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 1955-1956 Plymouth 12" Disc ConversionJump to page : 1 Now viewing page 1 [50 messages per page] | View previous thread :: View next thread |
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Powerflite |
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Expert 5K+ Posts: 9650      Location: So. Cal | Now that I am doing my 2nd 12" disc conversion on my '56 Belvedere, I decided to write up some detailed instructions on how to make it work using the Plymouth hubs. AAJ makes a nice big 12" disc conversion for the '55-'56 cars. I prefer their 12" conversion over their 11" version because it doesn't require you to tap your spindle and it's bigger, offering better braking performance. These cars came with 15" wheels so you can use these larger brakes with the original hubcaps. However, the stock wheels won't fit over them so you will need to replace them with newer 15" disc brake wheels. But the only catch is this conversion was designed to be used with Dodge hubs, not Plymouth hubs. The mounting flange on the dodge hubs are .1" thinner, and extend .275" further outward from the car, which would push your wheels further out on a Plymouth. The conversion requires you to remove your original drum from the hubs and place the new rotor on top of it, along with a .19" spacer and new, longer studs. AAJ designed the conversion to center the rotor on the extended shanks of the new studs that extend beyond the hub flange. Using this conversion on a Dodge will push your wheels out .59" due to the extra thickness of the .4" thick rotor flange & the .19" spacer. But on a Plymouth, using the Dodge hubs will increase that extension by an additional .275", resulting in .865" total. On the .1" thicker Plymouth hubs, the stud shanks no longer make any contact with the rotor to center it. Centering a rotor on the studs is not very accurate as there is still some play there which can affect your wheel balance if it is too far off. and doing it with only .1" depth isn't a good idea in my opinion. People have had better success by eliminating the .19" spacer on the Dodge hubs to allow the studs to center the rotor with more bite, but I'm not fond of the idea of extending the caliper further out on its pins, and I'm not sure what problems this may cause with it. This, combined with the extra wheel offset, and the pain in digging up Dodge hubs is what motivated me to make them work with the Plymouth hubs instead. (56 Dodge Plymouth Front Hubs.jpg) Attachments ----------------  56 Dodge Plymouth Front Hubs.jpg (243KB - 259 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | You'll notice from the pictures above that the Plymouth hub has a flat that can be used to center onto, whereas the Dodge hub doesn't. I decided to weld a ring into the spacer provided by AAJ that would center on this flat and also center the rotor to it. The thickness required to do that is almost exactly 1/4". So I purchased a 1/4" x 1" x 3 ft steel strip from Home Depot or other hardware store and carefully cut it down the center with a thin 3/32" blade on my die grinder. The length needed is about 10.5". Once cut out, you need to bend it into a circle. It turns out that an old small block/hemi crank timing gear has the same outside diameter as that hub shank. So I clamped the metal strip to the timing gear and used a hammer to bend it around it. (1955-56 Plymouth Disc Conversion 1.jpg) Attachments ---------------- 1955-56 Plymouth Disc Conversion 1.jpg (179KB - 276 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | I used a longer length than 10.5", so I had quite a bit of excess length on it. So I cut the obvious excess material off of it and pounded it all the way around the timing gear. Next, I removed the timing gear, and attempted to push the circular strip into the rotor. The taper at the outside of the rotor is really helpful to get the strip inserted into it, so I recommend that you do it from this side. No go. Still too long. So I cut more off of it. Edited by Powerflite 2021-03-30 2:57 PM (1955-56 Plymouth Disc Conversion 2.jpg) (1955-56 Plymouth Disc Conversion 3.jpg) Attachments ---------------- 1955-56 Plymouth Disc Conversion 2.jpg (188KB - 268 downloads) 1955-56 Plymouth Disc Conversion 3.jpg (118KB - 262 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Tried it again, and now I have a gap. Perfect. Don't be too concerned about getting the exact length because that gap will actually help you to get great weld penetration. But you don't want to have too big of a gap or it will be hard to bridge it and easier to weld into your rotor that's holding it. Next, I checked the fit to see if there were any air gaps between the strip and the rotor ID and hammered the strip into the rotor with the round end of a ball peen hammer. Doing this, I was able to close the gaps quite well and make it much more round. Afterward, I pressed the timing gear inside the strip, with the strip still inserted into the rotor. Now you are ready to tack weld the strip into a circle. Alternatively, you could use the hub here instead of the timing gear, which won't mar your ring if you have to force it a little. Edited by Powerflite 2021-03-31 12:20 AM (1955-56 Plymouth Disc Conversion 4.jpg) Attachments ---------------- 1955-56 Plymouth Disc Conversion 4.jpg (138KB - 263 downloads) | ||
