Ford Rear Diff Modification

[britbeam]

I have just disasembled my Ford 8" rear diff out of the 74 Mutt 2. I would like to hear from guys who have already accomplished this mod and have it running in their Alpines now.

Questions: Did you shorten each tube & how much?
What did you do for the parking brake?
What gear are you running & is it a Posi?
What gear ration?
Who shortened your axles?
What disc brakes have you found to work etc.?

I hear a lot of guys speculate on how they will do something now I would like to hear success stories with what will work. The thing about using a Tiger Dana is you still have those Rootie Tootie hubs,etc to deal with when you need to change bearings & seals. Once their off maybe next time wont be as bad but it might so why not go with the old faithful Ford 8"?Look forward to all the input and Jose please feel free to add your wisdom.
Dwain V6 Krazy

 

[Mark T]

Hi Dwain! I have the Ford 7 1/2" rear end so I can't help you with most of your questions. I can tell you that when I did the rebuild this summer I put 4:10 gears in with the new T5 and for the little amount of time that I got to drive the car before the salt hit our roads they worked great!

 

[V6 JOSE]

I have just disasembled my Ford 8" rear diff out of the 74 Mutt 2. I would like to hear from guys who have already accomplished this mod and have it running in their Alpines now.

Questions: Did you shorten each tube & how much?
What did you do for the parking brake?
What gear are you running & is it a Posi?
What gear ration?
Who shortened your axles?
What disc brakes have you found to work etc.?

I hear a lot of guys speculate on how they will do something now I would like to hear success stories with what will work. The thing about using a Tiger Dana is you still have those Rootie Tootie hubs,etc to deal with when you need to change bearings & seals. Once their off maybe next time wont be as bad but it might so why not go with the old faithful Ford 8"?Look forward to all the input and Jose please feel free to add your wisdom.
Dwain V6 Krazy

Hi Dwain,

When you have your housing cut, have the machinist put the pinion in the middle, between the spring pads. To accomplish this, he will need to cut a bit from both ends.

Since you are running the four cylinder T5, I wouldn't advise anything lower than a 3.70 gear ratio, because of the very low first gear ratio. If you went to a V6 T5, you could go with a 4.11 and still have a good cruising rpm. The only posi type that I know that will fit the 8", is a Detroit Locker, and they are a bit pricey. The Detroit Locker doesn't have the best street manners, so unless you intend on doing some type of competition with it, I wouldn't use one.

The little V6 loves a steep gear, because it lets the engine run at it's preferred rpm. A set of 4.11's is about ideal with the 3.8 V6 t5, because the first gear in that transmission isn't too low.

The only thing I can suggest for a parking brake, is the small disc brake that fits on the front of the differeitial, where the pinion gear sits. You can find them advertised in different car magazines. There is one that they want $300 for, and another one that sell for about $150. They are the same thing, so I would suggest getting the cheaper one.

If you want to go with a rear disc brake set up, you could use a set from a 1996 Mustang GT. You would need to swap the calipers side to side, because they come off of a coil spring set up and they interfere with the leaf spring, if you try to use them on the correct side. When the calipers are mounted on the opposite side, they have the parking brake on top, and it would be easy to connect a single cable with a split to each wheel. You would need to change the wheel bolt pattern to the four bolt pattern like the Alpine, but otherwise it works fine.

Jose

 

[britbeam]

Jose by positioning the pinon between the spring pads will this put the pinion in the same position as the stock Alpine diff? I was thinking of just taking the Alpine diff and tell him to match it up, flange to flange,spring pads and pinon to be the same as the Alpine. What do you think? I dont want to get a diff back I cant use just trying to cover all the bases. Ive heard some say that only one axle can be shortened because of the shaft taper but I dont see this taper on either shaft. They have the normal taper but it appears to be the same on both.
Dwain V6 Krazy

 

[Bill Blue]

Dwain, don't copy the Alpine rear axle if you are going to run a drive shaft larger than 2" diameter. The Alpine drive shaft is offset and yours will rub if you use the 2.5" shaft. Center it like Jose says. Been there, done that. Jose had told me the battery box would be an issue if the drive shaft is offset, it is not. Tunnel width is.

Don't follow you on the axle taper thing. Is this the axle housing or the axle shafts?

