Hot Rods Rear Diff Opinions...

So the Falcon is on the street...still working a few bugs out..but trans cooler lines aren’t leaking, fuel pumps good, no oils drips, broke it in and went for a quick ride..now it’s got a 2800 stall..what the cam card called for...but man the 2:79 rear end..they said it would need a gear change...they ain’t lying...gotta go..so I know “buy a 9 inch” well not in the cards...and with 375-400 HP thats around 300 at the tires..so I’m gonna have a 8” center section built for it...need opinions as to splurge the extra $240 for the Eaton unit or roll with the track lock diff..builder said he does way more track lock units..said “I guarantee you’ll be happy with it” I was just thinking that Eaton unit seems pretty stout with no real wearable items, no friction modifiers needed, etc..he said it would take years to kill the true trac units clutch system..and its rebuildable...so let’s here some
HAMB opinions...

Thanks in advance fella’s

 

I would find an Explorer 8.8" rearend if you're on a budget.

You can get a 3.73 LSD easier than falling off a log...

EDIT: Sorry, didn't see the part about wanting to stay with an 8". Good luck!

 

I thought the true track was a clutch-less unit

 

I read three different differentials in that post....might need more clarification of what the choices are?

Tru Trac is a good one. I don't know about the Eaton. The factory Track Lock is so-so.

 

Ok...sorry..so it’s Eaton True Track..or a Trac Loc posi unit..

I thought about the 8.8 and I’m thinking by the time I rebuild it all and get it to fit I’d be into for the same price. My 8” is good to go other than that center section.

I’ll likely look for a 57-59 9 inch and work on it as time and money permits and have it as a back up

 

I have a True track in my 31" Coupe in a 9 inch and one in my 64" Polara in a Dana 60, they work great ,no noise, instant, smooth around corners.

 

So........will the rear end of your choice fit without having to narrow it, and are the stock axles strong enough with the improved traction you will have with some off topic tires. If you try to cut corners with your initial choice you will pay for it later. The weakest part of the assembly you get will be what costs you later on. Don't just consider the centersection.

 

Y

Yes the rear end is in the car...fits perfect with my on topic chrome reverse wheels and M&H cheater slicks

 

When I was in my teens I broke at least three 8" differentials in a 1968 302 4-speed Ranchero. Basically stock Ranchero with a cast iron intake and a small 4 barrel Holley and 3.00-3.25 rear gear. As someone mentioned an Explorer 8.8 would be a nice fit.

 

Lower price? Maybe, maybe not. You mention HP, but it's the torque number that's important here. The 8" won't support torque numbers much beyond about 325 ft-lbs. A 302 with 300 ft-lbs got the 8", a 351-2V with 350 ft-lbs got the 9", so that's what Ford thought about it. If you stick with the 8", you're also stuck with 28 spline axles unless you spend big bucks to convert. I don't believe the 8" Trac-lok is available in anything other than 28 spline. It'll also be more expensive than a 8.8" unit.

Finding a 8.8 with 31 spline axles, a ratio you want, and factory posi should be relatively easy, finding a width that works will be the key. Move the spring pads and you're good to go... If you don't have to narrow it, it won't be any more expensive to rebuild than the weaker 8", and it may be a wash even if narrowing is needed.

 

I would go with the Tru Trac, over the trac lock, if you are buying new. The 8-inch uses the exact same axles as a small bearing 28 spline 9-inch does. So the weak link isn't the axles, it is the center section. Being automatic, you have a lot less shock load and that helps. Stay away from drag strips with prepped tracks and the 8-inch should live. Getting hard to find in a junkyard, but the factory had 3.55 gears in Must II and Pintos if you find the right ones. Aftermarket you can get higher numeric gear ratios.
Overall, I would probably spend the money to upgrade as suggested, to ensure no future problems. But understand it is easy to go with current setup and just change gears.

 

I can't tell you how many 28 spline axles I've broke... It was enough that when I returned to the wrecking yard where I usually bought replacements after a 8 year absence, they still remembered me... This was behind a 352 FE.

On the other hand, the 8" in my '64 308" SBF/4-speed Comet never broke but I did have pinion bearings fail twice. That was a weakness of them...

 

Don't waste your time on the 8", friend of mine replaced the clutch in a stone-stock 67 Mustang, SBF, three-speed, once the wrenching was done he took it out on the man drag to "test the clutch", dropped the hammer and the rear end spit the pumpkin clean out of the housing. (Of course it was a customer car)
An 8.8 would get you by for now, if you want something narrower than the 8" you have try a Foxbody rear, you can swap out the four lug axles for five lug Ranger pickup axles and drums, or you can get an Explorer 8.8 and narrow it using the same Ranger pickup pieces, or BroncoII pieces if you want it a tad wider.
Pet peeve time: I love youthful enthusiasm but a monster motor does not a "Highway Hero" make; A vehicle is a system of parts, to make that vehicle dependable and safe an engine upgrade also requires the rest of the drive-train be upgraded, especially the brakes. Best of luck with your project.

 

The 4 cylinder ones came with a 3.73 ring and pinion....
But those were in a 7.5 rear end....

 

You'll eventually hurt that 8" if you drive it like you should. So save the bucks, go with your cheapest option to upgrade the gears, and then start game planning the upgrade. As has been said, the Explorer 8.8s are pretty nice; strong, cheap, widely available, 3.55/3.73s, 5-lug and disc brakes, and 31 spline LSDs, easy to narrow and adapt. A 9" is terrific also, but they can get pricey quick.

 

I was told a 7 1/4 would not live behind a small block in my Valiant. Everyone said it would break the first time I abused it...I drove the hell out of that poor car and it never did.


Run the tru trac in your 8” and understand its limits and enjoy your car

Sent from my iPhone using H.A.M.B.

