Potential 14B FF I'm looking at thoughts needed

[SirRobyn0]

Ok so I'm looking at possibly purchasing this rear end. As some of you might remember I currently have a 3.41 14B SF in my 84 C20. I need lower gears and would like to go to FF. The one I'm looking at is a 14B FF, seller described as " 14 bolt FF that is a later model unit, but was modified to fit a square." I asked if he knew the approximant year of the axle he said no. He also said that modifications done were solid. He got the truck for parts, so he did not modify or install the rear end. I'm assuming it is out of a GMT-400 but obviously have no idea if it is out of a van or truck. IDK what modifications would have been needed from one of those rigs to make it work in a square. I know and understand the pit falls of buying a used rear end. The plan would be pull the cover, inspect, change fluid replace the brake shoes, springs, cylinders and drum / axle bearings. Hopefully the pinion and ring and pinion are ok.

The main thing I need advice on is what would likely have been modified to make a GMT-400 fit in a square? And any pit falls you can think of relating to that I should be concerned with if I go look at it in person? Given the limited information available what do you think is the likely hood of requiring driveline modification, beyond possibly a different U-joint. If it's a bad idea to get involved in this please say so.

Differential is priced reasonably and is geographically close to me, which both make it attractive. Here's the pic from the seller, maybe you'll see something in it noteworthy. (computer is being difficult hopefully will have a pic up momentarily.)

Thanks!

 

[SirRobyn0]

Ok here is a pic of the unit I'm looking at.

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[bucket]

It's just a matter of moving the spring perches and shock mounts to fit it in a square. Just make sure that the perch spacing (32.5" iirc) fits your C20 and the shocks are staggered correctly. If it was fit for a C/K 30, they will be staggered the opposite way.

Also keep in mind that there were two different track widths for the GMT 400. Iirc, one is a little narrower than a square, and one was a little wider. I know that's the case with the 5/6 lug trucks, but can't remember for sure about the heavier trucks.

 

[SirRobyn0]

It's just a matter of moving the spring perches and shock mounts to fit it in a square. Just make sure that the perch spacing (32.5" iirc) fits your C20 and the shocks are staggered correctly. If it was fit for a C/K 30, they will be staggered the opposite way.

Also keep in mind that there were two different track widths for the GMT 400. Iirc, one is a little narrower than a square, and one was a little wider. I know that's the case with the 5/6 lug trucks, but can't remember for sure about the heavier trucks.

So basically my take away on that is measure my current axle, make note of perch location, shock location and measure this axle to see if it will work as is. Thanks for the info.

 

[Bextreme04]

From the pic, it's not from a late GMT-400 if it came off one. I have an original 14BFF in my 1980 K25 and those look like the same perches and shock mounts that I have on my original axle. I also have a 14BFF from a 1997 K2500 Suburban and they are different perches and shock mounts. The one I have also has the drums that can be removed without disassembling the hubs. Later 14BFF will have the ribbed housing also.

 

[SquareRoot]

I agree with Bucket. I swapped in a 14FF out of a CUCV into my 85 K20. Figured out some tricks along the way if your going to do it in your driveway like I did.

Cut the spring perches and shock mounts off and throw them away! Don't be tempted to carefully remove them and reuse them. It's a PITA and more work than it's worth. Buy these new mounts/perches from Currie. They are HD and fit the tube perfectly. Use a digital level and weld the perches on at the EXACT same angle they came off the old one.

Mount the axle under the truck and then mount the shock mounts on the shock and THEN extend and position shock mount and tack weld in place. Then go back and weld them up. Don't forget to stagger them front/rear. If the axle is in the truck, it's impossible to screw that up due to the upper mounting location.

Driveline length wont change going from SF/FF. If you have an auto trans and NOT a Detroit Locker out back it should be a smooth ride. If yes, welcome to the Detroit Bang Bang club.

