if it'll just stay unbroken for a while.....
Gr8 outcome! Just a tiny bit of air can cause chaos!
 

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,877
1,610
113
Mid, South, USA
That machine may run for years.

Hope so. I have some spare parts stashed just in case it don't want to cooperate. Funny though. Exactly one year to the day after I bought this one, I found another one (well G1800)-and it was 3x cleaner than mine. Then Exactly one year to the day after I got the G1800, I found another G1900 (2 wheel steer). So now I still have my G1900S, dad has the G1800 and my brother has the other G1900. Whole family full of 30+ year old diesel lawn mowers. That's another reason I stashed some spare parts. Dad's is BY FAR the nicest, 243 hours on the meter (had 199 when he got it), and at $450 was a great price. I did the first major service and let him come look at it...and he fell in love. Gave me his old T1560, which I promptly cleaned up and donated to the DAV.

Speaking of which...anyone around the Little Rock area have a T1460 or T1560 with a 40" mower? Need one for my girlfriend's sister...small yard but she needs something better than that old Craftsman that I am constantly having to fix.