GS750E Brake Rebuild

[Guest]

Hi all!

So, because my front fork leaked oil before I completely rebuild them, I pulled my front brakes of a few days ago. I had to spend some time figuring out how to get the caliper axle bolts out and the only thing now left to do is getting the pistons out, for which Ill buy some new brake fluid to push them out. I'll have to wash the parts in brake fluid anyway. Unfortunately I don't own an air compressor, nor was there enough brake fluid in the lines to push them out... Which brings me to question one:

Does brake fluid go down in level over time, not accounting for the logical decline because of brake pad wear? I don't see leaks, and the brake fluid is almost black...

2: The manual states to replace quite some parts with rebuild kits, apparently original sets you could buy as a OEM Suzuki replacements. For example it calls for replacing the pistons every 2 years. Now, I saw a lot of guys just washing the seals in brake fluid, cleaning the pistons and be done with it. What do you guys recommend? I expect this stuff never to have been replaced by any PO (as with just about anything on this machine) and I am especially reluctant to be easy with the braking system. Question would probably also be which parts are easy to source. Seals seem to be ok, pistons might get harder maybe?

3: While I am at it... Should I replace all those advised parts on the master cylinder as well? I am replacing the brake lines, I guess replacing those things would make sense.

4: Buy a brake piston tool to push them back? I see guys do it with C clamps, the old brake pads (which are really dirty for me since the oil leak, so a no go).

5: Just out of interest: There were two different kinds of brake pads on the bike: A set of Dutch made ones, can't seem to find a brand, and a set of Ferodos. Is this normal? Or should you replace them both at once and with the same kinds?

6: Also, which brand would you guys advice?


I hope to buy everything I need this week, time for some good old bike maintenance over the holidays ^^

[Big T]

To cover some of your questions, replace everything rubber: caliper seals and boots plus master cylinder kit.
Pistons can be reused if not pitted or damaged.

Ferodo pads are best

Try to refill the fluid now to pump out the Pistons

Clean everything with Brakecleen, not fluid

Don't use any regular grease or oil on the parts, silicone only.

OEM parts are advised, except for the braided brake lines

[cowboyup3371]

It is also possible to push the pistons out using an air compressor and inserting the nozzle into the brake line hole; just be careful when it finally goes. I've also had to use a couple of screwdrivers to gently pry it up from the lip if it didn't get pushed all the way out.

Like Big T said, replace all rubber seals and be sure to thoroughly clean everything with brake cleaner

[mmattockx]

1) Brake fluid should not go down aside from the reservoir level dropping to accommodate pad wear.
2) Since you're in there you might as well do it all and know it is done.
3) I would.
4) No need for tools to push the pistons back before re-installation, you can do it by hand on the bench with no problem. It is only hard when the system is closed up and on the bike, forcing fluid back into the master cylinder.
5) I would buy new pads in case the old ones are contaminated with fork oil and to have a matching set.
6) I like EBC HH pads, but there is nothing wrong with any of the major brands.

Buy the proper high temp brake system grease for the sliding pins, don't use whatever random stuff you have laying around.

Ferodo pads are best

Oh, now you've done it. This might be close to an oil thread!

It is also possible to push the pistons out using an air compressor and inserting the nozzle into the brake line hole; just be careful when it finally goes.

+1 to the compressed air method. I wrap the caliper in a rag when I do it, to prevent projectiles flying across the garage. Safety glasses are also a very good idea.


Mark

[Drummert]

Oh, now you've done it. This might be close to an oil thread!

+1 to the compressed air method. I wrap the caliper in a rag when I do it, to prevent projectiles flying across the garage. Safety glasses are also a very good idea.


Mark

I already thought that was going to be a dangerous question

I would love to play around with a DIY air pressurized piston gun, but unfortunately I don't own a compressor.. Also I don't have electricity in the shed. Living in an appartment block, where I have to carry my tools all around the block every single time I want do work on the bike, since there's no easy way to access the shed via the building...

So that's a yes on all the seals. Then here's one: A lot of schematics and rebuild kits (often unavailable) I can find show 4 different rubber seals: piston boot, piston seal, sliding pin boots and... some small O-rings? I didn't find those when I took them apart. Wouldn't be the first time I didn't find something though. It does make me rethink the model I always look at, since I had this especially with the forks as well. It's a 1978 GS750E, for which I always end up at something like "Suzuki GS750EC 1978 (C) USA (E03). The forks it showed there were internally different from what I have. How many differences in brake systems were there on the 750s?

Also, what brake fluid do you guys use? I believe my cap states ISO 1703, which would be dot 4 I guess?

EDIT: Actually, I just found a brake caliper rebuild kit for a 1977 GS750 D B, that does state its for a European twin disc... It looks like it would fit, but again it shows the 2 tiny o-rings? Where should those go? I believe the diagrams show it goes on top of the washer between the slide pins bolts and the housing. Also, the rebuild kit is OEM standard, not Suzuki OEM, but maybe those are hard to find nowadays?

