new to me mack with 7sp (Did I make a mistake)

[mackncheese]

Been wanting a Mack Dump for a long time and finally bought a 1999 RD 690s. It has a E7 Etech that originally was 300hp but I had the Mack dealer uprate the engine to 400hp. The final drive gear is 5.32. I have only driven the truck twice (empty) but I can tell the difference in the increased horsepower. My only potential issue is the 7 speed transmission(2070). I am not shifting good yet but the gears seem to fall in at about 8-900 RPM then the rpms are slow to climb. Its making me wonder if when loaded it will always lug till it gets up to 1200 or so? I live in a somewhat mountainous area and have a 20 ton tag and will tow a 160 Trackhoe at times and I will be disappointed if it doesn't pull strong at the lower rpms. I have a LTL 9000 Ford with a 400 big cam with a 13 speed and it pulls really well. I just hope the Mack won't disappoint me. Do you guys think that the 7sp was a mistake for my application.

Edited March 1, 2012 by mackncheese

[Joe Ditchkus]

800 RPM is too low to lug down. All the constant torque engines I ever had 1200-1300 was downshift point. When your truck was built with 300 HP and 7 speed it was made to lug down 12-1300 RPM,with engine turned up to 400 Hp power curve could be different and you could possibly need more gears to work engine properly. I am trying to explain this without knowing any other information. Others will explain more thorough;ly. Joe D.

[mackncheese]

Joe thanks for the reply. When I first bought the truck I had to drive it 2 hours to the Mack dealer. the truck was not modified at this point and was 300 hp and it/I was shifting the same way and seemed to fall into gear at 800 or so. In other words the shifting behavior didn't change (at least that I can notice) when we uprated it to 400 hp.

[David]

I've never liked the huge step between direct and overdrive. You can't change to another trans with more gears without loosing top speed. Your at .6 overdrive now and no other trans comes close to that.

[GearheadGrrrl]

The "uprate" to "400 HP" sounds fishy... 300 HP was the top rating for a Maxidyne 6 cylinder until I believe 2004, when Mack bumped the power up to 370 HP at governed speed and 405 HP peak. IIRC there were a bunch of other changes to the engines besides just a software update. As for operating range, a vocational truck like the RD would probably have the standard Maxidyne with an operating range from 1200 to 2100 RPM. If that's what you have, downshift at 1200 and upshift at 2100. This assumes they didn't totally screw up the power curve with their "uprate". There's a slight chance you've got a low RPM maxidyne with an operating range from 1020 to 1800 RPM, but those were mostly installed in highway tractors.

[Lmackattack]

THE MAXIDYNE was a 1200-2100 RPM enigne. It was intended to use 5 or 6 forward gears as it had a big flat torque curve. this was good for flat land and limited shifting. the 400HP had a shorter torque range and was intended to have more gears to always keep it in the sweet spot.

In my opinion..your 7 speed is basicly just a 5 speed with 2 extra low gears. it does not give you the needed gears to keep the engine RPMs where they need to be. as soon as the RPMs fall and you need to down shift you will have to wait untill about 1300 RPM before you can downshift and catch the next gear. I think the new program may not be right for that transmission. A 9 or 13 speed would be better as it has less of a RPM drop between gears.

Just my .02

Trent