F body rear disc conversion for a G body rear.

[charlief1]

There have been quite a few people that've been wondering how to do this and I've been saying I would post a how to on this exact thing. You will need all the brake parts off the rear off a 4th gen F body except the cables, and I'll show you how to make the stock parking brake cables work. You need rotors, backing plates, all lines and hoses, except the one that connects at the top of the axle to the body, and the brackets that attach to the lower control arms and axle. You'll also need the parking brake lever out of the original drum brakes, so don't throw it out with the rest. You also need to take one of the disc backing plates with you to a hardware store and get 8 3/8" grade 8 bolts and nuts with lock washers or flanged bolts and nuts. Use blue lock tite on them to make sure they won't come off. Make sure they go through the backing plate and are at least 1/2" longer (2" bolts) than the originals from the F body donor. You also need a drill bit (25/64") that will fit into the holes on the backing plate to drill the holes in the flange, one that's the same size as the hole for the lower control arm bolt, and one that is 1/2" to drill a hole for the parking brake cables. The bits I have, have lost their markings but a 3/8" bit should fit tightly in the backing plate holes. Don't buy a cheap bits, they will break or burn while using them.

Tools are also fairly simple. A good tubing double flaring kit, a drill, preferably a 1/2" drive with variable speed, something to cut the flange down that the original backing plates mount to, and either welding equipment for you or someone to do some minor welding, various wrenches and sockets, and a good pair of wire cutters. I almost forgot that a pair of vice grips with the large jaws (see pics) are really handy but not 100% needed.

First thing you have to do is get the axles out, I'm not going to show that since my axle is already apart. Second is removing the original lines. Next the flange is held in place with 2 small bolts at the bottom. and the anchor pin at the top. The anchor pin may be frozen in place and I had to use a torch to get both of them off. Once you get the anchor off you'll be down to the mounting flange the backing plates bolt to. Here's where you'll get nervous. Mark a line across the flange at the bottom of the hole that the original wheel cylinder was in. This is your cutting line to make the flange more comparable with the F body backing plate. I used a porta-band band saw to cut mine off but you can use a hack saw, grinder, or any other method other than a cutting torch. The flange is thick so take your time.

Once it's cut you should have just a small indentation where the hole the wheel cylinder was. If you cut below that you may have some issues so make sure you don't cut more than at the bottom of the hole. The corners need to be trimmed at the edges at an angle, for the new backing plate. Don't take a lot off because you need to check with the disc backing plate as you trim it. Once the flange fits on the backing plate and looks centered (yes, eyeball it) then you should be good. Make sure you use the right side on the left and vice versa. Now comes the next fun thing. Use the front hole at the bottom of the flange and drill all the way through it. If you're not used to drilling through thick steel you need to take your time, use oil, and go slow with the drill speed. If you don't you'll either burn the bit or break it. The holes will look like they don't have a lot of meat to stay in place, but remember, this is rotational force for the brakes, not front to rear, so everything will work fine.

 

[charlief1]

Once the first hole is drilled then bolt the backing plate on tight enough to hold it in place but be able to move it with some force. This is so you can position it. If everything is in the right position you should be able to see the other hole in the center of the other lower hole. Look at the axle to make sure it looks center on the new backing plate. Leave the backing plate in place and drill through the backing plate so you have a guide of sorts. Once this hole is drilled them put a bolt in it to hold things together. Now use the drill to mark the top holes. You're not trying to drill through the metal but make a center mark so you can use a smaller bit to make a pilot hole. Basically just put the bit in and press hard long enough to see some chips starting to come out, then stop. At this point you switch to a smaller bit, drill the hole, and switch back. The larger bit will go through easier and be less likely to be damaged with the pilot hole. To line the bit up (I'm used to doing this) you might have someone watch from the side while you watch from the top to keep the bits lined up as square as possible.

Now that the scary part is, tighten all the bolts on the flange and mount the calipers and brackets to them. The brake hoses need to be on the calipers and make sure the bleeders are pointed up. Yes, I didn't do this the first time so I had to re-do a few things.

The funky bracket that you took off the bottom of the axle is now ready to be cut up. The 2 pieces you will be left with will hold the brake hose in place and allow you to hook up the stock parking brake cable so it works. It's a weird U shaped thing and one side is only there to mount to the original axle. Remove that section so you only have the parking brake cable section and hose mount. You cut the hose mount off the rest of the bracket and need at least 1/2" below the hole to mount it, but 1 to 1.25" is better. Once you get both of them cut then see which one goes to which side. Don't confuse them or you'll be cutting them off and swapping them. These are welded to the axle tubes to hold the hoses and keep from breaking the metal lines.

They're welded on the axle but center them on the lower control arm mount where it's welded to the tube. It's a pretty straight forward weld so tack it and then move it if you have to. It will be 90 degrees from the tube.

 

[charlief1]

Now comes the real fun. The F body brake tubing has one end that's an ISO flair (bubble style) and that goes on the caliper hose so don't damage it. Make sure the other side screws into the factory block on the other end. You need to straighten the lines carefully so you can bend them back the way they need to go. I used a vice to help but you can do it by hand if you take your time. The longer one is the passenger side and the shorter is the drivers side. The clips that hold the stock lines in place should be bent so you can fit the new lines and this is important. What you're going to do is make the F body lines look as close to factory as possible by bending them into place.

The easier side is the passengers so start with that. With the hose clipped in the the bracket screw the "new" line into place so you can get some spacing. Bend the line carefully so it comes off the hose at 90 degrees and then again at 90 so it runs in the same place as the factory line. Once it's past the old clip bend it straight up and around the tube until it lines up with the rib on the center section facing forwards. Cut the very end off that line and save the fitting. Take the line back off and remove the protection coil from around it. You'll be shortening it and putting it back on later.

