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i have a 2008 zero turn with 400 hours on it. Runs great but the left transmission seems to be having a hard time to turn. It whines and is obviously weaker currently than the right transmission. Any ideas?

The whining is oil escaping between the valve plate & cylinder chest in either the pump or the motor or both.
This is caused by running the engine too slow to control the speed rather than using the sticks .
Dirty oil makes it worse & hastens the demise
A belt that is too long or a tension arm that is not free, a bad tension pulley or spring all make this worse .

Basically the left is toast if you do not know some one who can machine the two surfaces then set the gap with with shims

Where in the hydro do you have a gap that needs to be set?

hlw49 said:

Where in the hydro do you have a gap that needs to be set?

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between the valve plate & the cylinder block
Too tight & they can not turn against each other and when they do that will grind against each other
Too loose and the oil will flow out the sides and not through the pistons or from the pump to the motor
And on top of this the surfaces require a very specific surface roughness.
I ones tried to recondition one and made the faces mirror finish smooth
No drive what so ever
I have not been able to ferret out the specific gap but it looks to be around the 0.00015" to 0.0003" range
This is why most who say they can repair them really mean they can fit replacement pump/motor units .

My tech machines the wear faces then resets the gap, fits in back in the box with new filters & seals fills & purges the units for 2/3 of the wholesale price of a replacement pump/motor unit .

An old farm mechanic showed me how to do it when we serviced the hydro on the 100Hp 1962 Oliver tractor.
Same system, just bigger and on that we did a mirror flat finish then ran the lathe in reverse and a fine hone block across the face to do a sort of internal pumping spiral hone
The theory was like an oil flinger, the hone will prevent the oil flying out of the faces because it creates an inward flow .

This probably why here it is best just to replace the center section.

What I find amazing is that the repair is fairly simple , once you know how to do it and have lathes set up to do it
Yet there does not seem to be anyone in the entire USA who reconditions they hydro units
Down here there are 2 problems
1) short supply of the drop in unit
2) they cost 1//2 the price of a replacement transmission.

The tech I go to is usually booked solid for at least 1 week in the off season & 2 during the summer .
Oz is only 30 million so I would have imagined that there would be a massive market in the USA.

In the US the difference between the time and cost to rebuild a consumer grade hydro vs. Replace with new is negligible. I don't know of any shops willing to open a hydro and then warranty it. I just replaced a hydro on a BadBoy Z. New unit was $1200. May have been a simple fix but why spend hours digging into it when unknown what parts or how much the parts might cost when i know the cost of replacement and can give the customer an estimate.

Hammermechanicman said:

In the US the difference between the time and cost to rebuild a consumer grade hydro vs. Replace with new is negligible. I don't know of any shops willing to open a hydro and then warranty it. I just replaced a hydro on a BadBoy Z. New unit was $1200. May have been a simple fix but why spend hours digging into it when unknown what parts or how much the parts might cost when i know the cost of replacement and can give the customer an estimate.

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hydrogear. pump, motor, center section. seal kit. filter, sealant, 3 quarts of oil, and 3 hours labor. 90 day warranty. Which is the same warranty that Hydrogear gives you on a new unit installed by an authorized service center. May run into charge pump issues, but don't know until disassembled, but that is the reason for the estimate. Or include the extra parts in the estimate and then can make adjustments from there.

ILENGINE said:

hydrogear. pump, motor, center section. seal kit. filter, sealant, 3 quarts of oil, and 3 hours labor. 90 day warranty. Which is the same warranty that Hydrogear gives you on a new unit installed by an authorized service center. May run into charge pump issues, but don't know until disassembled, but that is the reason for the estimate. Or include the extra parts in the estimate and then can make adjustments from there.

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I can sell you a sell you a Hydro Gear 3100 series right hand unit and you can rebuild it and sell it. LOL.

Hammermechanicman said:

I can sell you a sell you a Hydro Gear 3100 series right hand unit and you can rebuild it and sell it. LOL.

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Rebuild would run you about half of what the new unit cost to install.

Commercial guy and he needed it ASAP. I got the hydro in one day from stens. By the time i took it out, took it apart, ordered parts, waited on parts, put it back together again it was more cost effective to just replace it. Plus the unknown of parts cost and availability i just replaced it.