Brake system check

[hannibal]

I picked up a 1977 GS750 about a month ago. I've slowly been going through the bike one system at a time. Should be ready to start on the brakes in a week or two and have been trying to determine what needs to be addressed. Since I got the bike, the brake lever easily goes down to the bar without much braking force at all. I'm planning to change the fluid (got some Valvoline DOT3/4) and brake pads (EBC).

I plan to open up the front caliper and have a look. I'll replace the seals, boots, and bleeder covers (and the piston if it's pitted). Doing some reading showed me the part number for the front piston, seals, boots, etc is 59100-45813. Does anyone know if there's a rebuild kit without the piston? If not, I guess I just have to order the parts individually.

I know the front brake does most of the work but is rebuilding the rear caliper also recommended? What about the master cylinders? Should I plan to rebuild both as well? I'm still trying to find a part number for the rear caliper and MC kits.

Depending on how much I spend on rebuilding calipers and master cylinders, I would like to install stainless lines as well. I've been looking at Z1's Goodrich lines. Can I reuse me stock banjo fitting with the new lines

Finally, I'll adjust the brakes at the lever and pedal as shown in the service manual, and hopefully this gives me some decent braking and feel. In their original condition, it was downright scary, and as a new rider, good brakes will be needed.

Thanks!

[eil]

Can't answer all of your questions, but I can answer some.

I know the front brake does most of the work but is rebuilding the rear caliper also recommended? What about the master cylinders? Should I plan to rebuild both as well?

Yes, yes and yes.

Depending on how much I spend on rebuilding calipers and master cylinders, I would like to install stainless lines as well. I've been looking at Z1's Goodrich lines. Can I reuse me stock banjo fitting with the new lines

The Z1 lines are good. There's an ebay seller called rennsportauto out of Canada that makes great lines at a very good price. Search the forum for more info.

Yes, you can reuse the stock banjo bolts. You will absolutely need new crush washers, though. Depending on which lines you get, you may or may not need to order them separately.

Finally, I'll adjust the brakes at the lever and pedal as shown in the service manual, and hopefully this gives me some decent braking and feel. In their original condition, it was downright scary, and as a new rider, good brakes will be needed.

I've heard from a couple people that the pre-1980 brakes on GSes were iffy compared to later models. Don't know how much truth there is to that. You might look into saltymonk's brake upgrade here on the forum. I suspect it costs more than just rebuilding the stock brake system.

[hannibal]

Thanks Charles! I'm planning to pull off the calipers and cylinders this evening and do a thorough inspection. I'll definitely get new crush washers.

The Z1 stainless lines require you to buy the banjo fitting separately (or reuse the stock one). Does this just screw into the Z1 lines or is a special "crimp" tool needed?

[tkent02]

The problem with neglected brakes is not that they won't work, although that can happen. The real safety issue is that the brakes can come on and lock, sometimes even if you never touch the brake lever at all. Just cruising along fat dumb and happy and a wheel locks up. This will end badly at any speed and in any place.
Both Master cylinders, all the calipers, the lines, all of it need to be cleaned out or replaced.

1980 and later GS brake calipers are much better than the early ones. Saltymonk's brake mod is much better than the later GS brakes. Braided brake lines are great. Modern pads are great.

Have fun.

[hannibal]

^ That's super scary, especially given what I've found so far!

I pulled off the front brake and master plus the rear brake and master last night. Started opening up the calipers to clean and inspect. My GS750 looks a bit different than the GS1000S brakes shown in the write up on BassCliff's site but that's that guide I'm using.

I'm pretty sure the front piston was installed backwards. I've never seen a piston with the open end facing into the caliper body and the closed end pushing on the pad. This means when I hit the brakes, the fluid would have a lot more work to do before it can move the pad against the rotor. The piston seems seized as I can't push it back into the caliper body to remove the mounting flange. I'm guessing it's full of the reddish brown gunk I see around the edge of the piston. I'll take some pics this evening. I'm planning to take it to a shop by my house to see if they can blow the piston out for me.

Also, when I drained the brake fluid, I only got about 2oz of fluid, including front and rear. It didn't even fill the bottle to the bottom of the label of my 16oz water bottle. If the front caliper turns out to be unusable, I'll certainly look into the later model brakes. I would like to do a dual disc setup in the front at some point, but I was just hoping to get the stock system working for now.

