1995 k3500 CC RV Puller

[b1jetmech]

Hey all,

I'm putting up my DD K3500 that I bought non running. It's a retired farm truck that wasn't in too bad shape for it's prior profession. Originally 6.5 diesel powered, I couldn't get it running because of burnt wiring behind the turbo, so, I swapped in a TBI 350...all factory install including the harness. The dash harness was even swapped mainly for cruise control connection that the 6.5 diesel harness didn't have.

Truck has typical 4:10 gears.

I upgraded the mirrors to Boost auto mirrors for better towing and Movotor headlights because I can't see as well at night, they made a huge difference! Next thing is to upgrade the motor to pull our 12,500 lbs fifth wheel.

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[b1jetmech]

Truck has over 300K miles and the rear 14 bolt rear was making bad noise when the gas is let off, I assumed it was a bad pinion bearing and had a bad axle seal leak that continued after replacing the seals. So, I took the opportunity to upgrade to a modern rear end with disc brakes.

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The seller mentioned it was a "14 bolt" with 180K miles.

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But...it was this kind of a "14 bolt"...a 11.5 AAM out of a 04' 2500 HD 8.1 engine with 4.10 gears. Hesitant at first, I bought it.

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Has existing disc brakes and is about 2.5 inches wider then the 95' 14 bolt.

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I didn't have any pictures of the swap unfortunately, because I had to outsource the swap for I didn't have a welder.

 

[b1jetmech]

Here's the install, runs and drives great. Installed some air lift bags to help with the 2000 lbs pin weight of the fifth wheel camper.

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[b1jetmech]

Swapping in a rear with disc brakes posed an issue with braking, the 95' K3500 master cylinder with a 1.25 inch bore lacked the volume to actuate the rear disc of the 11.5' axle. So, I swapped in a master cylinder from an 2001-2007 2500HD/3500HD truck. It has a 1.46 in bore size, considerably larger then the K3500 master cylinder. I picked this year range because the brake line fittings are still standard which are 1/2in-20. Where as the 2008 and newer master cylinders switch to metric of M12-1.0, harder to find adapters.

As of now, this is all roughed in. Going to put a larger after brake line in.

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Here are the differences of the two master cylinder bore sizes...the K3500 has a 1.25 in bore (right) witch is smaller the the NBS 2500HD ton master cylinder of 1.46 in (left).

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[b1jetmech]

However, the NBS master cylinder with the bore size of 1.46 in had an outer diameter of 1.8 in will NOT fit into the factory K3500 hydroboost but ALAS! There is a solution for this by combining a newer hydroboost from a NBS truck to the OBS hydroboost.

Get a hydroboost that is sized dimensionally for the larger master cylinder...a parts one from the junk yard, even. Remove the front off it and remove the front off the OBS truck hydroboost while it is installed on the truck and discard. Install the NBS front half of hydrobost onto the OBS back half and it will fit perfect...including the piston in side. GM is good about compatibility and the NBS hydroboost just a had a different mounting for the master cylinder where everything else was the same.

The reason to go through with this is the pedal rod of the NBS is around 1.5 in. shorter and swapping them out is difficult. This is why I elected to swap the NBS front onto the OBS back half.

I didn't take pictures unfortunately, but I did this swap with the back half of the hydroboost installed onto the firewall and didn't replace any seals...LOL! They re on order, but it doesn't leak to my suprize.

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[b1jetmech]

Here are the Movotor headlights, they really light up the road!

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[b1jetmech]

Here's the old 14 bolt, tired and worn out. Notice how dark the right hub is from axle leak. Just put new brakes on a few weeks prior...

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[BNielsen]

Following this project! I've got a K3500 myself that's ultimately going to wind up being the family hauler for pulling a camper too; for the rear end swap, I assume you had to move spring perches and shock mounts but other than that was there any modifications that needed to be done? I've been toying swapping NBS rears instead of disc-swapping my current 14-bolts and running spacers to compensate for the width difference.

 

[b1jetmech]

Yes, the spring perches were moved inward an 1 in. The shock mounts stayed the same, my buddy said he didn't have move them which is nice. The E-brake even works so, Connecting the E-brake cables had to be dealt with was an issue. The Driveshaft had the 1410 mount added on for the larger U-joint. I am pleased with the swap.

 

[Road Trip]

Here's the install, runs and drives great. Installed some air lift bags to help with the 2000 lbs pin weight of the fifth wheel camper.

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Greetings b1jetmech,

Welcome to the GMT400 forum! Really appreciate the detailed blow-by-blow of how you
upgraded your truck to the NBS HD 4 wheel disc setup. Your original diff making noise
on decelleration is only fixable by a new ring & pinion (and bearings, etc) so I can understand
the motivation to swap/upgrade instead of fix what you got, especially with the seal issue.

But the new (to you) full floater axle you installed is a robust unit, and with periodic oil changes
should give you good service. (I have the original drum brake FF in my '99 C2500, and I'm
looking at the harmonic balancer at the input to your diff, and I think that's a nice upgrade
from the NHV perspective.) Neat.

****

By the way, your username makes me think that you worked on the BONE. If that's the case,
very cool indeed. And would also help to explain your obvious attention to detail.

Welcome aboard. See you around --