John Deere 644E transmission troubles

[Jerbearbroth]

I have a 1988 John Deere 644E wheel loader that has developed a transmission problem. When the machine is shifted from either forward to reverse or vice versa, it takes up to 3 seconds for the transmission to engage. Also, when it is traveling, and is shifted from 1st to 2nd, it takes up to 7 seconds to change gears. This problem came on very quickly (within about 50 hours). I suspected a modulator valve or something, but the dealer is saying that the transmission needs to be replaced. They say the clutches are bad, but when the machine is working, there is no slippage or performance problems other than slow shifting. I am just wondering if anyone has had a similar issue. I find it hard to believe that the clutches went bad within a period of about 50 machine hours.

Thanks for your advise!

 

[quackattak]

Bad clutches you would see a change in oil, maybe a oil sample would give you an idea. That trans was never one of my favorites, deere did everybody a service when the went to a zf in the next series. I would check pressure and see what happens when you shift, could be a seal problem in the trans. That is a screwy setup to someone that is unfamiliar with it, might have to check around for someone with some time working on older deeres.

 

[Nige]

If the clutches are "Bad" as the dealer says I would guess he means worn out, or close to it. That would indicate they are slipping a lot.
Does the oil smell burned ..?
Try removing the transmission pump suction screen (if there is one) and check it for flakes of clutch material which will be non-metallic.
Pull the filter and cut it open to look for smaller particles.

 

[Jerbearbroth]

I thought the same thing about the fact that if the clutches are worn out, the tranny would be slipping a lot. Not the case here. The oil hasn't changed any, and it doesn't smell burnt at all. I haven't pulled the filter or screen yet, but i'll give them a look. Thanks

 

[Jerbearbroth]

Bad clutches you would see a change in oil, maybe a oil sample would give you an idea. That trans was never one of my favorites, deere did everybody a service when the went to a zf in the next series. I would check pressure and see what happens when you shift, could be a seal problem in the trans. That is a screwy setup to someone that is unfamiliar with it, might have to check around for someone with some time working on older deeres.

I haven't taken an oil sample, but notice no change in the oil. It hasn't darkened or anything, and it doesn't smell burnt at all. I don't have a test manual on the machine, so I will have to do some investigating as far as pressures. I'm in a rural area and the only people I can find who have any experience working on older Deere's is at the dealership. Problem there is that I kind of feel like they just want to replace the tranny rather than spend much time really diagnosing the problem.

 

[Nige]

If the oil does not smell burned your clutches are not permanently slipping, that's for sure.

 

[oldseabee]

Manual that I have is for 644A. Not sure how the transmissions compare, but this one shows a trimmer valve in the top port of the control valve. Whenever you shift, there is a pressure drop and the trimmer valve shifts, oil going to the new clutch first has to go through an orfice in the control valve to shift the trimmer valve over a certain amount of time to allow an easy shift. If this orfice gets partially plugged with a piece of trash the trimmer will take a longer time to shift. there is also a check valve in the control valve that blocks flow and forces the oil through the orfice to the trimmer. If this check valve is not working there can be a delay in the shift of the trimmer valve. Not sure where in the control valve the orfice and check valve are located, but maybe something to consider.

 

[Jerbearbroth]

Manual that I have is for 644A. Not sure how the transmissions compare, but this one shows a trimmer valve in the top port of the control valve. Whenever you shift, there is a pressure drop and the trimmer valve shifts, oil going to the new clutch first has to go through an orfice in the control valve to shift the trimmer valve over a certain amount of time to allow an easy shift. If this orfice gets partially plugged with a piece of trash the trimmer will take a longer time to shift. there is also a check valve in the control valve that blocks flow and forces the oil through the orfice to the trimmer. If this check valve is not working there can be a delay in the shift of the trimmer valve. Not sure where in the control valve the orfice and check valve are located, but maybe something to consider.

Now we're getting somewhere! That sounds very plausable that my problem is a plugged orfice or something. The problem came on too quickly for it to be clutches (in my opinion). I will do some more checking for pressures and look over the valves you talked about. I truely believe I can save quite a few dollars over the replacement my dealer is suggesting.
Thanks for you insight!!

 

[Jimjoy]

Did you ever figure this out? I have same issue

 

[Bigbert]

Hi Jimjoy,

this really sounds like a half plugged modulation orifice. On older control valves it is fitted as a M5 screw with 0.7 mm bore in channel plate. Remove main valve block, gasket, steel plate, gasket, then access to channel plate.
Newer control block is die cast with orifice accessible from outside.
Please share pics from type plate or valve block, then easier to assist.
br
Bigbert

 

[Johnnyp]

I have this same exact issue with a 1991 644e. Can anyone point me in the right direction on where to find the modulation orifice?

 

[mg2361]

Welcome to HEF Johnnyp !

Please supply a complete machine serial number. Also, you state that your issue is exactly the problem as above. Did your issue start suddenly, or did it get worse over time?

 

[Johnnyp]

Serial number is DW644EB520853.
Yes the problem just started suddenly. Once in gear the machine operates fine no slipping of the transmission at all. The transmission fluid does not have a burnt smell or anything. Pulled the filter off and cut it open and didn’t find anything out of the ordinary in that either.

 

[Bigbert]

Hi Johnnyp, this is the sectional pic of the mechanically/hydraul. control unit which possibly still fitted on your loader. (There is mechanical linkage from gear levers to control unit?) A picture might help.
The issue might also be created from pressure cut off valve. I need to go through old documents to find the modulation orifice.
But please check cut off valve first. Issue is only present in 1st and 2nd or all gears?

 

[Johnnyp]

The issue is a delay in shifting all gears. Forward reverse and 1-4. Once in gear it doesn’t slip or anything.

 

[Steve Austin]

Have you cleaned the suction screen?