HOW TO Convert From Drum Brakes to Disc Multi Part Video Series

[bretcopsey]

Take this with a grain of salt as I know none of it as certain to be accurate:

Online search turned up OEM part numbers 15622343 & 15622344. Searching on those numbers I found a hit claiming to have multiple sources for those part numbers and ability to order each.

[QUESTIONABLE LINKS REMOVED]

I hope this helps and works out for you if you go this route.

Additionally, I had posted earlier in this same thread about possibly going the route of upgrading to nbs DRW rear discs using factory disc backing plates, rotors and calipers by cutting off the axle flanges and replacing with a set I bought off a member of Pirate 4x4 that will need to be welded onto the axle tubes. My posts are on these pages:

HOW TO Convert From Drum Brakes to Disc Multi Part Video Series

I don't understand. Goal is to go low, when going low you will run into clearance issues. If you extend fenders...situation averted. If you shorten the rear...same as well. If you do both you can get some wide tires in there with some cushion.

www.gmt400.com

HOW TO Convert From Drum Brakes to Disc Multi Part Video Series

I take great pride in educating the uneducated. This right here is what KILLS me. You're "teaching" the uneducated how to DOWNGRADE their brakes. You don't know enough about what you're "teaching" but you go and preach it like it's the gospel. I've seen too many videos where I know more than...

www.gmt400.com

I don’t know when or if I’ll ever get around to the project but it seems like the best option for disc brake upgrade short of swapping the entire axle.

 

[bretcopsey]

I also just remembered there is a 94 3500 DRW at my local Pick Your Part. It will be the weekend after this coming that I can make it up there, but I can see what I can do to help if the axle is still there and backing plates are in decent shape.

 

[fancyTBI]

Take this with a grain of salt as I know none of it as certain to be accurate:

Online search turned up OEM part numbers 15622343 & 15622344. Searching on those numbers I found a hit claiming to have multiple sources for those part numbers and ability to order each.

GM 15622343 Plate, genuine OEM part

Rear brake backing (with 13 x 3.50 brakes) GM genuine OEM part.

oemcats.com

GM 15622344 Plate, genuine OEM part

Rear brake backing (with 13 x 3.50 brakes) GM genuine OEM part.

oemcats.com

I hope this helps and works out for you if you go this route.

Additionally, I had posted earlier in this same thread about possibly going the route of upgrading to nbs DRW rear discs using factory disc backing plates, rotors and calipers by cutting off the axle flanges and replacing with a set I bought off a member of Pirate 4x4 that will need to be welded onto the axle tubes. My posts are on these pages:

HOW TO Convert From Drum Brakes to Disc Multi Part Video Series

I don't understand. Goal is to go low, when going low you will run into clearance issues. If you extend fenders...situation averted. If you shorten the rear...same as well. If you do both you can get some wide tires in there with some cushion.

www.gmt400.com

HOW TO Convert From Drum Brakes to Disc Multi Part Video Series

I take great pride in educating the uneducated. This right here is what KILLS me. You're "teaching" the uneducated how to DOWNGRADE their brakes. You don't know enough about what you're "teaching" but you go and preach it like it's the gospel. I've seen too many videos where I know more than...

www.gmt400.com

I don’t know when or if I’ll ever get around to the project but it seems like the best option for disc brake upgrade short of swapping the entire axle.

I think OEMcats is a spam site. I’ve seen their stuff pop up before but after doing some research last year it’s not super legit. They aggregate dealer’s information with their alleged inventories. It’s almost like a parts marketplace that isn’t accurate at all. Also no https. Wouldn't want to enter my personal data there.

 

[Caman96]

I think OEMcats is a spam site. I’ve seen their stuff pop up before but after doing some research last year it’s not super legit. They aggregate dealer’s information with their alleged inventories. It’s almost like a parts marketplace that isn’t accurate at all. Also no https. Wouldn't want to enter my personal data there.

Agree^^^

 

[95 Silverado]

Thanks all for your help!

There’s a Canadian dealer listed on the OEMcats site so I’ll call them and a few others tomorrow as my local dealer has been of little use.

If that doesn’t pan out I’d be forever indebted to @bretcopsey for checking out the wreck at his local yard.

I’ll post an update tomorrow.

 

[bretcopsey]

I think OEMcats is a spam site. I’ve seen their stuff pop up before but after doing some research last year it’s not super legit. They aggregate dealer’s information with their alleged inventories. It’s almost like a parts marketplace that isn’t accurate at all. Also no https. Wouldn't want to enter my personal data there.

