Brake adjustment Tap thread size..

Sport King Eric

Sport King Eric

Member
I have a Question for the experts, I have to apply heat (the old fire wrench trick) to loosen up the adjusting wedges on my backing plates. I was able to unscrew the adjusting wedges, but the the threads show tons of rust so i figured i would chase the thread with a 5/8 24 tap to clean them out..

I purchased a good carbide American Made tap, but the thread in the backing plate seems much tighter that what i would have expected. (I am in my 40th year as a tool and die maker so i have tapped a few holes in my day) Did Ford use a British Tap? or is it indeed a 5/8 24 SAE? am i splitting hairs, I did practice on an old "junk" backing plate first and the wedge screws right in but i removed quite a lot of material form that thread when i expected just to remove Rust.. I have not chased the threads on my " good" backing plates yet, as I am doing my research upfront.

Does anybody have any experience with this issue and what was your result?
 
Ford must have had a different specification for the tap that the factory used. The threads are all tight when using a modern tap. When installing a Flat Head Ted floater kit the instructions say to re tap the backing plate. The hardware in the kit is made to modern specifications and will not fit in the original holes. Even threads that are in excellent condition have to be tapped.
 
Sport King, as a tool and die maker you should have a good thread pitch gage set. I have sets all the way from 0-80 up. Sometimes rust is hard to gauge but a small wire brush cleans the threads good enough to check the pitch, if you have a good magnifying loop to see with.
Ed
 
I have the thread gauge but never use it. I just put the tap against the bolt to see if the threads mesh.
 
Agreed, I checked the thread on the wedge and it was a tight 24, however i just have an SAE thread gauge set, The tap went in in with no issues, My concern is why did i remove more material than just the Rust or build up from the backing plate thread.. I was concerned that Ford could have used a BSF (British Standard fine) Thread as they are super close to SAE fine taps, usually about half a thread off per inch, which could look like a tight fine thread on a SAE Thread Gage.. What I think happened is a Modern high quality OSG Grade Carbide Tap is much sharper than the HSS Taps of 95 years ago.. and i was just removing the material left behind from HSS Tap, heck how many holes did that tap, tap before it got to mine??? We will never know!! thanks to all for the help..
 
nkaminar said:
Ford must have had a different specification for the tap that the factory used. The threads are all tight when using a modern tap. When installing a Flat Head Ted floater kit the instructions say to re tap the backing plate. The hardware in the kit is made to modern specifications and will not fit in the original holes. Even threads that are in excellent condition have to be tapped.
Click to expand...

Yes, most taps today are Class 1 or 2 whereas Ford's engineers often specified Class 3A & B which stands for tighter internal & external threads. Also, many reproduction parts have cut threads whereas Ford often used rolled threads. Many taps & dies use Class 2 as their basis.
 
So should we go ahead and clean it out with a 5/8 -18 tap or just clean out the hole with solvent and a wire brush? Maybe Ford intended it to be a tight fit?
 
Tap it if you are going to replace it with the Flat Head Ted floaters kit. Otherwise clean up the treads on the adjusters and in the backing plates.
 
Cut a couple slots lengthwise in the old wedge threads and run that in and out a few times soaked with WD-40. It'll clean out the rust and not cut new threads.
 
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