1982 gs750t master cylinder Rebuild or Replace?

[Jimmbuzz]

I've finished my top end rebuild with the extra time I have with quarantine, but an engine is no good without any brakes. I took the master cylinder off and I noticed that it was leaking from the piston and not the line like I expected. No telling when it was serviced if it has at all. I was wondering if its worth dropping the $30 on a new piston/cup set or if anyone had any luck replacing with an aftermarket one. -Thanks

 

[Rich82GS750TZ]

I rebuilt mine with the OEM kit. Was probably @$30, like you say. Even replaced the nasty looking Sight glass. I think that was $1.00 on eBay. Really. One dollar. Works great now. Others like some of the other manufacturers MCs.

Be sure to replace the lid gasket. You can also find very cheap but excellent zinc-plated Allen-head lid screws on EBay. OPs like to chew up those MC lid screws for some reason. Speaking of, get yourself a JIS screwdriver set if you don’t have one. Every screwhead on your bike that looks like a Phillips, isn’t.

Welcome to the forum, from a fellow “T” owner. You have a great bike, but I’m biased.

Post pictures.

and create a signature that includes your bike year and model.

 

[GSXR7ED]

I completely rebuilt mine...can’t remember how much I spent. The results were fantastic!

Ed

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[LAB3]

I'd replaced my front M/C with a low priced aftermarket one and didn't take into account an important factor. If the handle breaks (Which mine did) there's no source for buying just the handle, you have to get an entire unit. If you go aftermarket, choose wisely.

 

[GSXR7ED]

Yep, take that into consideration...the handle/lever that is part of the MC.

I took the spare one I had off my parts bike and sent it to Tank...who I noticed is not showing on my friends list.

In the process of acquiring more spares for my “T”, I was sent another handle and MC assembly...which is cool.

These MC units can get very gunky but I soaked mine for hours in metal cleaning solvent and it worked wonders on my MC unit.

Ed

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[GSXR7ED]

Here's the way it looked before cleaning:

The solvent tank I soaked it in...

Components:

Clean parts:

On this thread beginning on post# 52: https://www.thegsresources.com/_forum/showthread.php?216696-82GS750T-Seal-T-M-Gear-Shift-Oil/page2

Ed

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[Jimmbuzz]

Thank you all for the info. Went ahead and ordered a new piston/cup set along with some exhaust bits from bike bandit. Hopefully will be road worthy soon for the good weather. Hope to get pics soon of all the stages the bike has been through.

 

[Nessism]

Key thing is to inspect the bore of the master; if it's free of pitting then it's a good candidate for rebuilding. Just be sure to use OEM parts, not aftermarket. Unfortunately, a lot of old masters have corrosion pitting in the bore and/or on the caliper pistons, and that means the parts need replacing, not rebuilding. Oh, and be sure to replace the OEM brake lines since they are sure to be full of sludge attached to the rubber on the ID. Failing to do this will lead to contamination your new brake fluid.

 

[Rich82GS750TZ]

More to consider:
Brake line. If your front brake hose is original, it’s 38 years old! Replace it, preferably with a braided SS one. I got a new line w/swivel fittings, banjo bolts and copper washers from Venhill USA for around $50, and I’m very happy with it. Others here like some of the other brands. Still others can guide you on putting your own lines together. With this bike, with only the one brake line, I made it easy on myself and just ordered it. If you want I can get you the Venhill invoice that shows all the parts you need.

Caliper. If your MC was crusty inside, bet that the caliper is too. Take it apart and clean everything. Replace the piston seal and oring, evaluate the piston and boots, replace if necessary.

 

[rphillips]

A little embarrassed to ask, but never replaced one. The sight glass on the M/C. I guess it'd be relative simple if I knew how. I guess they just push out & back in? Go in from the outside or inside? Are the seals made on the glass or are they separate?

 

[Rich82GS750TZ]

If you can see the fluid level, I’d leave it alone. If your glass is so clouded you can’t see the brake fluid level, Punch it out from the inside with whatever )0(You’ll probably punch a hole in the “glass” and just have to sort of dig out the rest. Once you feel like you got it all, the ring will probably be still there. That has to come out too. Clean out the whole, being careful not to gouge the aluminum. You want to line up the new one and rap it in with the appropriate size socket. I’ll see if I can find my thread on doing this and paste it in the post in a little while.

here it is

 

[Jimmbuzz]

So, I went ahead and ordered all the parts people previously mention: new brake line, caliper rubber bits, master cylinder piston. Well I went to put the new piston in and it turns out it was too small. My guess is the master cylinder was actually from a bigger bike like an 1000 or 1100, as the cylinder head is also a 1000/1100. Guess I have to track down the right piston assembly, or a new master cylinder again :/

 

[Rich82GS750TZ]

Dang, screwed by the Previous Owner again. That sucks. Sorry.
do you have 1 or 2 front rotors/brake calipers? 750T only had 1.

 

[Jimmbuzz]

Just one, and I'm fairly certain that the caliper is original as all the parts I got for it fit just fine.

 

[Rich82GS750TZ]

So it’s just your MC that isn’t correct for the bike? Also a larger cylinder head? That’s just weird but not unheard of.

 

[Jimmbuzz]

started a new thread to identify the master cylinder that I have:
https://www.thegsresources.com/_for...fying-a-master-cylinder&p=2599619#post2599619