Out for a drive:

[Rob]

I drove an '89 R690T with an EM6-250L that had a 5 speed. I believe 275 and 300 hp versions were available at that time.

I was wondering how the 9 speed worked with a torque curve designed for a 5 spd. I thought if the engine were allowed to lug down as usual, dropping a gear on the 9 speed would bring it back up to the middle of the power band and allow a higher road speed. I've read however (possibly on here) that it just doesn't work wel as a 5 spd.

I can't say much about the engine as I really don't know what it is but don't believe it is original to the truck, or has been worked on. The heads and valve covers are the red color my 1980 R612ST is, yet the block is dark gray. I was told by the deceased owner, (prior to his demise) the engine had been rebuilt. The pump itself has a "Remack" sticker on it so it's anyone's guess.

If I had to guess after working on this thing I'd say the pump is calibrated for the "Maxidyne" style torque curve. It was very responsive in the low rpm's and did not seem to be really linear in pull as the rpm's raised. It was however very manageable. With the trailer loaded it still didn't take hardly any throttle to get the truck moving from dead stop with no clutch slippage, or hopping. It did however, (now that I think about it) really "peak up" quickly as you would run out of gear. It drove so much different loaded from empty and I had limited time to familiarize myself that I think all will work together.

At first I didn't like how "low" the lower gears were as they run out very fast. Loaded was a whole different story and I quickly gained an appreciation for them. I do like the transmission better than I do either an RTO-125413, or RTO-14613 although this Mack trans takes a bit more "oomph" to pull out, and into the gear selections.

Rob

[Green Dash]

Have you considered skipping gears on the low side when light?

With an empty on a 10 speed, I'll start in 3rd, go to 5th, then 6th or 7th-no skipping on the high side, but you can skip "into" the high side. Because of the bigger step between gears, rpms need to drop as with a Maxidyne.

Forgive me if you already knew all this.

[Rob]

Have you considered skipping gears on the low side when light?

With an empty on a 10 speed, I'll start in 3rd, go to 5th, then 6th or 7th-no skipping on the high side, but you can skip "into" the high side. Because of the bigger step between gears, rpms need to drop as with a Maxidyne.

Forgive me if you already knew all this.

No problem Jim and I appreciate the insight. I was starting to take off in third when bobtail and second was alright with the trailer empty. I don't like to punish a clutch myself and this could be a problem in the future with a new and inexperienced driver so didn't mention skipping anything but stuck to a textbook approach to build upon. I did teach him to use the clutch only to start off, and unload the driveline during a downshift and other than starting and stopping leave it alone. There will be several hours of learing taking place with an empty trailer for a while I'm certain.

Thanks,

Rob

[Green Dash]

Okay, just checking. I work with drivers who started with the company as dockworkers 20+ years ago and have been driving for 15 years and have never heard of floating gears or progressive shifting because they've had no exposure to anything outside the company. I skipped gears with an empty while doing a ride along when I first started at PO and the driver I was with thought I was screwing up even though the shifts were as smooth as silk. I won't do anything that will cause unnecessary stress on the driveline.