I have been performing DIY small equipment repair and maintenance for many years, but have no experience with hydro-static drive transaxels until now. I recently picked up a Craftsman ZT7000 with a Kohler 20HP drive. The engine runs great, but I’m experiencing serious and uncontrollable lurching when trying to move forward or backwards. I have read many threads that have lead me to check for a missing/broken spring and to check the oil levels in the transmissions. I have modified both transmissions with 1/8” drains and drilled the tin to get access to the top oil fill plug, and drained and changed the oil with recommended 10W50 Diesel grade engine oil. I have adjusted the coil spring tension on the brake control shaft between the two transmissions to different tensions within the range of adjustment, but none of the work has corrected the lurching. The drive belt tension seems adequate so I don’t suspect drive belt slippage and the drive belt is new. Anyone have any direction for me before I condemn the transmissions?
ZT 7000 Static Drive lurches..
- Thread starter CaptainL
- Start date
ILENGINE: Your suggestion is interesting. Could you please give me a procedure to do this? Murray transmissions (left) 1727806SM and (right) 1727807SM. I dont find any openings or bleeders in the trans case besides the filler plug and the vent tubes on the top. Thanks for your input
This is the basic procedure no matter what brand or style of hydrostat unit. Looks like the wire style bypass rod coming off the top of the hydro units and then lock into a tab on the rear of the mower.. May be hidden under the rear of the mower. Looks like a pull and lock wire style bypass.
PURGING PROCEDURES
Due to the effects air has on efficiency in hydrostatic drive applications, it is critical that it is purged from the system. These purge procedures should be implemented any time a hydrostatic system has been opened to facilitate maintenance or any additional oil has been added to the system
.Air creates inefficiency because its compression and expansion rate is higher than that of the oil approved for use in hydrostatic drive systems .The resulting symptoms in hydrostatic systems may be:
1. Noisy operation.
2. Lack of power or drive after short term operation
3. High operation temperature and excessive expansion of oil
Before starting, make sure the transaxle/transmission is at the proper oil level. If it is not, fill to the specification.
The following procedures should be performed with the vehicle drive wheels off the ground, then repeated under normal operating conditions.
1 With the bypass valve open and the engine running, slowly move the directional control in both forward and reverse directions (5 or 6 times), as air is purged from the unit, the oil level will drop.
2. With the bypass valve closed and the engine running, slowly move the directional control in both forward and reverse directions (5 to 6 times). Check the oil level, and add oil as required after stopping the engine.
3. It may be necessary to repeat Steps 1 and 2 until all the air is completely purged from the system. When the transaxle moves forward and reverse at normal speed purging is complete.
PURGING PROCEDURES
Due to the effects air has on efficiency in hydrostatic drive applications, it is critical that it is purged from the system. These purge procedures should be implemented any time a hydrostatic system has been opened to facilitate maintenance or any additional oil has been added to the system
.Air creates inefficiency because its compression and expansion rate is higher than that of the oil approved for use in hydrostatic drive systems .The resulting symptoms in hydrostatic systems may be:
1. Noisy operation.
2. Lack of power or drive after short term operation
3. High operation temperature and excessive expansion of oil
Before starting, make sure the transaxle/transmission is at the proper oil level. If it is not, fill to the specification.
The following procedures should be performed with the vehicle drive wheels off the ground, then repeated under normal operating conditions.
1 With the bypass valve open and the engine running, slowly move the directional control in both forward and reverse directions (5 or 6 times), as air is purged from the unit, the oil level will drop.
2. With the bypass valve closed and the engine running, slowly move the directional control in both forward and reverse directions (5 to 6 times). Check the oil level, and add oil as required after stopping the engine.
3. It may be necessary to repeat Steps 1 and 2 until all the air is completely purged from the system. When the transaxle moves forward and reverse at normal speed purging is complete.
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Hmmm. Are sure about this. Most Hydro Gear hydrostatic transaxles uses 20W50 conventional engine oil. And 15W50 Synthetic can subbed on new units but with older units it is better to stick with the conventional oil.
IF you used 10W50 standard or synthetic that might be part of the problem as it is too thin as it would take longer to build to working pressure. The only time you might want to use 10W50 is in the extreme cold areas.
What ILENGINE is referring to is the release valve that you release to move the mower when you want to push it. Jack the mower up and place jack stands under it so it is secure. release the valves and start the mower and swipe the control arms forward and backward. I do it about 10 times. As to the lurching check the control brackets to make sure they are tight on the trunnion shaft. The bracket the control arms move on the hydros.
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Regarding the oil grade, I am sure of nothing. I just followed advice from another.
Thank you for the clarification.
I performed the purge procedure between rain showers today, but there has been no improvement. I inspected the linkage from the control levers to the transmission shifting pivot point and there doesn’t appear to be any lash or wear in the linkage. The drives seem to work smoothly while jacked up on stands both individually as well as together in both for and rev, but with the machine on the ground, it jerks and lurches forward and reverse.
bertsmobile1
Lawn Royalty
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You either still have air in there, not enough oil , a defective pump ( highly unlikely ) or a bad drive belt / tensioner or dragging brakes
Unless you pulled the hydros apart fully before you let loose with your Black & decker then I could guarantee you have swarf in the system so even if you get the lurching problem solved you would have wrecked the transmissions .
These things are made in a sterile dust free environment so why did you think it was OK to grab your drill & start making holes everywhere ?
A brain dead ego posting on Y-Boob ?
Unless you pulled the hydros apart fully before you let loose with your Black & decker then I could guarantee you have swarf in the system so even if you get the lurching problem solved you would have wrecked the transmissions .
These things are made in a sterile dust free environment so why did you think it was OK to grab your drill & start making holes everywhere ?
A brain dead ego posting on Y-Boob ?