mcman56 Posted September 15, 2017 Report Share Posted September 15, 2017 I'm chasing an issue with poor initial grab on a rear brake. It works when you stand on it but slight feathering on a slight down hill approach to an obstacle feels very weak. Anyway, I have heard of people putting pressure on master cylinders to strengthen the feel so I thought I would give it a try. I hung a 10 lb weight on the rear brake pedal for maybe a week. It sat in the truck all day with no weigh prior to my ride so I don't know if there was any impact but I noticed that the master cylinder had bled out a very small quantity of fluid. I'm guessing some number of drops. This had to have come through the seals. It still worked as before. Does this confirm a bad master cylinder? Having never tried this before, I don't know the affect on a good working system. Could they all weep a little under such conditions? Quote Link to comment Share on other sites More sharing options...
on it Posted September 15, 2017 Report Share Posted September 15, 2017 (edited) brakes are a sealed system so should not leak fluid out =air in not good , As for hanging a weight on it i can not see what that would achieve apart from putting seals under pressure = leak , May i suggest , the system needs a good bleed then go from there, also the type of pads you use will affect the braking effect also cheek the pads for wear as they wear uneven and look for lips on them Edited September 15, 2017 by on it add info Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 15, 2017 Report Share Posted September 15, 2017 Rear brakes on the Beta are a pain to bleed as the air gets trapped in the highest part of the system in the banjo bolt at the top of the master cylinder. Hanging weight on the pedal will only force fluid under pressure past the piston seal and possibly damage the seal. Try bleeding the rear by pressurizing the system and while holding the pedal down crack the banjo bolt. Tighten the bolt, repressurize and repeat. It usually takes four or five repeats to chase the air out. Refill the resevior and it should be better. There really should be a bleeder valve at the top of the master cylinder. 2 Quote Link to comment Share on other sites More sharing options...
huski Posted September 15, 2017 Report Share Posted September 15, 2017 What are you trying to achieve by hanging a weight on the brake pedal?I can see it would show up a poor seal or leak but nothing more Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 15, 2017 Report Share Posted September 15, 2017 It leaks, replace it as you seem to have had this pronlem for awhile. That said Beta rear brakes have always sucked. Wish I knew why. My first Beta was a 89 tr34. The revs were better, and my 16 factory both brakes suck. My 04 Raga"s were always great. Gas Gas always had good brakes. My sons 15 4t are good and firm, but they have no feel. Recently I noticed that the rear wheel alignment was pretty bad and now my rear are better. I have done everything I could for the front. Time to find an ajp replacement for both the m/c and caliper. Good luck. Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 15, 2017 Report Share Posted September 15, 2017 (edited) The problem is usually air trapped in the system. Air is an elastic medium (or at least much more than the brake fluid, Gas vs. liquid distance between molecules type of stuff) so when the pedal is depressed some of that fluid displacement is taken up compressing the air bubbles and doesn't generate the same force on the pads. Remove the gas from the fluid and you remove most of the problem. The only possible effect I can think of from putting a weight on the pedal to keep the fluid under pressure forces the gas in the system into solution with the brake fluid. Like CO2 in a bottle of soda. Once the pressure is released the gas will come out of solution. Try the bleeding from the top banjo bolt at the master cylinder. It's fast, it's easy and my guess is it will help. Since I just rebuilt the rear system on my '13 EVO (rear master and caliper) a month ago I can tell you it was the last step that finally got my brakes back to where they belong. Another issue could be contaminated pads/rotor. It's fairly common to get chain lube over spray or just finger grease on the pads and they lose a lot of their grip. Brake cleaner helps as does heating the pads to burn off any organics that may contaminate them. You can really heat up the metallic pads and they'll still be good. Just don't do it on the bike as you'll damage the seals in the caliper. I took a MAPP torch to mine and they were fine but I eventually told myself to cut loose with a buck and buy some new ones. The reason I don't recommend the pressure on any of the hydraulic systems on a bike is simply they are not designed for it. They are designed for short term application and it is possible to cause long term plastic deformation of the seals which will wear them faster. Fluid will weep past seals every time there is a pressure differential. In normal usage the amount of fluid that gets past the seals is so small that it will evaporate long before you would ever notice it. So a small amount of leakage from a seal under constant pressure that isn't designed for such duty is not surprising but it won't hurt to keep an eye on it. So I think it best that you start with the cheap (free) and easy bleed the caliper first with the bleed nipple just to be sure there is no air hiding in that high spot then bleed by cracking the banjo bolt at the top of the master cylinder. I think that will cure the majority of your problem. If that doesn't work then go ahead and try the other guy's tricks. I promise I won't have a tantrum. Edited September 16, 2017 by dan williams 2 Quote Link to comment Share on other sites More sharing options...
