JoeH

That's exhaust valve diameter? That has about 1.8-1.9 square inches of surface area, so that's about 40 pounds of pressure. At higher RPMs you need more pounds of spring tension because the valves have less time to close between cycles. 40 # of pressure on the valve leaves you 150# of spring pressure. Of course the back pressure doesn't push on the valve with that 40# until the valve is shut. At fully opened the valve spring might not have much resistance, as the pressure is vented into the cylinder. But, you also have vacuum created on the intake stroke which is acting to pull the exhaust valve open, which is takes from your remaining 150# spring pressure.

I got the 60 pounds of pressure because it's 20 pounds per square inch and a 2 inch valve has 3.14159 square inches of surface area. If it's a 3 inch valve the surface area jumps to 7 inches, which jumps to 140 pounds of back pressure acting on your valves, leaving only 50 pounds of spring pressure shutting the valves.

You have to take the 190# and convert it to psi on the surface area of the valve head. If it's a 2 inch diameter, πr^2 is 3.14159. Now take your 20 psi back pressure and you have 60+ pounds of pressure trying to open your valves, which leaves 130 pounds of spring pressure holding them shut.

What back pressure do they list for other brands like Cummins? You might be surprised.

I think the butterfly brakes are operated by an air cylinder. I assume you can put an air regulator on it to control the amount of back pressure the brake generates. Find out what # springs the exhaust valves are, and what diameter they are. Run a little math, you'd have to generate enough force to counteract the valve springs to cause valves to float. You'll need to leave a safety factor to ensure the springs can still hold the valves with some force. Your other choice is a traditional Jake brake that opens the exhaust valves at TDC of compression stroke to dump off the combustion energy. Doesn't generate any back pressure, and certainly doesn't take 700# off your payload.

Looks like it weighs a decent amount, not sure what maintenance is involved. A traditional engine brake or a butterfly style seems simpler and less maintenance. And weigh less.

Is it VMac II or VMac III? With key on, engine off is the lightning bolt on? If so, with cruise off hold down the set/decel button until light goes off. It should spit out a 2 digit code, which can be looked up to see which sensor is failing.

If they're double frame trucks, the best thing you can do to preserve them is split the frames apart one side at a time and sandblast/paint them. Some people even drill and tap the outer frame rail for grease fittings so they can prevent future rust jacking. Nowadays they make a "heavy single" frame, I wish they had started using them sooner.

That's a nice truck. I'd be a happy driver scooting around in that. Is the cab air ride? We just bought an '88 to put on the road, but it doesn't have an air ride cab. Makes a world of difference, I compare cab air ride to sitting on a cloud. I'm going to put air bags under this cab before I put it on the road.

Is it low on power steering fluid?

Not sure what you mean by large wheel pattern. This truck is 6 spoke hubs, with 11r24.5 tires. No idea if that's what it's always had, we've had the truck since I was 12 in 2001.

What are the visual differences on 55k Camelback vs 65k? Just curious what our retired DM686SX has. It's a double frame, each rail is 3/8" thick, for a total of 3/4" thick per side. Door doesn't have an axle rating sticker in it. Differentials are not original, we changed them out a few years ago when it ate a bearing to get the truck moving faster than 48 mph. Did the 65k only go in a triple frame truck? How thick are the triple frame rails?

You can always lengthen them.

Isn't there an engine tag somewhere on it? Just watched a video of a 4 cylinder Ford diesel in a Gardner Denver looking for something similar to that. Ford sounded a bit like a 2 stroke.

Sounds like a nightmare of a ride!

What gear oil are you running in it? Check with Eaton and see what that trans needs, running anything else may cause problems like that.

We rarely have drive tires all the same size, never have. Never had problems with our Auto or manual power dividers. Is it Camelback or air ride? If Camelback, did you replace the trunion bar bushings or the elephant pads? Spoke hubs or bud wheels? Is this a recent problem or has it been doing it for a while?

Yes. Start your own thread.

He's wondering about just juicing up his maxidyne to make it like a 350hp maxidyne, not changing to a different fuel pump.

K I'd get it repaired before it breaks at 60 mph on the highway.

The u joints are supposed to be clocked, if someone had it apart they may have put it together wrong. Joints fight each other if they aren't clocked right.

No it's a magic 8 ball. You shake it and it tells you if they truck is going to move or not.

Bump. Does anyone have insight on this? Is the MP series fully a Volvo product? Or did Mack have a hand in designing it?

Will likely be called Splitter Cylinder or Shift Cylinder on a 12 speed. Combination Cylinder is what it was called on my 8LL

I had a Combination Cylinder crack on my 8LL trans a couple years ago. It's the disc that air pushes against to change from high to low and low to high. Easy part to change. Air would leak through the crack to the vented side. Switch range and it'd still leak, because you're just inverting which side of the disc is pressurized and which is vented. I'll bet thats where you'll find your problem.