[TestDrive]

From MazdaMatt's posts - sliced, diced and transmographied

1994 Ford F350 box truck
7.3L Diesel
3-speed auto (C6)
Axle ratio - unknown
Tires & rims - unknown
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It began life as a Hostess (cupcake) city delivery truck.
Currently use to transport a track car.
Less aerodynamic than a brick.
Weighs ~5000 lbs empty & ~8000 lbs loaded.

Normal acceleration upshift is around 3k rpm.
Throttled deceleration downshift is around 2k rpm.

It is REALLY frustrating to be at 62km/h (38mph) @ 2900 rpm and the damn thing isn't shifting.

Redline is about 3200rpm.


It seems my THREE-SPEED tranny shift 95% based on speed and just barely based on load.
ie, accelerating up to 65, i can drop throttle and it will upshift,
or i could not drop throttle and it will shift at 70.
If i DO drop throttle, by the time i'm in the new gear, i'm only doing 61-62 and any amount of throttle will cause it to downshift again

Constant throttle is no good.
If I'm doing 80km/h (50mph) on the flat and reach a SLIGHT up-slope,
it will slow to about 65km/h (40mph) and down-shift.
Then that throttle position can't maintain the high revs and i slow down even more.

I drive 85-90 (percent of the time?) on the highway at 100km/h (62mph)
I drive 70km/h (43mph) in the 80km/h (50mph) zones.
My last trip was ~23L/100km (~10 mpg)

A city delivery truck designed to live in 2nd gear - not surprising you're unhappy with it's performance on the highway.

Originally Posted by MazdaMatt

Hostess apparently had a rock-solid maintenance schedule and the second owner runs a small trucking company. I can ONLY ASSUME that the fluids are doing fine, but who knows if that tranny is correct or the valve body is correct... he may have scooped it up chneap from an off-road racing buddy. I woudl LOVE it if i could replace a 40 dollar part and have it start upshifting at 2000rpm instead of downshifting at that!

Ok, let's assume Hostess had a rock-solid maintenance program. Ford's on-line maintenance schedules only go back to 1996, but let's assume '94 F-350 and '96 F-350 have the same schedule. According to Ford transmission fluid is to be changed every 30,000 miles and no mention of the filter. (You'd be hard pressed to find a transmission mechanic who wouldn't suggest changing the filter at the same time - but no knowing what Hostess decided was best). Did Hostess sell/trade the thing at 85,000 miles - 5,000 miles before the third transmission service. No chance the guy before you decide right away that he wasn't keeping it for long (too doggy on the highway) and decide to skip the 90,000 service - let the next guy do it?

The cheapest thing that MIGHT help would be a $20 vacuum modulator. You can test the integrity of the diaphragm by attaching a short piece of vacuum hose and sucking on it like a soda straw. If it won't hold vacuum, it's shot. A bad one will usually cause harsh shifts (clunk) and may move the upshift point to slightly higher rpm. You probably don't even have to drop the filter pan to replace it if it's bad. If the vacuum line leading from the engine to the vacuum modulator looks at all funky or cracked, replace it first.

The next cheapest thing that might make a difference is a $40 transmission filter. Add $$ for xx quarts of transmission fluid and 30-60 minutes labor charge if you don't do it yourself. Only special tool required is a large, wide drain pan and not at all difficult to DIY.

A dirty transmission filter can cause delayed shift and or shift hesitation.

Originally Posted by MazdaMatt

Funny enough, i think the best mileage trip i ever had, i spent about 3 hours in first gear at idle... it was stop/go traffic and i played the accordian by simply sitting there iwthout touching the pedals.

Originally Posted by MazdaMatt

But moving backwards a little... what about driving technique? I follow trucks and i drive f'ing slow, i try to maintain speed at the lowest possible in the highest gear... i refuse to neutral coast because i did that once and it clunked HARD on every shift for the next hour of driving.

Try the back-roads and keep to 2000-2200 rpm as much as possible. Higher rpms only when accelerating to get to next higher gear. If you can't keep to 2200 rpms or less, drop back a gear. Slow and steady wins the FE race.