Spongy front brake

[tlanders]

Help. My MC80 goes fast but doesn't want to stop. When I built it this winter, I put new Ferrodo shoes front and rear and a new Terry cable but the front is spongy. That is, I adjust the brake hand lever so that with very little movement the brake starts to engage. On all my other Pentons, it then only moves a little more when squeezing it hard for a full stop. But on the MC80, when sqeezing it hard, the hand lever keeps moving and almost makes it to the handle bar before it stops moving. Also, the front brake doesn't lock up the wheel if I'm riding it. On the stand, the front wheel is locked after if first engages. Also, when I sqeeze the hand lever, the front wheel rotates a little when on the stand.

I took the brake apart last night figuring I would find something wrong with it but there is nothing that looks bad. The shoes fit the diameter of the drum. The drum measures the same diameter across it's width, it's not tapered. I found a loose spoke or two but I don't think that would have anything to do with it. The shoes look like they are only hitting in the middle. The leading and trailing ends do not show much wear. I checked another new set of Ferrodos and they were the same diameter as the ones in the bike. The shaft the brake lever and cam are attached to is not wobbling on the hole through the brake backing plate casting. It is not perfect, the hole is a little wallowed out but no worse than any of the other bikes.

I don't get it. Something is streching. Help!!!

Teddy

[farmer58za]

Hi Teddy
Are the wear patterns even around the brake shoes?


Regards

David ('75 KTM GS400)

[OUCWBOY]

I am no brake expert by no means, but, I was told by an old Husky dealer that the brake wear pattern should be almost equal all around the shoes. If you are hitting in the center first, this could be your problem. I know there has to be a brake expert on this site somewhere....... Doug, John, Dwight, Mike, Randy, Kip, Larry, Ron........... One of us should be able to assist here.

Donny Smith

[Randy Kirkbride]

Teddy,
Did you have a Terry Cable on the front before?  If not, try a regular cable & see if it makes a difference.

[farmer58za]

Sorry, Teddy
I didn't read your post properly. Cables aside, if the shoes wear in the centre only then it's a sign that the drum has worn slightly larger and even new shoes will not follow the drum radius resulting in reduced braking area.

If you get the shoes re-lined with oversize linings and set the assembled brake backing plate up in a lathe, you can then turn the shoes down to the (enlarged) drum size.

Sounds simple, have not done it yet so I can't say for sure, but I need to do the same on my 400 rear brake.



Regards

David ('75 KTM GS400)

[Larry Perkins]

I would bet that the shoe is not touching in all spots.  Husky is most famous for that especially with Leleu hubs but any of them can be that way according to the roundness of the drum and the shape of the shoe.  Check and sand, check and sand, Grasshopper Teddy.  Also make sure the shoes are not glazed.

[tlanders]

Thanks for all your help. I will experiment tonight.

Teddy

[pketchum]

Teddy,

I've heard that poor front brakes were peculiar to the 1980 KTM's, and that a common upgrade was to replace it with a brake hub from one of the later model (81-83?) with double leading shoes.  I saw one on eBay one time and it sold for $80+ if I remember correctly.  I think this was ONLY for the brake hub too.

P.S.  Congrats on your outstanding performance in Marion, IL!

Phil

[LINDEMAN]

Hi Ted.I have found that terry cables are good quality but the housings are very spongy.I have cables made up at Steels Cycle in Denver.They copy your correct cable,only use a thick straight wire housing instead of spiral wound conventional housing that compresses like a spring.Then sand as much as needed to get full contact on the drum.When torquing front axle,place on stand with wheel of ground and hold front brake on.This allowes the small amount of play in all the components to self center.Then check that the fork legs are also in there relaxed centered position before torquing pinch bolts.This allowes the forks to operate full stroke with no binding.Smooooth!You may have to polish the axle and legs to acomplish this but its worth the time.Makes wheel changes much smoother too.Good Luck!

[TGTech]

Ted,
   There is one thing I haven't seen here, and it doesn't have anything to do with the individual parts, but rather the assembly process.

   When tightening the axle nut, you want to apply the brake as hard as you can. This centers the brake shoes in the hub, and makes sure that you get as much contact as the parts will allow.

   The issue of shoe contact with the drum is very important, but even with full contact, if you don't center the shoes in the drum, it won't make any difference.

Dane

[kds449]

hi. i have the problem. ive tried all the stuff you have read, cables new shoes, fiting shoes. i think the terry cablrs might be the problem. they seem to flex alot. just a guess

[Mike Lenz]

I have talked to Teddy about this and assumed he knew the holding the brake on bit as you tightened everything. The mc-80 hubs are not bad as a general rule. They are exactly the same brake hub arrangement as the full width hubs. I have them on two bikes with terry cables from Allen and they work fine. If his hub was out of round wouldnt it have an unsteady grab when pulling it lightly while moving? Couuld you actually wear a front hub enough that its so oversize new shoes wouldnt work? Couldnt he just have a bad set of shoes/bad or improperly mounted linings? The only time I have run into this is when installing used shoes from another wheel, and with the old Forma shoes from Hi Point. I couldnt ever get those to work right, still cant!

[tlanders]

THANK YOU for all your help!!!!! I was not tightening the brakes when I tightened the axle nut and I am now doing that, but that wasn't the problem. I tried it and it didn't help. Believe it or not, it was the powder coating on the backing plate and fork tube that was doing it. I discovered that if I loosened the axle nut slightly, I could adjust the brake cable tighter and then the brakes felt right. If I tightened the axle nut, I would have to loosen the brake cable to get the wheel to spin free. It had something to do with the final tightening of the axle nut. I pulled everything apart including pressing out the outer axle from the backing plate and that is when I observed the powder coat thickness looked a little irregular in the area around the axle hole where it presses against the fork tube. I took a large fine flat file and drew it across the backing plate and sure enough it did not hit evenly across the plate. Then I did the same thing on the fork tube where it was supposed to marry with the backing plate and I got the same result - uneven. I spent about 45 minutes carefully filing both surfaces until the file hit evenly all around the axle hole. Upon reassembly, and tightening the axle correctly with the procedures as delineated above, I now have a great front brake. As I said in my first post, something is streching. Well, it wasn't streching, the uneven thickness of paint made the backing plate cock slightly when the axle nut was tightened. You could not see this cocking movement it was so slight.

Thank you again everybody for your help. Now I can dive deeper into the corners before braking!!!!

Teddy

[Mike Lenz]

I always wondered why some brakes worked a little better than others. Maybe youve hit on something here!