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| 58coupe |
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Expert Posts: 1740  Location: Alaska | |||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal |  A lathe would be awesome, but it needs to stand in line behind the sandblaster cabinet, bead roller, sheet metal brake, english wheel, tig welder, rotisserie, car lift, mill, parts washer and all the other tools I would love to use, but don't have space for. I actually had a decent wood lathe that I used, but I removed it to make space and had to get rid of it. My miter saw recently got booted out of my garage for the same reason. | ||
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| 58coupe |
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Expert Posts: 1740 Location: Alaska | |||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | After tacking, pull the unit from the hub, crank the welder up and go for it. Welding spatter shouldn't really stick to your rotor because they come with a coating on them that prevents it from sticking. If there isn't, you can apply a thin layer of grease near the welding area to keep anything from sticking to it. Cleaning up the welds isn't too difficult if you can hold it well. A good vice will help a lot. Use a round carbide cutter on a die grinder to clean up the majority of the inside welds, and then use a rounded file to finish it. A die grinder with a cylindrical paper sander also works well to do the final touches on it as long as you don't push it hard. After you've got it close, check the fit inside the rotor & on the hub, and adjust as necessary. Welding can warp it a little bit, so sometimes it's necessary to hammer it into the rotor in a couple places again to true it up. Edited by Powerflite 2021-03-31 12:17 AM (1955-56 Plymouth Disc Conversion 5.jpg) Attachments ---------------- 1955-56 Plymouth Disc Conversion 5.jpg (103KB - 267 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Probably the hardest part of the conversion is having to remove the drum from the hub & replacing the studs with longer ones. I found that my press didn't have enough force to remove them effectively, even after cutting the top swage area. I end up putting a short 2x4 that fits inside the drum, and place it under the hub to pound against it. Then whack them out with a heavy hammer/sledge. It's painful, but that's the only successful way I have found. Be sure to clean the hub up before you put the new studs into it because it's a lot easier to do it now than after the studs are installed. Roger at AAJ recommends that you drill the holes out to a larger size (forgot what size), but I have found that you can just hammer the new studs in without opening it up and it makes for a nice tight fit. Putting the new ones in is a lot easier than taking the old ones out, even without drilling the hole out larger. (56 Plymouth Hub w-Long Studs.jpg) Attachments ---------------- 56 Plymouth Hub w-Long Studs.jpg (80KB - 234 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Once you are happy with the ring fit on both the rotor and the hub, you can then place the spacer & ring onto the hub for welding. It is important to get it well centered so if there is any play in the spacer, you can use little pieces of thin cardboard or other shim to ensure it is centered well. Then tack it into place....lightly, because these tacks will have to be removed later. (56 Plymouth Hub Spacer Tacked.jpg) Attachments ---------------- 56 Plymouth Hub Spacer Tacked.jpg (76KB - 250 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | This should leave a small gap at the bottom due to irregularities in the ring and due to the fillet at the bottom of the hub. This is good because we want to give it more height anyway; and this allows more room for weld material so you don't have to grind so much of it back off. (56 Plymouth Hub Spacer Tacked Bottom.jpg) Attachments ---------------- 56 Plymouth Hub Spacer Tacked Bottom.jpg (81KB - 237 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Then weld in, all around the bottom. It doesn't have to be really strong because this takes no real weight. But having it welded solid does prevent the ring from possibly coming loose, and losing it or having it jangle around. (56 Plymouth Hub Spacer Welded.jpg) Attachments ---------------- 56 Plymouth Hub Spacer Welded.jpg (82KB - 233 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Then clean up the weld to make it sit flat again. You will likely have to clean up the inside area where it sits on the hub if any of the weld gets a bit over the edge. Test fit it onto the hub and smooth it with a file or paper cylinder until it slides smoothly onto the hub and sits