Front brake binding, master cylinder or caliper?

[limey]

Hi All

I just bought a 1981 GS750, which I love already. The bike had been sitting for many years, and the previous owner had the carbs cleaned and synched and got it running and registered, new fork oil/tires etc.

I have lubed the clutch cable, installed a horn, and tightened up what were very loose head bearings. The bike is now very rideable and a lot of fun!

Last night I took the slider pins out of the front calipers and greased them up, as the brakes have been a little unresponsive and one was dragging a little, not a lot, but making it a little hard to push the bike when parking.

After putting everything back together, one of the front brakes (the right one) is binding way worse, now it is getting hot and smelling. I took the caliper off and pushed the piston back in a little. This helped - until the next time I braked ;-).

Since the left brake is OK, I am suspecting the caliper rather than the master, but have never rebuilt either before (I have done a lot of other mechanical jobs on cars and bikes).

Any advice for the GS-newbie? Is there a good source for rebuilt calipers, or should I rebuild myself?

Thanks!

[Dogma]

Old brake fluid is probably turned to gunk throughout the system. This only takes a couple years. Since this is your life on the line, I'd recommend a rebuild of everything, just to be sure. It's not that hard to make sure the brakes are working and will stay that way. If you clean it just enough to get it working, you won't know when it will fail next.

You can do this yourself, though disassembling the master cylinder will require a long pair of snap-ring pliers. I had to grind down a pair of needle-nose pliers. The main pitfall is the little hole (of two holes) leading to the reservoir. This has to be clear before you can bleed it effectively, and just a little gunkified fluid will plug it.

At least flush the fluid in the rear, while you're at it, but it may start dragging soon too. Rebuilding the rear is easier than the front.

Z1 Enterprizes will get you just about the best deal on rebuild kits (seals+pistons) and they also offer stainless lines. Call them if you need help finding the parts. I fell in love with stainless, and besides, the original hoses' factory recommended life is only two years.

Be safe and have fun.

[Nessism]

I agree with Dogma, a full system tear down is highly recommended to clean out all the chunkies, and replace the brake lines while you are there since the old lines build up scale inside. In my experience, OE brake system seals/pistons are superior to the aftermarket K&L stuff as sold by Z1 Enterprises. For brake lines, you can build your own from Earl's components for cheap, and the quality is as good as anything on the market. Search out the thread on that subject if interested.

[bwringer]

Agreed -- the available aftermarket caliper and M/C kits are incomplete low-quality crap. (Yeah I'm lookin' at YOU, K&L! ) OEM kits include a new piston and are much higher quality. And even cheaper in most cases.

The choice is clear, especially since low quality brake components can kill you dead.

[oldgsfan]

I was in exactly your shoes last summer when I bought my 1980 GS850G. I had the exact same problem.. my front brake was dragging, and I couldn't push the bike. It wouldn't roll.

On the advice of Nessim, and several other posters, I did the full tear down.

I'm no mechanic, but with the info available on this forum, I was able to rebuild my front brake calipers, install new stainless steel brake lines that I fashioned myself, and take apart and clean the master cylinder. I also installed a new brake fluid resevoir.

What I found when I took my system apart was the brake fluid had become like coffee grounds. There was a ton of junk in it so when I pressed on the brake lever, the fluid went through to activate the braking, but it couldn't go back into the reservoir 'cause it was so clogged up.

If you do some searching, you'll find plenty of posts from other GS'ers who have had to redo their brake systems. It really isn't that difficult. It just takes a little patience.

You'll find good prices at flatoutmotorycles for your pistons, if you need to replace them. Z1 Enterprises also had good prices on the reservoir.

I recommend doing a search for homemade stainless steel brake lines and you'll find a tutorial on how to make them. It's way easy. Even a total newbie and former desk jockey like me was able to do it.

Good luck, man.

[iDodgimus]

On the advice of Nessim, and several other posters, I did the full tear down.

