Hello all!

Now that I have attracted every math related major with this title, I may begin my post!

Tomorrow(rather later on today) I have plans to put down the cash for a 1979 F-150 that has been previously restored. The truck is advertised as..
factory 4x4
factory air(missing a compressor)
6" suspension lift with rear add-a-leaf
33" pro-comp mud tires
"built" 400 with a nice lopey cam
True duals
Spray in bed liner
Indy 500 interior(or something like that)

The truck was built up for mud runs and as a result has a Detroit locker in the front diff and a full spool in the rear.
This truck will be my daily driver and also a bit of a toy. Im coming from a 2wd and am tired of getting stuck. I have a budget of around 500 for parts and 300(quoted) for labor to do this swap.

MY question for this post is as follows.. What diff is going to suit my purposes best?

I have done some research and now somewhat understand air lockers, elockers, Detroit lockers, limited slips, and the open carrier. As of now I am heavily leaning towards a Detroit locker for simplicity and usefulness. A Detroit seems like it will be consistent with the way it locks up on pavement. I like the way it does not really compromise in off road situations. A limited slip seems boring and watered down.

These are the gear sets I am looking into. I do not understand the difference between the two. Why do they look so different? Are they both the ratcheting style Detroit locker? is one a limited slip?

http://www.summitracing.com/parts/dt...view/make/ford

http://www.summitracing.com/parts/dt...view/make/ford

 

Honestly, this truck sounds like a big money pit, a poorly engineered truck that will neither be a good Mud Rig, nor be a good daily driver......Well, with a spool in the rear, a detroit in the front, a built motor...i would question how bad its been thrashed? It doesnt sound like a good candidate for a daily driver, and for that matter most dedicated mud rigs have at least 3/4 ton running gear, if not heavier........Most serious mud guys run D60 fronts, D70 or equivalent rear, or even bigger. As a daily driver on the street, a Detroit has handling quirks, a Limited Slip is much better suited for normal driving, especially on a relatively light weight, moderately lifted, modified engine truck.

 

From what the owner tells me the truck was in the process of being built to run in the county fair mud runs. The engine is supposed to have less than 5k on the build and there is zero rust. Paint work was obviously done within the past few years. If this !truck was ever thrashed around, it was repaired quite well.

 

Thrashing can take place without body damage......., more importantly, its not likely the best suited to be a daily driver either. mud tires and a locker arent really good on wet pavement, add in a built motor and relatively lightweight and lifted truck, and it has rear add-a-leafs, so its probably a super stiff suspension( BTW is it a short or longbed?), so id be hesitant to call it a good daily driver, assuming your daily drive calls for much paved roads, highway driving, or busy city roads. If you live in a rural town, and dont face a lot of traffic, it might be great!

 

I must admit that I'm not big on 4x4s but from what I can tell from the way that the truck was built, it is made to go in a straight line through the mud. A 400 is a torque monster when built right, but it must be built for the way you want to use it. I've had 4 of them in various work trucks, ie my Avatar. If it has a hydraulic cam you'll have a shorter than average lifespan motor. If it's a roller lifter cam that's the way to go. 400s don't like dual exhaust unless you run them at full throttle. For road use you want a 2 into 1 exhaust about 2 1/2" entering the muffler. Think of a mud bogger as a heavy drag car. Not to be a negative Nelly but from what you said you want to use the truck for, dual purpose on and off road, there will be a more appropriate truck out there for you. Keep looking and don't be afraid to post pictures of the truck. We're not here to snag trucks, but we'll be honest in our opinions of them. Hold onto your money for a couple of days and watch your thread for responses, I'm sure there will be a variety of them. Have a good day, keep looking, you'll find your truck.

 

You mentioned cams and how different ones can affect engine life. How are these two so different that they can effect longevity? Is there a way to tell by the way the motor behaves rather than just yanking the cam? If it is a big factor in engine life, I have no problem with a cam swap sometime down the road.

I suppose some more information would help. The truck is a standard cab, short bed setup. I live in a small town with minimal traffic, 90% of my driving will be on Kentucky back roads.

Its also worth mentioning that I have budgeted in money for a few modifications to the truck. I have planned on around 800 for the rear diff and about 400 to buy a RoughCountry 2.5" or 4" lift kit. I think a few inches of drop will suit my purposes for this truck

Its been so long since I posted that I just cannot remember how to post pictures! Can anyone help?

 

If it were me I would just drive it if everything else is in decent condition. When you get time and money swap out the rear diff for an air locker or a truetrac (best limited slip in my opinion). Then do the same in the front. Most people don't use 4wd as much as they think they do.

By the way those 33" tires should fit without a lift, maybe it already has a 2 or 4" lift. 6" is a bit excessive for 33" tires on an f150. If you stick with that size of tire I would use 3.50 or 3.73 gearing for on and off road.

 

 

 

Bottom line, rear spool and pavement bad idea. A spool is NOT for pavement driving.

Leave the front Detroit alone, you will get use to its peculiarities.

Have the rear spool pulled and put in a LS or better yet another locker, there are high dollar Detroit's, or cheap lunch box locker. Just have them match the front ratio.

Call these folks and pick there brains over the phone for real time answers.

Randy's Ring & Pinion

I like the truck and would buy it as a DD/weekend wheeler, for sure.

 

^ A locker is at the top of the list, a spool will not do.

http://www.summitracing.com/parts/dt...view/make/ford

what is the difference between these two? they look so different. Front and rear gear ratios are the same. I think a locker would be nice in the rear.


http://www.summitracing.com/parts/dt...view/make/ford

 

I can't figure out the difference other than 1 is a 28 spline and the other is 31 and appears to be heavy duty for circle track racing. Your truck should have a 31 spline.

It definitely has a 6" lift. Nice looking truck. I used to have an orange freewheeler which had the same interior.

 

Well guys, I am the proud new owner of a dentside! It's with my mechanic to install a detroit locker rear end and should be finished up next week

 

Well that was funny. He asked for all this advice and went and did what he was going to do in the first place.

 

You got my interest with "Differential Equations". I never did like Calculus 4 when I took it.

My opinion for a daily driver: Open front and open or limited slip rear.

Reasons:

A locked front will not steer very well on roads and would really bind up if you hit a dry spot. It just seems crazy to have a locker in the front unless it is a selectable locker.

I have a lunch box locker in my Dana 60 year now and I cannot stand it anymore always locking up taking turns in town. I find myself creeping around turns like an 80 year old man. I am going to be putting an open 14 bolt differential in soon (the Cummins seemed to exacerbate the locker locking up).

If you really "need" the extra tires spinning for street driving you need different tires. I gave up driving mine with big mud tires and now military tires in the snow because it is just downright scary trying to drive on these tires.

My rear wheel drive BMW 335D with winter tires goes better in typical snow on the roads than with 3 wheels on my truck going. Tires make a HUGE difference.