Mid Year Brake Drums

[Pete VanSeggern #30920]

Question 1: What is the maximum diameter that '63 - '64 drums can be turned to?
Question 2: What is a good method to get the surface finish requirements for J65 metallic shoes?
Thanks in advance for any help here.

[Duke W.]

Re: Mid Year Brake Drums

Maximum diameter debossed in later replacement drums (This is a FMVSS that went into effect circa '68) is 11.090".

I don't know the exact process for obtaining the desired 20 microinch finish, but I doubt if a brake shop could do this. You should contact some machine shops and ask them how they achieve such a finish. If they can answer the question, they might be a good bet to finish the drums properly.

My experience is that once the linings are worn to replacement thickness the drums are worn .060" to .080", so they probably aren't worth turning. Replacement drums are readily available and inexpensive, so I would recommend buying replacment drums, but have the friction surface polished by a machine shop that knows required process to achieve a 20 microinch finish.

Duke

[Pete VanSeggern #30920]

Re: Mid Year Brake Drums

Duke- thanks for the response. Any idea of what the lining thickness was new and what is considered "replacement" thickness? My car has a lot of miles on it, but they were fairly easy brake wise. I bought new shoes, but am now debating whether to redo the old drums for the new shoes (assuming they aren't too far gone) or just reassembling the old shoes with the old drums. I think new drums would go for about $300 or so and I consider that to be an expense that I'd rather avoid now.

[Duke W.]

Re: Mid Year Brake Drums

I'm assuming you still have the original or correct replacement J-65s. The segment thicknesses are in the AMA Specs that are part of the no charge GM restoration package (1-800-222-1020 and have the VIN handy). The primary segments (front shoes) are .175" thick, and the secondaries (rear shoes) are .295" thick.

J-65s are very long lived and since the segments are welded to the shoe you can essentially run them to zero, because the drums will probably be beyond turning when the shoes are completely worn. You should also measure your drums. They are probably worn, but if they're still less than 11.090" they are serviceable.

If there is still lining thickness remaining just disassemble and clean everything, but be careful to mark the shoes and drums so they go back in the same spot along with the drums, and DO NOT turn the drums. Recommend you overhaul the m/c and overhaul or replace the wheel cylinders. They are inexpensive.

Put everthing together and flush the fluid every two years and you might not be doing any brake work for a long time. If you overhaul all the hydraulics consider silicone fluid. If you go with silicone all the hydraulics should be assembled with silicone fluid and the lines flushed with alcohol and dried, which should also be done even if you go with conventional glycol fluid to ensure that any old contaminated fluid is expelled. Replace all the brake hoses, too.

If the lining and drums have some life a hydraulic system overhaul and bienneiel fluid changes (if you use glycol fluid) should keep you from doing any brake work for a long time. If you use silicone fluid there is less maintenacne because fluide changes can go at least twice as long, but you must start with everything clean and dry with no residual glycol anywhere in the system.

Duke