Check back in when you can't figure out how to bleed the air out of the brakes. That's another story that gets asked weekly. LOL

 

[SirRobyn0]

From the pic, it's not from a late GMT-400 if it came off one. I have an original 14BFF in my 1980 K25 and those look like the same perches and shock mounts that I have on my original axle. I also have a 14BFF from a 1997 K2500 Suburban and they are different perches and shock mounts. The one I have also has the drums that can be removed without disassembling the hubs. Later 14BFF will have the ribbed housing also.

That's a really good point. Seller said it was modified to fit a square, so when I was initially reading your post I though well the perches were swapped. But it's very obvious that those drums don't slide off. Given what @bucket said I wonder if it was modified from a C30 to go in a C20 or 25. Huh. I guess the thing is to pay attention and be sharp if I go look at it. Thanks for the info.

 

[SirRobyn0]

I agree with Bucket. I swapped in a 14FF out of a CUCV into my 85 K20. Figured out some tricks along the way if your going to do it in your driveway like I did.

Cut the spring perches and shock mounts off and throw them away! Don't be tempted to carefully remove them and reuse them. It's a PITA and more work than it's worth. Buy these new mounts/perches from Currie. They are HD and fit the tube perfectly. Use a digital level and weld the perches on at the EXACT same angle they came off the old one.

Mount the axle under the truck and then mount the shock mounts on the shock and THEN extend and position shock mount and tack weld in place. Then go back and weld them up. Don't forget to stagger them front/rear. If the axle is in the truck, it's impossible to screw that up due to the upper mounting location.

Driveline length wont change going from SF/FF. If you have an auto trans and NOT a Detroit Locker out back it should be a smooth ride. If yes, welcome to the Detroit Bang Bang club.

Check back in when you can't figure out how to bleed the air out of the brakes. That's another story that gets asked weekly. LOL

Well it's been modified so the hope would be that the modifications were done well enough that I can simply install it. If I think I will need to cut and install new perches then I'm going to use that for leverage for a lower price.

I was going to say this. I have no idea if it's an open diff, a gov-lock or Detroit or??? Many moons ago I had a friend with a 72 C30 with a Gov-Lock and I will say it helped get me out of a tight situation or two, but I can also remember a few down falls too. Honestly I don't think I really care to much either way. With the trailer I'd probably like the security of the extra traction though when I have to drag it around someones farm to get a load.

 

[Blackbeard44]

theres quite a few 14 bolt fullfloaters from squares to be had around Tacoma/Oly, I had a posting last week on CL looking for one and had quite a few replies, had my brother get one from fed way for $200 to rebuild and ship down to me, I wouldnt mess with something thats modified to fit unless its dirt cheap

 

[bucket]

Well it's been modified so the hope would be that the modifications were done well enough that I can simply install it. If I think I will need to cut and install new perches then I'm going to use that for leverage for a lower price.

I was going to say this. I have no idea if it's an open diff, a gov-lock or Detroit or??? Many moons ago I had a friend with a 72 C30 with a Gov-Lock and I will say it helped get me out of a tight situation or two, but I can also remember a few down falls too. Honestly I don't think I really care to much either way. With the trailer I'd probably like the security of the extra traction though when I have to drag it around someones farm to get a load.

How far are you from Sultan?

 

[Grit dog]

How far are you from Sultan?

He's close. John Addington probably has 1, or 8 of them!

 

[SirRobyn0]

How far are you from Sultan?

I'm responding to you VIA PM.

 

[SirRobyn0]

He's close. John Addington probably has 1, or 8 of them!

And you.

 

[AuroraGirl]

heres 80 gmc with 4.10 and c6p. the shock mounts are larger and sturdier looking. brakes are bigger

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heres a 76 c20 with smaller brakes, prob ratio like robyn but im unsure, and smaller shocks

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his seems it may be diff than an OE from atl east 80?

 

[Craig 85]

Probably everything you ever want to know about a 14 bolt.

14 Bolt Bible
http://www.billavista.com/tech/Articles/14-Bolt_Bible/index.html