966D brakes

Hello men, have a 99y loader that brakes won’t release. This is a list of new parts. Both reservoirs, brake chambers, 4 wedges and wheel cylinders, and left brake pedal. And some brake lines. Here’s what’s happening. Start tractor and let build pressure, once you hit the brakes the wedges move and apply the brakes, but when you let off pedal they won’t release. We can bleed the air off tractor and they will release. But once you hit pedal again they won’t release without bleeding off air. We have the inspection covers off all 4 wheels. Any ideas?

Must be flowing through the right pedal. They tend to get used less then the left so more prone to sticking. .

Thanks grandpa, will order one today.

Is there any other part of this brake system, left to replace?

Not to be critical here but it sounds like instead of spending some time trouble shooting the problem someone is just throwing parts and money at the machine hoping that at some point the problem will go away!

Just to refresh my memory on the brakes in a 966D I went to SIS and as I thought this is a very basic air over hydraulic system.
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Basically air from reservoir goes to the foot valves and then when one or the other is actuated the air is sent to the air/hydraulic cylinders and the hydraulic oil is then sent to the wheel cylinders which push the wedges to force the shoe against the drums.
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If I was presented with the problem of brakes not releasing on a 966D first thing I would do is clean the floor in cab to be sure there isn't crap under the brake peddles holding one or both slightly applied.

Next would be to push down on each one to fully apply then give a good tug up on each one to make sure the peddles were not binding on their pivots.

If still not releasing go to the brake roto-chambers and loosen one or both the air lines from the foot valves to see if there was even a slight amount of residual air pressure there. If there was air there I'd go back up to the foot valves and loosen the lines that connect to the upper side of foot valves to determine which one was leaking air pressure while in the release brake position.

Once you know which one is leaking I would remove it and take to a good truck parts shop and have them match it up to a Bendix brake valve I'm thinking it's a Bendix E-3 valve that you should be able to get a reman one for about $75.00 or less.

Actually was surprised to see them at that high a price online, seems we used to get them for half that price or less! But compared to the time and money spent to this point with no success that price is pocket change!

Between the brake valve and treadle their is a plunger that corrodes and seizes, so changing the valve may not fix the problem or pulling up on the treadle may not fix it either
check that the plunger is free
Mark

Mark250 said:

Between the brake valve and treadle their is a plunger that corrodes and seizes, so changing the valve may not fix the problem or pulling up on the treadle may not fix it either
check that the plunger is free
Mark

Click to expand...

True, but just cracking the lines would give you a way to narrow down where the air that is causing the brakes to come on. If the air is coming from the right valve one could only hope that while replacing or rebuilding that valve one would notice that plunger was stuck. And that is one more reason to keep the cab clean inside and not let crap build up around the brake peddles!

Of all the complicated systems on equipment these days I'd love to have to be trouble shooting the brakes on a 966D!

Just to add a little more clarity to this discussion:

Item 1 in the above would be the plunger refered to above that can bind.

And here it is in red in a cut away drawing that gives a better idea of how it is in the position between the treadle#3 and the valve #10

Not sure what lines were replaced but I have seen lines that look good on the outside, be deteriorating on the inside and causing a 'check valve' type of condition, keeping the pressure to the brakes.

highwayghost said:

Not sure what lines were replaced but I have seen lines that look good on the outside, be deteriorating on the inside and causing a 'check valve' type of condition, keeping the pressure to the brakes.

Click to expand...

Another reason to do a step by step trouble shooting job. If you find the air being vented out of the foot valve but still there is pressure being held at the air over hydraulic cylinder you would know there was a problem between those two points.

Maybe the Systems Operation for the air system would help the original poster, attached here:

kshansen said:

True, but just cracking the lines would give you a way to narrow down where the air that is causing the brakes to come on. If the air is coming from the right valve one could only hope that while replacing or rebuilding that valve one would notice that plunger was stuck. And that is one more reason to keep the cab clean inside and not let crap build up around the brake peddles!

Of all the complicated systems on equipment these days I'd love to have to be trouble shooting the brakes on a 966D!

Just to add a little more clarity to this discussion:
View attachment 211760
Item 1 in the above would be the plunger refered to above that can bind.
View attachment 211761
And here it is in red in a cut away drawing that gives a better idea of how it is in the position between the treadle#3 and the valve #10

Click to expand...

I've seen dirt and crud build up in the top of the E-3 valve and hold the valve open slightly even with a loose pedal plunger. Even with a good boot on the pedal plunger a certain amount of dust will crawl in there, probably from under the floor board.

Sorry it took so long to get back. Had some good weather and had to make hay while the sun shines. Replaced right pedal valve and now it stops better than it ever has. Thanks for the help men