Posted by Owen Aaland on July 25, 2011 at 14:48:27 from (216.47.33.9):
In Reply to: MCV Issues posted by chris706 on July 24, 2011 at 21:32:00:
The hitch and auxiliary valves have a different hydraulic pump than the steering, brakes, and TA so we can leave them out of the discussion here.
You have an interesting set of circumstances. Why was the brake valve changed? Were thing working OK before the clutch was replaced? Was the MCV removed when the clutch was replaced?
The brakes valves are different between the 706 and 766 but the newer one should work better in the 706. The original valves were open center style and bleed off 1 GPM of the oil flow from the MCV whether or not the brakes are not being used. The valve for the 766 should be a closed center valve and will only allow 1 GPM flow when the brakes are being applied. That should give you 50% more flow for the TA controls and TA lube.
The 200 PSI for the MCV pressure is a little low. You did not say but does that pressure rise when the brakes are applied? I would guess that it does since it makes the TA respond differently. You should see a reading between 230 and 250 for low pressure and between 250 and 280 for the high pressure. The pressure should be high when the TA lever is in either TA or DD position and drop 20 PSI when shifting half way between the two positions. Do you see a pressure drop when shifting the TA? Doing the testing is probably the only time you want to shift the TA slowly.
My first guess, only it was apart , is a problem with the brakes valve leaking enough flow that the pressure regulator valve never reaches the opening pressure so no flow is passed on to the lube circuit. Is the 1 GPM orifice in the brake valve under the inlet fitting? Capping the line to the brakes would soon eliminate the brakes as being the problem. If the MCV was apart then all bets are off since there is now way of knowing if things were reinstalled correctly.
The more common reason for the low pressure in the TA control circuits but the steering being good would be the steering check valve leaking.
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