Poor Brake Practice and Runaway Ramps

[Sleddgracer]

you could always hang a potato on a string over the exhaust pipe, with a wire running to the dash - pull the wire, the potato plugs the exhaust pipe, and bingo, you have an exhaust brake - lol

[HazMatt]

LOL Showing your age, my friend! Didn't potato-plugging pipes go out with the Poodle Skirt..?
Tho, you're right- your system beats the snot outta running to the back of the bus, which is precariously careening down a 10% slope, and getting back up front in time to forestall crashing thru the guiderail, experiencing flight for a few glorious seconds, ending in a spectacular, Hollywood extravaganza-style *splat* at the base of a cliff.
Guess I'll stick to the flatlands for a bit.

Originally Posted by Sleddgracer

you could always hang a potato on a string over the exhaust pipe, with a wire running to the dash - pull the wire, the potato plugs the exhaust pipe, and bingo, you have an exhaust brake - lol

.

*owwie* [emoji856]
If something sounds too good to be true,
It probably ain't true!

Originally Posted by Booyah45828

Well, although many have done it, Ford and Navistar are both against it. Because of the hydraulic lifters used in the engine, using the ebpv as a brake in certain circumstances can cause the exhaust valves to hang open and hit the pistons.

I don't understand how the exhaust pressure could affect oil pressure, thence the lifters being forced into the open position...
How to know what special circumstances would lead to such a catastrophic fail..?

[Free Bird]

Originally Posted by kidharris

Will someone please clue me on what a locking transmission is? How do I find out if mine is one?

A locking transmission behaves like a manual transmission once underway. During acceleration you will see your tachometer and speedometer climb in sync. When a transmission is slipping (like the AT545) you will often see your rpm increasing while you are not gaining speed. I think some transmissions are deigned to slip in the lower gears but lock up in the high gears.

[WARGEAR]

The lockup torque converter came to existence as a way to increase vehicle fuel economy. By having the transmission input shaft RPM be as close to crankshaft RPM as possible you save fuel and reduce friction-generated heat. This will, in turn, extend the fluid and transmission life. Less energy is wasted as heat which means more is put good usable work.

I know not of one example of a new road going vehicle whose transmission does not have a lockup feature in at least one high gear. They could exist but would have to be for special circumstances (rock trucks in quarries, or very low speed applications, etc.).

[EastCoastCB]

The allison 545 doesn't have a locking TC. Lots of roadgoing vehicles have this transmission.

[WARGEAR]

Originally Posted by EastCoastCB

The allison 545 doesn't have a locking TC. Lots of roadgoing vehicles have this transmission.

I should’ve specified “new”! I own an AT545 equipped bus myself! *hand slapping forehead emoji*

[Booyah45828]

Originally Posted by haz.matt.1960

I don't understand how the exhaust pressure could affect oil pressure, thence the lifters being forced into the open position...
How to know what special circumstances would lead to such a catastrophic fail..?

Hydraulic lifters take up the slack in the valve train via oil pressure. Once off the base circle of the cam though, the lifters are locked in whatever position they're in. Navistar thinks that in scenarios of high back pressure and high rpm the valves will float and then the lifter will adjust to take up the slack created by the valves floating, which will hold the valve off the seat. Valve hits piston on next go around and you have problems.

[HazMatt]

OIC (I think...)
So, during the interval when the lifters are not on the cam's lobes, hydrostatic pressure keeps them extended? That can't be right...
When ON the lobe, during high RPMs & back-pressure, the valves are pushed out of their seat, into the combustion chamber at an inappropriate time, and *CHUNK* instant hand grenaded engine.
Thinkin' I gots some studying to do. Know next to nuttin about how my diesel works, and that ain't a warm & squishy feeling.

Originally Posted by Booyah45828

Hydraulic lifters take up the slack in the valve train via oil pressure. Once off the base circle of the cam though, the lifters are locked in whatever position they're in. Navistar thinks that in scenarios of high back pressure and high rpm the valves will float and then the lifter will adjust to take up the slack created by the valves floating, which will hold the valve off the seat. Valve hits piston on next go around and you have problems.

Wonder if sliding my Spicer 5 speed out of gear, & letting the revs drop out of load, if the damage danger would still apply...
Hey, thanx for taking the time to answer!

[Booyah45828]

Originally Posted by haz.matt.1960

OIC (I think...)
So, during the interval when the lifters are not on the cam's lobes, hydrostatic pressure keeps them extended? That can't be right...
When ON the lobe, during high RPMs & back-pressure, the valves are pushed out of their seat, into the combustion chamber at an inappropriate time, and *CHUNK* instant hand grenaded engine.
Thinkin' I gots some studying to do. Know next to nuttin about how my diesel works, and that ain't a warm & squishy feeling.

Wonder if sliding my Spicer 5 speed out of gear, & letting the revs drop out of load, if the damage danger would still apply...
Hey, thanx for taking the time to answer!