Bill

 

[V6 JOSE]

Jose by positioning the pinon between the spring pads will this put the pinion in the same position as the stock Alpine diff? I was thinking of just taking the Alpine diff and tell him to match it up, flange to flange,spring pads and pinon to be the same as the Alpine. What do you think? I dont want to get a diff back I cant use just trying to cover all the bases. Ive heard some say that only one axle can be shortened because of the shaft taper but I dont see this taper on either shaft. They have the normal taper but it appears to be the same on both.
Dwain V6 Krazy

Dwain,

Some guys claim that their Ford 8" axles were like the Chevy axles. The Chevy axles have the splined end larger than the axle just behind it. These axles can't be shortened, because there isn't enough material to put splines on it. The Ford axles I have experienced are larger in diameter than the splined end, having been turned down to the spline size, so can be cut and turned down to the spline size again and then have the splines cut in them. You want the pinion in the middle so that the narrow tunnel won't be hit by the drive shaft and you won't be close to the battery box, if you move it toward the passenger side, like the stock Alpine rear has it. You definitely want to copy the width, drum to drum, plus the spring pads should be the same distance apart as on the stocker. You can have some later series style shock mounts made and welded onto the housing and then you can have teliscoping shocks, like the later series cars.

Bill,

I have had problems with an offset pinion on a modified Ford 8" rear end, and it wasn't from the drive shaft hitting the tunnel; it was from the battery box being so close, that it was difficult to bolt up the drive shaft. Your experience may have been different, but mine was the battery box.

Jose

 

[Bill Blue]

Jose, I have axles that are narrower behind the spines. No claim about it, I will take one to the next Invasion to show you. They would have to have spines rolled onto them. Most places mill the spines, which would give undersized spines.

These can be narrowed, but the minimum they can be shortened is 4". If both sides are narrowed, you have to buy one axle. The long axle is long enough to be used on the short side.

Bill

 

[britbeam]

Dwain, don't copy the Alpine rear axle if you are going to run a drive shaft larger than 2" diameter. The Alpine drive shaft is offset and yours will rub if you use the 2.5" shaft. Center it like Jose says. Been there, done that. Jose had told me the battery box would be an issue if the drive shaft is offset, it is not. Tunnel width is.

Don't follow you on the axle taper thing. Is this the axle housing or the axle shafts?

Bill

Ok so I center the pinon and I will have purchase a new axle to replace the shorter axle. The taper Im talking about is axle taper behind the splines. So do I have to send the axles to Moser to be shortened and resplined? I will measure my drive shaft tomorow but Im sure its smaller than most have used. I didnt use the TBird shaft. I seem to remember someone saying they only shortened one side . Is this a myth or has someone actually done this. Im not doing anything quick and Im listening to you guys just trying to get the absolute word on this and looks like I have.I will comment more after the car is in the air where I can measure tomorow.
Thanks
Dwain V6 Krazy

 

[Bill Blue]

Ok so I center the pinon and I will have purchase a new axle to replace the shorter axle. The taper Im talking about is axle taper behind the splines. So do I have to send the axles to Moser to be shortened and resplined? I will measure my drive shaft tomorow but Im sure its smaller than most have used. I didnt use the TBird shaft. I seem to remember someone saying they only shortened one side . Is this a myth or has someone actually done this. Im not doing anything quick and Im listening to you guys just trying to get the absolute word on this and looks like I have.I will comment more after the car is in the air where I can measure tomorow.
Thanks
Dwain V6 Krazy

Not quite. If your axles are narrower behind the spines, you must purchase a new axle to replace the long one, the old long axle becomes the new short axle. That is true if you have the work done by Moser. I took my old axle to Moser and they said "No". Need a new one.

I shortened one side and left the axle longer than stock, had tunnel rubbing issues. Shortened the other side to bring the axle back almost to stock width. The amount the axle has to be narrowed dictates that both sides be cut unless you do surgery to the Alpine.

If you want to go to rear discs, make the decision now so the axle flanges can be cut down to fit the rotors you plan to use.

Bill

 

[V6 JOSE]

Dwain,

If your axle is larger in diameter than the splined end, they can be turned down and resplined by any competent machine shop. I have been lucky that every axle I have encountered in a Mustang II 8" rear end, has been larger in diameter and had been turned down in order to have the splines rolled on at the factory. I wasn't calling anyone elses experience into question, just saying what my experience has been.

I don't think you necessarily need to have Moser cut and respline your axles. Whoever you have cut the housing, should be able to do that for you. it might save you some money too.

Bill,

I put a set of Mustang GT disc brakes on the 8" Ford rear end, and didn't need to turn down the flanges. In fact, I needed to have a couple of brackets made and welded to the flanges in order to space out the calipers so they would clear the discs. It was a pretty straight forward modification. The only inconvenience I found, was that since the calipers are reversed and the bleeder is now facing down, the calipers needed to be rotated forward till the bleeder was high enough to purge the system of air. Once that was done, I just rolled them back into place and bolted them up. Rolling them around the disc is possible because the disc brake set up needs a hose, rather than the hard line, a set of drums require. I had a custom set of hoses made up and it looks like it came from the factory like that. It looks good, and I'm sure that they will work great too. I am using a Tilton dual master cylinder set up, and have the cylinders matched up for each set of brakes.