mcman56 Posted September 16, 2017 Author Report Share Posted September 16, 2017 I burped the banjo bolt about 10 times but it feels the same. The pedal does not feel particularity spongy. Low pressure on the pedal produces a very slight drag by the brakes. High pressure provides strong braking. The problem is that there is nothing in the middle. Is this what is called wooden brakes? I guess this could be a bubble or slight fluid leak. I have a new brake disc to try. After that I'll go for a 2017 master cylinder. It also looks like dropping the shock would allow removing the brake system in one piece for off bike vertical bleeding. I have tried all recommended brake pad brands but they feel the same. The only pads I have not tried are the non metallic. I replaced the caliper with a 2017 caliper. I have also done a lot of bleeding but it keeps feeling the same. Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 16, 2017 Report Share Posted September 16, 2017 (edited) It sounds like your master cylinder is working as it should so now we move to the mechanical realm of possible misalignment of the caliper, bent disk or one piston sticking causing only one pad to move towards engagement (fairly common on older calipers that haven't been rebuilt in a while). The calipers aren't bad to rebuild. Fiddly but not really difficult. Can you pull your rear wheel to check if your disk is true and see if it is easy to push both of the pistons back into the caliper. Firm steady pressure should slide the pistons back into their bores. If both move freely then the caliper is probably good. If only one piston is moving it will do exactly as you are describing as the one working piston will chase the disk into engagement with the other pad rather than meeting in the middle at the disk. Caliper rebuild kits will include pistons, squarish looking O-rings and possibly a small O-ring that goes between the two caliper halves if it is a split caliper. By far the biggest pain in rebuilding a caliper is getting a stuck piston out of the bore. Once you've decided to go the rebuild route you're kinda committed anyway so you can take the caliper and use the pedal to pump the pistons out of their bores before you disconnect the caliper from the brake line. They're going to want to come out one side first so a small C-clamp is helpful to let you chase out one piston to where it is about to come out clamp it in place and then the other will move. Otherwise one pops out and it's pliers and swearing time to get the other one out. I find two main sorts of spooge in the caliper. Corrosion of the aluminum which seems to be an effect of moisture absorbed into the brake fluid and what appears to be a crust of the fine dust that sneaks in along the side of the piston. When I rebuilt my current rear caliper it was the silicate dust that packed into the O-ring groove and also built up in the corners of the bore. What worked like a charm to clean it out of the bore and grooves was a dental pick. I swear a set of these should be in every tool box. If you're careful you can pick out the crud without scratching the aluminum bore of the caliper. I've noticed replacement pistons usually seem just a bit smaller than stock. I'm not sure why that is but it could just be random chance from a small sample. Once the caliper bore is clean, fit the O-rings, put a little assembly lube on the pistons and slide them in. They will protest until you get them past the edge of the O-ring. Then you're in for the bleeding session again. On my bike I got to this point and figured I might as well do the whole system and rebuild the master cylinder as I had a kit on hand. Cleaned out the bore of the master cylinder and put the new piston in and it stuck. Badly. Nice lesson in manufacturing tolerances. I had to pull the master cylinder off and run a cotton wheel with polishing compound through the bore to get the new piston to fit. That was a real pain. Polish, flush, fit, polish, flush, fit until everything got along. Please let us know what you find. Knowledge shared is knowledge multiplied. Edit: Ah I didn't see you replaced the caliper. Well it's still worth checking to make sure your disk is in the center and both pistons are meeting in the middle. Edited September 16, 2017 by dan williams 1 Quote Link to comment Share on other sites More sharing options...
mcman56 Posted September 17, 2017 Author Report Share Posted September 17, 2017 The disc is flat. It did have one little gall mark and some wear but I have seen much worse. I have been looking and the gall mark must have occurred on the last ride so it can not be the long term issue. I installed an Apico FIM solid rear disc Beta Evo 09-on made by NG. This was a big improvement but not sure why. Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 18, 2017 Report Share Posted September 18, 2017 That is a wild looking disk. Just like the pads different disk materials will have different friction characteristics. I don't have any new ideas other than alignment of the caliper. I'll keep my brain running and maybe it'll pop into gear and spit out a new idea but for now I've spewed out all I can think of. Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 18, 2017 Report Share Posted September 18, 2017 (edited) Hmmmm did you use any kind of anti-squeal rubber goo on the back of the pads? Are the pads properly planar to the disk? I'm wondering if there could be something putting the pads at an angle to the rotor. Edited September 18, 2017 by dan williams Quote Link to comment Share on other sites More sharing options...
mcman56 Posted September 18, 2017 Author Report Share Posted September 18, 2017 No goo. It actually feels pretty good. I need to ride another bike back to back to see if it is lacking. Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 18, 2017 Report Share Posted September 18, 2017 That's great. One thing I noticed on my bike after I did the bleeding is the braking was weak until I had some time on the bike. I attributed this to the mechanics of the caliper. Basically the pistons are self calibrating. They can move a small distance but are pulled back from engagement by the O-rings. Exceed the elastic limit and they slide in the O-ring which is the self adjusting bit. Until they have moved in the O-ring far enough it's possible to have them contact the rotor but pull back too far to be in the proper working range. The clearances are so small that it's amazing it works as well as it does. This could explain why the weight trick helps the feel as constant pressure forces the piston/O-ring position closer to the rotor and gives more time for the O-ring to move on the piston. I could see this causing a bit of drag too if the piston slides a bit past the optimum position. Ain't mechanical engineering fun! Quote Link to comment Share on other sites More sharing options...
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