Hi fellas, Recently in the Allison Section we had a discussion regarding grade braking in T/H mode. There were many points of view as you might expect. I personally don't like my engine going into the redline area even though the dealer, Allison and a few other people say it's ok or they think it's ok. I personally haul a$$ uphill but I go slow on the way down for safety reasons. At 55 or 60mph it would go into 3rd and about 4100rpm and would stay there unless I sped up or played with the accelerator. I decided to take it out of T/H and OD and slow it down with the brake occasionally to keep my speed around 55-60. This works fine for me and I curious if It's ok for the tranny. Also what are your opinions about running a 4 mile grade in third gear at 4100+rpms?...Your opinions would be greatly appreciated. My rig is in my sig that's the Lance and the boat attached....Cal

I have never hit that RPM. I have traveled the big hill going on the 395 (by Mono Lake) in Ca, and the most I have ever hit was 3000, and that was only for a second or so. That was while towing aprox 7k. Maintained speed between 50 & 55.


As far a a 4 mile grade doing 4100, I don't think I would feel to comfortable with that.


Bill

Hey Bill, that's far out. You know the Cuesta Grade on the 101 North of San Luis Obispo? I come down that towing my boat with the camper on and when my speed gets up to around 60 I ease on the brake and it shifts into 3rd and spins up to 4100rpm. Allison says "no worries it will shift into 4th at 4800rpm" Over on the lb7 topic, there is a thread in there. I have no clue how to pull that up but if you are interested in some other guys comments check it out. Look for Grade Brake question or something like that maybe a week ago....I was hoping one of the official site Techs would chime in and comment but that has happened yet.....Cal

Bill, It's in the Allison subject under "Help with Grade Braking" 8aug04

Cal,


I followed your link, and the method that you describe is exactly the method my dealer told me to use to activate the grade braking feature of the allison. I have towed multiple times over that pass, and I am familiar with the grade that you are refering to. Are you in T/H mode? I noticed that it will rev higher when there as it will wind it more before shifting. I am in T/H mode when I go through that pass. Others may say that they are comfortable with that RPM, Even if it is "windmilling" downhill with little or no load. I am not comfortable with that RPM. I have not had my ECM flashed either. It appears that you are not alone however. I am thinking that (and this is a shot in the dark), is it possible that the 4" exhaust is allowing the higher RPM. Less back pressure, better volumetric efficiency (more air flow). I don't know.


Bill

Bill, In T/H it will downshift into 3rd everytime I hit the brake on the way down between 55-60mph. I find that annoying and worrisome as it will stay in 3rd at 4100rpm the rest of the way down. Or if I let it run out, they say it will shift when it gets to 4800rpm. I haven't tested that yet. I circumvent that by taking it out of T/H and OD. at the top of the hill. Now I'm in 4th and I keep my speed down by using the truck and trailer brakes. I'm actually deactivating the Allison from automatically shifting into 3rd by taking it out of t/h. I'm not riding the brakes so I'm compfortable with that. I go to Lake Naciemiento a lot and I don't like seeing the tach in the RED area. Your taller tires might be just enough to keep you out of 3rd or the RED. I haven't a clue about the 4" exhaust's effect you mentioned. Good theory though!


I would like to here one of the Techs opinions about coasting in the RED zone of the tach.......Cal

RedApple........Hey Bill....There is gonna be a dyno day on 8/21 in Ontario see events and LA Dyno day or something like that. I'm gonna try to make it. Should be interesting! See how these guy Hop up their DMax's........Cal

Hadn't thought about the tires, but you may be on to something there.





Bill

Gruber, I too was alarmed the first time that my engine RPM's went into the red (4300). I talked to the GMC dealer about this high RPM condition. They said that it was not going to damage the engine. I then talked to an Allison tech (from Allison); he assured me that Allison was not going to program the transmission in a manor that would cause damage to the engine. The liability would get very expensive. This technician said that the absolute maximum RPM for the Duramax was 5,000. After 5,000 RPM's engine damage could occur. The transmission will shift at 4,800 RPM's. I have spoken to tech's from Detroit, Cat, and Navistar; the Allison will allow the engine RPM to raise above the rated RPM, however it will not allow the RPM to go to maximum RPM. They said that Rated and Maximum are two different numbers. I hope they know what they are talking about!http://www.dieselplace.com/forum/smileys/Ermm.gif

10851, There was another thread on this in the Towing section. What you say is the general consensus. I'm not sure myself but the thought scares me. I just can't see me letting it go in 3rd to 4800rpm! Whatever! I'm going to continue taking it out of OD and Using my brakes I'm certainly not abusing them and that's the cheapest replacement part. Picture yourself at the dealer telling him you didn't over rev it I was in T/H mode......Thanks for the info....Cal

10851, Read the one in the towing section. Yamahauler makes a good pitch on the latest post.....They've made a believer out of me..http://www.dieselplace.com/forum/smileys/Cool.gif