Being that I am building my first Ford and will be using a ford rear for the first time I have some questions about the 8" vs. 9". 1. Why is it called and 8 or 9" (is this a measurement of the center section?) 2. Do the pumpkins and axles go together the same (axles bolt on from the of the housing and then slip out which allow the pumpkin to come out in one piece (unlike a GM 10 or 12 bolt with C clips) 3. Are the axles the same (if both are 28 spline) diameter and strength 4. What kind of power will an 8" handle I know lots of folks run the 8" without problems but I have the option of going with either one out of a Maverick (56.25" or 56.50" which is the perfect width I have been told for a full fender Model A) or a 9" out of a 57-59 (57.25" wide) which I think may have to be narrowed an inch or so to fit correctly. I know finding an 8" posi it difficult and they are expensive but if to pay someone to narrow a 9" then the cost may not be that much different (I can get the 8" for $100 to 150 less also). Thanks for the tech info
A few answers... I believe the 8" or 9" refers to the diameter of the ring gear. A 8" rear is lighter than a 9", so it might be the better choice if you're not running crazy amounts of horsepower. My understanding is that a 9" is usually overkill for a mild performance V8.
yes twice (the first two answers). The axles don't interchange. The ring gear dia is where the nomonclature comes from, but everything in the rear is heavier on the 9. I run 9s cause I'm into overkill, but about everyone I know is going to an 8. Unless you're building a real heavy ride or intend to pull a trailer the 8 ought to handle 400 hp easy.
Number one reason to use a 9in is gear selection. Many choices. 28 spline will handle plenty HP in a Model A. Over 400 HP. Yes pull the axles and the whole center section comes out. Change one in less than an hour. (Done it between rounds at the drags once.) 8 and 9 inch axles will interchange, with the rite bearing and length. Easy way to narrow a 9in, use short 8in axles. Measure carefully.....OLDBEET
what about bearings on the ends? do they interchange as well? I now there's bout 3 or 4 different types....
hey Ken,I am going to send you the info on my 8 inch, i wanted a 8 to keep the sleeper look of the current project, plus it fit right in the A coupe, had a local guy do it,garuntees i wont break it.limited slip and after market axles......i will dig up the info and mail it to ya
axles will interchange providing it is a small bearing 28 spline 9 inch I have often used 8 inch axles (maverick) in a 9 inch to narrow the rear
1 - As mentioned, diameter of ring gear 2 - Yes 3 - Depends on wheel bearing size 4 - 400HP+ The 8" ring gear is as strong, if not stronger when set up correctly than a GM 10 Bolt if that gives you any indication. 9" is overkill for about 85% of street driven vehicles. The 8" has the same 3-bearing pinion setup that the 9" has. This prevents the pinion from "flexing" away from the ring gear under hard acceleration. Posi, while not as easy to find as 9", are not impossible. Most likely junkyard candidates are Mavericks. Gear selection too, while not as wide as the 9", isn't bad either.
Boones Some 8" axles will fit some 9"rears. The 57 to 59 9" will fit under a 65/66 Mustang with the stock Mustang axles and brakes if the axles have the same spline. 57/59 spring pads are about 1/8" wider and we used to just force the springs out and never had any problem. If I remember correctly the 57/59 rear fits 67/68 Mustang springs. I never had to shorten a 57/59 rear to fit 65/66 Mustang and I don't remember a Maverick being narrower. It's been 30 years since I messed with a Ford though. Judd
The easy and CHEAP way to get 9" Ford, 31 splines and narrow is the start witha 66 - 68 Ford passenger car rear. They are fairly easy to find and nobody wants them because they are too wide.... The short axle is 29 and 13/16 inches long The long one is 32 and 1/16 long Narrow the long side of the housing 2 and 1/4 inches......and the stock short axle fits....as is Narrow the short side of the housing.....4 and 5/16 inches Have the long axle resplined to 25.5 inches. Now you are 55 and 3/4 inches wide, have 31 splines and have paid for 1 axle. Donor cars are..... 66-68 Fords 68 Lincoln Mark III 66-68 Mercury 67-68 Thunderbird Some of these donor cars have 28 spline also......check the tag before you pay the money. I cut mine with a tubing cutter.......and clean the ends up on a lathe so I can reuse them. The 66 - 68 Fords have big nice brakes, self adjusters and the replacable parts are available at NAPA .
If your going to re spline 31 spline axles you may as well just use stock 28 splines cause you take out all the hardening when re splined. Not a bad idea to use the short axle as the long one and buy just one aftermarket axle.
I believe in overkill when it comes to building for performance. My 9 inch has a set of 3:89.1 and a Detroit Locker.
Thanks everyone for all the details. I am not more knowledgeable then I was 30 minutes ago.. As a chevy guy I have lots of Ford things to learn.. I will be enjoying the ease of pimpkin swapping of the ford rear. Some strong gears for around town and whopping on FlamedAbone's ride and then a nice set for taking those longer drives to distance shows.. Again, I appreciate everyones help....
[ QUOTE ] If your going to re spline 31 spline axles you may as well just use stock 28 splines cause you take out all the hardening when re splined. [/ QUOTE ] 28 spline axles taper down after the spline......not enough meat to respline....... The upper one is a 31.....the lower one is a 28 Ken ...go here..lots of neat Ford rear end info. http://www.kevinstang.com/Ninecase.htm
What I meant was a re splined 31 spline axle is only as strong as a 28 spline factory stock axle because when you re spline the axle you are removing the induction hardening the factory puts there thats only .100" deep (aprox) I would even bet that a re splined 31 spline axle is weaker than a factory 28 spline axle.
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