*oof! I updated my post to remove the links, don’t want to cause any heartburn. Not sure how that is reflected since my original post was quoted

 

[fancyTBI]

*oof! I updated my post to remove the links, don’t want to cause any heartburn. Not sure how that is reflected since my original post was quoted

They still show up in mine. I think you’re good.

 

[Caman96]

It doesn’t trigger me either, lol. I just don’t believe it’s a legitimate parts source. I only use it to occasionally get part number supersessions.

 

[95 Silverado]

I think OEMcats is a spam site. I’ve seen their stuff pop up before but after doing some research last year it’s not super legit. They aggregate dealer’s information with their alleged inventories. It’s almost like a parts marketplace that isn’t accurate at all. Also no https. Wouldn't want to enter my personal data there.

Yes it appears OEMcats scrapes websites of dealers for part numbers and info but their scraping doesn't drill down to find the "discontinued" indicator on the parts and none of the suppliers I checked actually had the parts.

So still on the hunt for drum backing plates, but in the meantime I thought I'd break out some basic engineering math on the conversion kits to see how much theoretical stopping power they actually have versus the original drums.

Assuming all other things are equal (e.g. hydraulic pressure, pads, rotor surfaces) the friction behind braking power mostly comes down to hydraulic piston diameter and how much torque the system has due to rotor/drum diameter.

The kits for my truck typically use this rotor:
03 Chev Express 3500 DRW GVWR 9,600lbs
Rotor diameter 12.8”
Effective torque radius 5.5”

And this caliper because it has an e-brake:
77 Cadillac Eldorado
Caliper cylinder diameter 1 x 2.5” -> area 4.91 sq in

But how do these compare to the K3500 drum?

95 Chev K3500 GVWR 9,000lbs
Drum cylinder diameter 2 x 1.19” -> area 2.22 sq in -> effective area 5.24 sq in* (see below for explanation)
Drum diameter 13"
Effective torque radius 6.5"

* To make this an apples to apples comparison we need to multiply the cylinder area by 2 because the geometry of the drum brakes applies the force at the end of a a lever arm which effectively doubles it, plus we need to multiply by another 1.18 to account for the difference in effective torque radius because the drums have a larger diameter, for an effective cylinder diameter of 5.25 square inches.

Braking force is directly proportional to cylinder area so the Eldorado calipers are slightly less powerful as the original drums as some suspected they might be, but at 94% they are still somewhat in the ballpark.

Digging a bit deeper the front brakes on the 95 K3500 have 3" cylinders (7.07 sq in) versus 2.5" cylinders (4.91 sq in) for the Eldorado brakes, on about the same sized rotors, which still gives a 60/40 front/rear stopping bias, so if you can solve the bracket issue it actually doesn't seem like a terrible idea.

A better idea might be to use the Express 3500 caliper as well as the rotor, with a cylinder diameter of 2 x 2" -> area 6.28 sq in. This would bring the braking bias closer to 50/50 but the Express 3500 appears to use the same sized calipers and rotors on both the front and rear, which would give a 50/50 stopping bias anyways, unless it has some kind of pressure proportioning system. The Express 3500 also has a higher GVWR so the system would not be undersized in any way.

Of course all of this is just theoretical fun and games until I figure out what I'm going to do...

 

[95 Silverado]

I've done some more digging and found that my truck actually has larger front brake cylinders than I listed above. I also found that Lugnut4x4 has a larger JB7 style rear caliper than I listed above with E-brake based on the Cadillac Eldorado design. With all of that taken into account I've created a new table with theoretical relative stopping power for each solution, with the Eldorado calipers on the 03 Chev Express 3500 DRW disks:

Brake System	Rotor/Drum Diameter	Effective Rotor/Drum Radius	Piston Diameter	Number of Pistons	Piston Area	Stopping Power
95 Chev K3500 DRW Front Disk	12.5​	5.48​	3.285​	1​	8.475​	46.445​
95 Chev K3500 DRW Rear Drum	13​	6.5​	1.1875​	2​	2.215​	28.796​
03 Chev Express DRW Rear Disk	12.8​	5.63​	2​	2​	6.283​	35.374​
77 Cadillac Eldorado Rear Disk Standard	12.8​	5.63​	2.5​	1​	4.909​	27.636​
77 Cadillac Eldorado Rear Disk HD	12.8​	5.63​	3.15​	1​	7.793​	43.875​

Given all of this I'm inclined to go with the "77 Cadillac Eldorado Rear Disk HD" calipers on "03 Chev Express DRW Rear Disk" solution.

I will also see if it's possible to alter the brackets to apply holding force to the centre of the caliper once I get the parts.