[mmattockx]

I already thought that was going to be a dangerous question

You bet, religious discussions are always fun!

So that's a yes on all the seals. Then here's one: A lot of schematics and rebuild kits (often unavailable) I can find show 4 different rubber seals: piston boot, piston seal, sliding pin boots and... some small O-rings? I didn't find those when I took them apart.

On two part caliper bodies (typically the opposed piston types) there is often an O-ring between the body halves to seal the fluid passage but I don't think that applies to your GS calipers. I never took mine apart, just replaced them with Salty Monk's brake upgrade using CBR600F2 calipers. Hopefully someone else chimes in that is more familiar with the GS calipers.

Also, what brake fluid do you guys use? I believe my cap states ISO 1703, which would be dot 4 I guess?

You can use DOT 3 or 4, our bikes never get brakes hot enough for the higher boiling point of 4 to matter unless you are racing. I typically use 4 just because it is a higher spec, but have used 3 when I couldn't find 4 and needed some. Never noticed any functional difference between the two. If someone has a good evidence based case for only using 4 I would be interested to hear it.

Also, the rebuild kit is OEM standard, not Suzuki OEM, but maybe those are hard to find nowadays?

I have never bought a rebuild kit as such, I have always just ordered OEM parts as needed from a dealer. I would use Suzuki OEM parts if at all possible on a brake system, aside from the lines.


Mark

[limeex2]

Without air the pistons can be very difficult to remove. All the corrosion must be removed from the pistons and caliper. I use red Scotchbrite on the pistons and my Dremmel tool with a stainless steel bristle on the caliper. Move quick with the stainless steel. I sparing use Volvo PTFE silicon brake grease on the seals and pistons. After cleaning change the brake fluid every 2 years and corrosion will never return. Use only OEM parts unless not available. Here's a pic of my homemade brake bleeder. Use plumbers putty to seal up the hoses on the lid. Dont recall the hose size, bring the bleeder with and buy 4 ft of bulk hose. Suck on 1 hose, brake fluid gets pulled in the other. I labeled my hoses. Dont ask why...

[Drummert]

Here's a pic of my homemade brake bleeder.

Thats a pretty nifty solution, I might try that one. I was going for the normal method now of pull the lever x3, then slowly twist etc.

Allright, I guess I got the idea now then. I'll buy some silicone brake grease as well then. I imagine the greases the manual calls for are easy if you are a suzuki motorcycle shop, but owning all those different kinds of grease are going to be a expensive part of the restoration XD

I never took mine apart, just replaced them with Salty Monk's brake upgrade using CBR600F2 calipers. Hopefully someone else chimes in that is more familiar with the GS calipers.

I had that idea originally, but I am scared of not being able to find the right parts, nor do I have the tools to make adjustments to the parts. I might try the modification later, since it definitely looked promising, but for now I'll just make these one as good as they can be.

[Drummert]

So, I got the pistons out today. Adding some new brake fluid not only did the trick, it also showed me how dirty the brake fluid in there was.

Since I knew brake fluid was going to spill, I padded things up with some paper towel. Right after the pistons popped I wiped everything down, not noticing I still had some on my glove with which I was holding the brake calipers... End result: they let go of some paint and bare metal is showing in tiny spots.

So I guess, since they're now apart anyway, this is the time to redo their paint job. What do you guys recommend? Powder coating or High temperature spray paint? I also saw they sell a special paint made for brake calipers. Other question: any good advices on how to properly prepare the calipers for paint other than cleaning and getting rid of the grease? Maybe a good way to plug up the holes?


Thank you all already with your help,

Drummert

[cowboyup3371]

Painters tape in the holes works well to plug up for painting. On that question, it really is which ever you prefer and can afford. Some people have built out their own powder coat systems as it's not that much trouble to get started on.

[1978GS750E]

I've used the aerosol caliper paint with good results. Just be sure to bake it like it says on the can. Not as durable as powder coat but you can touch it up if needed.

[Drummert]

Last parts are coming in tomorrow and I already have all the Suzuki parts at home, all original .

I bought the small o rings just to be sure, art no 49111-45001, but I don’t think I need them. I don’t see any way these callipers would be two part callipers. Or am I really wrong in this?

Anyway, weekend is calliper and master cylinder rebuild time!

[Big T]

Nope, the early calipers are one piece and one piston

You diud buy new brake lines?

[standswithabeer]

did you mean 59111-45001? item #3, on bolt? listed under "caripers"

https://www.partsfish.com/oemparts/a/suz/50d3ff8cf8700230d8b4dfa9/front-caripers-gs750ec

[Drummert]

You diud buy new brake lines?

Yes I did! If we are doing brake calipers and master cylinder/piston it wouldn't make sense leaving those old lines on. New nice black braided lines came in this morning ^^

did you mean 59111-45001? item #3, on bolt? listed under "caripers"

https://www.partsfish.com/oemparts/a...ripers-gs750ec

Haha, exactly. Those rings, Item 3 on the bolt. Puzzles me.

Now, I only need to find out what exactly "caripers" are XD