Swapping from 14B semi-float to 14B full float

[SirRobyn0]

My 1984 C20 is currently equipped with the 14 bolt semi-float. I'm not happy with the gearing for towing as it has the 305 and 3.41 gears. We've had discussions on other threads about changing the gearing and pretty much decided I'd be best served with 4.56 but a 4.10 would do. I've always wanted to go full floater for the obvious reasons, since I haul a lot with the truck and often take it 100 miles or so for feed hauls.

I've always figured I'd re-gear the existing rear end one of these days and just live with the semi-float, but now it appears I have a bent right rear axle. So basically to turn this rear end into something reasonable for my uses, I'd need to rear gear it $300 if I do it myself, and I'd want to replace both axles, at a cost of about $175 an axle plus shipping. So that totals up to about $650 assuming I don't find any other problems in there and it's still the semi-float.

So I'm taking another more serious look at swapping to the 14B FF, this would have to come out of a wrecking yard. Since I'm in the auto repair business, and there are not many wrecking yards left near me I'd probably order it from LKQ. The good news in this is that I'll be able to order a full floater that has came out of a truck of the same or close year. I've done some research and searches already, but it seems like most threads guys are moving to much newer rear ends or swapping in something they have on hand like van rear end.

So my questions. Truck currently has 14B SF, want to swap to 14B FF.

Will I need a conversion U-joint or is this only needed for 1/2 trucks?
Will I need to shorten or lengthen the driveline?
Will I need the U-bolts for the FF?
Any down sides to switching to FF?

Anything else ya'll can think of?

I'm open to discuss if looking for Gov Lock unit is a good idea.

I'm sure if I prep ahead of time I can get the swap done in an afternoon. My main concern is major snag like driveline difference and the truck is apart, because I can't afford to have it down for to long as the farm depends on this truck.

Thanks.

 

[75gmck25]

I have a 14 bolt FF in my ‘75 K25, but can’t really answer your detailed questions. GM was not really that consistent sometimes, so u-joint and driveshaft setup seemed to change over the years. My transfer case length sets the front u-joint farther back, and I have a one-piece driveshaft with my 8 foot bed. On a 2WD you might need a center carrier and two piece shaft.

I have 4.10 gears and an operational gov-lock, and it works fine for hauling heavy loads. However, all the aftermarket limited slip and locking differentials require an open carrier to start with, so swapping to anything better is more complicated . Upgrading to an aftermarket locker might be worth it for off-roading or if I was hauling in a lot of mud or snow, but I am usually on pavement or good quality gravel roads.

If you buy a 14;bolt FF axle, make sure you service the brakes before you install it. You have to pull axles to get the brake drums off, and those big 13” drums are more expensive. It could add quite a bit to your cost.

 

[Bennyt]

Will I need a conversion U-joint or is this only needed for 1/2 trucks?
Will I need to shorten or lengthen the driveline?
Will I need the U-bolts for the FF?
Any down sides to switching to FF?


I'm open to discuss if looking for Gov Lock unit is a good idea.

Thanks.

I swapped a 14b SF in a friends K5 and a 14b FF in my K5 many years ago so not exactly fresh in my mind but from what I recall...

You may need a conversion joint based on what you have and what you buy. I think 14B sf came with two diff sizes; 1350 and the R style, while the 14B came with both a 1350 or 1410.
You should be ok without shortening the driveshaft. I do believe that the FF is slightly longer than the SF but not by enough to bottom out. Neither of the trucks I swapped required a shorter shaft. One originally had a 12B and the other a 10B.
Yes, the axle diameter is larger, so you'll need new U-Bolts.
No downside except for weight. The later ones don't require you to pull the axles to service the brakes if I recall.
The van 14B FF are wider which some people like to match the width of the front axle.
Isn't the Gov-Lock also known as the Gov-Bomb? I have no experience as I used a Detroit in mine.

 

[Bextreme04]

My 1984 C20 is currently equipped with the 14 bolt semi-float. I'm not happy with the gearing for towing as it has the 305 and 3.41 gears. We've had discussions on other threads about changing the gearing and pretty much decided I'd be best served with 4.56 but a 4.10 would do. I've always wanted to go full floater for the obvious reasons, since I haul a lot with the truck and often take it 100 miles or so for feed hauls.

I've always figured I'd re-gear the existing rear end one of these days and just live with the semi-float, but now it appears I have a bent right rear axle. So basically to turn this rear end into something reasonable for my uses, I'd need to rear gear it $300 if I do it myself, and I'd want to replace both axles, at a cost of about $175 an axle plus shipping. So that totals up to about $650 assuming I don't find any other problems in there and it's still the semi-float.

So I'm taking another more serious look at swapping to the 14B FF, this would have to come out of a wrecking yard. Since I'm in the auto repair business, and there are not many wrecking yards left near me I'd probably order it from LKQ. The good news in this is that I'll be able to order a full floater that has came out of a truck of the same or close year. I've done some research and searches already, but it seems like most threads guys are moving to much newer rear ends or swapping in something they have on hand like van rear end.

