john deere 450 crawler HLR pressure fluctuation

What will cause the HLR pressure reading to start out in the normal range and drop to 0 when it shifted into gear? The pressure rises back to 60-80 lbs. after about 20 seconds but will not engage the transmission. The pressure will also drop to 0 after a couple of minutes even if the HLR is not shifted. Any ideas?

Jump on over to the "JD Crawlers Message Board" some one their will be able to answer your question..

Thanks Jo Bird.
I've already made that jump. Last I checked I had over 300 views with no replies. This has been a long running problem that I can't seem to get solved. I hoped that someone on here might have an idea where to look.

Have you checked the manifold pressure? with a gauge.

It should be around 180 psi

The pressure port on top of the accumulator housing is where I'm getting the readings that I posted. The tech manual says 145 psi.

Have you done this?

Engine Clutch Assembly


1-Free Travel 3-Pedal Detent Adjusting
2-H-L-R Linkage Stop Nut Screw
Fig. 1-Adjusting H-L-R Linkage
Whenever the clutch and H-L-R linkage have been
removed, or clutch pedal free travel becomes less
than 3.25 inch (88.9 mm) or whenever H-L-R shifts
from high to reverse too aggressively, the linkage
must be readjusted. Be sure to make both adjustments
in the sequence given below.
First adjust clutch pedal free travel to 3.75 inch
(95.3 mm) at the clutch pad as follows: Remove left
footrest from crawler. Observe detent set screw on
clutch pedal arm on left side of clutch housing (Fig.
1). Loosen detent to increase free travel or tighten
screw to decrease free travel. Always end up with
screw in the detent (locked position).
Refer to Section 70, Group 25 and install pressure
gauge as instructed at the bypass valve port in the
accumulator housing through the access hole in the
transmission top cover.
Turn H-L-R clutch valve stop nut down until clutch
pedal just starts to pull away from stop, then back it
out five turns.

With both gear shift and H-L-R levers in neutral
and brakes locked, start engine and run at slow idle.
Turn the valve operating linkage stop nut (2, Fig. 1)
clockwise until the pressure at the gauge just starts
to drop. Then turn the nut in one additional turn.
NOTE: As the nut is turned, the pressure at the
gauge will increase to approximately 160 psi (1103
kPa) (11 bar) maximum and then drop approximately
5 psi (35 kPa) (0.35 bar) as the nut is turned further.
Check the adjustment by depressing the pedal 112
to 3/4 inch (12.7 to 19 mm). The pressure at the
gauge should rise approximately 5 psi (35 kPa) (0.35
bar). If the 5 psi (35 kPa) (0.35 bar) requires more
than 3/4 inch (19 mm) pedal travel, turn nut counter-
clockwise. If 5 psi (35 kPa) (0.35 bar) is at less than
1/2 inch (12.7 mm) pedal travel, turn nut clockwise.
Depress clutch pedal and be sure that the pedal
hits the firewall to prevent damage to the clutch
adjusting lever.

Here is a link

http://forums.yesterdaystractors.com/viewtopic.php?p=7127385&highlight=#7127385

I also used the procedure Roy Suomi outlined to fix my issue. Not saying that is your problem, just something else to try.

Thanks Dr Loch
I have adjusted the clutch and valve linkage according to the Tech Manual, but didn't see the second part in the manual. The manual says to turn the nut clockwise until the pedal just starts to pull away then back off 4 1/2 turns and adjust in or out to fine tune. I will try your procedure this weekend if the pressure will stay up that long.
Thanks, Joe