I'm in the process of building a 1988 F-250 4x4 with a built-for max-torque 460, C6, and 4.10 gears. Over the weekend, I stumbled across a 1993 F-250 4x4, freshly rebuilt 351 (runs strong), 5 speed, headers, flowmasters, with crappy 3.55 gears for a cheap price. I picked it up this morning. The truck needs body work. Anyway, I'm going back & forth between parting out the '93 F-350 & finishing the current tow-rig in progress vs. regearing the '93, fixing the body, and using it as the tow rig. I also plan to use it as a part time DD. Some people don't like to tow with manual transmissions, but I'd personally prefer it over an automatic. I'll be towing about 9000 lbs of combined trailer & trail rig once per month in the winter, twice per month in the summer. The average trip is 100 miles each way, but I would be taking it out of state a few times per year…up to 500 miles each way.

I've had one other F-250 with the ZF 5 speed, but I didn't tow with it. I've heard that some 5 speed transmission aren't meant to be used under heavy load in 5th gear. The reason I ask is because if I go with the '93 F-350 as a tow rig, the 3.55's definitely have to go. If the ZF isn't meant to tow in 5th gear, I'd use 4.10's & tow in 4th gear. If the trans is meant to be towed with (obviously if the engine has sufficient power to pull 5th gear) I'd slap a set of 4.88's in it and be able to use 5th gear most of the time while towing, and have increased low end power. Here is what I want to know:

Is the ZF trans designed to be able to use 5th gear while lugging 9K lbs behind it?

Anyone else towing a lot of weight with a 351 5 speed?

Thanks,
Roy

 

I think the issue isn't just the weight, but on a flat surface it's mostly the air resistance of your trailer. If you have a 'big box' you probably can't use the 5th.

 

As I already responded on Pirate4x4, towing 9K with a ZF is nothing. I tow up to 20K with mine, 15K regularly, and its given me 204,000 reliable miles so far.

 

As I already responded on pirate, towing 9K with a ZF is not a problem whatsoever, even in 5th gear. I tow up to 20K with mine, 15K regularly, and its given me 204,000 reliable miles.

(btw mods, I think it is BS that we can't use the words 'pirate'4x4' on this forum)

 

Thanks guys (double thanks for both replies BigBlock). If I run 4.88's, I'd be around 3200 rpm in 4th at 65 mph, and 2500 rpm in 5th at 65 mph with 33" tires. I don't have any interest in going over 70 mph while towing.

 

78Buford,

I've seen post that say that the ZFs have plastic bushings in their top gears, 5th for the ZF5 and 6th for the ZF6.

Sounds a little odd to me, but that was the reason I've seen for not pulling under a strain in top gear with these boxes.

Maybe someone wheo has had one apart could respond and clear that up.

Gene