Bleading the BLINKING brakes!!

[Easter]

I finally found a spec for the front MC in the service manual for the 1800. It is 14mm and since as pointed out, it was designed to actuate three caliper pistons, it should be big enough. ? (I won't attempt to calculate the actual volume of the three caliper pistons of the 1800 compared to the four caliper pistons of the '87 1200 calipers used in this situation.)

Anyway we endeavor to perservere

[bigscheaf]

I also delinked the brakes on my 83 GL1100, and as I recall my stock front MC was 14mm. It wasn't until I upped the ante and swapped on the front MC from my other bike that I got good lever feel, and that one was a 5/8". Since the GL1800 is also a 14mm MC, you may have done an apples for apples swap.

I'm not a master of hydraulic brake systems, but there's a couple of factors when it comes to selecting an MC, number of pistons and size of pistons. I believe front wheel size and rotor size also contribute to the overall equation of brake feel, but that's out of my expertise.

I swapped out my 25mm caliper for a 32mm unit, so my application differs a bit, but if it doesn't have good feel with the 14mm unit, try out a 5/8" MC. Helped quite a bit on my bike. https://www.vintagebrake.com/mastercylinder.htm also has a pretty handy table for seeing what ratio you'll end up with depending on piston size and number. Also, his recommendations are based on racing applications, so his definition of feel might not be within street taste.

[Easter]

I have come to the same conclusion and a 15mm / 5/8 MC is on order. Just for giggles I disconnected one of the lines to a front caliper and the lever firmed up considerably. Choices for the larger size MC are considerably more expensive although I did find a cheap Chinese MC.

[bigscheaf]

I was actually thinking about going larger myself, as it does feel a tad soft yet. Seems like getting the perfect brake setup can be rather challenging on a bike after you've made some changes. I did read on a different forum that the setup on the older Hondas breaks the trend in that formula due to how the brakes calipers are mounted to the forks. The poster said you can essentially double the figure in the chart due to the Honda variance.

Thought I'd comment on this, though it's been a while, given the recent posts on improved braking an such. I spoke w/ Fred @ Yoyodyne and he added that setups like ours tend need a different ratio versus a system that has a fixed backing and not a pivoting "arm".

And it goes on to explain further:

Said he spent some time talking to the Brembo engineers (take it with a grain of salt, could be tooting his horn). From what I took from our conversation, our systems kinda of act like a dual setup already, so you can just double the ratio we already have for a single caliper, which would give us 14.74, slightly over the optimum range. Maybe it's accounting for our oh-so-wooden brakes.
He added that if the ratio were truly 7.37, our brakes would be super mushy.

Given a 14mm master -
caliper piston: 38mm

38^2/14^2 = 1444 / 196 = 7.367

or roughly doubled ratio with our system, 14.72.

Given a 15mm master -
38^2/15^2 = 1444 / 225 = 6.417

or roughly 12.8.

This would put us almost smack dead in the middle of the 12-14.0 range stated on the chart you cited.

And since the devil is in the detail, I'll throw in the link for further detail: http://forums.sohc4.net/index.php?topic=22383.0

So if that's truly the case, my setup of 32(4) would be happiest with either an 11/16" or 19mm MC. Like you said Easter, going larger than 5/8" gets to be expensive, and I doubt the larger MC could be returned since it would be "used". I think I'll keep using the 5/8" for now since it has enough bite for everyday riding and reassess if I take a front end swap seriously on this old girl.

And yes, I have a tendency of over researching dang near everything when it comes to working on my bikes. Blessing and a curse, really.

[Easter]

I owned a nice low mileage '83 Aspencade for several years and because it had been sitting for years when purchased, one of the first orders of business was to redo all the brakes. Other than stainless brake lines all around, and abandoning the linked system, I stayed with the original stock components. I recall being quite satisfied with the brakes even though there were different sized pistons in the left caliper than the ones in the right. MC worked fine.

In part that is why I have been surprised this build has been the problem it has.

[bigscheaf]

That does seem rather strange. The main reason why I went the way of ditching the linked brakes was because one of the previous owners had already partially completed the task. The feed to the front caliper was already plugged, but lines were never ran to make the front work together. Poor 25mm caliper was trying to do all of that work by itself.

Due to that, I decided to swap out the 25mm caliper so it would be 32mm for all of the calipers on the bike. Also makes it easy when buying rebuild kits.

Also means that I will never trust the work that a PO may or may not have done on a vehicle.

[Easter]

16mm MC received and installed. Problem solved. Thanks all.

[jim_stop_trolling]

I've had luck using a zip tie to compress the brake lever overnight. Before I head to work in the morning I'll bleed it and then tie it down again and bleed after work. Did this for a couple of days on my friend's CB750 in order to get all of the air out, my GL1000 didn't have this issue.

Good luck!

[bigscheaf]

BAM! Glad the 16mm did the trick.

[Explorer]

Far be it from me to be the one to tell you that I told you so, but it worked, didn't it!

[rcmatt007]

Far be it from me to be the one to tell you that I told you so, but it worked, didn't it!

[Easter]

Yes, Roger you were right (for once ) but I really thought I was already using the larger size MC.
by the way, I bought a spot to park the RV in north NC. So maybe I will be in riding distance of the East Coast rally in WV after all.

[rcmatt007]

I am like a stopped clock.... right twice a day.... would be great to see you at the eastern run