Jose

 

[Bill Blue]

Jose, in a large portion of the country, there is nobody that will shorten axles. When I first shortened mine, there was no one in the Indianapolis market that would do it. Some offered the "service" but they just shipped them off to Moser and tacked on their fee. Maybe if I'd shopped around gasoline alley...

I'm talking about the flange on the rotating axle. Maybe that should be called the hub? Had to remove about a quarter inch to clear the Saturn rotors. Sounds like you are have solved the rear disc problem. Will they clear 13" rims and how is the fore/aft brake balance? The Saturn calipers clear my 13" rims by less than an eight of an inch. And that required making a bolt for the banjo hydraulic fitting from a button head bolt.

Bill

 

[V6 JOSE]

Bill,

The Ford 8" axle flange fits perfectly inside the Mustang disc hat. You would think it was made for it. I can't opine on whether the brakes will fit inside a 13" wheel, because I haven't tried to fit one, but I doubt it. They will fit a 14" wheel easily, so maybe, since you only lose .5" per side. It would be interesting to find out. I don't think in terms of 13" wheels anymore, because tires to fit them are getting hard to come by. We are thinking about using a 14" wheel on the blown Alpine, because I would love to use the old American Racing Wheel, Torque Thrust wheels on it, and they don't make a 15" wheel with the right back spacing to make it work. Maybe a 14" wheel will have the correct back spacing.

If there is no one who will/can shorten the axle housing in the local area, then Moser is the best option. I have always tried to do things locally, but if it can't be done, then you do what you have to do. I have bought hardened axles from Moser and have been verry happy with his work, so it isn't because of quality, or the lack thereof.

 

[daniel luna]

Hi members,
I my self have done the 8" rear end from stang II 1975 and
also have the problem of finding the parking brake
the kit places a small disk that fits on the pinion yoke of the differential.
I remember a person from san diego I think the name was Dean and was
retired or any other person that has done it please give me some help on
the source from were I can get this parking brake

Thank you for help in advance
Sin Dan N Luna

 

[V6 JOSE]

Hi Dan,

The guy that you mentioned, was called Dean Mitchell. He has now passed on and left his beloved Alpine to one of his sons. Dean was seventy five when he started his conversion project, and learned to weld and do body work to be able to restore his Alpine himself. He was a real Alpiner.

Dean bought one of the small disc brake parking breaks from an add min one of the car magazines. I can't remember which one, but if you begin looking in all of them, especially one like Street Rodder, I'm sure you'll find it advertised there.

Jose

 

[britbeam]

Hi members,
I my self have done the 8" rear end from stang II 1975 and
also have the problem of finding the parking brake
the kit places a small disk that fits on the pinion yoke of the differential.
I remember a person from san diego I think the name was Dean and was
retired or any other person that has done it please give me some help on
the source from were I can get this parking brake

Thank you for help in advance
Sin Dan N Luna

Daniel did you keep any measurements on the diff mod you could pass on to us?
Dwain

 

[Ken Ellis]

That parking brake design is also used on RVs, as an aftermarket thing. You might search under emergency brake, too. Although they might be too large to fit, they could likely be modified.

Ken

 

[V6 JOSE]

Hi Dwain,

Do you have a fax number that I can fax my build sheet to? I can't read it very well, but it does give the length of the two shortened axles. The long (right) axle is 26 3/16, and the short (left) one is 22 3/16 long.

These dimensions are from the mounting flange surface, to the end of the splined end. There is more info on the page, but I can't read it. I think if you took it to the machinist who will shorten the housing, he would be able to decipher it.

Jose

 

[britbeam]

Hi members,
I my self have done the 8" rear end from stang II 1975 and
also have the problem of finding the parking brake
the kit places a small disk that fits on the pinion yoke of the differential.
I remember a person from san diego I think the name was Dean and was
retired or any other person that has done it please give me some help on
the source from were I can get this parking brake

Thank you for help in advance
Sin Dan N Luna

Daniel here is what Ive found so far.

Total Performance @ tperformance.com
P/N Bp169M $325.00 complete with cable/lever mech

TSMmfg.com
$229.95 Brake mechanism only

I havent found any for les bucks yet. Its good to have the parking brake but it really shouldnt be considered an emergency brake in my opinion. The best mod on my Alpine has been going to a dual brake system. I feel much safer on the mountain roads knowing all my brakes wont fail at one time.
DwainV6 Krazy

 

[oldflotsam]

How about adapting a motorcycle disc brake setup for use as a parking brake on the driveshaft? Anyone tried this?

Wayne

 

[britbeam]

I would say a guy could make his own pinion brake setup.Somebody had to design the first one right. Now to keep the cost down,well you would only know if you tried. I think probably the hard part would be mounting the disc to the yoke.The bracket for the puck anybody could make but that disc might be the hairy deal.
Dwain V6 Krazy