I'm no mechanic, but with the info available on this forum, I was able to rebuild my front brake calipers, install new stainless steel brake lines that I fashioned myself...

If you do some searching, you'll find plenty of posts from other GS'ers who have had to redo their brake systems. It really isn't that difficult. It just takes a little patience.

I recommend doing a search for homemade stainless steel brake lines and you'll find a tutorial on how to make them. It's way easy. Even a total newbie and former desk jockey like me was able to do it.

Good luck, man.

+ 1 on all of that, really easy and very worthwhile

[limey]

Thanks All!

Thank you all for your awesome help! Based on this response I am really looking forward to hanging out on this forum!

Looks like I have a project on my hands! Thanks for the links to the resources, and for the info on the coffee grounds and general nastiness of 28 year old brake fluid. The PO did say he'd flushed the brakes, however I doubt he dismantled the system, so the evil residue is still in there I'll bet.

I am going to price up the options, but homemade steel brake lines, and OEM rebuild kits sound like the way to go.

Thanks again all!

[hillsy]

The PO did say he'd flushed the brakes, however I doubt he dismantled the system, so the evil residue is still in there I'll bet.

Whilst the PO may have done this, corrosion forms in the seal channels and forces the seals out towards the piston, causing the caliper to bind. You need to remove the seals and scrape out the corrosion from the channels before you put the new seals in.

And check the pistons for corrosion - if they are pitted they will leak.

[81ZUKI75]

Watch Out.... Reservoir

If your '81 is like mine it has a plastic reservoir on the master cylinder. Until I removed the reservoir I couldn't get to the TINY return-orifice which has to be cleared. There are two holes in the bottom of the M/C, the smallest is hidden under a tab that's extends from the plastic reservoir. I couldn't move the tab enough to get anything into the hole and I couldn't access it through the cylinder bore. Mine was original and the plastic was shot, so I wound up installing a reservoir kit.

[spchips]

Plus one on everything. for me it has been the damn ^%##* pin sized return hole on almost every one I've ever done.

[oldgsfan]

The only part of the entire job that was tough for me was getting that little circlip out of the master cylinder, even with the special tool, probably 'cause a bought a cheap one at Harbor Freight.

I don't know what you're reservoir looks like, but mine was original and so badly damaged, I couldn't even see into it to know how much fluid was inside. I ended up installing a new one. Wasn't expensive and wasn't difficult to do.

The only other special tool you might consider getting is one of those brake bleeding kits. You'll need to remember to prime the master cylinder when you're ready to put fluid back in the system. It takes a little patience to bleed the brakes, but I was able to do it alone with a cheap little brake bleed kit.

[bpdutton]

I had the exact same problem with the front brakes on the '80 GS1000G I bought a couple of years ago. The left side caliper would lock up so tight that cracking the bleeder was the only way to release the pressure. Followed all the excellent advice on GSResources and completely disassembled, cleaned and rebuilt the front master cylinder and calipers. There was nasty jelly like crud in every nook and cranny. A word of advice - remove the brake lines from the splitter underneath the headlight and clean the splitter -there was nasty gunk in there too. I would also replace the front master cylinder resevoir screws and diaphram plate if they have any rust/corrosion on them and check for cracks along the edges of the rubber diaphragm and replace if you find any. This will let in air/moisture which will turn the brake fluid to gunk. Also, be prepared to really work at getting all of the air bubbles out of the rebuilt master cylinder. I found some good tips by searching this forum. Good Luck!

[limey]

Hi All

Thanks for the excellent advice.

I rebuilt the wheel calipers (new pistons) and the master cylinder, built steel braided brake lines, with the 'loop over' to the left caliper, eliminating the splitter.

The brakes are strong now, and release after braking ;-).

There may be still some air in the system despite my best efforts to fully bleed - the lever moves a fair way before the brakes start to get effective. However it is now impossible to squeeze the lever all the way to the bar - which is much better than before.

As predicted, there was gunk throughout the whole system, and the master cylinder reservoir was brittle and cracked on disassembly.

Thanks again!