28 spline or 31 spline

[undercnstrction]

i've read the term "28 spline" and "31 spline" on here numerous times. can someone tell me exactly what that means and if i should change mine over to a 31 spline, how hard it is to change, etc? my intentions are to (at this point) run 351/408. will a 28 spline hold up?

i believe it means the number of "teeth" on the end of the axle that goes into the diff?

there is a guy on corral that is selling stuff off of an '88 saleen that sounds like it should convert my 4 lug to a 5 lug and i'm wondering if this stuff will bolt right up to my '87 without going through the "hassle" of converting to
sn95 pieces. if that is the case, will i be limited in other areas (brake discs, wheels, etc).

i sent him an email and this was his response......."yes i have the front five lug rotors,and the rear five lug axles,but the axles are 31 spline,and the factory axles are 28 spline"

i believe he's asking $250 for the pieces so i don't know that it's worth the price since i can get the junkyard sn95 parts for less than that, but it's an option......

 

[302Feen]

i've read the term "28 spline" and "31 spline" on here numerous times. can someone tell me exactly what that means and if i should change mine over to a 31 spline, how hard it is to change, etc? my intentions are to (at this point) run 351/408. will a 28 spline hold up?

Technically yes, a 28 spline axle and trac-lok will hold up, but it all depends on how much torque your making and if you plan on doing a lot of racing. The 31 spline will hold up better under harsher conditions.

i believe it means the number of "teeth" on the end of the axle that goes into the diff?

You are correct. It is the amount of splines on the end of each axle.

there is a guy on corral that is selling stuff off of an '88 saleen that sounds like it should convert my 4 lug to a 5 lug and i'm wondering if this stuff will bolt right up to my '87 without going through the "hassle" of converting to
sn95 pieces. if that is the case, will i be limited in other areas (brake discs, wheels, etc).

i sent him an email and this was his response......."yes i have the front five lug rotors,and the rear five lug axles,but the axles are 31 spline,and the factory axles are 28 spline"

i believe he's asking $250 for the pieces so i don't know that it's worth the price since i can get the junkyard sn95 parts for less than that, but it's an option......

In order for you to use those 31 spline axles, you have to get a 31 spline trac-lok. You can actually get a 31 spline t-lok out of the earlier Explorers/Mountaineers with the 8.8 rear end. I currently have a 31 spline t-lok out of a '97 Mountaineer, I'm going to hold on to it until I can afford the matching axles.

 

[undercnstrction]

thanx for the info.

at the risk of sounding like a complete newb......how can you tell which rear end a certain vehicle has? are they stamped "8.8" or "7.5" on the housing?

i just went through the JY sticky and there are a number of cars/trucks that have usefull rear end parts but you have to know which diff they are coming out of.

 

[skunk21]

The rear covers/bolts pattern are different between the 7.5 and 8.8.

The 7.5 cover is much more flatter at the top and more oval looking than the 8.8. The 28 splines do hold up but they also do snap, better grade aftermarket 28's are better than stock ones but 31's do provide extra strength over the 28's. If you go with 31's you will have to change out the differential to a 31spline unit since the stock one only takes 28spline axles. I have read post's with stock motor cars breaking stock axles and decent powered cars not breaking them, but your chances improve with the 31's of not breaking. If you are going to make some decent power which it look like you are then going the 31spline route might not be a bad idea and while it's apart welding the tubes would be smart also. I'm running 31's with the '03 cobra diff set up for future motor mods.

 

[undercnstrction]

welding the tubes would be smart also./QUOTE]

thanx for the response. that clears it up completely!

what do you mean by "tubes"?

 

[90lxcoupe]

If your already on corral find somebody ditching a axle they already built with the gears you want in it, it will save you hassle and be easier just to swap out the whole axle rather than doing everything with it still in the car

 

[undercnstrction]

good point.

my only hesitation i don't have the slightest idea what gears i'm going to need/want with the new motor. i believe it has 3.08s or 3.27s now but don't know for sure. i would suspect that i'll want to change over to something a bit "steeper" but i don't know how steep.

 

[90lxcoupe]

It all depends on what trans your gonna run, what tire size and what RPM you wanna cuise at on the highway at a given MPH.

3.73's are an excellent all around gear, thats what im running now and at 80mph im only turning about 2500 rpms with a 28'' tire, im switching to a 4.30 gear and its gonna make me turn 2500rpms at 70mph now, but im sacrificing highway cruising a little bit so i can be at a better rpm through the traps. Before i was at about 53-5500 at the line, now i will be around 6500 which will put me on the limiter on my current cam setup... but the cams probly gonna change too

 

[skunk21]

welding the tubes would be smart also./QUOTE]

thanx for the response. that clears it up completely!

what do you mean by "tubes"?

