I just bought a John Deere 4840 and found that it has very little power in the first 4 forward gears and all thereverse gears. The 5th gear has a lot of power and I finished harvesting my harvest in 5th gear. Could someone give me a hint how to fix it?
If you’re planning on doing it yourself, get the manual and read up on the shift sequence and see if you can find a common denominator in first forward gear and all reverse gears. There could be a clutch or a brake that is common to all those selections and then you are very suspicious of it.
The other possibility is the shift selector valve. We had a tractor ready to pull out the cab and go back to the shop to detach, when the book and a little logic told us to check the function of the shift valve and check the two gaskets behind the valve. If this gasket is bad or is leaking (internal) the clutch pack (or brake pack) will not have enough pressure to prevent slippage in those gears.
Ten bucks worth of gaskets on the outside is a much better job than 4500 on the inside, if the problem is fixed. All I’m trying to say is don’t automatically assume it’s a clutch pack. The manual describes the transmission test procedure with all the gauges that will give you a good idea of the fault. If you find the normal pressures, then it is more than likely a set of liners worn out in one or more paks.
These discs last quite well and I am a fan of measuring and reusing them if they meet specification, because they can be expensive. Other guys won’t even take a separate clutch pak and think its crazy if you don’t replace everything while its right there. It all depends on your own mechanical confidence, how much money you want to spend, and how comfortable you are with a wrench.