Rear disc brakes, VERY HARD pedal, weak brakes????

[TrikerDoone]

We've got a problem that I want to ask for help with. My VW trike has disc brakes on the rear only. It has a 22.2 mm single circuit master cyl. The brake pedal has very little travel and is VERY hard to mash. I also don't have much brakes. I can't lock them up and slide the wheels at all. Do y'all think the bore of the master cyl. is my problem? We've bled the brakes and there doesn't seem to be any air in them...but I've read that the pedal would feel "spongy" if air WAS present. We're stumped!

Please give me your thoughts about this. Thanks in advance for your help!!

[slick rick]

I've got the same set up on mine and I can't slide 'em either , they stop well but can't lock 'em up . What would make a big difference is to have front wheel brakes , but that would ugly up the front wheel . That statement will bring on the troops

[Loner]

Actually three primary factors come into play when addressing the problem(s) you describe; 1) master cylinder bore, 2) actuating pedal leverage ratio, and 3) slave cyliner bore. Assuming the third is the least effective variable, and one that is usually a standard part, improvement in brake operation can be had by changing one or both of the first two.

In your case(s) sounds like you need more pedal-to-brake leverage. With master cylinder bore, more leverage (and easier to push) is gained by decreasing the bore size. You have an 7/8" bore now, and I'd recommend changing to an 11/16" bore master cylinder. You're not going to find one as an off-the-shelf part for VWs (maybe special for a dune buggy, but unlikely), so you'll need to look at an aftermarket solution. Jamar and similar off-road manufacturers can supply what you need but be prepared to modify your mounting method to adapt to the new part. That change alone (7/8" to 11/16") will make a tremendous improvement toward your perfect solution.

Secondly, your actuating pedal should provide for about 8:1 leverage (distance center of pedal to center of rotating point versus distance of rod attachment point to center of rotating point) for effective operation and easier to push. As with most engineering rules, the finite numbers may vary a little bit to achieve the maximum solution, but 8:1 is an accepted baseline. Changes in this area will most likely require fabrication work since off-the-shelf pedals with varying lengths are rarely offered.

We'll discuss achieving the absolutely perfect solution between the two factors when we address the absolute perfect solution of rake and trail.

As to beefing up (opr adding) front brakes as a solution, just visualize the effectiveness of the rear tire contact patches of about 120+ square inches total with maybe 600 pounds downward force versus about 8 square inches with abouth 200 pounds of downward force. Not much of a comparison, right?

Plus remember - the front brake is at best no more effective than what it takes to lock the wheel, and that's pretty easy to do on a trke.

Any specific recommendation that I'd offer would have to based on good photos and some specific engineering info.

Hope it all works out!!!

[slick rick]

,,,,Dang Loner could you slow down a little !!!!! Great post if I had that knowledge I'd build trikes ,,,,wait you did !!! VERY HELPFUL even in my case Rick

[DeathBySnuSnu]

Loner is correct.
I have a fairly light and small trike.
I run the 22mm master with good ratio and I can skid the wheels, but not to easily.
If you are fairly light you may want to work on the pedal ratio. If you are heavier you may want to go smaller bore. Either ratio or bore size will make your pedal move further to do the same amount of work.
3/4" bore is common for rear brakes on a buggy.

[TrikerDoone]

Loner, thanks for all the technical information. I have purchased a 17mm master cylinder and will be installing it in the next few weeks. My VW trike is a homemade one and the builder was a "body man". He built it very strongly and the entire body is metal...and I mean not flimsy metal. There's not much I can do with the pedal because of the way it's made. I'll try to post some pics sometime this weekend since I'm new on here and haven't put up any pics yet.

Thanks again!
Lorna

[Bobby Stubbs]

The front brakes on my trike were acting up (due to being stored) in much the same way your rear brakes are acting..solution was new rubber flex lines as mine were pinched shut ! inside was almost totaly blocked..take off the flex lines and see if you can blow compressed air through them..if not or very little air ..replace the lines..

[extreme10]

[QUOTE=Loner;227243]Actually three primary factors come into play when addressing the problem(s) you describe; 1) master cylinder bore, 2) actuating pedal leverage ratio, and 3) slave cyliner bore. Assuming the third is the least effective variable, and one that is usually a standard part, improvement in brake operation can be had by changing one or both of the first two.

In your case(s) sounds like you need more pedal-to-brake leverage. With master cylinder bore, more leverage (and easier to push) is gained by decreasing the bore size. You have an 7/8" bore now, and I'd recommend changing to an 11/16" bore master cylinder. You're not going to find one as an off-the-shelf part for VWs (maybe special for a dune buggy, but unlikely), so you'll need to look at an aftermarket solution. Jamar and similar off-road manufacturers can supply what you need but be prepared to modify your mounting method to adapt to the new part. That change alone (7/8" to 11/16") will make a tremendous improvement toward your perfect solution.

Secondly, your actuating pedal should provide for about 8:1 leverage (distance center of pedal to center of rotating point versus distance of rod attachment point to center of rotating point) for effective operation and easier to push. As with most engineering rules, the finite numbers may vary a little bit to achieve the maximum solution, but 8:1 is an accepted baseline. Changes in this area will most likely require fabrication work since off-the-shelf pedals with varying lengths are rarely offered.

We'll discuss achieving the absolutely perfect solution between the two factors when we address the absolute perfect solution of rake and trail.

As to beefing up (opr adding) front brakes as a solution, just visualize the effectiveness of the rear tire contact patches of about 120+ square inches total with maybe 600 pounds downward force versus about 8 square inches with abouth 200 pounds of downward force. Not much of a comparison, right?

Plus remember - the front brake is at best no more effective than what it takes to lock the wheel, and that's pretty easy to do on a trke.

Any specific recommendation that I'd offer would have to based on good photos and some specific engineering info.



I would like to improve my rear brakes on my abs gold wing. I also can't lock the rear brakes uk no matter how I try. The abs has never come into play. There is no air in the system. The model of trike is the adventure kit by motor trike.
Perhaps you may have some knowledge of this braking system. The reply from motor trike said that you should be able to lock the rear up .

[TrikerDoone]

After messing around for 2 years with less than adequate brakes, we finally got around to installing a new 17mm brake master cylinder and remote reservoir yesterday. Man!! Do I evermore have brakes now!! Never knew my trike would be able to stop like it does now! I'm not running a front brake at all, just disc on the rear, but can lock down the back wheels now and hear them squall on pavement! What a difference!! Had been running a 22mm Bus master cyl. and other than finding a place to mount the remote reservoir and running the new reservoir line from the master cyl. to it...no problem! It even fit right in the same holes the other master cylinder was bolted in.

Took a little adjusting of the rod going from the peddle into the master cylinder, but after a few adjustments it's now doing great! Special thanks to Loner for the suggestions of a smaller master cylinder...THAT did the trick!!

[stinger608]

That is great that you got that issue fixed!!!

[Loner]