Odd 450G Tranny Problem

Hello,

I have a 1994 JD 450G Dozer (farm machine) - direct drive machine (793 991) with an odd transmission problem.

I was doing some light clearing of brush hardly loading the machine at all. I had just started so the machine had run less than five
minutes so it didn't really have much time to heat up. (Engine and hydraulic levels/operation are good.)

I was going up an incline of probably about 25 degrees and I notice this medium frequency whine start. About a minute after that I got
the STOP alarm light and the "Transmission Oil Temp/Pressure" light on.

I stopped the machine and checked the transmission fluid level, found it low and was surprised to find that it took about five GALLONS
(out of 27 total capacity) to get it back on the stick. Have had no signs of leakage. (Bought the machine about a year ago and had not
had a problem with it in that time. The tranny had been fully rebuilt.)

I topped it off with Hygard and the STOP light went away, but the whine was there only very faint. The following morning it started fine
and I went back to work, but not 3-5 minutes after I began, on flat ground, I started getting the same Stop/Temp/Pressure alarm, but only
intermittently cutting in and out. I again stopped the machine and started looking again.

What I see in detail:

Switch of bulb check shows all alarm lights working.

The transmission oil filter restriction light is not lighting up when the problem occurs. Transmission fluid level is slightly above the
mark and has not leaked off.

The machine moves fine. When I dig in the transmission does not slip. Shifting is timely and smooth, it sits still in neutral, steering
clutches operate smoothly, both tracks pull evenly/straight and brakes operate smoothly with reasonable pedal pressure.

The only indication of trouble is that light whining sound plus the stop & transmission press/temp alarm cutting in and out.

After reading everything I could get my hands on the only external thing I could find wrong related to the transmission is that the
filler cap had the tension screw backed off and air pressure couldn't build up in the tranny case. Tightened that and it seals fine. But
that is likely unrelated.

My first thought is an intermittent/marginal pressure problem related to the transmission pump that is piggy backed to the hydraulic
pump. My problem comes in that the op/service manuals show disassembly/reassembly, but don't give any testing procedure to measure the
pump pressure/etc as a diagnostic procedure. (other than "see your dealer") Sure would be nice to know what the tranny output pressure
range should be and where to plug in a test gauge.

I am about two hours drive from any major city with a Deere dozer equipment dealer (and I have heard that these folks are not as heavily
interested in the Deere mystique of keeping older machines running as they used to. Giving me the impression that costs/help would be
harder to get or way too expensive for the small farm guy that is not going drop a couple hundred grand on a new earth mover.)

I am looking to see if anyone here has run into this or similar issue and might pass along some advice about how to find the real
troubleshooting procedure that a Deere Tech would use to see if I have a bad pump or something further down the line. Or even a reasoned
guess about it.

All comments welcome and appreciated!

Bruce
Exurbs, TN

Welcome to YT
I will recommend to change hyd filter if it hasn't be changed recently. My knowledge of JD industrial equipment is very limited.

Jim,
Thanks for the response.

You got me thinking.

Since I didn't have the Transmission filter alarm set, I figured it was OK. On second thought, if it was getting marginal ... maybe it is in that zone where it was not bad enough to cause the filter alarm to
kick, but just enough to cause the pressure alarm to ring.

Not a bad idea. Will give that a go. Filters are a cheap/easy test.

Thanks!
Bruce

Bruce
In my younger days I was taught to perform the easiest diagnostics 1st & changing hyd filter is usually easy.

Well, interesting positive development and learning opportunity that other uninitiated G owners like me might find helpful.

After picking up the filter from the JD Ag dealer and before dinner, I was boning up on the 450G service manual about where the filter, pump, lines, etc were arrayed ...and I came across this gem in the transmission pump reassembly section:

"IMPORTANT: Damage to pump may occur if pump is not primed with oil. The transmission oil reservoir IS LOWER THAN THE PUMP INLET and pump cannot draw oil fast enough after initial start up."

It hit me that my trans fluid was low enough going up that incline that the pump ran dry ... thus creating the whining sound and STOP/pressure alarm. Click ...

So after double checking the fluid level again, I backed the machine up the same hill and the whine disappeared immediately as the level in the tank became higher than the pump intake. So far no peep out of the alarm since, going uphill/downhill, load or no. That was a very pleasing thing. LESSON: Flat ground priming will not happen in this machine if the level at some point has starved the pump dry. As I guessed, getting the machine's fanny up 30-40 degrees evidently will raise/tip the tank far enough to get fluid flow started again to the pump inlet and avoid a pump teardown.

I am quite thankful that I didn't have to run the Deere mechanic on the four hour tour for that. Plus it drives home just how much I need to step up my maintenance care of levels and get out in front of the filters. It will be a real blessing if I got off easy this time.

The only loose end comes down to troubleshooting data on the transmission. At a minimum what the pump pressure range should be and where to take it. Etc, etc. Don't really want to do that, but it sure would be good to know.

Jim, thanks for the discussion. Sometimes it is a big help to just talk over an issue to get the right thoughts to click into place :^)

Best regards,

Bruce

Thanks for update & I'm glad you got it going.
Jim

Well, our 450G worked fine for about another ten hours of good work, but now I am now getting the same Transmission Temp/Pressure combo stop light. Only this time the machine occasionally ceases to roll when the light comes on where before it didn't. I have to have a pressure problem.

Even with some further digging, I have yet to run across any info on where to measure transmission fluid pressure and what is the valid range for the pressure to be.

Anyone out there know this or have a suggestion as to where I could go to find the info?

Thanks!

Bruce

Well, I think I can bring this problem to closure now. Here is what I found for a fix that finally worked.

After a half hour discussion with a very helpful Pro at Leslie Equipment Company, I pulled the transmission suction screen by accessing it by removing the two left side cab floor panels.

It is a credit to Deere Engineering that the transmission would move the machine at all with the tiny squirt of fluid going through that screen. (See photo).

It is not exactly clear that the screen housing is ABOVE the level of fluid in the transmission, but it is and draining the transmission is not required to check the screen. The Pro also said that it isn't uncommon for the suction tube nut (going into the transmission case) to back off and damage the O ring seal ... allowing the line/pump to lose prime. Not much else to go wrong there.

Hope that might help someone else out there with a farm machine!

Bruce


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What is all the stuff on the screen? Brake material? You may have more issues to deal with soon.