Can using the factory exhust brake hurt the engine?
I have a C-5500 with a Allison 5 speed, and a LLY 2005 Duramax. When traveling down a grade with a load I observe the RPM gauge get as high as 3500 RPM. Also when traveling on a flat and by letting of the fuel peddel I see the RPM increase. Thanks in advance for all information and advice. Lou. I hope I wrote this clear.

All perfectly normal with Allison and exhaust brake. You can go to Allisons website and get a lot of info.

Yes it is normal. When the exhaust brake is activated, the transmission downshifts to 5th gear (4th gear with the 5 speed ali) automatically. The only way I could see you possibly hurting anything is if you were going downhill too fast to begin with and the engine RPM was already maxed out when you lifted the accelerator pedal and the exhaust brake came on. You shouldn't let the speed/RPM get up that high pulling a load downhill in the first place in my opinion.

the ali will not over down shift it self this one of the built programs of the ali.

On a down hill grade I always go slow. I am in the 62 MPH drivers department on the flat and 50 to 55 on the down hill. Thanks for your help. And sharing your knowledge. This C-5500 is under a motor home and I tow a F-250 crew cab with tools. Thanks again. Lou

The 3500 RPM redline is with the engine under load.
The 3500-4800 RPM shaded redline is used when Grade-Braking.
See explaination on Allison link below:

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=SA3931EN.pdf

Been meaning to ask this question. Do you leave the brake switched on all of the time or just when hauling? Or do you use it only when in the hills? Just curious if there was any reason not to use it all of the time? Thanks!

I leave mine off,only use when going down steep grades like Mont Eagle in Tn.Every time I heavley use the exhaust brake I lose a set of injectors,Idont know why.animal

I used the exhaust brake when going down a grade. On the flat I turn it off due the increase engine RPM when I let off on the fuel peddle. The above, is unless I am in heavy stop and go highway driving them I leave the E/B in the on position. Going across the flat desert or valleys I leave the E/B in the off position. Lou

It kills mpg b/c u have no cost time. I use my when I loaded heavy or heading downhill I see no need for it when runnin light