Adding a second brake caliper to a '79

[Hammer65]

Was wondering if anyone had any experience adding a second brake caliper to a single caliper bike.  Do I just need a disc, caliper and hose?  The front brake on this thing is a little scary at times.

[wilcom]

Do I just need a disc, caliper and hose?  

Yes. You may need a splitter, but as I remember when I did mine I think the splitter was there with one port blocked off.  The dual disc set up came with a bigger master cylinder which I upgraded to $$$$ at the time.

I would try the stock single disc MC before I invested in the larger master cylinder....... you may like the feel but it could be a tad sensitive. No more $$$ to change after than before

My brakes ( on the sadly departed R65) went from sketchy to 2 finger brakes with the dual disc upgrade.

[nhmaf]

Does the other fork leg have the mounting bosses for the caliper (not all of them did on the earliest models)?

Given the model year, I am assuming that you've got ATE caliper on your bike?   The ATEs are harder to find in good shape (assuming you'll want to match), otherwise you may be looking for a matched set of Brembos.   They are less expensive, more easily found, and rebuild kits are more easily found.   The internals of the ATE and Brembos are different though, even though they look similar from the outside.

Are you certain that the brake system is in good shape now?    Sometimes old pads are badly glazed.   Even with duals on my 82 R65, braking performance wasn't great until I cleaned out the calipers and installed some new organic EBC pads.   Changing the brake hose to stainless also helped.   Now it does have some decent stopping power - still not like a modern sport bike, but not bad either.

[Semper Gumby]

Yes I did it. In fact I still have the bits as I changed out the whole front end.

Mine now has a 1988 K100RS front end.  Much more stable at speed with bags and a Lufty fairing.

[soulmachine]

I have an early LS, and it's equipped with dual ATE calipers. As I found out the hard way, not just any Brembo calipers will work.

Spacing for the mounts need to be 107mm.

The later Brembo calipers are threaded at the mounts, AND the bottom mounting point is far too inboard (it resides where the bottom ear is on the stock R65 legs) to be able to work.

The calipers I tried this with were from an '85 K100.

SO, be aware that it isn't all that easy to find the correct Brembo calipers. Thankfully, I got a very understanding seller on eBay and they allowed a return.

[georgesgiralt]

Hello !
I can't find where I read this nor find a reference. So this comes from memory.
The Brembo calipers are P08 and there are 36mm dia. The right side caliper has a different diameter hole for it's installation (bigger, allowing the use of hat spacers to center the pad on the rotor)
This size is specific to BMW and, as such, commend a high price. Brembo make a more standard caliper with 38 mm diameter piston (from memory). Which is way cheaper. If I'm not mistaken it is the one Guzzi and/or Ducati uses.
As you will certainly have to change the master cylinder to accommodate the 2 disk brakes, you may well save a lot of money going for the more standard Brembo ...
I was given a web site in the USA having both size available but I'm unable to find it. Maybe some of your neighbors will chime in ?

[mrclubike]

Here are the standard 38mm Brembo F08 calipers they work perfectly on a 1982 R65 at least on the left side not sure about the right
It may need some kind of special shims or spacers
http://www.mgcycle.com/index.php?main_page=product_info&products_id=1034
 http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_115&products_id=834
You need to use a left on the right side and a right on the left because our calipers are mounted below the fork
This is the exact caliper I used on mine with a 12mm master cylinder and EBC disc and shoes  
The picture was taken before I replaced the OEM rotor
 I can easily lock the front tire with a single caliper set up.
It appears they are out of the right side that we use on our left side  

[Barry]

Does the other fork leg have the mounting bosses for the caliper (not all of them did on the earliest models)?

For what it's worth my 79 was manufactured in Oct 78 and it does have the mountings for a 2nd caliper.

My guess is most all have them although there were a few bikes manufactured before Oct 78 but not many e.g. 2 bikes were built in Jan 78, 4 in March, 2 in April etc. Serious production didn't start until Sept 78. Even if some very early bikes didn't have the mountings exports to the US started a little later in Dec 78.

[Hammer65]

My bike has the mounting holes for the second caliper so that's not the issue.  I do like the ATE brakes, they look nice on the bike I think.  My pops has a lathe so I'm sure if need be I could turn new pistons on it (after some trial and error).  

I swapped out the brake pads...HUGE difference.  I'll be researching the second brake and saving up for it for a little bit longer.