So my questions. Truck currently has 14B SF, want to swap to 14B FF.

Will I need a conversion U-joint or is this only needed for 1/2 trucks?
Will I need to shorten or lengthen the driveline?
Will I need the U-bolts for the FF?
Any down sides to switching to FF?

Anything else ya'll can think of?

I'm open to discuss if looking for Gov Lock unit is a good idea.

I'm sure if I prep ahead of time I can get the swap done in an afternoon. My main concern is major snag like driveline difference and the truck is apart, because I can't afford to have it down for to long as the farm depends on this truck.

Thanks.

I have a 14BFF from a 97 K2500 Suburban with the big 13" drums that I'd give you a good deal on. It is 4.10 open diff. It would give you the benefit of having the drums that can be removed without removing the axle, but you would need to cut off the old spring perches and weld on new ones in the right location.

If you want something that can just drop in, check with Jon Addington at Mr. A's chevy parts near Vancouver, WA or one of the other squarebody parts sellers in the area. There is a place called Squarebody Ranch in Battleground and also a few guys that part them out. You can probably go into the PNW K5 & Squarebodies group on facebook and ask around, I bet more than 1 person has an axle sitting in their backyard that would work.

 

[SirRobyn0]

I have a 14 bolt FF in my ‘75 K25, but can’t really answer your detailed questions. GM was not really that consistent sometimes, so u-joint and driveshaft setup seemed to change over the years. My transfer case length sets the front u-joint farther back, and I have a one-piece driveshaft with my 8 foot bed. On a 2WD you might need a center carrier and two piece shaft.

I have 4.10 gears and an operational gov-lock, and it works fine for hauling heavy loads. However, all the aftermarket limited slip and locking differentials require an open carrier to start with, so swapping to anything better is more complicated . Upgrading to an aftermarket locker might be worth it for off-roading or if I was hauling in a lot of mud or snow, but I am usually on pavement or good quality gravel roads.

If you buy a 14;bolt FF axle, make sure you service the brakes before you install it. You have to pull axles to get the brake drums off, and those big 13” drums are more expensive. It could add quite a bit to your cost.

Thanks for the info. My biggest concern on the Gov Lock is not owning one. I had one in a 72 years ago that held up fine. I don't do anything that would constitute abuse for a Gov lock, my biggest concern would be getting an diff, installing it and finding that the Gov lock is already damaged or non-functional. The benefit would be in the fields on the farm / dirt and snow. Good point on cost of servicing the new axle.

I swapped a 14b SF in a friends K5 and a 14b FF in my K5 many years ago so not exactly fresh in my mind but from what I recall...

You may need a conversion joint based on what you have and what you buy. I think 14B sf came with two diff sizes; 1350 and the R style, while the 14B came with both a 1350 or 1410.
You should be ok without shortening the driveshaft. I do believe that the FF is slightly longer than the SF but not by enough to bottom out. Neither of the trucks I swapped required a shorter shaft. One originally had a 12B and the other a 10B.
Yes, the axle diameter is larger, so you'll need new U-Bolts.
No downside except for weight. The later ones don't require you to pull the axles to service the brakes if I recall.
The van 14B FF are wider which some people like to match the width of the front axle.
Isn't the Gov-Lock also known as the Gov-Bomb? I have no experience as I used a Detroit in mine.

Good info on sizes U-joint ect. I did not know. Thanks.

 

[SirRobyn0]

I have a 14BFF from a 97 K2500 Suburban with the big 13" drums that I'd give you a good deal on. It is 4.10 open diff. It would give you the benefit of having the drums that can be removed without removing the axle, but you would need to cut off the old spring perches and weld on new ones in the right location.

If you want something that can just drop in, check with Jon Addington at Mr. A's chevy parts near Vancouver, WA or one of the other squarebody parts sellers in the area. There is a place called Squarebody Ranch in Battleground and also a few guys that part them out. You can probably go into the PNW K5 & Squarebodies group on facebook and ask around, I bet more than 1 person has an axle sitting in their backyard that would work.

Though I could do the welding I'd rather stick to as close to original as possible for the purpose of simplicity and time for install. So thanks, but I'll pass on the one you have. I was unaware of the Mr A' or the Ranch I will check them out!

 

[Bextreme04]

Thanks for the info. My biggest concern on the Gov Lock is not owning one. I had one in a 72 years ago that held up fine. I don't do anything that would constitute abuse for a Gov lock, my biggest concern would be getting an diff, installing it and finding that the Gov lock is already damaged or non-functional. The benefit would be in the fields on the farm / dirt and snow. Good point on cost of servicing the new axle.



Good info on sizes U-joint ect. I did not know. Thanks.

