"J" brakes in a diesel

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75sling

Well-known member
Joined
Sep 13, 2009
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Location
Southern NH
Hello Everyone,

Well as a newbie, I got a chance to drive a Class A diesel.  As I was coming down a hill, I noticed something like "downshifting" in a car, in that the MH started to slow down.  I asked and I was told it's the "J" Brakes kicking in (or Jay brakes???) ....I was shown the system from uoutside the MH and it looked like a cylinder about 7 inches in diameter and about 16 inches tall....

is this something that is in common in MH's?

thanks
75sling
 
The Jake Brake is AWESOME !!

I don't know how common they are in motorhomes, but every big rig on the road has one. They assist them in slowing down when needed.

If you have one, it's a BIG plus !!
 
Don't know what coach you were in but what you describe sounds more like an exhust brake not a true Jacobs brake as used on trucks and busses. The difference is, a "Jake" brake is a device mounted to the top of the valve train inside the engine and an exhust brake is a valve mounted in the exhust pipe to close off the exhust. Both do the same job, just differently. Most Diesel coach's will have them.

Jerry
 
It could be a Jacobs Extarder exhaust brake, also sometimes referred to (mistakenly) as a Jake brake.
 
You just discovered the BEST feature of a DIESEL engine, a great way to control your downhill speed.  For us, if a new coach offered 100 more HP or a Jake Brake that was twice as efficient slowing you on the down hill, we would opt for the more efficient Jake brake.  Some folks may be surprised but we are more interested in good control going downhill than how fast we can go uphill.

JerryF
 
As others have said, it sounds like it might have been an exhaust brake aka PacBrake. PacBrakes are usually located in line with the exhaust system, whereas most of the parts for a Jake Brake, except for a control module and one or more switches, are internal to the engine.

Just for clarification, Jacobs, the manufacturer of the Jake Brake, also makes an exhaust brake.

As I was coming down a hill, I noticed something like "downshifting" in a car, in that the MH started to slow down.
Click to expand...

Irrespective of the braking system, Alison automatic transmissions downshift in response to taking your foot off the accelerator.

I was shown the system from uoutside the MH and it looked like a cylinder about 7 inches in diameter and about 16 inches tall....
Click to expand...

Where was this cylinder? I can't imagine what they showed you - maybe the air filter?
 
Tom said:
Where was this cylinder? I can't imagine what they showed you - maybe the air filter?
Click to expand...

My guess it was the air tank used to store the air to pressurize the brake
 
Maybe I'm confused, but it doesn't take much.

I thought/assumed that the Jake Brake was electrically operated via solenoids on the valves. I checked out their parts and installation procedures, and they didn't show or mention an air cylinder. When the CAT mechanic had the valve covers off the big CATs in our boat, he showed me where the Jake Brake solenoids go if the same engine was used in a commercial truck on the road.
 
I think he probably showed them the actuator for the exhaust brake that is usually mounted in the pipe aft of the turbo.
 
jerryarlyne said:
I think he probably showed them the actuator for the exhaust brake that is usually mounted in the pipe aft of the turbo.
Click to expand...

That's what I meant ... I just couldn't think of the right word

;D
 
Hi All,

Yes, i confirmed it is a PacBrake/Exhaust brake.

The cylinder to which i referred is located on the pass side of the mh in one of the storage compartments. It is a 2004 Fleetwood Discovery 39S.

I will put a deposit on it this weekend via a private sale and hopefully the financing will go through so that i will have it just in time to store it for the winter.... :)

Will let you know how it turns out.

Best
75sling

 
If it's a Pac Brake, then it's definitely not a Jake Brake.

Bem sue you know what you're buying  ;)
 
All this jabber about Jake Brake vs Pac Brake vs Extarder is all so much technobabble. They all do the same thing: slow down the coach substantially without using the brakes when you take your foot off the gas, a major feature on many diesel powered coaches. It used to be an option but in recent years has become pretty much standard on diesel pushers. You will LOVE it - provides much more speed reduction than doing the same thing with a gas engine. Especially useful on steep down hills.
 
The PacBrake is a small lever mounted on the engine, not in a bay. Sounds like you have one of those salesmen who haven't a clue about what they are selling.
 
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