The "tubes" are the hollow part of the rear end where the axle shafts are inside of basically. you would weld the tube where it's pressed into the diff housing. This can be a weak spot and the tube can rotate, etc. here is a pic of a welded up 8.8.

 

[undercnstrction]

The "tubes" are the hollow part of the rear end where the axle shafts are inside of basically. you would weld the tube where it's pressed into the diff housing. This can be a weak spot and the tube can rotate, etc. here is a pic of a welded up 8.8.

GOT IT! thankx.

 

[undercnstrction]

It all depends on what trans your gonna run, what tire size and what RPM you wanna cuise at on the highway at a given MPH.

3.73's are an excellent all around gear, thats what im running now and at 80mph im only turning about 2500 rpms with a 28'' tire, im switching to a 4.30 gear and its gonna make me turn 2500rpms at 70mph now, but im sacrificing highway cruising a little bit so i can be at a better rpm through the traps. Before i was at about 53-5500 at the line, now i will be around 6500 which will put me on the limiter on my current cam setup... but the cams probly gonna change too

that's all still up in the air. i suppose i should probably just run the gears i have, use the 28 spline axles out of a ranger/explorer or sn95, and see where the RPMs end up once the motor is done and back in the car. all of that is a ways down road. i've seen many, many guys that are running 3.73s but if i end up with the 408ci motor that i'm leaning towards i'd hate to guess where that would put me RPM wise. i don't want to cut my top speed back too much if i plan to run any open road races.

 

[GSP393]

For mine I'm going to have a 393/auto with 4:10s. I've got a brand new motorsport 4:10 set in 28 spline. I'm going to use either Moser or Superior axles.

 

[undercnstrction]

what are your intentions for the car? is it going to be a drag car?

 

[Repostyle]

I would just run ranger axles, and only change the gears to 3.73's. Switching to 31 spline axles is costly and unless its a track only car running 500hp+ on slick tires, the chances of them braking are pretty slim for a street car.

You do need a 31 spline differential to go with 31 spline axles. Stock gear ratio is 2.73 for 8.8. 5.0's have 8.8 and 4 silly's have 7.5" rear ends.

 

[projectfiveo]

not to hijack the tread but whats the best way to beef up the rear end to hold a 408 stroker without going with a 9" rearend? all i have right now is 5 lug conversion a girdle with 3.73...

 

[GSP393]

I'll be cranking atleast 500hp and as long as everything is hardened with 28 splines, I can't see how adding 3 more splines is going make or break the rearend. I can see how it would break the bank though.


Update: 28 spline hardened axles behind an automatic will work. 500hp with a standard needs 31 splines.

 

[undercnstrction]

I'll be cranking atleast 500hp and as long as everything is hardened with 28 splines, I can't see how adding 3 more splines is going make or break the rearend. I can see how it would break the bank though.


Update: 28 spline hardened axles behind an automatic will work. 500hp with a standard needs 31 splines.

just out of curiosity, what made you go with the 393 instead of a larger displacement stroker? i haven't decided 100% on what i'm going to do with the engine but i'm seriously leaning towards the 408.

why does the standard need the 31 spline? while the AT does not?

 

[SVT32VDOHC]

I made 414RWHP with my 96 Cobra. 4.10's, diff cover and Nitto's. Ran for 5 years at the track, no problems with 28 splines. You know what went out?.....my clutches in the diff. I had them rebuild my diff with an Explorer carrier and new clutches and upgraded to 31 splines just because they were out already. I would not have torn it apart just because.

If you got up to 5 lug, and you are building a rear, just get the 31. It's already out and you gotta buy parts anyways. If you bolt on slicks, you better get them. My friend ran 11's on radials and was fine with 28's, but when he got into the 10's with slicks....after a few hard launches, he twisted them.

CLIFFNOTES: You only need 31 splines if you launch hard and hook up. If you spin...you don't need them.

 

[undercnstrction]

i really have no plans to hit the drag strip with this car. it will be used on the street with the occassional autocross, roadcourse and possibly some open road racing. from what you guys have said, i should be fine with the 28 spline. but like you've stated, if i pull the rear end apart, i'll probably seriously consider looking at upgrading at that point since it would be in pieces anyway. thanx for all of the input

 

[SVT32VDOHC]

No problem. 28's will be fine with all that but like I said, if it's apart and you need to buy anyways...go 31. You don't have to spend 500-600 on an Eaton or Aurburn carrier. My shop built me an explorer carrier for $40.00. Usually they charge 125-175, but I always take care of them...so that was their return.