Change of Brake Ratios

G

ghwallice

Hero member
Location
Ipswich
I've just pulled a 12.7mm(?) front master cylinder of my MK2 Lemans and stuck it on my 3CL, so it has a ratio of about 36:1. With my arthritic right hand at 60klm it now feels as if I'm almost pulling the back wheel off the ground. F08's are rear mounted.

I've also taken an F09 of another guzzi and put on the back, giving about an 18:1 ratio. The pads are shit, and pistons etc need work, but I can lock up the back wheel.

These ratios are way over what is recommended on the Laverdamania site, and I feel comfortable with them.

My concern is I don't know what I don't know. Are there problems inherent with what I have done?

Regards

Greg
 
Likely you now have too great a ratio at the front. The stock 15.7mm m/c to me gives little feedback and results in a 'wooden' feel. My own preference is for a 14mm master cylinder but these are not so easy to obtain. A more modern approach would be to use a radial m/c but I can't suggest a suitable one.

Somewhere on the internet there is information on the range of ratios which are considered suitable for motorcycle brakes. I think the issue with what you have done is that it is likely too easy to lock the front brakes without knowing. In which case you will fall off!

Happy Easter,

bazzee
 
I tthink as long as the lever pull doesn't feel too 'squidgy' it's fine.
 
Bazzee

Thanks for your comments. Did you get to share a slab with the Easter Bunny like I did?

I have read the article on Laverdamania "http://www.laverdamania.net/freingb.htm" with the ratio's etc, but in the fine print it does qualify that ratios of wheel sizes vs disk size, and hand lever ratio all have an impact, but no calculation/formulae is given. However, given wheel size, disk size, bike weight, and unknown lever ratios, maybe the 38:1 changes?

As far as locking up. Fair call, but I think I've got more chance of locking the front wheel on my Zane 750S than on the 3CL. I have done another couple of hundred klm's today, and I'm finding they really pull me up, but with good progression(?) in the braking field of the lever. (I don't race, so I can't give technical terms..)

The unit itself is off a Guzzi MK2 Lemans that has interlinked brakes (ie the front m/c only does one front disk), but I think they used it on the 350's to 650's in the 80's as well. Should be shitloads around.

My concerns are more like around brake fluid pressures (ie will calipers and stainless hoses be ok) fork lug strength, disk mount strength, impact on steering head, and whatever else I don't know.

I've rear mounted the calipers, and was reading a Guzzi publication the  other day that suggests it changes the unsprung weight under braking, took tension off shock lugs, and allowed shocks that were working hard to cool quicker. Not really sure.

The f09 at the rear however, hard to find. Has anyone got a spare???

"I tthink as long as the lever pull doesn't feel too 'squidgy' it's fine." I've got about 15mm of lever that seems to give "progression" and then it gets solid. I find it a good feel for my fucked right hand. Thanks Reggie!

Regards to all

Greg


 
Greg,

The 13mm M/C on the F08s does result in a very high ratio.  Lever travel will be a bit excessive and feel on the spongy side.  As long as the system is perfectly bled and the fluid not allowed to age too much, it may be fine.  Let the fluid deteriorate and/or allow air into the system through whatever reason, it may be a bit dodgy in the event that you need just that little extra braking power.  The lever will most probably be hard against the grip by that time...

For safetys' sake, I'd advise you to modify the lever slightly for more piston travel.  IIrc, the M/C housing allows for about 2-3mm more travel than the stock lever offers before the spring goes block.  This will increase the span to the lever, but if your arthritis allows it, it may well give you that tiny little extra sometimes needed in an emercency.

piet
 
Piet

Thanks for your advice. At least I can safe about the rest of the system

When I pull the lever in with my (good) left hand with full strength it will just pull into the grip, which means I may still have air in the system. I was sorting out my bits and pieces today and found a lever with a thread and bolt that meets the m/c piston, that would make the lever "adjustable". At the time didn't understand it. But now I do. I'll pull it back out and refurb it.

But Piet, this 3cl nearly stands on it's nose without a lot of pressure! It would be a 2 finger brake for most people. It is really good. Almost as good as the Zane (which doesn't have a crank at the moment...)

Thanks mate, Stay safe!

Did you get to share an ale with the Easter Bunny?

Regards

Greg
 
ghwallice said:
But Piet, this 3cl nearly stands on it's nose without a lot of pressure! It would be a 2 finger brake for most people. It is really good. Almost as good as the Zane (which doesn't have a crank at the moment...)
Click to expand...

Fully aware of that!

I ran my 3C with a 1/2" jap M/C for a while, brake was really powerful.  Got away with it because the lever ratio was different to the Brembo lever.  But, being the slob that I am, I neglected to replace brake fluid when it was necessary and embarked on a little trip through the alps.  All was fine untill I decided it was time for some fun charging down the Grossglockner.  Nibbling past quicker (in theory at least) bikes, I needed to use the brakes quite hard.  At one particular long, slowish corner, I felt brake pressure all but disappear!  Slowed down and stopped to investigate.  Two problems showed up.  I had felt brake pressure continuously deteriorating shortly before, obviously the fluid started boiling because of water contamination (fluid was about 5 years old by then ::) ).  The other issue was that the reservoir was empty!  A glance at the pads told me why...  That particular trip cost me about 5 spokes in the front wheel as well.  I was already running 300mm discs on the stock wheel in the M1R.  Got really fed up with the wire wheels after that and fitted the Gixxer wheels!

Smaller diameter M/Cs are normally used on either single large calipers or twin small calipers.  The amount of fluid stored in the reservoir should be enough to compensate fluid needed in the calipers to take up pad wear.  My small jap M/C did not have anywhere near enough reservoir volume to compensate.  Your PS13 M/C will be similar.

ghwallice said:
Did you get to share an ale with the Easter Bunny?
Click to expand...

Nah, the bastard just hobbled on by... maybe I'll get a chance with Santa. :D

piet

 
Thanks piet.

M1R?

Will put down yearly brake fluid changes and keep going the way I am with the brakes, and we probably don't have the roads you have. I will use resorviour bellows and keep it topped up.

I spent quite some time with the Easter Bunny. Got pretty pissed, went through a slab plus. Can't remember what we did, what it was about,  or where it went (Don't you hate those nights..). Woke up next morning with Her Indoors asking me if I wanted coffee. Stupid question... For some reason she still loves me. And she's not even Italian. She's Hungarian. Was there ever a motorcycle made in Hungary?

Stay safe, have fun! Greg
 
... Pannonia is not the only Hungarian motorcycle make, but:

BMG - 1939-44
CSEPEL - 1932-75
DANUVIA - 1955-63
DORMAN - 1920-37
EMMAG - 1924-27
FP - 1924-25
MATRA - 1938-47
MERAY - 1921-44
NOVA - 1925-28
PANNONIA - 1951-1975
PANNI - 1959-62
TUNDE - 1959-72
WHITE - 1950-1975

... no, I am not an expert for Hungarian motorcycles ;)

Ciao, Gert
 
Those Hungarians were prolific little motorcycle breeders weren't they!

What are the lockhheed variable ratio master cylinders worth?

Regards

Greg
 
1968 Volvo 142S Hydraulic Clutch and Brake issues: One thing I learned was to bleed the Brake Fluid with a few ounces every year unless you risk frozen pistons and bleeders.

Never had to change a Caliper or Disc on that 68 Volvo before 500,000 miles when she rotted out not saying I went through a few pads.

My Breganze 71 SF is Cable/Drum and thru maintenance still have the original parts including the shoes.
 
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