250 Monza weak front brake

[cooperplace]

there seems to be more stopping power available from the rear brake. The front works, but you have to squeeze the lever hard. The linings seem to have lots of meat left and don't look glazed to my amateur eye. I have no idea where the linings came from, the previous owner passed away some years ago. Any suggestions for improvement would be much appreciated.

[Sam]

Personally If the shoes are that old for what it costs I would get a new set or better still get them relined with a good quality liner, they will then machine the shoe to the dia of the drum.

I bought a set of aftermarket shoes for the rear of my wee scrambler and was amazed at how out of true they were when fitting

Spigot gripped in the chuck of a lathe, with the lathe running counter clockwise it keeps the bolt tight.



Machining the aftermarket shoes to the correct dia, I took 3mm (0.120 almost 1/8) off the shoe from initial touch before it was running true and machined over the whole width of the lining.



p.s. if machining old liners they will more than likely contain asbestos so be aware!

[Jordan]

To get the best out of a drum brake, the shoes can be ground to suit the drum size.
Drum should be without scores and not out of round or tapered, so check that first and rectify if necessary. Drums should be machined after lacing to rims, so a big lathe is needed.
Method is to mount shoes to the brake backing plate, rig up so the brake is slightly "on", then mount the lot onto a lathe. Shoes can be ground with an angle grinder mounted to the lathe's toolpost. Watch out for the dust.
If this isn't done, new shoes could take a long time to bed in so that both are actually touching the drum when the lever is pulled on. And, by the time it does, the shoes might be deformed somewhat. Machining the shoes gives the brake the best start and performance improvement.

[Jordan]

Wow, Sam beat me to it by a few minutes.
To just add something to Sam's description, it's best to arrange for the brake to be slightly on before grinding the shoes. That's so the shoes will touch the drum for their whole surface, which won't be the case otherwise, as they would be "round" when machined, but slightly unround when touching the drum.

[Sam]

Wow, Sam beat me to it by a few minutes. Good info.

Reading from the same page as well!

[cooperplace]

Thank you everyone for that great advice. I had been thinking that it must be a situation where not the whole area of the linings is pressing on the drum, which I think accords with the views expressed above. I'll get new linings and have them and the drum machined to match. I'll take it to a brake place.

Thanks again.

[DewCatTea-Bob]

[quote= cooperplace ...
" but you have to squeeze the lever hard.
Any suggestions for improvement would be much appreciated. "

____ Did you ever remember to get-around to making-sure that the activator-arm is set at the optimum angle ? - (As previously discussed last-spring [at the following thread-post].) ... viewtopic.php?f=3&t=1786&p=13105&#p13105
Cuz if you have the full-engagement angle set so that it's at any other more or lesser angle, then the hand-lever will accordingly require greater hand-pressure !
When a stock front-brake is properly set (with it's activator-arm set at the optimum-angle), I've always found the brake to be fairly quite-good for it's stopping-power per hand-pressure ratio !


Hopeful-Cheers,
-Bob

[Nick]

Here's what you do:

Step 1. Get some sticky backed sandpaper (used on electric sanders, etc.). Cut out strips to stick on the inside surface of the brake drum. That is, cover the entire surface of the brake drum with the sandpaper.
Now install the brake plate with shoes installed into the drum, mount it in the fork and slide the axle through and snug everything up.

Then, while slowly turning the wheel by hand, actuate the front brake so that the brake shoes are sanded to shape by the sandpaper.

Don't sand too much, you don't want to wear out the shoes! When the shoes look good, remove sandpaper and clean any residual glue from the drum.

Step 2 Proper installation of drum brakes into the fork is important! You don't just put it in there and tighten everything up.

Here's what you do: Install wheel in fork, put the axle and pinch bolts in but only tighten them finger tight. Now spin the wheel as hard as you can by hand, then grab the front brake lever and bring the wheel to a stop. Don't let go of the brake lever! Keep holding it. The brake plate is now properly centered in the drum. Without releasing the lever pressure, tighten the axle and pinch bolts.

These two steps can transform a very mediocre drum brake into one that really stops.

Note: if the drum is not laced to the wheel, you can mount the axle vertically in a vice and turn the drum by hand while sanding the shoes.

[Jordan]

While Nick's sandpaper suggestion may improve upon just installing the relined shoes and hoping for the best, I can't agree it's the best improvement possible.
You'd end up with the shoes with less than the drum's diameter, by maybe 2mm. Then they'd need to wear in to a point when they'd give maximum surface contact.
And, no effort has been made to rotate the cam slightly before grinding. That ensures full-circle contact when the brake is applied.
To completely nick-pick, machining a bare drum can be done but isn't best practice. It can be pulled out of round when spokes are tightened. However, that's how some factories did it, even if not ideal.
The suggestion to centralise the brakes before tightening is good.

[DewCatTea-Bob]

____ Interesting posts by Nick & Jordan...



[quote= Jordan ...
" You'd end up with the shoes with less than the drum's diameter, by maybe 2mm. "

____ Is that assuming that the sand-paper is near 1mm thick ?
I don't see the resulting-difference in the drum's radius being greater than the shoe-pad's resulting outer-radius by any greater amount than the thickness of the sandpaper itself.



" Then they'd need to wear in to a point when they'd give maximum surface contact. "

____ The supposedly worth-while/significantly improved radius-matching (by Nick's suggested process), should of-course still cut-down the remaining wear-in period (for finally reaching the optimum max.surface-contact goal),, which is the bottom-line reasoning for bothering with the usually ignored matching-work, (with respect to the shoe-pad's radius). _ However that remaining wear-in period could still be further cut-down even more-so, by not allowing the sand-paper shaping-process to completely finish it's radius-contouring goal, and rather quit that grinding-process at a happy-medium (near 'full-circle') contact goal,, thus, if skillfully judged, then cutting the final wear-in period nearly in half !



" no effort has been made to rotate the cam slightly before grinding. "

____ Am I missing some intended point you've meant to point-out ? _ As I-myself find that Nick's stated wording: " while slowly turning the wheel by hand, actuate the front brake so that the brake shoes are sanded to shape by the sandpaper.", seems to cover the required 'rotation' of the activator-cam ! _ So did you actually intend some-other aspect-point (that I'm apparently not getting) ?



" The suggestion to centralise the brakes before tightening is good. "

____ Indeed so ! _ As it could possibly make a worth-while difference.
__ In-fact, I'd bet that that extra effort (suggested by Nick), combined along-with making-sure that the cam-activator lever-arm is properly adjusted for a 'right-angle' leverage-angle, is actually all it'll take to satisfy much acceptably good front-brake performance.


Dukaddy-DUKEs,
-Bob