4520 Synchronizers

Grey

Member
I have a 4520 synchro that upshifts great on the go like from 4 to 7 and 6 to 8. Works good in all ranges that way. However it won't downshift like from 8 to 6 on the go without grinding. You have to almost come to a stop to downshift it. Is this an issue with the synchronizers or is it an adjustment issue? Other than this, I have seen no other issues with the shifting or transmission. I have owned it for a few years and its always been like this. Hasn't gotten any worse in that time. Total hours on tractor is almost 5k. Thanks for any advice.
 

Hmmm...I don't consider the syncrorange transmission a shift on the go type of deal. But Then I've rebuilt lots of transmission input shafts on syncro and quad shift transmissions...and it's almost always the synchronizer parts that wear out first.

I'm interested in what other JD guys say about this topic
 
It's simple enough..the low side of the synchronizer is worn,, there is a high side and a low side,It will need split and serviced, do both sides,collar,drums and disc,,give the shifter a good look over they wear to and will not place the shift completely in place..
 

The shifter in the 4020 I just rebuilt the topshaft in was worn bad...all the hi/lo syncro parts were shot....put the gears in it too as they were spent(and not cheap)

The reverse synchronizer parts were ok and I reused all that except discs and plates got renewed.

So in all the years of working on John Deeres for John Deere and on my own....I have never seen a owners manual for one!

My old 4010 has some basic info in a little dash booklet(that's barely legible now)....so just what is the syncro-range transmission shift procedure??

Can you just clutch and shift between adjacent gears on the roll?

I always have just stopped and stuffed them into the desired gear.
 
They were made to shift on the go. At least when lever is moved to the gears on the slots on the right hand side. 2 gears and a reverse in each of 4 ranges (first 3 on our 4020). The 4 ranges on the left side of the slots you MUST stop to shift those. The ones on the right side you push the clutch in and shift. For reverse I don't know if it works good if you are going very fast , but I slow down to about a stop you can still be rolling and it should shift right in.
 

I always wondered why JD bother to synchronize the reverse on the old 10 and 20 series tractors

I bet a high speed reverse shift could explain the couple broke in half reverse topshaft pinions I've seen over the years

Think I will likely just keep stopping and shift my old 4010. It has had the top-shaft overhauled in the past(distant past)...and it's feeling a bit loose now. I did work over the shift quadrant in the dash and vastly improved the shifts.
 
Deere did get rid of the rear reverse syncro on the late 20 series: 4320-4620 and 6030. Mainly to put wider pinions, but also because shift on the fly was not used too much.

The syncros are very useful when pulling wagon, and also because it is so much easier for the motor to start in 6 gear and go in 8 than starting in 8 gear.
 

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