I don't know what to title this...

[Goofyexponent]

Ok, at work we have 5 trucks, but only two are involved here.

Truck A: Donnie's truck.

L9000 Ford, 855 Cummins, 15 direct, 3.90's in the rears....old 38 housings that we had apart and KNOW we put 3.90's in her.

Truck B: My truck

L9000 Ford, 3406B Cat, 15 direct and 3.55's in the rears....again, we put the 3.55's in her so we KNOW it's 3.55's.

The Story:

We were both climbing out of Fall River onto the 118 Southbound. I was in front and smokin' away. I shifted into high gear and was at about 1900 RPM and I looked in the driver's mirror to see Donnie come flying up behind me, pull out beside me, shift into high gear, and pull away. I was into the govenor at 2000 RPM and he was into the govenor at 2100 RPM when he passed me.

The problem.....I have 3.55's and he has 3.90's. We both have a 15 direct. With 3.55's I should outrun him...not by much, but I should have stayed in front.

Why did he pass me with the same trans and lower rearend gears?

I know a direct is supposed to mean direct, but is it possible to have a 15 OD with the direct shift pattern?

I know what you're thinking....15 speed....yes, we are old school..

The 1985 we have has the inverted shift pattern 15 (15OD) and 4.63's that will outrun truck A (Donnie's truck) on flat ground and not fall far behind on the hills.

Am I making sense?

Didn't think so....

Were there different final drive gears for a 15 direct?

 

[nevrenufhp]

He may not be telling you he has big injectors, a 0 button, and a huge turbo.
Maybe its time to back the fuel screws all the way out, and upgrade the turbo on the B.

 

[Goofyexponent]

He may not be telling you he has big injectors, a 0 button, and a huge turbo.
Maybe its time to back the fuel screws all the way out, and upgrade the turbo on the B.

But the problem isn't in horsepower, the power is in gearing. If I had 3.55's and he had 3.90's, I should be able to outrun his truck at top end if we both have the same transmission.

I am going to pull the model numbers off the transmissions today as the trucks are both parked side by side at the quarry.....might give me some numbers to work with.

 

[Freight_Train]

Betcha he has his governor tweeked.You can turn the snot out of a cummins for a little while.You was turning 2000RPM but he might have been twisting that Cummins 2300RPMs.

 

[nevrenufhp]

I see what you're saying now.
There's guys running the B Cats to 2300, and even more. I've even heard of 2700 on a couple. Add that to some good gears, and you'll be top dog.

 

[Dieselcrawler]

also u didnt say anything bout tires. does it have tall or short rubber on it? going from tall rubber to short rubber is almost changing one gear set. ie 390 would be 373 with tall rubber installed where short would be

 

[Goofyexponent]

also u didnt say anything bout tires. does it have tall or short rubber on it? going from tall rubber to short rubber is almost changing one gear set. ie 390 would be 373 with tall rubber installed where short would be

Well, I upped my govenor to 2300, but he still swamps me.

We both have 11R22.5 rubber, all new recaps on both trucks.

It's like 2 IDI's having a ZF, one with 3.55's and one with 4.10's......and the one with 4.10's having more top end than the one with 3.55's..I don't get it.

The tags are gone off both transmissions.

 

[spg]

The other part of this is the weight of each truck with load. Lighter load faster. Heavier load slower.

 

[FordGuy100]

He is saying, at the govenor, since each tranny is direct, and he has 3.55, his truck should be going faster at the governed speed.

Something is fishy.

 

[Goofyexponent]

He is saying, at the govenor, since each tranny is direct, and he has 3.55, his truck should be going faster at the governed speed.

Something is fishy.

Exactly! My truck will SWAMP his off the line. My 425 tune on the 3406B just has WAY more pep. Big cloud of black and I'm gone.

I run to top gear, hit the govenor, and he passes me while shifting into HIS high gear....I am already in high gear as he shifts into his high gear and passes me.

 

[OLDBULL8]

A couple years ago my boss bought a Ford drop frame, the stronger type and started building a truck. He took a 3406B 350HP and dropped it off to Cat. Told them to rebuild it to 425HP specs and call him when it was done. The transmission, a 15 direct, was dropped off at another shop and COMPLETELY rebuilt along with both 3.55 geared rearends.

Could this be the problem?

 

[RLDSL]

Are you positive both boxes are 15 direct? Some older boxes came with some strange mixed up combinations of shift patterns that can make it near impossible to tell sometimes. If a rebuilt box was slipped into one of them, it's very possible that one of them got an overdrive box.
I had a place drop a 13 direct in my kenworth ..by *mistake*, so they said, one time due to the same reason, and it had to be yanked back out and made right.( I made the punk get in the jump seat and watch the speedometer as it topped out , but it wouldn't reach 118 anymore... after he got through cleaning out his underwear he agreed to put the right tranny in