Here's what I got; 83 f100 flareside 300ci. Pretty sure rear end, tranny, and suspension are all stock. Only mods are to the engine; holly 390, offy dp, and headers. Camper is yet to be purchased, know I can't go too big. But what modifications should I do to the rearend, suspension, and possibly tranny (4 on the floor)? VIN: 1FTCF10Y3DLA08296

 

Just the VIN won't tell us much. Give us a shot of the Certification Label on the door jamb. That will tell us what the tranny is and what axle ratio you have - both of which are important to know. If the tranny is an NP435, with the granny 1st gear it is TOUGH and nothing needs to be done. But, if it is the SROD, which I think were sometimes installed in the F100's, you do have a bottleneck. And, the axle ratio is also critical. Some of the F100's were set up for mileage and had numerically low axle ratios which kill the torque and seriously limit towing capability.

Once we know what the components are you can look in the owner's manual and find the towing capacity. Or, if you don't have one I can look in the '81 manual I have. And, we can tell you what the weak link is so you can change if need be. But, I can tell you now it won't be the engine. Give that six a reasonable axle ratio and you can tow a lot. Just as Rogue_Wulff, our Sapulpa neighbor. He's trailered his father's '74 F100 as well as his RX7 race car several times behind his '80 with the big six.

Another problem you will have is brakes as the F100's usually (always?) had smaller brakes. So, you are going to have to be careful how much you tow as you may have the ability to tow more than you can safely stop. You might want to watch for brakes on an F150 in the salvage. Or, come see me.

 

Yeah the lable on the door jamb is pretty much unreadable. I'll have to see if I can fill it in with a sharpie pen or something like that. I had planned on replacing everything related to the brakes; power booster all the way to the rear drums, I'm guessing just replace the whole system with one out of an f-150? What brake/rear end stuff do you have? And what junk yards are good up here? I keep finding the places that turn em into scrap metal.

 

The brakes on the f100 and f150 are not always the same...I think most likely not the same.

 

Shaun would be good here, perhaps he'll stop by.

An F100 is not really suitable for towing anything heavy - like, over 1,000 lbs. Look at your GVWR for more information and, like Gary says, the Owner's Manual.

 

I think you & Gary are mostly right.

BTW I asked Shaun to stop by.

 

I don't know anything about the JY's around here. I've bought a couple of trucks and have parted them out, and have gotten parts off of others. I do have an F150 with brakes on it that may bolt onto yours. But, I don't know how much of the front suspension is different between the F100 and F150, so don't know how many of the parts you would need.

The one thing I don't have, at least in good shape, are rear axles. The ones I have are worn on the splines. And, you need different rear axles since going with the larger brakes will give you the 5x5.5" wheel bolt pattern on the front, so you need to do the same on the rear.

PM me if interested.

 

From my understanding, and from what I've looked up in the parts catalog, there were F100 that shared the same GVRW as the F150 and therefore share brake and axle components.

But when that time came to change, would have to look up specifically what is installed in the truck now.

I know on my F100, it has the smaller bolt pattern, but I think some had the 5.5" pattern. There is also a difference in brake rotors and drums...but not on all. Some are the same.

 

Just to avoid confusion on his part... he'll need to make 2 more posts before his PM capability is turned on.

 

How many more

 

Times do I need to post?

 

zero now

 

Heh....

Your PM capability should be turned on overnight, you can start using it tomorrow.

 

So, measure your wheels to see what bolt pattern you have. And, measure the rear drums and the front rotors. From that we should be able to tell what you have. Maybe you won't need to change.

Or, maybe we can tell from the GVWR.

 

No F100 and F150 ever made between 1980-1983 shared the same GVWR. That would defeat the purpose of the highest level GVWR F100, and vice versa. The highest GVWR for an F100 is 5150, and that was only on single cab long bed F100's. The F150's lowest GVWR is 5250, and that was on a single cab Flareside and the Styleside. Big difference I know, but it is still a difference.

As far as brakes are concerned, the brake system, spring rates, and the emblems are the only things that separate an F100 from an F150.

Here's how the brake system differences are separated.

-F100's with manual brakes came with the 11" brakes, and a 5x5-1/2 lug pattern, just like the F150.

-F100's with power brakes came with the 10" brakes, and a 5x4-1/2 lug pattern, which is similar to many Ford cars of the era.

Here's where it gets tricky.

-F100's with power brakes AND a GVWR of 5150 received the 11" brakes, and the 5x5-1/2 lug pattern. The larger brakes were included because of the rise in GVWR. However, these special F100's were only available in single cab long bed form.

And the final factor, is your rear springs. Your F100 will have lighter springs in the rear than an F150, and after 30 years, your springs are probably tired, and have nowhere near the capacity they did in 1983.


The truck in question will have either the 4700lb GVWR, or the 5000lb GVWR. Neither of these can haul much of anything, nor can the 5150 F100's. We'll use the 5,000 GVWR as an example. The maximum allowable payload for the 5,000 GVWR F100 Flareside is 5149 lbs. That includes the weight of all passengers, the weight of the truck, cargo, and equipment. Say your truck weighs about 3500 lbs. Subtract that from 5149 and you're left with 1649. Say you carry two passengers with a combined weight of 400lbs. Now you're down to 1249. If I remember correctly, a gallon of gas is around 6 lbs. Multiply that by a single full 16 gallon tank, and now you're down to 1153. We still have yet to add in the fact that you may have a hundred or so lbs of equipment, nor have we included the weight of the camper.


So, as you can see, your F100 in stock form is meant to be a cruiser, and an occasional hauler of less than 1K in lb weight.


If you truly want to haul a camper safely, your best bet is to completely rebuild your suspension and brake systems, including upgrading your bearings, seals, and all the other things associated with the rotors and the axles. Upgrading to F150 stuff is a definite plus, and isn't incredibly hard due to it's bolt-in nature. No machining of new parts is required at all, which makes it one of your better bets.