I also noticed the front master cylinder body is cracked where the lever mounts to it (red circle). Any advantage to going with a later model used cylinder or should I just look for a used GS750B cylinder?


Thanks!

[chuck hahn]

Jordan..the spring goes in and then the rubber cup that looks like a mini Reeses Pieces. The cupped out side of the seal goes in facing the spring...flat side facing the piston. Then theres a flat metal disc bewteen the seal and the piston.

[chuck hahn]

Any front master from a 750 or 1000 will work..its the same cylinder. May be others but these two I know personally very well.

[hannibal]

Thanks Chuck. I'm not sure what you're describing exactly about the caliper but it sounds like I'm freaking out over nothing. Hopefully I'll get the calipers pulled apart today.

Thanks for the tip on the MC. Time to check the classifieds and Ebay...

[tkent02]

I would consider a new master cylinder off Ebay or Amazon. You get a brand new MC, and a rebuild kit for less money than the Suzuki rebuild kit. Modern design, adjustable levers, etc. Get one with a slightly smaller bore and you get more brake pressure for a given finger pressure, it's all good.

That and Saltymonk's mod and you will be stopping a whole lot better and easier than even the best original GS brakes.

[hannibal]

I've gotten the rear caliper opened up. Overall, it looks good but still planning to order a rebuild kit. Still trying to unstick the circlip on the rear MC so I can open it up.

Tried using compressed air to remove the piston on the front caliper but no luck. Tried hooking it up to the front MC and pumping it out, but the MC wouldn't build up any pressure. Dropped the whole caliper in my can of Berryman's and I'll try again in a day or two.

I've been looking for a new MC over the last few days. Going for this 12.7mm MC on Ebay: http://www.ebay.com/itm/121417022234...%3AMEBIDX%3AIT or this adjustable one (if it's 14mm or less): http://www.ebay.com/itm/291487137060...%3AMEBIDX%3AIT

I took the beginner MSF class this weekend. I went from knowing how to operate a bike to learning how to ride. I feel a lot more comfortable and ready to practice some of the exercises on my bike.

[850GT_Rider]

I would consider a new master cylinder off Ebay or Amazon. You get a brand new MC, and a rebuild kit for less money than the Suzuki rebuild kit. Modern design, adjustable levers, etc. Get one with a slightly smaller bore and you get more brake pressure for a given finger pressure, it's all good.

That and Saltymonk's mod and you will be stopping a whole lot better and easier than even the best original GS brakes.

Color me confused.....

Doesn't a smaller bore MC mean less volume per unit of stroke? Doesn't the 4-piston Salty Monk conversion require MORE volume, as it's pushing 4 pistons instead of 2?

What am I missing?

[hannibal]

I would definitely get a larger MC if I had 4 pistons instead of one (77s are all single disc I think). I believe his recommendation for a smaller MC was for the stock single disc setup.

[hannibal]

I came across this MC size guide. Seems like the OEM MC's are "too" big (both 14mm single disc and 5/8" dual disc).

http://www.vintagebrake.com/mastercylinder.htm

Still trying to get the right part number for the rear caliper rebuild kit. I see 69100-45810 listed on several sites, but it is not available on any of them. 69600-45820 is listed for 78-79 GS750. Aren't the 8 valve 750 rear brakes the same?

[hannibal]

When upgrading to stainless lines in the rear, do you guys bypass the stock hard line attached to the frame? If I just find a spot to attached the stainless line to the frame (to keep it from moving around too much) I should be alright I think.

See #4 in the attached pic...
rear brake lines.jpg

[tkent02]

Color me confused.....

Doesn't a smaller bore MC mean less volume per unit of stroke? Doesn't the 4-piston Salty Monk conversion require MORE volume, as it's pushing 4 pistons instead of 2?

What am I missing?

A larger bore gives a larger volume at a lower pressure. A smaller bore gives less volume at higher pressure. It's the same old mechanical advantage thing.
Modern calipers need less volume of fluid movement to operate the brakes, so the smaller bore will do it, you get more braking at a lighter finger pressure.

I have also used them on the original round pad GS calipers, even the ones with dual brakes. It has been an improvement.
If you have crappy original brake lines full of air it might not move enough fluid. All I can say is try it.