I will be swapping my current engine for a bigger one. I hear many times that a bigger engine can stress the rear end, and could break or damage it? What exactly happens? How can I prevent and/or fiix this?

Tyl

 

What engine are you putting in and what rear axle do you have? If you have a small rear axle adding more torque to it you will break it. The only solution to this it to swap in a stronger rear axle.

Matt

 

I currently have a 330 HD which will be replaced by a 390. It is a dually rear.

Tyl

 

I think the rearend should be OK, unless you intend to take your dually to the dragstrip.

 

It's a '79 F350 UHaul truck, isn't it? I remember you from the FE forum

The rear end in that thing should be at least a Dana 70 or 80, right?

Should be able to handle a mild 390 without any issues - I ran a pretty hot 390 in my '74 highboy through a Dana 60 (SRW) 4.10 rear with 33" tires on it - could smoke them without any issues. I broke that rear end more with a whimpy stock 360 for some reason...

From looking at your truck, I assume you are going to be using it for heavy hauling? That rear should do you just fine - it's most likely the same rear that was used with the 460 engine in regular F350's. No worries.

 

Thanks, I don't know much bout mechanics. Troughh the truck and this site, I am learning quite a bit.

The vin plate says it has dual shocks, single heavy rear.

What exactly is a broke rear-end?

Tyl

 

Usually, Ford and most other manufacturers use weaker rear ends and transmissions with the weaker motors. In passenger cars, and in many cases trucks.

However, what you have is a hybrid special-ordered truck. U-Haul orders an F350 chassis-cab with a 330HD engine. The 330HD in an F-150/250/350 is unheard of. Never happened in "real life". But U-Haul ordered them special from Ford with that engine, probably because they already used lots of other heavier-duty trucks that had the 330HD and had parts and suppliers already setup for years.

In your case, I'm thinking Ford would put the only available dual-wheel rear-end available for the F350 in 1978. I think that's a Dana 70 you have. Can you take a picture of the rear-end from the back of the truck?

When you break a rear-end from too much torque, all sorts of things can happen. You break an axle, spider gears, side gears, the spider gear shaft, the pinion gear, teeth on the ring or pinion gear. It means it either makes one heck of a racket, or it doesn't move at all.

In your case, the rear-end you have is probably beefy enough to handle an FE 390.

Any Ford DRW (dual rear wheel) from the 70's can handle that 390 easily.

If you look at the backside of the rear-end, under two bolts holding the cover on, there will be a tag. Might be hard to read, if not impossible, but get the numbers/letters off of it, and post back.

 

That dana 70 will have no problem handling a 390 becuase my friend has a 93 dodge with a cummins in it and those came stock with 160 hp and 400 ft. lbs. of torque and hes got his pump cranked and injectors and hes runnin 38 inch tires.

 

I'm not sure which axel it is. I can't ggo out for a pic or verify till spring. It's its winter hibernation.

I talked to a U-Haul technician about the truck a while ago. When I bought the truck 500 miles from home, and rode it home, I was stuck behind two slow transports and a winnebago that was the size of a transport alone. I was told the engine was a 302, which doesn't look like a 302. I figured whatever the engine was, it was probably used in NASCARs long time ago. Steered to pass the two trucks and rv on a two laned highway cuz I want to get home. Performed grand, however the speedometer climmbed to 120 km and was stuck there.

That was my introduction to speed governor, the engine being a 330 HD and U-Haul's favor of the engine and low gearing.

The trucks were suppose to get 351 engines, but got 330 HD engines for better fuel mileage. I don't know how or why a 330 HD engine. The 330 engine is an industrial engine for commercial trucks/buses only. The 330 HD is an advanced engineered engine bigger than the stabdard 330, and only availlable in U-Haul trucks. It is said the 330 HD engine block is equivalent to a 390 block mixed with 330 and 352 parts others? I'll find out when I take it apart. My current fuel mileage is 7.65 mpg.

Tyl

 

I am fairly certain that all the HD/FT engines got forged steel cranks and rods, that combined with the deep skirted FE blocks and you have one bullet proof motor.

The rear end in that truck is at least a Dana 70, plenty strong enough for anything you want to throw at it.