Hydraulic brakes on a 30K GVW chassis?

[lxt]

well due to the fact the diesel motor is a bit heavier than gas!!!!! this is 1 reason, 2nd reason......refer to my description of asplundh power units!!

diesel at over 30,000lbs with hydraulic brakes?????? yep all the big truck mfg`s are going that route........NOT!!! there is a reason air brakes are prefered especially at certain weight ranges....check with any diesel mechanic & he`ll give you many reasons!!! personally I wouldnt but it........there is a reason its for sale...dont be the poor sucker to get stuck with the boat anchor!!!



LXT..............

 

[lego1970]

One more tid bid of info in case you didn't already know. If your brakes are weak and the truck is not stopping good after going down a long hill, or a quick stop this is what to look for. If the peddle goes to the floor then your air supply is not adequate enough and or your hydaulic systems is boiling, has moisture in it, or air in it. If your not stopping yet have good pressure on your peddle then your pad or shoes are gassing out and therefore it basicly pneumatic versus pneumatic or in your case pneumatic versus hydraulic (which hydraulic should win, but doesn't always). If that's the case then you can switch out your shoes or pads to a higher heat rating, and the only downside is that it will cost more and have less initial bite then lower temp pads. Good luck.

 

[les-or-more]

I was being coy last night but maybe there's a difference compression-wise for engine braking on a down shift? I don't know. I guess I'll assume that if it's been manufactured as is there's no real reason to be afraid of it.

Unless the diesel has an exhaust or engine brakes built in the throttle body on the gas engine will allow more engine braking.

 

[lego1970]

Unless the diesel has an exhaust or engine brakes built in the throttle body on the gas engine will allow more engine braking.

Why would gas provide better engine braking? Diesel has much higher compression and while the rpms are much slower, the piston speed is pretty much on par with gas engines. Am, I forgetting something? Also, while there are numerous engine braking or retarding systems out there, from my understanding, most just cut off the fuel and use a coil to open up the exhaust valve on the "dead" fire stroke.

 

[les-or-more]

Why would gas provide better engine braking? Diesel has much higher compression and while the rpms are much slower, the piston speed is pretty much on par with gas engines. Am, I forgetting something? Also, while there are numerous engine braking or retarding systems out there, from my understanding, most just cut off the fuel and use a coil to open up the exhaust valve on the "dead" fire stroke.

Because the engine when driven backwards becomes an air pump the diesel has nothing to retard the airflow through the engine. The gas engine has a butterfly in the throttle body or carb to restrict the airflow.

 

[lego1970]

Because the engine when driven backwards becomes an air pump the diesel has nothing to retard the airflow through the engine. The gas engine has a butterfly in the throttle body or carb to restrict the airflow.

The engine doesn't spin backwards but otherwise I get what your saying. Thanks, never took that into consideration.

 

[les-or-more]

The engine doesn't spin backwards but otherwise I get what your saying. Thanks, never took that into consideration.

Yes , poor choice of words its late lol, the engine turns the same direction, just a lot faster when the direction of power is reversed.

 

[jandh@amtelecom]

Yes , poor choice of words its late lol, the engine turns the same direction, just a lot faster when the direction of power is reversed.

Guys: When an engine brake activates in a diesel, the exhaust valve is actually kept from opening on the exhaust stroke, thus causing the piston to recompress the already burnt previously compressed hot gases left in the combustion chamber. (On some engines they actually reinject some fuel into the chamber to get even more braking) This said, the piston tries to stop the crank from rotating, but the forward load is still greater, and all the cylinders together start to reverse load the crankshaft to the point where braking and sometimes hard braking is experienced. I know of some engines, Cummins for example that were rated at 400 HP and had 460 BHP or brake horse power!:cool2:

Hope this helps!
Jandh

 

[lego1970]

Guys: When an engine brake activates in a diesel, the exhaust valve is actually kept from opening on the exhaust stroke, thus causing the piston to recompress the already burnt previously compressed hot gases left in the combustion chamber. (On some engines they actually reinject some fuel into the chamber to get even more braking) This said, the piston tries to stop the crank from rotating, but the forward load is still greater, and all the cylinders together start to reverse load the crankshaft to the point where braking and sometimes hard braking is experienced. I know of some engines, Cummins for example that were rated at 400 HP and had 460 BHP or brake horse power!:cool2:

Hope this helps!
Jandh

I thought BHP was something different. It's like hp w/out the accesaries. I think my old detroit 500 was 500hp/1650 tq but only around 380hp/1000 tq worth of retardation. Also how does a valve close if cam is pushing it open? A hydraulic lifter only moves so far, and I think they have solid liftersj, but I could be wrong on that. Not saying your wrong, just curious. Thanks.

 

[djones]

It's an exhaust valve located in the exhaust system not in the engine, sometimes referred to as en exhaust brake. The biggest problem with hydraulic brakes is the age and climate that they were previously operated in. Anything past 10 years of age are susceptible to rust and rot and require good inspections of the lines and seals. Most of the hydraulic brakes on diesel engines also have an electric motor back up system in case of belt/pump failure. Since most of the duty with boom trucks is stationary hydraulic brakes are just fine. Air brakes are great but here in NY it also requires that all operators be licensed certified in air brake operations from the State. Another hassle we don't need.

