Community Forums

SSteve · 03-22-2013, 05:15 PM

I recently discovered my engine brake was not working, and I suspect it never has worked. The electrical connector for the brake air solenoid was not (and it looks like was never) connected to it's mate.

After 40K miles, I sure wish I'd have known this sooner.

I've never owned a diesel before and am wondering, how should the rig behave when using the engine brake with the trans downshift vs just the downshift (all I've had)? In other words, what should I feel and hear?

Thanks
Steve

1ciderdog · 03-22-2013, 06:29 PM

I don't hear a change in engine noise but there is a definite change in momentum when the exhaust brake engages unless the engine is above a speed that will not allow the transmission to shift down. On mine the exhaust brake is more noticeable at speed under (say) 50 mph. The transmission gear indicator shows it shifts to second - it doesn't but that is the target gear.

Hooligan · 03-22-2013, 08:33 PM

Steve: My Cummins has a PacBrake, when it is engaged it is very noticeable. Leaving the interstate, on the exit ramp at freeway speed, the PacBrake will bring the Mh almost to stop by the end of the ramp. It disengages below 10mph.
At speed, engaging the PacBrake quickly slows the Rv, the transmission will downshift and engine rpm will build to almost redline and then decrease as speed decreases, as soon as the tranny can downshift w/o overspeeding the engine it will go to the next lower gear. The increase in engine noise is almost the same as pulling a grade.

SSteve · 03-22-2013, 09:46 PM

Quote:

I don't hear a change in engine noise but there is a definite change in momentum when the exhaust brake engages unless the engine is above a speed that will not allow the transmission to shift down. On mine the exhaust brake is more noticeable at speed under (say) 50 mph. The transmission gear indicator shows it shifts to second - it doesn't but that is the target gear.

1cinderdog,

That's seems to be EXACTLY what I was experiencing.

But, the more I think about it, it seems the engine (or pac) brake should function regardless of MPH. The transmission has to stay within it's programmed range and that is governed by MPH.

Quote:

Leaving the interstate, on the exit ramp at freeway speed, the PacBrake will bring the Mh almost to stop by the end of the ramp. It disengages below 10mph.

Hooligan,

In your example, was that exit ramp uphill, downhill or level?

I only ask because my rig would slow significantly on an uphill (depending on the grade), but not a level or downhill. I now know that my trans was doing the work.

Thanks for the replies
Steve

1ciderdog · 03-23-2013, 10:39 AM

Quote:

Originally Posted by SSteve

1cinderdog,

That's seems to be EXACTLY what I was experiencing.

But, the more I think about it, it seems the engine (or pac) brake should function regardless of MPH. The transmission has to stay within it's programmed range and that is governed by MPH.

Steve

Steve - Yes, the exhaust brake should work at all speeds above 10 or 15 mph but it is less effective at higher speeds because of the transmission gearing. If you are above a speed that won't allow the transmission to shift down the exhaust is hardly noticeable. If I'm driving at 65 mph and use the exhaust brake the effect is hardly noticeable until slow enough for the transmission to down shift.

I'd suggest you try driving about 50 mph with the exhaust brake on/off switch in the off position then down shift the transmission until the engine rpms are well above 2000. Remove your foot from the fuel pedal and the RV starts to slow. Now switch the on/off exhaust brake switch to the on position and you should notice a significant difference in the slowing of the RV if the exhaust brake is functioning correctly.
Bob

Hooligan · 03-23-2013, 12:43 PM

Quote:

Originally Posted by SSteve

Hooligan,
In your example, was that exit ramp uphill, downhill or level?

I only ask because my rig would slow significantly on an uphill (depending on the grade), but not a level or downhill. I now know that my trans was doing the work.

Steve

Even on a downhill exit, I seldom have to use the service brake. On a long exit I often have to release the PacBrake or add a little throttle. May be worthwhile to ride in a MH that has a good PacBrake... (Excuse to-Test drive a new one...

)

SSteve · 03-23-2013, 03:42 PM

We're hitting the road in 10 or so days, so I'll get the opportunity to try the now functional (hopefully) pac-brake. Now I know what to look for.

Thanks much for helpful info!
Steve

Tony Lee · 03-23-2013, 09:57 PM

Since it may never have operated, it might pay to exercise it manually and at the same time make sure it has been lubricated with the correct high temperature lubricant.

Easiest way might be to disconnect that connector again and run a couple of leads from the nearest 12V battery to the sockets of the connector. Solenoid valve operation will be obvious but need to check visually to make sure the pacbrake butterfly valve is operating. Need to have normal air pressure up so the system can work

SSteve · 03-24-2013, 07:16 AM

Tony,

Right you are!

That's actually how I found the REAL cause. After reading another post about engine brake failures, I learned the brake requires periodic lubrication. I obtained a bottle of Pac-Brake lube (4 oz for $10) and proceded to lube.

Just for giggles, I tried to move the brake actuator before applying the lube. To my surprise, the actuator moved smoothly. I applied the lube and decided to look further and that's when I found the connector issue.

When we head out next week, hopefully all will work well. I do have my doubts about the connector itself, what with all the junk each end had packed in. If the brake still has issues, I'll probably remove the connector and splice the wires.

Wayne M · 03-24-2013, 08:22 AM

Exhaust brakes only retard power in a diesel engine and hold the compression in the engine and slow the crankshaft rotation. This will slow the engine. The Exhaust brake doesn't produce much of a sound like engine brakes. The exhaust brake is designed to be used all the time when used in accordance with MFG's recommendations. The exhaust brake will save you money in brake service.

With that said, typically when the exhaust brake is used the transmission is programmed to drop to a specific gear. The only time that the transmission will go into a lower gear is when the engine is at the correct RPM. So when the exhaust brake is applied the compressions reduces the crankshaft speed and when the speed gets down to an acceptable level the transmission will shift. When this happens you will notice a rapid increase in RPM and a decrease in speed with engine noise increasing. PAC Brakes are typically exhaust brakes.

Engine brakes are commonly known as Jake brakes because the largest manufacturer is Jacobs Vehicle Systems. I'm not up on those but they do make a lot of noise.

I'm assuming you have an exhaust brake since you were able to lubricate the butterfly valve.

Google "how exhaust brakes work"

Go to Jacobs web site for engine brakes.

Happy trails.

Edited: p.s., found this: http://www.pacbrake.com/index.php?page=mechanics

Tony Lee · 03-24-2013, 09:41 PM

Quote:

I tried to move the brake actuator before applying the lube. To my surprise, the actuator moved smoothly. I applied the lube and decided to look further and that's when I found the connector issue.

When you say it moved smoothly, was there a fairly strong spring tension you had to struggle against or could you easily move it full movement by hand.

SSteve · 03-25-2013, 06:45 AM

OH yeah! Real strong spring. But, there was no roughness in the movement. I was expecting the assembly to be seized up.

Steve

Tony Lee · 03-25-2013, 10:09 AM

Still had the factory lubrication in place.

At least you now have a bit extra safety margin to play with when you come over the top of a mountain.

SSteve · 04-04-2013, 05:44 PM

Just an update.

We got back on the road yesterday. Alas, I forgot about the pac brake for the first 20 miles. I missed many opportunities to test it. After remembering, the next chance to test it provided a great demonstration. Even my wife noticed the braking difference.

Hooligan and 1ciderdog , the effect was just as you explained.

I hope Freightliner didn't miss this connection too often. I can't say how many times the extra braking I felt yesterday would have come in VERY handy.

Next week, I'll do a better job trying it out.

Thanks for the replies!
Steve