A Pacbrake Question

JDT · 02-07-2008, 08:05 AM

Read the question from redeldo and reminded me of something about how my Pacbrake works on my 05 Ambassador with the 330.

Mine has always disengaged as soon as the engine rpm's reach 2300. As soon as it drops below 2300 it will re-engage. It usually happens on long, steep downhills if it gains enough rpm's or on the first downshift in the transmission, which causes the rpm's to spike.

I have been told by Pacbrake, Monaco and Allison that this is normal and is protecting the engine from over reving but my argument has always been that 2300 is too low as I think the engine can go to 2600??? The brake works well except for this minor irritant.

Before I take it to a shop to see if the rev limit can be upped for the Pacbrake could those of you who have the same drivetrain tell me if yours does the same thing?

Thanks,

Jim

JDT · 02-07-2008, 08:05 AM

Read the question from redeldo and reminded me of something about how my Pacbrake works on my 05 Ambassador with the 330.

Mine has always disengaged as soon as the engine rpm's reach 2300. As soon as it drops below 2300 it will re-engage. It usually happens on long, steep downhills if it gains enough rpm's or on the first downshift in the transmission, which causes the rpm's to spike.

I have been told by Pacbrake, Monaco and Allison that this is normal and is protecting the engine from over reving but my argument has always been that 2300 is too low as I think the engine can go to 2600??? The brake works well except for this minor irritant.

Before I take it to a shop to see if the rev limit can be upped for the Pacbrake could those of you who have the same drivetrain tell me if yours does the same thing?

Thanks,

Jim

SilverBlivit · 02-07-2008, 02:32 PM

JDT
Mine does exactly the same: you described it perfectly. At about 2250 the PAC brake disengages and the transmission upshifts. Whether it is the Allison or the Pac brake controlling, I don't know. When this happens I have always assumed I was back to foot brake only and have never been keen about that with 6500lbs of tow vehicle behind me. So I use the foot brake to keep below the PAC Brake/ or Allison RPM threshold. The M & G tow brake now makes this a simple tap on the pedal.
Hope this helps.

Happycarz · 02-07-2008, 06:17 PM

I'm on my third Monaco ('93, '99, &'08) and all have upshifted between 2600-2700 rpm on extreme downhill grades. The Allison upshfts to keep engine from over revving. When I talked to Cummins at a rally, the rep said they are safe to 3000 rpm. Check with Allison for programming parameters. This is an Allison issue, not a PacBrake problem.

JDT · 02-07-2008, 07:20 PM

Thanks for the replies. I have also assumed it was an Allison issue, not Pacbrake.

I did install a Brakeswitch 2 years ago so all I have to do is tap the brake pedal to re-engage it. I think I'll just live with it for now.