Now for the fun side. You need to carefully make a 90 at the fitting that goes into the drivers side hose and another one about 1/2" below that. This should line the tube up with the axle and put it in the clips welded to the axle for holding the line. On the center you'll need to temporarily hammer the clips down to hold the line, and tighten up the fitting so the line doesn't move easily. The line's then wrapped around the axle and then bent towards the block that the hose is mounted to. Once positioned over the block and it looks like it's lined up, make it about 3/8" past the block for the line fitting. Cut the end off and cut the coil back enough so you can put the fitting back on (about 1.5") and double flair the line. Once properly flared and installed then that side's done. Now you're going to bend the other side around the center section, cut the line, cut the coil and re-install it, install the fitting, and then double flair the line so you can install it.

 

[charlief1]

The next part is about making your parking brake work. The original F body parking brake cable mount has a hole in the end for the cable, and a slot for mounting. Cut the bracket 1.5" behind the slot, leaving the the cable section in place. You're going to drill a hole in the area behind the slot so you can mount it where the lower control bolt goes. The pics aren't great but it should give you some idea of how it works. The hole should be centered on the lower end of the slot and 3/4" to 1" behind the slot. A 1/2" bit will work or you can get the correct bit to do the work. You don't need to weld it in place but I do. The bolt will hold it in place. The original hole for the cable is to far out so you'll need to cut the bracket as you see in the above pic. On the bracket is stamped L or R and you want to leave just enough of the letter to be able to tell something was stamped on it. In the section between the bend and the area you just cut, you need to drill a hole, centered in that area, so the cable will go through it for the parking brake. Do NOT weld the bracket on until you get the next process done. You will need to align it with the new lever.

Now that the bracket is made you need to make it fit the lever for the parking brake. Remember where I said you needed the old parking brake lever for the drum brakes? What you'll need to do is take the lever out of the disc parking brake, cut it as well as the drum brake lever, and weld the 2 together. This is something you'll need to eyeball because I've never taken measurements on it. Just looking at it for alignment is enough for me. Again, the pics didn't come out was well as I'd like but it should give you some idea of how it should look. Make sure it's welded so it won't break since this is what your parking brakes are going to be using to work. I had to do a little grinding to clean off splatter but it's still nice and thick and the weld looks good.

 

[charlief1]

Some say the shocks will mount without any issues, but the last 1 I did, it looked really close, so I made my own relocation bracket out of 1/4" thick angle iron. Here's a pic of what this one got. I'm not going to go into the details because I doubt most will want to go this way, but I've found that it aligns the shock better. It looks really crude right now but the end where the shock mounted originally is rounded as well as the sharp edges on the inboard side. Then it's welded into place top, bottom, and around the original shock mount.

Hope that he;s those of us that like the idea of going with this rear disc set up. The cost is right and the parts are easy to come by so it's a good set up. If you don't like it then you can easily go back to drum brakes by getting the backing plates ect off a second gen S-10, or if you want to go bigger, find a B body and steal the parts off one of them. You can't go back to the stock backing plates but you can go back to drums if that's what you want, and they should look almost stock.

 

[jdpolzin]

Looking good Charlie!

 

[jdpolzin]

I like the idea of cutting the drum brake bracket as well a the disc brake bracket. Good idea.

 

[charlief1]

That's what I've been trying to tell you Jeremy. It's simple and cheap, plus it works fine. All the parts you need are off the F body and in the stock drums. Just a little fabrication is all you need to make it work. It's not my best write up but it does solve the issue of having to buy extra parts that may not fit, and with the cable adjustment you can make it easy to find parts without going through a non stock supplier.

 

[JasonBall1977]

Once the first hole is drilled then bolt the backing plate on tight enough to hold it in place but be able to move it with some force.View attachment 270840 This is so you can position it. If everything is in the right position you should be able to see the other hole in the center of the other lower hole. Look at the axle to make sure it looks center on the new backing plate. Leave the backing plate in place and drill through the backing plate so you have a guide of sorts. Once this hole is drilled them put a bolt in it to hold things together. Now use the drill to mark the top holes. You're not trying to drill through the metal but make a center mark so you can use a smaller bit to make a pilot hole. Basically just put the bit in and press hard long enough to see some chips starting to come out, then stop. At this point you switch to a smaller bit, drill the hole, and switch back. The larger bit will go through easier and be less likely to be damaged with the pilot hole. To line the bit up (I'm used to doing this) you might have someone watch from the side while you watch from the top to keep the bits lined up as square as possible.

Now that the scary part is, tighten all the bolts on the flange and mount the calipers and brackets to them. The brake hoses need to be on the calipers and make sure the bleeders are pointed up. Yes, I didn't do this the first time so I had to re-do a few things.

The funky bracket that you took off the bottom of the axle is now ready to be cut up.View attachment 270841 The 2 pieces you will be left with will hold the brake hose in place and allow you to hook up the stock parking brake cable so it works. It's a weird U shaped thing and one side is only there to mount to the original axle. Remove that section so you only have the parking brake cable section and hose mount. You cut the hose mount off the rest of the bracket and need at least 1/2" below the hole to mount it, but 1 to 1.25" is better.View attachment 270842 Once you get both of them cut then see which one goes to which side. Don't confuse them or you'll be cutting them off and swapping them. These are welded to the axle tubes to hold the hoses and keep from breaking the metal lines.

They're welded on the axle but center them on the lower control arm mount where it's welded to the tube. It's a pretty straight forward weld so tack it and then move it if you have to. It will be 90 degrees from the tube.View attachment 270843

I am really trying and needing to see this post but they're all the pictures are gone can you please help me to see them jayball1469@gmail.com

 

[Pronto]

That's highly unlikely since Charlie has gone to the big G body forum in the sky.