rear brake conversion

[scdrtramp]

Hello all,, I have an 83 Heritage Special. It has the spoke wheels and a drum brake on the rear, which is terrible.I also have a 78 650 special that has mags and disk brakes front and rear. I love the disks. I want to change the heritage to disk on the back. I have a parts bike that has the mags and disks , so I have most of what I need, however the 83 frame does not have the mts for the master cylinder. My question is is there a kit to mt the bolt bosses onto the 83 frame, or does it have to be the hard way??

 

[Jim]

The hard way unfortunately. I've got some dimension drawings around here somewhere's. Let me see if I can find 'em...

 

[Jim]

 

[scdrtramp]

I was afraid of that. thanks for the drawings

 

[650Skull]

If the drum is set up properly it is better than a disk brake.

 

[jetmechmarty]

If the drum is set up properly it is better than a disk brake.

Agreed. The drum hauls it down if it’s in good order and properly set up. I set mine a bit tight and it stopped me from going anywhere once it heated up.

Look at the actuating arm on the drum in this photo. Set up like that, performance is abysmal. If you’re that disappointed in it, I suspect your brake is simply out of proper adjustment or maybe even has contaminated brake linings. Get it right and it will haul the bike down.

 

[Grewth]

Buy a set of number stamps and re-stamp the parts bike frame with the Heritage frame numbers.
Just remember that it's only a crime if you get caught

 

[Kevin Werner]

Before you exchange that drum brake, make sure you check this entry in the tech section about setting up drum brakes.
The whole thread is pretty interesting too.

I fashioned a way to measure the brake cam's lobes spread, or displacement values relative to cam rotation angle.
View attachment 136938

The lathe chuck has a degree wheel. A flat strip rides against the cam lobe, and a dial indicator shows the displacement.

Numerous measurements of the cam lobes of both brake cams, from 0° to 20° of cam rotation, revealed that one lobe produced about 90% of the displacement value of the opposite lobe, confirming that the factory did indeed produce non-symetrical brake cams. And, the Mysterious Dimple aligned with this dissymmetry.

The Mystery Dimple indicates the slower spreading cam lobe, which would be the lobe for the Leading shoe.

Shown here, "L" for the Leading shoe, "T" for the trailing shoe.
View attachment 136939

The "L" lobe is inboard, toward the axle.
The "T" lobe is outboard, toward the rear of the bike.

Imperceptible by eye, we're talking tenths of a millimeter differences in the leading curves of the cam lobes.

 

[FB71]

Jim beat me to it... Those are the same pics he supplied me when I did my conversion. Not hard if you can weld.

 

[FB71]

and it's more than just the m/c mounts; swingarm is different, and some other tabs on the frame are different also.

 

[scdrtramp]

I've been riding for 50 years and there is no way a drum brake is better than a disk brake period. I will get it changed, I have the swing arm and all that is needed. I can and will weld the bosses on my heritage frame. thanks everyone.

 

[jetmechmarty]

I've been riding for 50 years and there is no way a drum brake is better than a disk brake period. I will get it changed, I have the swing arm and all that is needed. I can and will weld the bosses on my heritage frame. thanks everyone.

I did not intend to imply that the drum is better than a disc brake. I simply weighed in on it’s adequacy versus the work and/or money involved in replacing it. I’m not in a position to know what your level of mechanical talent is.

A thread on your upgrade could prove useful on this forum. It has been discussed, but I don’t think it has been documented. Best wishes.

 

[650Skull]

You already have the gear that just needs to b changed over. At least you will have the original bike to measure from.

My point about drum over disk brake is the drum can be made to brake hard without locking the rear wheel and going into a skid. Once in a skid the bike is out of control,( unless your very experienced), where a disk brake is easier to lock up the wheel.

A drum brake can b set up to lock up the wheel if that is the objective.

https://www.xs650.com/threads/rear-brake-conversion-drum-to-disk-or-disk-to-drum.51944/

 

[Jim]

I've been riding for 50 years and there is no way a drum brake is better than a disk brake period

Having ridden both the disc and drum on the rear, I'm of the opinion that the drum gives a much better feel. Both will easily lock the rear wheel. That to me makes the drum better.

.... and you'll find that almost everyone that regularly post's here has at least 50 years of riding under their belt.

 

[FB71]

a few pics here; https://www.xs650.com/threads/long-time-comin-82-heritage-restomod.51701/page-2

 

[Grewth]

I rode a Suzuki GT750 for years, the cable operated rear drum was the worst feature of the bike, wooden feeling, weak braking followed by a locked rear wheel
Swapped to a GS750 the rear disc was a relevation, powerful and progressive, you could take it just to the edge of locking up, squealing the tyre slightly but still under control.
In comparison the single piston sliding caliper brakes fitted to the 650 Special aren't brilliant at either end, just adequate.
I feel that the earlier twin piston Yamaha calipers were much better.
But do you really need disc brakes on a 46 Bhp motorcycle that won't top 100 mph ?
I'm quite happy with my XS1B

 

[jetmechmarty]

... and you'll find that almost everyone that regularly post's here has at least 50 years of riding under their belt.

I’ve only been riding a motorcycle for 40 years. I’m a relative novice here.

 

[Jim]

First bike was in '68... so 55yrs

 

[jetmechmarty]

First bike was in '68... so 55yrs

My XS650SK is my first bike. I purchased it new. It’s an old friend.

 

[Mike G]

I've only been riding for 36 years so still wet behind the ears...