1967-72 Chevy Axle Swap to 9.5", 14-Bolt w/ Disc Brakes

[bry593]

How I installed a 90's, 14-bolt, semi-float axle in my 1971 C20 pickup. This swap maintains the original axle width (65 1/4") and adds 13" disc brakes. All parts are GM so it will be reliable and work great.

Axle = 1989 - 2000 Chevy & GMC light duty 3/4 ton with drum brakes. 2WD and 4WD are same width if 13" drum brakes.
Disc Brakes = Early 2000's Chevy & GMC light duty 3/4 ton. Calipers mounted on back side so parking brake cable routes correctly.

Other necessary parts:
1. Axle perches cut for 3 3/8" axle tube
2. Laser cut brake mounting flanges (1/2" thick)
3. Laser cut backing plate concentric rings (3/16" thick)
4. 3/16" custom brake line kit and 3/16 to 1/4 adapters at distribution block
5. 2X LH brake hose from 2001 C2500
6. 2X LH parking brake cable from 2001 C2500
7. 9/16" wheel studs for 80's 9.5" axle

https://www.youtube.com/watch?v=e-AF0CLiAQA&t=638s

[Getter-Done]

Great Video of the swap.

That was a very clean install.

Which Auxiliary tank is in your truck?

[bry593]

Originally Posted by Getter-Done

Great Video of the swap.

That was a very clean install. Thanks! I spent way too much time on it.

Which Auxiliary tank is in your truck?

I don't know. I'd guess a dealer installed addition. Poorly done. I never use it. Will be removed soon enough.

[Getter-Done]

There is a Thread about NL2 options.

This is what Sparked my interest.

Does your Glovebox list this tank on the SPID?

[bry593]

Originally Posted by Getter-Done

There is a Thread about NL2 options.

This is what Sparked my interest.

Does your Glovebox list this tank on the SPID?

No, no option code on the glovebox decal.

It is poorly mounted. You can't even get a gas cap onto the filler neck because it is too close to the bed wall.

No sending unit, just a hose going to a tee valve. I stripped all that stuff out soon after I bought the truck. Just haven't gotten around to removing the tank.

[bry593]

I should mention that I had to run 1/4" spacers to fit my old school 16x6.5 GM wheels. The calipers hit on the side of the center drop of the rim. I also used 1/4" longer wheel studs from the front hub of 80's model Chevy 1 ton to provide sufficient thread engagement to lug nuts.

After trying a Ford 16x7 (90's issue), I found the same problem. Later model GM wheels are designed differently in this area and would not require spacers. For example the 16x6.5 2500HD aluminum wheels should bolt right on.

[57taskforce]

I did something semi similar a few years ago and mounted the late model disks to an old school 80’s 14 bolt FF from a K30.
Nice work on your swap!

[bry593]

Originally Posted by 57taskforce

I did something semi similar a few years ago and mounted the late model disks to an old school 80’s 14 bolt FF from a K30.
Nice work on your swap!

Thanks!

I've got about 500 miles on it so far and I'm very pleased with the results!

It is very quiet and smooth compared to the HO52. I think shimming the carrier bearing also helped with the NVH. I've got the trans and first shaft at 4 degrees down, the axle pinion at 4 degrees up. Haven't checked to see what the second shaft angle is, but it is clearly very slight. For those who say you shouldn't have the first shaft and trans in-line, it's really not an issue. It isn't perfectly in-line and only a 1/2 degree or so is needed to keep the U-joint needles spinning.

Handling is improved, likely due to the track bar rebuild.

It certainly takes the bumps better with the lighter axle. Used to be a bump at 80 mph would really kick the tail end up in rebound.

The brakes are bedded in and seem to work better than the drums as far as being able to modulate. There's a fine line between on and locked up with drums since they are self energizing.

Happy to report my wheel spacers are not causing any issues, no vibration. I did buy some PYO wheels (2500HD) at the swap meet last weekend and these would eliminate the need for spacers altogether. But, not sure I want to give up the awesome look of the classic steelies and caps.

Gas mileage is improved although I'm not sure what I'll peak at. Still messing with the transmission programming to get the shift points, tcc disengage and lockup right where I want it. Should have that sorted this week.

[bry593]

Just wanted to provide an update on this thread.

I did end up adding a brake valve and reduced the rear caliper piston size from 2.00" to 1.75". This allowed me to tune the discs so that the rear brakes do not lockup in a panic stop. This resulted in excellent braking.

I used a BAER valve and mounted it in series with the existing GM combination valve. This compounded the effect and provided full control of the brake tune. It also allows me to dial in a few turns when hauling a load or pulling a trailer.

If you are interested, I made a video showing some of the details:
https://www.youtube.com/watch?v=_WWka224rgs