 

[les-or-more]

It's an exhaust valve located in the exhaust system not in the engine, sometimes referred to as en exhaust brake. The biggest problem with hydraulic brakes is the age and climate that they were previously operated in. Anything past 10 years of age are susceptible to rust and rot and require good inspections of the lines and seals. Most of the hydraulic brakes on diesel engines also have an electric motor back up system in case of belt/pump failure. Since most of the duty with boom trucks is stationary hydraulic brakes are just fine. Air brakes are great but here in NY it also requires that all operators be licensed certified in air brake operations from the State. Another hassle we don't need.

The exhaust brake is a butterfly in the exhaust to retard flow, an engine brake is internal of the engine. Engine brakes open the exhaust valves just before firing to use compression, then close the valves to take advantage of vaccum on the down cycle of the piston. Normally you can select how much braking you want by choosing how many pairs of cylinders are used for braking. The valves are disconnected via the rocker arm I believe.

 

[lego1970]

The exhaust brake is a butterfly in the exhaust to retard flow, an engine brake is internal of the engine. Engine brakes open the exhaust valves just before firing to use compression, then close the valves to take advantage of vaccum on the down cycle of the piston. Normally you can select how much braking you want by choosing how many pairs of cylinders are used for braking. The valves are disconnected via the rocker arm I believe.

That would make sense. Yes, your right, you can select 2,4, or 6 cylinders.

 

[jandh@amtelecom]

I thought BHP was something different. It's like hp w/out the accesaries. I think my old detroit 500 was 500hp/1650 tq but only around 380hp/1000 tq worth of retardation. Also how does a valve close if cam is pushing it open? A hydraulic lifter only moves so far, and I think they have solid liftersj, but I could be wrong on that. Not saying your wrong, just curious. Thanks.

When an engine is outfitted with an exhaust brake, jake brake, engine brake etc. there is an adaptor fitted between the engine rocker shaft housing and the valve cover. There are collapsible solenoids like lifters connecting to the exhaust valves only, that in normal operation move with the cam lifters, and when the engine is to be braking, these solenoids open up, dropping the engine oil trapped inside, allowing the exhaust valve to remain unopened. When this occurs, the burnt compression gases come up against the compression chamber and recompress, causing braking to occur.
Regards
Jake

 

[lego1970]

When an engine is outfitted with an exhaust brake, jake brake, engine brake etc. there is an adaptor fitted between the engine rocker shaft housing and the valve cover. There are collapsible solenoids like lifters connecting to the exhaust valves only, that in normal operation move with the cam lifters, and when the engine is to be braking, these solenoids open up, dropping the engine oil trapped inside, allowing the exhaust valve to remain unopened. When this occurs, the burnt compression gases come up against the compression chamber and recompress, causing braking to occur.
Regards
Jake

Got it...Thanks. When I used to have my truck overhead done every year at the shop, I remember seeing those black soleniods/coil looking things but I never knew that could close a valve, I just assumed they could only keep a valve open. Thanks again.

Sorry for getting the thread off the main topic.

 

[Blakesmaster]

Sorry for getting the thread off the main topic.

Don't be sorry, this is interesting stuff. Never knew how a jake worked before. There's no jake on this truck though, just the hyd brakes. From most guys I talked to they're less desirable than air but not a deal breaker by any means. I doubt the few hundred pound difference of a diesel vs. gas engine is of any significance on a truck this size either.

 

[jandh@amtelecom]

Got it...Thanks. When I used to have my truck overhead done every year at the shop, I remember seeing those black soleniods/coil looking things but I never knew that could close a valve, I just assumed they could only keep a valve open. Thanks again.

Sorry for getting the thread off the main topic.

No probs. Maybe it'll help some one make a decision sometime
:smile2::smile2:

 

[utilityman]

I would not buy a heavy truck with hydrualic brakes. If you blow a brake line with a heavy truck you will have a hard time bringing it to a stop.
On the other hand if you loose air pressure with air brakes the maxi breaks will be applied and stop the vehical. (If kept properly adjusted)

Also unless the hydraulic brakes have a micolock type system for parking I would not want to be 60' in the air depending on just the small emergency brake cable to hold the truck.
With properly adjusted air brakes the vehical will stay where you want it due to the maxi brakes being applied.

 

[Mikecutstrees]

Also unless the hydraulic brakes have a micolock type system for parking I would not want to be 60' in the air depending on just the small emergency brake cable to hold the truck.
With properly adjusted air brakes the vehical will stay where you want it due to the maxi brakes being applied.

Chocks....

 

[mckeetree]

Don't be sorry, this is interesting stuff. Never knew how a jake worked before. There's no jake on this truck though, just the hyd brakes. From most guys I talked to they're less desirable than air but not a deal breaker by any means. I doubt the few hundred pound difference of a diesel vs. gas engine is of any significance on a truck this size either.

Do what you want to, Blakes. You always did have your little mind made up before you posted some question anyways.

 

[treevet]

I got no air on my big Teco 70 footer and no problemo.

You gonna have to break down and get a CDL if you get those air brakes Bud.