flat on it. Also grind a small chamfer into the center edge with a grinder to make it fit over the fillet on the hub. A large flat file is good to go over the bottom surface to indicate where any high spots are and smooth them down. (56 Plymouth Hub Spacer Welds Cleaned.jpg) Attachments ---------------- 56 Plymouth Hub Spacer Welds Cleaned.jpg (99KB - 247 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Then carefully cut down the tack welds on the front side with a die grinder until they are mostly gone. Using a large diameter wheel helps to be able to cut them from nearly 90 degree angles. Try not to gouge the surrounding material. Finish cleaning up the inner edge and any remainder with a hand file. Test fit it in the rotor and use the file to adjust it if necessary. Now it's ready for paint and use. Edited by Powerflite 2021-05-14 12:08 AM (56 Plymouth Hub Spacer Tacks Removed.jpg) Attachments ---------------- 56 Plymouth Hub Spacer Tacks Removed.jpg (94KB - 235 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | To take advantage of your shorter Plymouth hubs, you will need to move the caliper bracket inward as well. The total difference is around .27", but 1/4" is close enough to work without any issues, so that's what I used. First, put the bracket on the spindle and mark where it needs to be cut, such that the moved section won't interfere with the spindle. You have to cut further away from the end than I expected at first, so be sure to check it out. Then I cut the ends off the caliper bracket using a cut-off wheel on a die grinder and chamfered the edges so that I could get great weld penetration. Then bolt & clamp it to the other bracket to use as a template, with a 1/4" steel plate between them. Be sure to put the offset in the proper direction to move the caliper further inboard. I screwed two bolts into the caliper holes to line up with the other bracket, but I didn't screw them into it as that would likely cause it to angle at some random position. Just use the tips of those bolts to ensure it is centered where it is supposed to be. Once it is all clamped together, tack it in four places. Remove the clamps and tack it in four places on the other side as well. Now is the most critical step in this build. Check the angle of the plates by putting a straight edge on it an making sure that the gap is even all along it. This will ensure you have it tacked on there straight. Also, put it on the spindle and make sure there are no issues with mounting it. The bracket fits very close to the spindle so you may have to clean any dirt or grime from the outer diameter first. If you finish welding it before thoroughly checking it out, it is nearly impossible to bend it back without cutting it back off and re-welding it. So this will save you an enormous amount of headache to test it out now while it is still bendable. (56 Plymouth Caliper Bracket Tacked.jpg) Attachments ---------------- 56 Plymouth Caliper Bracket Tacked.jpg (198KB - 244 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Once you are satisfied with the position of the plates, crank up the welder for 3/8" plate and go for it. Use a wide circular motion in the weld to get a gentle slope to the transition between the plates. Weld all along both sides of the bracket. So far, I have not had trouble with the angles shifting once the tacks were positioned properly. If you do have a shift for some reason, a strong press is about your only hope to bend it, and you may still need to cut the weld area a bit to help it move. I will likely clean up the welds a little, especially on the ends, clean up the spattering, and smooth it out a little, just for aesthetics before I paint it. Edited by Powerflite 2021-05-15 7:56 PM (56 Plymouth Caliper Bracket Welded.jpg) Attachments ---------------- 56 Plymouth Caliper Bracket Welded.jpg (164KB - 227 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | Setting up the second bracket is more troublesome because we no longer have a flat jig to bolt & clamp it to. But you can use the other one you just made by inserting a 1/2" spacer this time since the offset will be placed in the opposite direction from the other one. Once again, be sure to check that everything is parallel and fits onto the spindle before you do the final welding. (56 Plymouth 2nd Caliper Bracket Jig.jpg) Attachments ---------------- 56 Plymouth 2nd Caliper Bracket Jig.jpg (136KB - 235 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9650 Location: So. Cal | After welding and any cleanup on them, the fab work is complete and you can install them to the car. (56 Plymouth 12in Disc Conversion.jpg) (56Belv 12in Disc Conversion.jpg) Attachments ---------------- 56 Plymouth 12in Disc Conversion.jpg (89KB - 235 downloads) 56Belv 12in Disc Conversion.jpg (103KB - 236 downloads) | ||
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| samstrader |
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Extreme Veteran Posts: 443 Location: Beaumont TX | |||
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