Been wanting a Mack for a long time and finally bought one. It is 1999 RD690S with a E7 ETECH (400HP) it has a 7sp transmission (2070) with a final drive of 5.32. The truck is in really good shape and it is Rolls Royce compared to my 79 LTL 9000. My potential problem is the 7sp. I am not shifting it good yet but you have to let the rpms drop to about 800 before it falls into gear then the rpms are slow to climb till it gets to 1200 or so. I am wondering when I put a load on it if it will always lug a little at the low rpms or once I get the hang of shifting that it won't be an issue. Why did they make a 7 speed? Why not give us a few more gears. My ford with a 400 big cam and a 13 speed pulls my 160 track hoe good and I will be disappointed if the Mack does not pull it as well. Let me know what you think. Thanks
Actually sound slike you are some how stuck in low range. My 96 granted has an 8LL but operating range is 12-1800.
a mack engine lugs lower and pulls deeper. you cant really drive one like a cummins or cat.
Never seen any engine yet, apart from pre-WW2 Cats, that will pull well from 800 RPM. The normal operating range of Mack engines is 1200-1900 RPM for economy engines and 1200-2100 RPM for the older, standard versions. If the engine is having to drop back to 800 RPM to engage the next gear, then something is seriously wrong. If this is happening on steep grades, because of rapid road speed decay, then you have to stick with the gear you're in, until you reach a flatter section of grade. I used to run an old 6 speed F-series Mack that was a two-stick tranny. The bottom 5 speeds were on the main stick. You kept the second stick in direct, and when you got to maximum RPM (2100) in 5th, you shifted the second stick to overdrive or 6th. With this setup, the biggest RPM drop was between 5th and 6th, because it was about a 38% overdrive. 5th would give you about 42mph, 6th gave you 58mph. Even with that kind of gap (5th to 6th), the RPM drop between 5th and 6th was only 900 RPM. I had to max out the RPM to 2100 in 5th and with the change to 6th, the RPM would come back to 1200 RPM. At that, the old 237 HP six would pull away happily, because maximum torque was at 1200 RPM. However, below 1100 RPM, the torque levels dropped dramatically. You need to find what is happening that is creating the problem of not engaging the next gear until 800 RPM. No diesel truck engine built since the 1950's will pull happily from 800 RPM. You may not be getting full RPM in the gear you're in, if the change point to the next gear is 800 RPM.
I agree with OzDozer.I owned dozens of Macks over the years and their hi-torque engines do not and are not designed to pull under 1200rpm's whether they are in front of a 5,6,8,12 or 13 speed transmission. Although I have never owned or worked on "we have our or gear shop and take in outside work" a 7 speed. I can't imagine lugging a Mack and not even a Cummins custom torque 270 or an N-14 525 to 800rpm's on a pull between gears.
7spd is goofy to drive, we have one in a water truck behind a Cummins. Takes a while to get the hang of it.
Thanks for the replys. I am getting used to it but I think I will always want more gears. I was driving the old ford pulling an empty tag trailer and my buddy was in the Mack in front of me and I could not keep up with him. He said he was getting the hang of it so maybe I will like it better as I get used to it. Other than the 7sp issue I love the truck.
I am in the same boat as far as wanting more gears. MY 690 has the 8ll with a 350 in front of her, pulling hills the LL is either to much or not enough. Got no other complaint than that really, she is getting 7.75 mpg!!
The Macks are a different beast to drive. I drove a DM600 with a 237 and 5 speed Maxitorque transmission for a couple years and it took some getting used to. On uphill grades you often get gear bouns as the engine rpms take too long to drop to catch the next gear. An engine brake can help with quicker shifts but you have to be very precise to avoid transmission damage. As the others mentioned, about 1200 rpm is where your upshift should drop to, that can be dificult climbing a hill.
The E-tec can be can be "arranged or RE-arranged" to suit your needs. All you need is a qualified Mack dealer with a laptop, I'm SURE, if you tell them the problem they can "reprogram" the tranny to the engine rpm's you need.
I own an 89' RD690 that has the same configuration yours does. The truck is older so they made some changes. No computers on mine that can be "reprogrammed". What I have learned is that the 7 speed is not easy to drive. You can not down shift climbing a hill easily when you are first learning to drive it. Find the correct gear at the bottom. Most hills can be climbed in 3rd and some you will need 2nd. Up shifting is also impossible while climbing a hill. The reason for this is the space between gears is so large that the road speed slows down to fast before you can down shift. Then you are stuck in 1st for the climb. Very slow process. It took me a year to learn before I could drive it well. The up side is the Mack RD690 are a very dependable truck and worth keeping. I own a RD688 also that has larger motor and Eaton 8LL that has been a good truck also. The new truck is very easy compared to the 690.
All great comments above. I think your going to like it once you get used to running and shifting it........MACK trucks are cool.