 

Unless you go with a tubbed rear on that Foul-coon you are gonna be severely limited on tire width. Which can be a good thing!!........... Your tires will lose traction before you tear up a good 8.8 rear end. 225-60-15 tires will be about max (me tinkx) Sorta like a .....fuse!
It being an A/T will lessen the shock you can slam into the rear tires too. 400 HP small block Fords (it can be done fairly EZ!) will be a time bomb if its not kept FINELY tuned. IF it detonates/sneezes/runs lean one time at "full song" it COULD be ugly quickly.
Racing fuel will be your very good friend.
That being said..........I'd love to go fer a ride when you get'er done!
I had a 64 Sprint (back in 66) Never shoulda traded it for that 70 Challenger that I traded for a Toyota Corolla ............yeah...I know.
6sally6

 

It depends on the year of the Falcon.

The earlier ones had a 56" wide rear axle, stock. I run a 56-1/2" wide 8.8 in my 1960 Falcon. Than one came our of a Ranger, not an Explorer. Unless the arches are cut, an Explorer axle will not fit, and allow for a meaningful tire. If you have stickey-outy tires, then an Explorer 8.8 will work fine. You can find one in a yard with good gears, and just swap the carrier.

Mine is 28-spline, but has alloy axles, and it has an Eaton TrueTrac. I put them, or the equivalent, in everything with two drive wheels. The Model A has a DPI Gold Track, the wifemobile has a Quaife, the Falcon has a TrueTrac. Each works on the same principle.

 

There are 8.8s with 3.73:1 gears. I have seen several.

 

It is a torque biasing gear driven limited slip differential. There are no clutches.

 

Guys thanks for the insight..I’m running 215/65/15 M&H Dot Muscle Car Tires...aka cheater slicks..and they are “aired up” and will stay that way..on 15x6 chrome oe wheels...not a wide tire by any means

I understand the “shock of launch” this car has a warmed over C4...so no clutch dropping going on..that’s hard on any rear end. I’m also more of a “go from a roll” kind of guy..don’t plan to take it to the track..just wanted a hot little street car.

There’s a guy on here with a 64 Fairlane that’s gone into the mid 12’s and raced for 6 years with an 8”, stock axles, and a spool..Had a C4 and 4:11 gears...now it’s on the street with an AOD and a different converter still running that same 8”, takes it to the track a couple times a year, and still running slapper bars..I know it can be done..

 

I have a Mark VIII center with 3.70 gears and true trac laying around here somewhere...I should part it out....

 

A 9" Ford is like a small block Chevy it is by far the cheapest and easiest way to go.

Plus changing gears is pretty easy by just changing third members unlike a 8.8 Ford, or 10 or 12 bolt Chevy.

 

8" centers are getting expensive - especially the '67 up cases - if I were on a budget and in your shoes, I would get a repop 9" small bearing housing ($400 or so with perches) and re-use your 8" axles and brakes - you can get a 9" chuck cheaper than the 8" (due to heavy aftermarket support) and use some of those funds to pay for the housing.....it will be the exact length of what you have now and "bolt in"

 

Such a cool car. Get it how you want it and drive!!

 

You all make good arguments for moving on to a 9 inch..but if your gonna do it...you’d wanna do it right..and that means 31 spline axles..and that means new brakes, etc, etc, plus a new drive shaft..I’d be looking at 3K vs $900.00 for the center section.
I see a lot of “get a 9 inch “ ....but I also see a lot of this...

 

If I were you I would drive it like it is since you have the rear in the car already. Instead of spending money to upgrade, I would keep my eyes open for a 9" rear at a reasonable price. I'm talking about $125 or so. While you are enjoying your car and are in no real hurry, measure the 8" and narrow the 9". See if the axles can be narrowed or not. Some axles have a taper in the wrong spot. Actually its probably best to just purchase some new 31 spline axles from Moser than to shorten old axles because you probably won't have 31 splines. Costs a little more but you won't break them with that combo. Take your time and over the course of a year or so you will have most of what you need. Then worry about the ratio you want and the type of posi. The money you would have spent for the 8" posi will go into the 9" posi. Now put your 8" up for sale and you can get a good price out of it to partly offset the 9". Or put it in a corner and if you ever decide to sell the car, put the 8" back in and you have a valuable 9" that you can get most of your money back or put in another project.
The thing is ........you already have the rear in the car AND you want to believe the 8" will do the job.
NO ONE is going to convince you otherwise at this point.
That said, NONE OF US know for sure that your 8" won't hold up because we don't have actual data on your engines capabilities. The actual ability of your engine will decide whether it works forever.......or not. Most of us old guys have learned to plan for the worst case scenario because its usually cheaper in the long run.
If a rear end breaks, tow charges, inconvenience, and the cost of rebuilding will mean you now own an 8" with as much money in it as a 9"........and you will always have to worry every time you mash the gas again. I wish you luck with the 8" and hope you don't have problems, but I'm trying to help you see the possible future problems.


Ya pays yer money and ya makes yer choice.

 

Buy once... cry once...I use that a lot....I’m just tapped out..If anyone know of a 57-59 9 inch for sale send me a PM...I’d rather do that than the 8.8

was thinking instant gratification..I could change that center section in the morning and be rolling..

 

So I was looking at some new 9 inch options..I was shocked to see this for the stock non nodular option:

 

I have an 8.8 out of a 2000 ranger - its a 3.55 posi - new brakes, sandblasted and spray bombed black to protect it - it had the original mounts cut off and mustang perches just crudely tacked on.....It is 58.5 WMS to WMS - could probably ship it fastenal asking $500 - but I'd still do the 9 inch - even 28 spline - it will likely cost you only 2-300 more for the housing and chuck than just the 8" chuck