Have cub cadet z force, left side control almost no power, right side forward only. is there an adjustment I can make or do the hydrostats need to be replaced?

If your 1986 Cub Cadet Hydro 1210 is experiencing difficulty moving forward but works fine in reverse even after changing the transmission filter and fluid, there could be a few potential reasons for this issue. Here are some steps you can take to troubleshoot the problem:
1. **Check Drive Belt:** The drive belt is responsible for transferring power from the engine to the transmission. A worn or damaged drive belt can affect forward movement. Inspect the drive belt for any signs of wear, fraying, or damage. If the belt is in poor condition, consider replacing it.
2. **Check Tension of Drive Belt:** Ensure that the drive belt is properly tensioned. A loose drive belt can lead to slipping and difficulty in forward movement. Adjust the tension according to the manufacturer's specifications.
3. **Inspect Linkage and Connections:** Examine the linkage and connections between the control lever, transmission, and the drive system. Loose or misaligned linkage can result in improper engagement of gears, affecting forward movement.
4. **Hydrostatic Transmission Issues:** Since your Cub Cadet Hydro 1210 uses a hydrostatic transmission, there could be issues with the hydrostatic unit itself. Check for any signs of leaks, damaged hoses, or worn components in the hydrostatic transmission system.
5. **Transmission Oil Level and Quality:** Ensure that the transmission oil level is correct and that you're using the recommended type of oil. Poor-quality or incorrect transmission oil can lead to performance issues.
6. **Air in the Hydraulic System:** If there's air trapped in the hydraulic system, it can cause issues with the hydrostatic transmission. Bleed the hydraulic system to remove any air bubbles.
7. **Transmission Pulley and Sheaves:** Check the transmission pulley and sheaves for wear or damage. If these components are not functioning properly, they can affect the movement of the drive belt.
8. **Check for Obstructions:** Inspect the underside of the mower deck and the drive system for any debris, obstructions, or objects that might be interfering with the forward movement.
9. **Professional Inspection:** If none of the above steps resolve the issue, it might be a more complex problem requiring the expertise of a professional technician. They can perform a more in-depth diagnosis of the hydrostatic transmission system and identify any underlying issues.
Keep in mind that working with mechanical and hydraulic systems requires knowledge and expertise. If you're not comfortable performing these checks and repairs yourself, it's recommended to consult a qualified technician who has experience with Cub Cadet or similar equipment.

Service the clutch and trans. Haynes or clymer make a shop manual for ur model. Umust do monthly maintenance

check the trans fluid reservoir. if it is low that may be the problem.

Internal problem on the right side transmission.

In most cases the hydrostatic drives are not made by the company tractor or lawnmower.
This is in the owners manual.

Hydrostatic Transmission
The hydrostatic transmission is sealed at the factory
and is maintenance free. The fluid level cannot be
checked nor can the oil be changed. Always keep the
area around the transmission cooling fan free of grass
and debris at all times

Cub Cadet LT1024 Operator Manual

How to Change the Hydrostatic Fluid in Cub Cadet Lawn Mower

https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1GGGE_enUS385US385&ion=1&espv=2&ie=UTF-8#q=cub%20cadet%20hydrostatic%20fluid%20change

I hope that this can help. Tom

you need to change thr hydr fliud in the transmission and the filter

maybe a bad bearing if stiff or need lube job

linkage is connected correct? Did it work prior correct? Did you prurge after changing fluid

Check the hydraulic oil level for the hydrostat drives(if it has a reserve tank located under the seat. Some ZT's don't have the reserve tank. Don't over fill that tank. 1/4 inch above the bottom is all it needs.)

Also, check the steering arm bolts. Very often they work themselves loose and the arm doesn't pull the valve rod that controls the hydrostat unit.

I hope this will help you...under the side panels on each side of the mower, there are "reverse lockout safety switches", they are supposed to stop the blades when both handles are pulled back. If one or both of the switches are out, the deck will not engage. Also, under the right side panel (when sitting on seat) there should be 3 relay switches, the one closest to the motor controls the PTO., if this is out, the PTO will not engage.