Hydraulic lifters are always in contact with the cam's lobe. When the lobe starts to push on the lifter and open the valve, the oil passage seals off, making the cushion of oil inside incompressible, and essentially a solid lifter.

With hydraulic lifters, your spring tension on the valve has to be light enough when closed so that the lifter can open the valve. Too strong of a spring and it will "collapse" the lifter, which makes noise and isn't good. Too light of a spring means the valve will bounce on the seat after it closes, which also isn't good

More rpm means the valve is moving that much faster, and needs more spring to prevent bouncing.

Now add in a bunch of psi of exhaust back pressure trying to open the valve, coupled with worn springs, a valve bounce happens and hangs the valve open, which then hits the piston. Valves hitting pistons is never good.

If you're sliding your transmission out of gear, the engine is no longer braking. Every engine brake made works better with more rpm. So it's just natural for you to drop down a gear, raise the rpm, and let the engine and it's brake do the work.

[HazMatt]

Duh! I knew slipping into neutral would remove any possible engine braking. Was thinking out loud, which is why I should never do so live on a keyboard... 🤤
Many thanx, sir, for the most excellent explanation! iYo comprendo! That makes perfect sense, now.
BTW, was using the wrong nomenclature, I guess. I always thought the lobe was just the elongated portion on the cam, not the entire circumfrence in contact with the lifter.
Learn something every day, if you're not careful...

[goldpan]

My Telma retarder works well down to about 2 or 3 miles per hour when it disengages. This causes you to loose braking and you need to use more pressure to engage the regular brakes. This takes some getting used to. As stated previously the retarder has 4 stages and on mine the first stage begins when I let off the accelerator. From highway speeds I can slow down for a light or intersection without using the regular service brakes.
My bus is an E450 10,000 lbs gvw and after about 10 years of service the inspection that I had done showed the service brakes to be almost brand new.
I have not had to make a panic stop but the combination should make that very quick.
As I have an automatic transmission I don't have the option of downshifting on hills so a light touch on the brake pedal serves that purpose without overheating the service brakes.
As this is my first post on this forum I hope you will tear it apart so that I can learn.

[Sleddgracer]

Originally Posted by goldpan

My Telma retarder works well down to about 2 or 3 miles per hour when it disengages. This causes you to loose braking and you need to use more pressure to engage the regular brakes. This takes some getting used to. As stated previously the retarder has 4 stages and on mine the first stage begins when I let off the accelerator. From highway speeds I can slow down for a light or intersection without using the regular service brakes.
My bus is an E450 10,000 lbs gvw and after about 10 years of service the inspection that I had done showed the service brakes to be almost brand new.
I have not had to make a panic stop but the combination should make that very quick.
As I have an automatic transmission I don't have the option of downshifting on hills so a light touch on the brake pedal serves that purpose without overheating the service brakes.
As this is my first post on this forum I hope you will tear it apart so that I can learn.

I've had a series of trucks, mostly Chevy/GMC, ( one Ford 1 ton flat deck ) ranging from 1/2 ton to heavy duty one ton crew cab flat decks, from 69 to present, all with automatics and I'd gear down with them on hills and sometimes stopping or slowing and my brakes seem to last forever too - hauled heavy trailers at times and often heavy loads and always relied on my transmission to retard - on super icy steep hills even used reverse instead of my brakes to slow down - so slippery that touching the brakes would have sent me careening out of control into the toolies - your automatic should be the same

[kidharris]

Originally Posted by WARGEAR

The lockup torque converter came to existence as a way to increase vehicle fuel economy. By having the transmission input shaft RPM be as close to crankshaft RPM as possible you save fuel and reduce friction-generated heat. This will, in turn, extend the fluid and transmission life. Less energy is wasted as heat which means more is put good usable work.

I know not of one example of a new road going vehicle whose transmission does not have a lockup feature in at least one high gear. They could exist but would have to be for special circumstances (rock trucks in quarries, or very low speed applications, etc.).

Does the AT545 lockup in any gears?

[o1marc]

Originally Posted by kidharris

Does the AT545 lockup in any gears?

No, that why it is not desirable, no lock up can cause several issues on the road.

[HazMatt]

Nope, got nothing to tear down in your inaugural post. It sounds like an awesome set up!

Originally Posted by goldpan

My Telma retarder works well down to about 2 or 3 miles per hour when it disengages. This causes you to loose braking and you need to use more pressure to engage the regular brakes. This takes some getting used to. As stated previously the retarder has 4 stages and on mine the first stage begins when I let off the accelerator. From highway speeds I can slow down for a light or intersection without using the regular service brakes.
My bus is an E450 10,000 lbs gvw and after about 10 years of service the inspection that I had done showed the service brakes to be almost brand new.
I have not had to make a panic stop but the combination should make that very quick.
As I have an automatic transmission I don't have the option of downshifting on hills so a light touch on the brake pedal serves that purpose without overheating the service brakes.
As this is my first post on this forum I hope you will tear it apart so that I can learn.

Unfortunately, mine has a retarded Louise...
BTW, welcome to the insane asylum!