The gov-lock in the 14BFF is incredibly simple. Make sure you take the cover off and inspect the ring gear and inside of the case and you should be fine. If it is bad, you'll know by all the carnage that you will see inside there when you take the cover off. Otherwise they are almost indestructible, but I would suggest a full rebuild of the new-to-you diff when you get it. Parts aren't that expensive for it and it's a super easy rebuild with lots of info out there for how to do it. The only special tool you will need is a monster press for the pinion bearings and crush sleeve. Seriously, you need at least a 20 ton press to get the crush sleeve to start going(which you will want to do before you install the nut and start setting preload for real). If you don't get the crush sleeve going in the press first, it can take upwards of 500 lb-ft of torque on the nut to get the crush sleeve to start going. Once it starts it takes very little force to crush it further though.

 

[SirRobyn0]

The gov-lock in the 14BFF is incredibly simple. Make sure you take the cover off and inspect the ring gear and inside of the case and you should be fine. If it is bad, you'll know by all the carnage that you will see inside there when you take the cover off. Otherwise they are almost indestructible, but I would suggest a full rebuild of the new-to-you diff when you get it. Parts aren't that expensive for it and it's a super easy rebuild with lots of info out there for how to do it. The only special tool you will need is a monster press for the pinion bearings and crush sleeve. Seriously, you need at least a 20 ton press to get the crush sleeve to start going(which you will want to do before you install the nut and start setting preload for real). If you don't get the crush sleeve going in the press first, it can take upwards of 500 lb-ft of torque on the nut to get the crush sleeve to start going. Once it starts it takes very little force to crush it further though.

Thanks for the Press tip. I have a 20 ton at work so that is doable.

 

[Curt]

Get a FF 14 bolt from pre 1980 3/4 ton.2wD or 4WD,don’t matter.I believe starting year was 1973’.Can’t be a 1 ton as the perches are narrower. .I believe the spring perch center to center is either 42.5” or 43.5”.Somewhere there.It’ll bolt right.No conversion ujoints needed.

 

[SirRobyn0]

Get a FF 14 bolt from pre 1980 3/4 ton.2wD or 4WD,don’t matter.I believe starting year was 1973’.Can’t be a 1 ton as the perches are narrower. .I believe the spring perch center to center is either 42.5” or 43.5”.Somewhere there.It’ll bolt right.No conversion ujoints needed.

Good info thanks, yup I really want this to be a simple as possible, partially because I like simple but also because I can't have the truck down for to long this time of year.

 

[Rusty Nail]

Where are all of the 84 C20 pix yo?

 

[SirRobyn0]

Where are all of the 84 C20 pix yo?

@Rusty Nail I'm terrible I know. I've always been terrible to think of taking pictures, and the ones I do take are usually crappy. But just for you. Not that any of these pictures are related to the axle but I know you got to see them.

Below: After a recent wash and wax, but the pic must be a few months old because she's got her old tires on still....

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Below: There's the new tires! And the big trailer.

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Below: The truck and the big trailer, on a jobsite. What I'm doing is removing a storage building. This was a 7 X 14 building so it should have been able to fit in the trailer in one piece but the location of the shed made taking it apart a requirement. I don't do these jobs much anymore, because they often end up being more complex and time consuming then I'd like. Also more physically demanding than what I'm up to these days, but I use to make a side income with it.

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Below: Feed haul for the farm, at a highway rest area. That's 8 55 Gallon drums of feed.

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Below: Last winter heading out for a run over the pass. I remember being concerned about trailer and snow in the pass, but the trip was uneventful and the tire chains we not needed.

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[Rusty Nail]

Man that's exciting it's such a good lookin 20...what a great year for that truck! I bet she gets all the whistles. Thanks for the picks.

 

[SirRobyn0]

Man that's exciting it's such a good lookin 20...what a great year for that truck! I bet she gets all the whistles. Thanks for the picks.

I guess I should tell you the story of the truck. So This truck was owned by a friend of mine who purchased it used from the original owner in the mid-90s. He installed a bed dump kit. By the time I met him in the early 2000's he had just retired. And if I'm honest I didn't have an interest in the truck at the time and I had my Dakota by then. As the years rolled on I somewhat lost contact with them, partly because they live 150 miles away. In the summer of 2018 I heard though the grapevine that he had passed the year before, so I reached out to his wife to offer condolences and just to say hi. She mentioned that she was getting their house ready to sell and that if I wanted any of his tools or equipment that I could come by and she'd make me deals I couldn't refuse. For a few years prior to that I'd been wanting a full size truck again as the Dakota just couldn't handle some of the feed hauls I needed to do for the farm. I asked about the truck and she said she still had it but it hadn't run in 6 months and was not in the shape I remembered. So I went down, got the truck running, which all that was required was to charge the battery and turn the key. I asked her how much and she said $800 I went to the bank. It needed a lot of cleaning, tuning and minor work but would you believe it there is virtually no rust on the truck at all. I had to replace a couple missing hub caps and trim. Once I did that I started getting the "hey, nice truck", comments. And thanks I agree.

Let me see if I can find a Beer, oh yup there it is!

 

[pduffyd]

Heres a 14bff for yea. In the back of my 76 C20 131.5" WB. 8200lb GVW

Did the blazer fuel tank mod, 31 gal,

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That is really for Rusty, lol