[Barry]

One thing to be aware of is that although the ATE and Brembo calipers have the same piston size, the master cylinder sizes are different.  A 79 single disc bike will have a 13mm master cylinder while 81 on models with Brembo calipers are 12mm. That doesn't sound like a big difference but it amounts to a 17% reduction in piston area which will translate into a 17% reduction in effort needed at the brake lever (assuming the lever pivot ratios are the same).

BMW were too conservative when they specified a 13mm master cylinder and 12mm or even a touch smaller is more appropriate without brake lever travel being compromised too much. If my master cylinder ever needs replacement or sleeving I wouldn't hesitate to go down in size.  Conversely with twin discs the master cylinder size should go up to 16 or 17mm and that  would still give a better ratio than you have now.

[soulmachine]

That brings about a question for me.

What is the size of the master cylinder for the dual disc brakes?

Also, are the masters the same between the ATE and Brembo's?

[montmil]

Here are the standard 38mm Brembo F08 calipers they work perfectly on a 1982 R65 at least on the left side not sure about the right

http://www.mgcycle.com/index.php?main_page=product_info&products_id=1034
 http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_115&products_id=834

You need to use a left on the right side and a right on the left because our calipers are mounted below the fork

It appears they are out of the right side that we use on our left side  

Another.source for Brembo bits:

<https://store.bevelheaven.com/>

[Barry]

That brings about a question for me.

What is the size of the master cylinder for the dual disc brakes?

Also, are the masters the same between the ATE and Brembo's?

When I checked the information I have, a stock twin disc set up on a 79 would have had a 16mm master cylinder.  The later bikes with twin Brembo calipers were  1 mm less at 15mm.

You might reasonably have expected that they would have simply doubled the piston areas to keep the master cylinder/caliper piston  hydraulic ratio the same but in fact they improved it as the area of a 16mm cylinder is somewhat less than double that of a 13mm. In other words they increased the hydraulic ratio to make the brakes feel more powerful.

EG:

13mm area = 132.75 mm2

16mm area = 201 mm2


Whether single or twin disc set ups the master cylinder sizes were different for ATE and Brembo calipers even though the caliper pistons were the same size. So that you can tell them apart they also changed from a round fluid reservoir on the ATE to a rectangular one on the Brembo's.  To check sizes, master cylinders have the size imprinted in the casting underneath.

[georgesgiralt]

Barry, I respectfully disagree.
I bought my bike new with ATE calipers (dual set-up). It is an 1982 model and had the square bowl master cylinder. It was 15 mm dia. The square bowl came with the 1981 model, no matter what caliper the bike had.
After 4 or 5 years, the master cylinder leaked because is has oxidized during the wo years the bike was stored at the dealer's. So I replaced it for a 16 mm dia (for two reasons : the brake was spongy with the original 15 and the 16 was the only one in stock at the dealer's and I needed the bike). Man, you need Tarzan grip to brake ! The handle is very very hard to maneuver ! So If I need to change the master cylinder, I reduce diameter... Next, the ATE experienced pitting on the piston One piston on both caliper. At that time, ATE piston and rebuild kit was not available so I bought a set of Brembo at the dealer ... Ouch, it still hurts. And the handle is still hard as wood to press.....
In 2013 I renovated the bike and put braided lines to replace the 30 years old BMW original. The brake is very very hard to use but the braking power is excellent. (on dry roads, wet roads is an entirely different matter altogether..)

[nhmaf]

I agree - the 16mm for dual discs is waay to effin big!   The 15mm that came on my LS (and which I replaced with another 15mm) provides almost no travel, and a very 'wooden feel'.  It will stop the bike right now, too.  It is the only airhead I've ridden where stoppies are possible.  I would prefer to have more than a few mm of travel to have a more linear/progressive braking action out of it, but over the years have built up the muscles in my right forearm to be able to  squeeze that sucker.     The lever travels much less than 1/2 way, maybe only about 1/4 of the way, to the handlebar - at which point the front wheel is locked up tight and skidding on paved roads.

If I could find a 14mm or a 13mm in new condition I'd consider swapping.   I also have stainless braided front brake lines, which do not expand like the OEM rubber originals, so there is virtually no "loss" in hose expansion - this makes the transfer of braking power all the more efficient - but I think things can be taken a bit far.   I have to mentally recalibrate my braking fingers when switching to my 700 pound Kawasaki Councours, as squeezing that hard will bring the lever to the bar and will flip the bike head over heels.