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/5 Front Drum Brake
Posted: Fri Dec 26, 2025 10:13 am
by JohnT
The eccentric cam in the front drum brake.
Am at a loss as to what it does and its function.
Re: /5 Front Drum Brake
Posted: Fri Dec 26, 2025 3:56 pm
by Kurt in S.A.
Duane is usually good describing these things...but I don't see any mention of an eccentric:
https://w6rec.com/5-front-drum-brake-ad ... nd-repair/
Kurt
Re: /5 Front Drum Brake
Posted: Fri Dec 26, 2025 5:06 pm
by Rob Frankham
JohnT wrote: ↑Fri Dec 26, 2025 10:13 am
The eccentric cam in the front drum brake.
Am at a loss as to what it does and its function.
The eccentric cam is indeed mentioned by Duanne about 1/4 of the way down the page shown in the above post... It's purpose is to limit the retraction of the rearmost shoe. the foremost shoe is adjusted using the cable adjuster. This ensures that both shoes are pulled clear of the drum when the lever is released. With any leading shoe, if it is in contact with the drum, it will tend to be pulled 'on' by friction so a dragging shoe is a bad thing on a twin leading shoe brake.
For adjustment, I can do no better than to reproduce Duannes words of wisdom...
I suggest that you confirm that the arms are installed correctly first. Then set the front arm travel first. It should have about 3-4 mm (1/8″ to 3/16″) of travel. Don’t obsess over this measurement, as you just may change it later anyway.
To adjust it, you must adjust the stop screw or cam. The adjustment is located just behind and below the forward arm pivot. It is shown above as the “13 mm locknut” in the center of photo #2. Inside it is an Allen screw that uses a 4mm wrench. Loosen the lock nut first. The screw can’t be adjusted due to pressure from the brake shoe. To remove that pressure, reach up and pull the front brake lever with your left hand while you turn the wrench to its limit, with your right hand. Turn the 4mm wrench either way, as it amounts to the same thing. When it comes to a hard stop, back it off a “smidgen” and tighten the lock nut. The thing I can’t tell you is what is a “smidgen.” To test it, pull the brake lever and release it a few times. Check the travel distance of the arm. The wheel should spin freely, which means it has no brake drag. You want the least amount of lever movement that still has no drag of the wheel with brakes off. This will get you very close.
Rob
Re: /5 Front Drum Brake
Posted: Sat Dec 27, 2025 7:10 am
by JohnT
Thanks guys. More involved than first thought.
Who is Duane? That is certainly a comprehensive detailed explanation.
Re: /5 Front Drum Brake
Posted: Sat Dec 27, 2025 7:17 am
by Kurt in S.A.
JohnT wrote: ↑Sat Dec 27, 2025 7:10 amWho is Duane?
Duane was a pioneer with his BMW shop on the west coast. He was quite the hands-on guy and had good people around him at his dealership.
https://w6rec.com/me/
Kurt