79 Gs850 brake upgrade

[MapleK]

After doing some searching I’ve answered some questions I had about the 80+ rotor/caliper upgrades. Although I have a few things I’d like to confirm before sourcing my parts.
First, my bike is a “850g”. I read a thread where someone was having clearance issues with their rotor hitting the caliper and it was determined that he potentially got some parts off a “gl” model that we’re not the same as his “g”. So basically the rotors and calipers HAVE to be specified as a 80 up 850g correct?
Second, did the master cylinders change also between 79 and 80 or am I good to use my mc?
Third, this is probably a dumb question but is the rear brake upgradable? Everything I was finding was talking about front brakes so I was just curious about the rear.
I appreciate the help in advance!

[Grimly]

Yep, calipers and caliper mounting brackets have to come from a non-L model.
The rotors are optional, but there is a worthwhile difference in wet weather performance with the slotted discs.
Master cylinders on 79 and 80 are 5/8", but you'd probably like a more modern 5/8" m/c with adjustable span, etc. I use Nissin mcs from Honda Deauvilles, NTV650/700 for that. They work well and don't look out of place.
Rear is over-braked anyway. More performance isn't needed.
A way of keeping it going without sticking and binding is better.

[MapleK]

Yep, calipers and caliper mounting brackets have to come from a non-L model.
The rotors are optional, but there is a worthwhile difference in wet weather performance with the slotted discs.
Master cylinders on 79 and 80 are 5/8", but you'd probably like a more modern 5/8" m/c with adjustable span, etc. I use Nissin mcs from Honda Deauvilles, NTV650/700 for that. They work well and don't look out of place.
Rear is over-braked anyway. More performance isn't needed.
A way of keeping it going without sticking and binding is better.

That is exactly what I was looking for Grimly, thanks for that.

[salty_monk]

The Ex650 mc makes a good upgrade. Has a mirror mount and adjustable lever if you get the right year. Much more common here in the US.

some have had issues using the older rotors with the newer calipers, I haven’t tried it myself.

the rear brake is opposed piston, the caliper is more powerful that the front and in general as powerful (if heavier…) than any modern equivalent you will find.

I looked into it once… it was a lot of work for no real gain.

You can also fit the twinpot calipers and CBR rotors to that bike…

[MapleK]

The Ex650 mc makes a good upgrade. Has a mirror mount and adjustable lever if you get the right year. Much more common here in the US.

some have had issues using the older rotors with the newer calipers, I haven’t tried it myself.

the rear brake is opposed piston, the caliper is more powerful that the front and in general as powerful (if heavier…) than any modern equivalent you will find.

I looked into it once… it was a lot of work for no real gain.

You can also fit the twinpot calipers and CBR rotors to that bike…

Good info! I ended up buying some rotors and calipers from a 85 g last night on eBay for 80 bucks shipped. Calipers may need rebuilt still but the rotors looked to be in good shape. It’s definitely a budget build/use what parts I have in the garage so I’ll be happy with these as a cheap upgrade from the 79 brakes

[Grimly]

Good info! I ended up buying some rotors and calipers from a 85 g last night on eBay for 80 bucks shipped. Calipers may need rebuilt still but the rotors looked to be in good shape. It’s definitely a budget build/use what parts I have in the garage so I’ll be happy with these as a cheap upgrade from the 79 brakes

When I rebuilt a pair of low-mileage calipers and fitted them with Carbon Lorraine pads, the stopping power was eye-opening. I hadn't realised just how bad the old ones had got, and I'd totally forgotten how good they used to be. Of course, they're not like modern four and six-potters but never the less, I'm less likely to simply run out of road because of bad brakes now.