Community Forums

scep · 11-01-2014, 08:05 PM

(98 8.3) I swapped the air cylinder out as it had seized over the years. I have ran with the bed lifted and watched as the switch is depressed that the cylinder closes the butterfly valve but it just doesnt have any effect on slowing it down.

Theres no cracks in the exhaust manifold that I can see. I almost suspect someone took the butterfly plate off of the brake. But thats just too odd.

Any guesses?

KIX · 11-01-2014, 08:14 PM

Look for soot. Soot is a tell-tale for exhaust leakage.

BFlinn181 · 11-01-2014, 09:30 PM

I think you'll have to dismantle the exhaust on either side of the engine brake to get an eye on the butterfly flap. Are you sure the shaft is actually rotating when the cylinder pushes? If the shaft is frozen, perhaps the lever is just sliding on the shaft without turning it.

Tony Lee · 11-02-2014, 04:47 AM

Is your transmission selecting downwards at the same time.

If you are in a high gear coming over the top of the hill, you will feel very little braking because the transmission won't actually downshift and the engine revs are low so the exhaust brake doesn't appear to add much. Often need to manually brake until the transmission can drop a gear or two and then the revs increase and the exhaust brake becomes effective.

H. Miller · 11-02-2014, 04:49 AM

At what speed are you doing all this??? Ours shows very little "stopping power" at 55-60 mph or higher.

Mr_D · 11-02-2014, 07:53 PM

Quote:

Originally Posted by H. Miller

At what speed are you doing all this??? Ours shows very little "stopping power" at 55-60 mph or higher.

Same with ours, the trans is programmed to preselect 2nd gear but we have to slow down for the trans to drop down to 4th before we feel much, if any, retarding effect.

bobguigley · 11-03-2014, 08:48 PM

I had the same sense that my engine brake wasn't very effective at higher speeds and was wondering if it was working.

From what was posted above it seems that what our MH brake is demonstrating may normal function….afterall it's not a jake brake.

Ray,IN · 11-03-2014, 09:42 PM

The TCM/ECM interface will not allow downshifting until it reaches a set-point where the engine will not over-rev. You may select 3rd gear, but it will not downshift until it reaches a safe shift-point RPM. The when it does downshift, it does so with a bang. I allow the TCM to select the correct gears at it's scheduled RPM/time, unless I'm on a steep downgrade at low speeds, then I select 2nd gear. The RPM's must be over 1,800 before you really feel the PacBrake, but over 2,000 RPM is where the PacBrake works best. I think the TCM's automatic up-shift point is 2,600 RPM, to keep from destroying the engine. Allow it to do that and then you must rely on your service brakes for control until you slow enough for the RPM's to allow downshifting again.

I agree with BFlynn, check the butterfly shaft for proper rotation. Use special PacBrake high-temperature grease on the shaft bushings to prevent it from galling.