rear brake failure

macvette

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The rear brake drum on my open D failed as you see above so I'm busy making a list of what I need to fix the damage ( lots!). As you can see, the right side of the RFM is slightly bent ( about 1/8 ins as far as I can tell). Richardson has a very short description on how to fix this and the dimensions but it's not very detailed so I would be grateful if someone out there can provide a step by step procedure.
It appears that the drum has been cracked for sometime. If you look at the left side of the drum you can see the crack is rusted whilst the right hand side is bright and fresh.
PS
I managed to stay upright.
Thanks Mac
 
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davidd

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Mac,

I had a Rapide drum break on the racer many years ago at Daytona. John Healy sent a Shadow drum overnight, so there was no downside. The chain was intact and there was not much damage except scrapes. The next season I made a rule to change all the brake drums to new Shadow drums and it is now the first thing I do on a racer. I also made an adapter to carry the sprocket instead of the brake, and I moved the brake drum to the non-chain side. This was for a single, and based on Greg's experience with his twin racer cracking the adapter, there is a lot of stress on these parts.

I also noted that the hubs can shatter as has been reported in MPH. Based on that, I also replace the hubs with new ones made from billet rather than cast. The wheels are the only area that I do this. If I were riding on the street I would probably be happy with old Shadow drums and cast hubs, but I would not ask too much of them. If something goes wrong with a hub, drum or brake plate there is a good chance of going down. I am glad that you were able to ride through it.

David
 

macvette

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Mac,

I had a Rapide drum break on the racer many years ago at Daytona. John Healy sent a Shadow drum overnight, so there was no downside. The chain was intact and there was not much damage except scrapes. The next season I made a rule to change all the brake drums to new Shadow drums and it is now the first thing I do on a racer. I also made an adapter to carry the sprocket instead of the brake, and I moved the brake drum to the non-chain side. This was for a single, and based on Greg's experience with his twin racer cracking the adapter, there is a lot of stress on these parts.

I also noted that the hubs can shatter as has been reported in MPH. Based on that, I also replace the hubs with new ones made from billet rather than cast. The wheels are the only area that I do this. If I were riding on the street I would probably be happy with old Shadow drums and cast hubs, but I would not ask too much of them. If something goes wrong with a hub, drum or brake plate there is a good chance of going down. I am glad that you were able to ride through it.

David
Thanks for the good wishes. I was doing 60, changed down for a roundabout and braked with rear brake all at the same time so I was able to de clutch immediately I heard the bang. Chain is ok but mudguard, lifting handle, drum, backplate one shoe, cam etc are all toast.
I will probably replace the rear drum with finned one, the original was plain. The fronts are finned and the same age as the rear so I'm thinking I'll replace those as well. My main issue is fixing the RFM. I could actually spring the axle in but that would be a bodge and it would make adjusting the chain difficult if not impossible.
 

Bill Thomas

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Hello Mac, Sorry to hear of your trouble, I thought "D"s had ribbed drums ?, I tried ? to help Chris with his rear frame, It's on page 9 of these threads, Under Early/later RFM, I asked Bob Culver if he had a Jig, He said no but he would have a go at straightning mine cold, So I did it myself, For me I only run Twins with an adapter for the sprocket, I did one like you years ago with an outfit !, The ribbed drums are much better so I run one with a sprocket on the Comet. Cheers Bill.
 

macvette

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Hello Mac, Sorry to hear of your trouble, I thought "D"s had ribbed drums ?, I tried ? to help Chris with his rear frame, It's on page 9 of these threads, Under Early/later RFM, I asked Bob Culver if he had a Jig, He said no but he would have a go at straightning mine cold, So I did it myself, For me I only run Twins with an adapter for the sprocket, I did one like you years ago with an outfit !, The ribbed drums are much better so I run one with a sprocket on the Comet. Cheers Bill.
Mine came with finned drums at the front and a plain one on the rear. So how did you straighten your RFM?
Mac
 

Bill Thomas

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I had the frame out of the bike, Locked it up in a strong vise and used long bars !!, It depends where it's bent But I was lucky, I took the bolts out where the two parts of the frame meet which gave me more control, I could bend one at a time, I had a known good frame on the floor to match it with, After Bob told me he would do it Cold, I thought what's to lose !!, Good Luck, Bill.
 

davidd

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I use a large table that is one inch thick. Like Bill, I use a loose frame to measure against. I have some angle iron that I weld to the table and and I can run an axle through. I do it all based on the bend, in or out up or down and I can position a side off the table if necessary. I would work the RFM to get the rear axle fork to be square to the table and square with the angle iron holding the the RFM in place.

It is a little hard for me to see from the photo what force bent the frame, but it looks like the bottom somehow tucked in and brought the top bolted-on tube with it. Like Bill, I would take the bolt out and see where the stresses leave the parts. If the upper tube is holding the lower frame in, I would start by bending it out. I would do this by slipping a tube over it and pulling on it at or along the bend or tacking some structure to the table to jack against. If it is the flat on the tube that is bent, sometimes one or two large (12-18") and cheap open end wrenches can be used to bend it locally. Once you are happy with the top tube, try and get the lower tube with the fork square up and down first and then try and get the width between the two close. With luck it won't have much of a twist, but I use several of the open end wrenches to twist it with the warning that the cast end it quite easy to break or damage, so as little point loading as possible. I usually bend cold, but I have never had to take a severe twist out of the fork and I would inclined to heat the lower tube rather than risk breaking the casting, but I have never run into a twist that would not come out.

You usually can't get closer than 1/16" away from original. I am usually happy with that number as long as things are square.

I did not mention this process at first because it is a little like making sausage. The process can be complicated and unsettling even though the results are quite rewarding.

David
 

greg brillus

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And I've had experts tell me that those rear frames look weak as water........I tell them, have you ever tried to straighten one. Although I guess the swing arm off a Featherbed frame would have to be stronger, wouldn't it........o_O...........NOT. Cheers.............Greg.
 

davidd

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The RFM may look spindly, but if you have replaced the tubing it is very thick walled. I have always admired the Parkin lads for their riding skill considering the stiffness of their swing arms.

David
 

Bill Thomas

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Just blown Mac's photo up, I think most of the trouble is in the tube coming down to the casting, Which I think would be the more easy one to bend, I would take the bolt out that side and spring that tube a bit to see how that left the casting ie the bottom rail, And see if the width of the frame has changed ie Does the wheel fit nice between the castings, I would do this with out taking the frame out. Good luck, Bill.
 
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