Brake Feel: Early style caliper vs. late model

[scott s]

I have a '75 that had rebuilt stock brakes: New pads, new fluid, bench bled master cylinder, new hoses, etc.

The brakes worked, but the lever was soft and I felt like there was more there. All the bleeding in the world made no difference.

I picked up some braided stainless hoses and a new master cylinder from David Silvers Spares in the U.K.
I've used this same m/c on my Honda CB500 and it works great. Vintage look and a rock hard lever. Excellent, firm brakes.

However, the same m/c on the XS650, while much better than stock, still has a soft feel to it. The bike stops MUCH better now and is 100% safe to ride, but I'm wondering why the lever feels so much different than on the Honda.

Could it be that the early style caliper with the two floating pistons just has a different feel than the later calipers with the single piston (which is what the Honda has, although a slightly different set-up than the XS).
I've always been able to get good brakes with a hard, firm lever...until I had this early bike with the different caliper.
Could it be the two piston caliper?

 

[5twins]

You have to match the MC bore size to the piston area you're moving to get the proper feel.

 

[scott s]

So why was the stock m/c with stock rubber hoses and a stock caliper so mushy? Is this just something that goes along with the early, round style m/c's and 2-piston calipers?
Prior to this bike, I've had late model XS's with the other style m/c and single piston caliper.

Also, the David Silvers m/c is a huge improvement over stock, but the lever just feels different on this bike vs. the Honda with the same m/c.

 

[scott s]

BTW, here's the m/c. It has a 5/8" bore. How does that compare to the early, round reservoir Yamaha m/c?

http://www.davidsilverspares.co.uk/CB500K0-FOUR-1971/part_123892/

 

[XSLeo]

My 75 M/C is a 5/8 or 16 mm bore. I think a 14 mm bore would be better. It might give you the feel you are looking for.
The piston size of the caliper needs to have certain ratio to work well. If the M/C gets to big compared to the caliper the feel gets wooden, Hard to pull then the brake locks up, no feel.
If the M/C gets to small the lever has great feel but very touchy. Very little finger pressure and it can lock the brake.
What is the piston size in the Honda?
Leo

 

[scott s]

My 75 M/C is a 5/8 or 16 mm bore. I think a 14 mm bore would be better. It might give you the feel you are looking for.
The piston size of the caliper needs to have certain ratio to work well. If the M/C gets to big compared to the caliper the feel gets wooden, Hard to pull then the brake locks up, no feel.
If the M/C gets to small the lever has great feel but very touchy. Very little finger pressure and it can lock the brake.
What is the piston size in the Honda?
Leo

The David Silvers m/c is 16mm, same as the stock '75 XS650, right?

The lever doesn't feel wooden. It's soft and spongy, almost like there's air in there, but I'm 99.99% sure there isn't. It felt the same way with both master cylinders.

I have another early caliper and it would be fairly easy to go with dual discs. Would that help the feel of the 16mm m/c?

Or am I doomed to run a modern looking 12mm master?

Is there anything special about bleeding the brakes with those 2-piece, 2-piston early calipers?

 

[scott s]

Bumping this one...hoping someone might have some insight.

I'll be doing fork seals later in the season. Maybe I can check the operation of the caliper when I have the wheel off. Maybe only one of the two pistons is working as it should?

I'd love to hear from you guys with the early '74-76 bikes and how your front brakes work/feel.

 

[XSLeo]

On my 75 with the two later single piston calipers the 16mm M/C feels a bit wooden. On yours with two two piston calipers if should feel ok.
I have not done much with the two piston calipers.
I have used a 16 mm, a 14 mm and a 13mm M/C with dual single piston calipers and the 14 mm gave the best feel and action. The 16 a bit wooden, the 14 about right, the 13 a bit sensetive. Too easy to over brake and lock the wheel.
Right now because the 14 mm M/C leaks I have the 13 mm on with a one single piston caliper and it feels about the same as the 14 mm single piston caliper as on the 81. A slight bit better. I think an 11 mm M/C on there will feel just about right.
At Vintage Brake there is a chart that lists the caliper size and number of pistons and tells you the best size M/C to use.
Leo

 

[irristeve]

those early (2 piston) calipers have the bleed nipple in the wrong positon its not at the top of the caliper which makes it hard to get all the air out,I had 650c back in the 80s that I bought as a basket case spent hours trying to bleed them,on advice of mate I secured the brake lever back to the bars with duct tape & left it for 24 hours,problem solved.hope this helps