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coppertop

Brake system troubleshooting

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I've been doing a "little" maintenance  on my 1998 fifth gen VFR.  I rebuilt all the calipers (right front, left front, and rear), installed new brake pads, rebuilt all the master cylinders, (at the handlebar, at the left front caliper, and at the rear brake pedal), and I replaced the stock brake lines with the Galfer braided stainless steel lines kit.  The instructions for the Galfer kit seemed pretty clear to me, and I have bled the brake system per the Honda shop manual.  The brakes feel firm, but on a short shakedown cruise in the neighborhood, the brakes (especially after applying the rear brake pedal) don't release when I release pressure on the brakes.  If I stop and wait a short while, they do release, slowly.  What might be going on?  Got a set of troubleshooting tasks to work through to zero in on the issue? 

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I would start by double checking the master cylinders, sounds like something is obstructing the fluid return on release. 

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Here's one thing that is easy to check (and it's something that is known to cause exactly the problem you've described in your post)

 

You should visually check that Part #13 is installed in the correct orientation.

 

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I just went through this with a friends 01. Long story short, what appeared to be stuck rear pistons was actually a faulty SMC. The SMC was not allowing the pressure on the line to be relieved when the SMC was released. At first it seemed like to two outer pistons were the culprit and they probably were part of the problem because we had a hard time pushing them back into the caliper by hand. After replacing all three (for good measure) the problem only pointed to the center piston (which is associated  with the SMC line).

 

A fellow member here (Sfdownhill) had a used SMC and after swapping that one in, the brakes worked like a charm. Note that I did pull the SMC apart and gave it a thorough cleaning and even put in a rebuild kit but there must have been something that either wore out, was still clogged in the portion that feeds the rear piston. Take if from me, if it’s the rear that is locking up, determine which piston(s) is getting stuck. If it’s one or both of the outer pistons, it’s related to the rear master cylinder, if it’s the center one, then it’s the SMC.

 

Note that when you press the rear pedal, the two outer pistons are applied with full force from the rear MC but the center one will also move but not with the same force, that “extra” force actually gets applied when the SMC activated.

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It's nice to have a simple thing to check, if only to rule it out.  The piston in the front brake master cylinder is correctly oriented, one possible cause down.  Unfortunately, I also have to re-adjust the steering head bearing nut (I had to replace the steering head bearings while all this was going on too.)  I believe it could be either a master cylinder issue or the SMC thing.  When I was going about the brake rebuilding, it was drug out over several weekends, so its very possible the dregs of old brake fluid crusted up in the SMC or master cylinder fluid passages.   I'll report back when I've either found out which is the problem, or if I'm still stymied.  Thanks!

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Check the return ports in the reservoirs. I have an ST1100 that had a completely blocked return port on the clutch side that resulted in the clutch "pumping up" over a short ride and not allowing it to engage until I cracked the banjo to release the pressure.

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After a careful review of the Galfer instructions, I believe I have found the problem.  

My mistake was quickly scanning the written instructions, then installing the lines in alphabetical order going by the photos and *not* looking back at the written part.  In doing so, I connected line G to line F with the double banjo bolt. 

That connected the left caliper middle piston to the auxiliary master cylinder input line and line going to the PCV. 

Line G should go from the left caliper middle piston to the auxiliary master cylinder output port and the line which runs to the delay valve.  

Note:  it is very difficult (but not impossible!) to get the short G line routed the way I did, and the double banjo bolt in that position was very difficult (but not impossible!) to install with almost zero clearance with the front rim.  Furthermore, even after installing, the double banjo at the auxiliary cylinder input made it difficult (but not impossible!) to remove and install the front wheel when I was going through the bleeding process.   I should have stopped and re-read the instructions when that part of the install was getting so difficult, as everything up to that point had gone very smoothly. 

I will report back when I have fixed my error and tested.  It's too hot to do it right now, and life is happening, so it might be a few days. 

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I hate that "ug, why do they make this so difficult. It's stupid. Who engineered this stupid thing?!" Only to find out you've been doing it wrong.

 

Another thing that happens a lot but doesn't appear to be associated with your problem is the valves for the simultaneously braking system. They're all pretty small and can easily create problems. 

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