Swapping Out Coarse Slpine Birfields

[Boone73FJ]

I know yall have seen this question before but I couldnt seem to find an answer to my question. I have a 73' 40 and I am getting ready to put lockers in the front and rear. I have been reading alot about how weak the coarse spline birfields are. My drum brakes run great and I was wondering if I could swap out the coarse spline birfs. for the later/stronger fine spline birfs. without converting to disc brakes??.. Would the price be about the same either way?

 

[jcj_78FJ40]

This might point you in the right direction.

https://forum.ih8mud.com/showthread.php?t=86570&highlight=birfield

 

[Boone73FJ]

Yeah I saw that post. Still wondering if it can be done without converting to mini truck disc brakes.

 

[zetasig]

You gotta change the lock outs too. the course spline birfs mate up to a course lock out.

Need to get later Warn Premium hubs or Aisins from a mini truck, I think that would work though.

Kind of like polishing a turd though.
Problem is, your drums are working fine now. What will happen when you take everything apart to put in the new birfs. Plus, when you put in the lockers are you going to rebuild the axles? Knuckles etc.

My problem always seems to be when it works fine and I dick with it it doesnt work fine any more.

.02

 

[Degnol]

Plus, I think you need to grind a little off the axle housing end to fit the slightly larger birf ..... the 27 spline. By then, you have the knuckles off and might as well swap in the disc knuckles....I mean you gotta put something back there.
Yes, can be done, but it is kinda like replacing the throwout bearing without doing a clutch and rear main seal at the same time. At least to me, but that is not relevant

Ed


ED-it......Whoops...covered by Poser in the link!

 

[jcj_78FJ40]

Are the course spline birfs really that much weaker than the fine splines? I always assumed that most people did this conversion to get the disk brakes.

Since the inner splines are the same, I would put in the lockers with the birfs that you have. You can always upgrade later if you have problems.

 

[Mark W]

The coarse spline birfs are a lot weaker than the fine spline. Smaller bell and smaller stub shaft.


Mark...

 

[Degnol]

"Front locker" is the deal breaker here....I believe

Ed

 

[Ian Rogers]

I run coarse spline birfs and an ARB locker, i will tell you that i only flip the switch on when i need it and then right back off. It works but you have to be on your a game.

 

[1973Guppie]

swap to mini discs and put some longfields in there while you are at it.

Noah

 

[jcj_78FJ40]

Question after reading Tech Trivia;

Are the 76-78 fine splined birfield bells larger than the course splined axels yet smaller than the mini axels?

 

[Mark W]

In '79 the Cruiser and the mini birfields got a slightly larger bell.


Mark...

 

[numtel]

I run coarse spliners with a locker and discs with my cruiser with 34's. I haven't broken one with lots of wheeling. I've got tons of spares but haven't needed them. If you're running big enough tires to need the the better birfs though, you need disk brakes in the front. It's that simple.

 

[pygpen]

As Mark eluded too, the fine spline birf has a larger stub so he will have to swap the spindle, hub, birfield, and lockout at a minimum (probably more). At that point he may as well do the complete conversion.
Also, there were fine spline drum brakes available overseas for a long time after north america got the disc brakes, but they are the exception to the rule.

PMK

 

[jcj_78FJ40]

In '79 the Cruiser and the mini birfields got a slightly larger bell.


Mark...

Just to clarify because I’m running stock 78 birfs with an ARB;

Pre 79 fine spine and course spine birfs have the same bell size and are relatively equal in strength. The 79 and later birfs are stronger due to the larger bell?

Thanks

 

[DSRTRDR]

I run coarse spline birfs and an ARB locker, i will tell you that i only flip the switch on when i need it and then right back off. It works but you have to be on your a game.

same here, coarse spline and ARB; some combined 30 days of challenging wheeling in Moab and Arizona over the last two years have not broken a coarse spline birf yet (in its previous life, thr truck also lived for a while in Moab and and POs left itl coarse spline). My take is that if you don't beat on it, they can hold just fine.

 

[Mark W]

Just to clarify because I’m running stock 78 birfs with an ARB;

Pre 79 fine spine and course spine birfs have the same bell size and are relatively equal in strength. The 79 and later birfs are stronger due to the larger bell?

Thanks

No. All the fine spline birfs are bigger and stronger than all of the coarse spline ones. The post '78 are just a little bigger and stronger still than the '76-78 parts.


Mark...

 

[Mark W]

As I think about this question a bit more, I don't think it can be done. I do not thinl that the stub shaft of the fine spline birf will fit through the sindle of the drum brake knuckle. That ends the swap right there, ';casue I'm pretty sure that the bearings to fit the larger spindle will not fit the drum brake wheel hub. I could dig out some parts and check to be sure, but to be honest, it's not worth it. Loose the drums and install discs.


Mark...

 

[Boone73FJ]

Yea thats what Im going to do. Converting to disc seems much more practical in the long run. Thatnks for all of the feedback.