Rear End Swap for 1968 F100

[Subzero]

My truck currently has a 3.25 9" rear end on it. One of my axles is bent and it was suggested that I just go ahead and swap out the entire rear end. The idea being I could pick one up, redo everything, paint it, and swap them out. I need to keep my parking brake. I would like bigger gears, and possibly a posi lock if that's an option and is relatively cost effective. Budget is under $1000 and the new rear end needs to be a direct fit. What are my options as to what I could use besides finding another 1968 rear axle? Thanks

[HIO Silver]

Your potential donors are 68-72 F100s half-ton of course.

Is it an axle that is bent or the housing??? I would just replace the axle and deliver the carrier to have its gearing changed and either a locker or limited slip installed.

Btw, 'bigger' gears is bad syntax... saying 'numerically lower' or 'numerically higher' and we might understand what is meant by 'bigger'.

[Subzero]

Numerically bigger gears is what I meant, sorry about that. Thinking about 4.25 but not quite sure how that will affect drivability compared to my 3.25 ratio now. I'm having trouble locating a bumpside rear end in my area. I did however find two 1973 F100 individual axles for $25. I don't know if they will fit into my 1968 rear end. But I was wanting to find a whole new carrier. Do any other newer years fit these trucks with little modification or is it only bumpside years?

[HIO Silver]

I don't think 4.25s are available but IIRC 4.10s and 4.30s are. However, I wouldn't go that high.

Why do you want to change the rear gears anyway? 3.25s are decent. The generally recommended compromise between off the line acceleration and highway driving is 3.50 gears. A three-speed automatic is a 1:1 third gear. Unless you go overdrive, a set of 4.10s with 30-inch tall tires will be turning 3,300 RPM.

That 73 likely has 31-spline axles and yours are likely 28-spline. I understand there was some crossover so anything is possible. A direct bolt-in as an assembly? Nope.. the 73's leaf spring pads are located more outboard because the Dentside frames are wider (except for HighBoy 4x4s). They'd need to be cut, moved, and rewelded. As far as the gear carrier, a ring and pinion is about $200 and a limited slip is about $450. Plus set-up costs. Try surfing CraigsList.. someone's gotta be parting out a Bump somewhere in the tidewaters.

How about looking at early Econolines for a carrier?

On the other hand.. buy a welder! Having one allows the freedom to make parts fit instead of beng held to what is available for your specific application. I suggest a Miller 211 or Miller 212.. can do sheetmetal and steel up to 3/8ths thick.

[Subzero]

I've searched some more and found a 1967? F100 rear end across the state, the owner doesn't know what gears are in it and is not sure of the year but hes still looking for the information. Those 73 axles would have been cheap fix but I thought they wouldn't work. Really need a welder too, that'd be nice as I often have to take things to get welded, it's on this list for sure. I see your point on the gears, 3,300 rpms with my exhaust is defining for long periods of time.

[cep62]

While you can bolt the whole "67 axle in ..,if you want to use just the shaft they are different.as far as iI remember the distance from the bearing to the wheel flange is different on '67 and earlier.

[ultraranger]

I'm not certain on the '67 axle length but they may be a little shorter than the '68-'72 9-inch axles. The '67 rear drum brakes are definitely narrower than the '68-'72 F100 rear brakes.

The '68-'72 axles are the same length on both sides. Any of the '68-'72 F100 9-inch rear end assemblies will be the correct width and will have 28-spline axles/differentials.

If the axle is bent and the housing tube isn't, it would be simpler and cheaper to just swap the damaged axle out of the existing rear end housing.

The '73-'79 F100s or the '75-'79 F150 9-inch rear ends will be 4" wider than the '68-'72 F100 9-inch rear ends. It can be installed under your truck but, you'll have to move the spring perches in by 2" on each side and a good chance you would have to move the lower shock mounts inward on the axle housing tubes. The '73-'79 9-inch rear end would put your rear wheels out to the same distance the front wheels are located.

There were some Ford Equa-Lok 28-spline differentials available in the '67-'68 Ford F100s. In '69, the Ford Traction-Lok differential replaced the older Equa-Lok. The 28-spline Traction-Lok differential is much better than the older Equa-Lok but, the '69 model Traction-Lok differential is weak due to (4) large holes in the casting on the left half of the differential. The '70-'86 Traction-Lok is a much better differential.

Starting in 1973, MOST of the trucks had 31-spline axles and differentials. Open (single track) differentials were standard, Traction-Lok was optional.

Any Ford 9-inch 3rd member (car or truck) will fit in any 9-inch rear end housing --as long as the number of splines of the differential match the spline count of the axles.

Trucks will generally come with better, lower (higher numerically) ratios. Passenger cars will generally have higher (lower numerically) ratios. Passenger cars with 9-inch rears will also, generally, have 28-spline differentials.

From 1968-1972, Ford also produced a 9-3/8" rear end in the F100s. It was similar to the 9-inch but the 9-3/8" 3rd member was a little different from the 9-inch 3rd member. The 9-3/8" rear ends came with 31-spline axles that are the same length as the 28-spline axles in the '68-'72 F100 9-inch rear ends.

I have a pair of '71 F100 31-spline axles that came out of a 9-3/8" rear end in my '69 F100's 9-inch rear end, with a 31-spline Traction-Lok differential in a 9-inch 3rd member and 3.50 gears that came from a '75 F150 4x4.

You won't find any factory 4.10 gears in a 9-inch 3rd member but, there were some 4.11 ratios in the 9-inch 3rd members. The most common ratios were 3.25, 3.50 and 3.70.

A lower rear end gear (higher numerically) is going to make your speedometer inaccurate (without correction) and it's going to make your highway RPMs much higher and consume even more fuel, without an overdrive transmission.

[sargentrs]

The "Slick" generation ('60-'66) is also a viable option. When my 3.25s locked up I got a 3rd member out of a '65 F100 with 3.89 gears. Bolted right in. However, the oil plug on the "slicks" was in the housing, the "bumps" is in the 3rd member. I didn't realize this until after I had it bolted in and went to fill it with gear lube. Drilled a hole in the top rear of the housing and used a self tapping bolt with a fiber washer for a fill port.