7 speed has gotta go

[mackncheese]

Got a 7 sp 2070B in a 1999 RD 690 S with a 400hp E7. I love the truck but hate the transmission. Would like a 13 or 18 speed. The truck is a low mileage and in very nice shape and I got it pretty cheap. I know I will have to change the rear gears as mine are 5:32. I realize all of this will be expensive but I have been looking at trading the truck in and can't find a truck in similar shape as mine for close to the money. My question is how complicated is this swap. A parts guy at a Mack dealer acts like I am crazy for even considering this. Thanks for your time.

[pmolitor]

what do you hate about it? I've been considering getting one.

[David]

The big step between direct and overdrive is why everyone started specking roadrangers in the nineties. You might consider looking for a wreck and sell off the parts you don't need.

[mackncheese]

The space or step between all gears is too much. I pull a 20 ton tag with a 160 trackhoe in a hilly region and it is really sluggish. even on a pretty flat road in 5th you can watch the pyro temp rise. I think fuel mileage will improve but I realize there will be no return on this "investment". I just don't enjoy driving a truck that won't go. I have a 79 Ford LTL with a 400 big cam and a 13 speed and that truck really pulls. The Ford is old and rough so the Mack is the main truck.

[fullfuel01]

I hate 7 speeds. Never came accross one that was shifting good. Worst mack tranny in my opinion.

[mackmack]

I agree. My 99 RD690 has a 7 speed with a 350 Mack engine and under load goes from 0 to 60 in about three days.

[rsb502]

I would swap it out for another Mack trans, with gears as low as yours you can go to a std range trans the low in a T313LR or T318LR would just be wasted. Remember the old LTL with the 400 Cummins is going to pull better eaverything else being close to equal, your comparing a 14 liter engine to a 12 liter engine. Your egg's shouldn't climb over 900 with a stock 400 no matter what the trans or rears and especially not with rears in the 5's, that's a lot of torque multiplication. I would recommend checking the engine out first, if your egt's are getting high on a stock 400 with low gears your probably not getting enough air to the engine, check for boost leaks and other issues before you swap your trans. I agree the gear steps in a 7 speed are pretty ridiculous but with 5.32 rears and a 400 I find it hard to believe it doesn't pull good. I've run tri axle Mack RD dumps with 350hp, 8LL, and 4.42 rears on tall 24.5 rubber and they ran fine around 74000#, mind you 460's run better but my poi t being your not heavy enough to be that bad off with 5.32 rears.

[slpwlker]

Hell but there is a difference from an 8LL to a 7. my recolection is the 7 speed is a 5 speed with 2 gears in lo. Moved a mixer with one wasn't bad for the little I drove it. But I would say it is a flat ground trans at best.

[mackncheese]

Thanks all of you. Yes, it basically is a 5 speed with 2 compound lows. I have never seen the EGT over 1000. My boost is as high as 28lbs. The truck was originally a 300hp E7 VMAC lll that I had a dealer modify to a 400 hp. I assume this swap has been done before.

[Dirtymilkman]

You poor guy. I had that seven speed in a 89 R model. It grossed 85,000 and that shift from 6 to 7 was terrible. For some reason we also had lots of clutch wear, and we even switched drivers in that truck to see if it'd make a difference. For rear ends you can buy a whole back "cutoff" for $1500. As for the tranny, I put a 9spd in mine and it was so much better

[russoniellov]

Do the swap you won't regret it.

[RFCDrum]

My least favourite trans. The first Mack I drove was an 89 RD 690, 300 with the 7.

[GreenGiant2]

2070 and 2080 trans suck for running the road and climbing hills. I have a 2080 from stock and I would love to change it. if you have a lot of hills that you pull i would go with an 18 so you can split the bottom for off road.

gg2

[rsb502]

Egt still shouldn't climb on flat ground definitely not to 1000, and 28# of manifold press sounds low for a Vmac 3 300 or 400hp engine seems it should be closer to 34, my 400 was anyway.

[RowdyRebel]

Why not just add an aux trans? That would let you "split" the gears you've got now, give you another OD to compensate for those low rear gears...biggest downside would be the extra weight.

...just a thought.

[storkmack]

I have never ran one, but I haven't meet anyone that did, and liked it.

[GreenGiant2]

there is a BIG jump between 4th and 5th. your either lugging it or flat to the floor.

[farmer52]

Is the 7 to 8 split the same as the T2050?

[mackncheese]

I am in Virginia, can anyone of you recommend a good dealer or independent to do the work for me that is in Virginia?

[j hancock]

Could try Stricklands in Cana, VA. They have a salvage yard and shop and the father is big into Macks and the kid is into KW.

(276) 755-4429

[GreenGiant2]

you drive it like a straight 5. on the 2070 , 1st and 2nd split button down, are used for off road deep red. on the 2080 1,2,3 button down off road but you can use all 5 if need be. not recommended.

[Lmackattack]

Hated the 2060/2070/2080 transmissions. All seamed to be behind a low rpm engine with real slow rear ends. It gave you no options besides replace the trans,the rear ends and up the rpm to 2100.

At work we have a RD lowboy truck e7 400 with a 8LL and 4.17 rears. That truck pulls 100k+ with ease. Only thing better would be a trans with more reverse gears.

[rsb502]

More reverse gears? you have 3 already! lol

[2stacksuperdog]

ill take a 6 speed any day over a 8LL. Low gear in a 8LL is like 1D in a 6

[pmolitor]

I think he means more usable reverse gears.lol my 9LL drives me nuts trying to back up. of course I'm usually shifting gears backing up with my 6 speed. if the 6 speed just had a small overdrive it would be perfect.