10 bolt to 14 bolt SF

[Alumbaugh]

Found a local donor truck (1984 Pickup) with a 14 bolt SF 9 1/2" ring. Was originally told it was a 12 bolt, but I need to crawl under it to check. I know (think) I'll need a special u-joint to mate up, but will there be any modifications I'll have to do to mount it under my '91 Blazer? I know a 14 bolt FF has to be modded a little, just not sure of the SF.

 

[lectric80]

Neither axle has to be modified to fit if it is out of an 84 3/4 ton truck. You will need a conversion joint to mate up, since the 14b uses a 1350 joint. I have a 14bsf sitting at the house that I haven't gotten around to getting installed.

 

[Alumbaugh]

PS - Also, is there any way to tell what the gear ratio is other than to open the case or spin the tire and count? Was curious if there should be any stickers or markings on the body.

 

[lectric80]

There won't be any outside markings that I am aware of. Spinning tires and couting or counting teeth are the only ways that I know of to get the gear ratio.

 

[dyeager535]

You can check for the RPO, if the sticker is there, and if the axle is original.

RPO's start with "G" for axle stuff, G80 will be a gov-lock on these trucks, while any other "G" RPO should be the ratio. If the RPOs are four characters then the second character is where it actually starts.

1984 not sure where the RPO tag was put, my '83 was on the engine side of the inner fender. Others are in the glove box.

 

[Alumbaugh]

Are there any codes to decipher? My Chilton's doesn't seem to address this. There are good articles on thr FF axle, but not much on the SF. Will the brake lines mate up? And what about the e brake cables? Didn't say before, but I'm running a '91 with coporate 10's front and rear with a 700r-4. All stock.

 

[dyeager535]

On *MY* 10 bolts (about 1985 donor) the fitting on the brake cylinders was at a different angle for the brake line, but not a big deal.

E-brakes will be different, I *think* the 10 bolt e-brakes will work if you remove the cables from the backing plates. Don't cut any of the cables on the '91. The '84 e-brake setup is completely different and isn't directly "swappable".

You can probably google "GM RPO Codes" and just write down all the ones that start with "G" that deal with axle ratio. The "standard" RPO won't do you any good, have to deceipher that based on year, trans, etc.

It's just easier to pop the cover. I wouldn't pull a diff before removing the cover, checking ratio, and most importantly checking condition.

 

[Alumbaugh]

Yea, need to check out the condition of the gears anyway and verify if the gear ratio anyway!