If you look at most mass produced drums the adjustment and weep holes are broached and not necessarily drilled. By rounding the sharp edge on both ends of these holes you will reduce the tendency to act as stress risers or crack starters.
It is not the heat checking cracks that cause the drum failures demonstrated by the radial cracks around the spindle area or bearing races. Nor is it a disparity of heat ranges. It is my humble theory that the vibrations and pulsing caused by heat checked drums that is stressing the attachment area surrounding the spindle and causing those cracks. If you look at most front drums there are radial curved casting webs winding out from the race bosses. These are designed to strengthen the connection between friction area of the drum and the spindle area which is fighting those twisting forces. A pulsing drum is just too violent to resist failure and overwhelms those extra casting reinforcements.
There have been several threads about vibration and tramping under braking on this forum. I believe these negative actions are also generally triggered by drum vibrations.
As I adjust my brakes and sneak up to a rubbing point, I listen to hear if the duration, or amount of time the shoe is rubbing, is very short. If your shoe just hits one small area, chances are the drum is no longer true and could be prone to having vibration issues. I have found a great machine shop that turns my drums just slightly enough to make them round again and minimize this issue. I ask for a slow cut, which will give a very fine finish and would never take my drums to "Brakes are Us".
Front drum part number
Re: Front drum part number
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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CitationFV21
- Posts: 272
- Joined: July 6th, 2006, 10:49 pm
Re: Front drum part number
[quote="jstoezel"]
ChrisZ, I use custom wheels built for the Canadian FV series (WCMA and F1200). There's 2 models available, I have the older type. I torque at 55lbs.[/quote]
It was a long time ago, but I tried a set of similar wheels with EMRA. Torqued to 65 ft lbs and the brakes were like full anti lock with the pulsing - had to run 50 to keep the drums from warping.
The standard FV wheel has some flex to it so it does not put a strain on the drum, but those "Nascar" wheels don't flex - so something has to give. You might want to see if a machine shop can true up the mounting surface of the wheel or at least see how much it is out. You might have a bad set.
ChrisZ
ChrisZ, I use custom wheels built for the Canadian FV series (WCMA and F1200). There's 2 models available, I have the older type. I torque at 55lbs.[/quote]
It was a long time ago, but I tried a set of similar wheels with EMRA. Torqued to 65 ft lbs and the brakes were like full anti lock with the pulsing - had to run 50 to keep the drums from warping.
The standard FV wheel has some flex to it so it does not put a strain on the drum, but those "Nascar" wheels don't flex - so something has to give. You might want to see if a machine shop can true up the mounting surface of the wheel or at least see how much it is out. You might have a bad set.
ChrisZ