GT750 single disc setup

Buffalo-guy · Post by **Buffalo-guy** » Sun Dec 20, 2009 6:04 pm

What you have there is most likely a set of forks and caliper from an early GS 550/650, that came with that style of caliper, were 35mm tubes, and went right into stock triple trees, and the stock wheel bolted right in with no mods to the axle, or spacers. I've done it myself in the past, but from an E model, with twin discs. I suspect you could get an improvement in brake action, by switching to a master cylinder from one of those donors. Try one of their rotors as well, as they are made of better material for stopping power. It all rides on what the budget allows, of coarse. Good luck. Cheers.
Fred

Post by **oldjapanesebikes** » Sun Dec 20, 2009 6:10 pm

Buffalo-guy wrote:What you have there is most likely a set of forks and caliper from an early GS 550/650, Fred

The fork drain holes appear to be facing front - tough to tell from the photos - but if so would make them just reversed GT forks.

tz375 · Post by **tz375** » Sun Dec 20, 2009 6:45 pm

I think Ian and Fred are right. It's probably GS750 or maybe 550 caliper on Gt750 legs turned back to front.

Post by **Suzsmokeyallan** » Mon Dec 21, 2009 2:25 pm

Those calipers found their way onto bikes right up to the GSX1100 of 81 so they have been around for a while. Its got little clear wear indicator windows in the body and they carry a rectagular shaped pad. They also used the same slotted y shaped spoked rotors, again found on many GS bikes from the early to mid 80s.
That ft fender is from a late 70s to early 80s mid size model GS it looks like the 77 GT one but the front and rear ends have a more curved appearance and a raised lip on the edge.

tz375 · Post by **tz375** » Mon Dec 21, 2009 3:36 pm

Didn't someone say the fender was actually from an XS11 Yamaha?

That's useful info on that caliper. Are the GS calipers any different to a GT in function or are they just as horrible a design?

Post by **oldjapanesebikes** » Mon Dec 21, 2009 4:26 pm

tz375 wrote:Didn't someone say the fender was actually from an XS11 Yamaha?

Yep - MotoMartin said its from a XS1100 (its his bike)

That's useful info on that caliper. Are the GS calipers any different to a GT in function or are they just as horrible a design?

I'm not an expert - have never owned anything newer than 1977

but I would have said the early GS callipers (1977 through to 1979) are marginally better than the GT ones only as the pads appear to have more area. Otherwise, not much difference. I put a set of 1978 GS forks and callipers on my custom, and they work OK - the rotor on the dual GS is a slightly smaller diameter than the GT rotor.

pjmcburney · Post by **pjmcburney** » Mon Dec 21, 2009 8:55 pm

That caliper looks suspiciously like the ones on my '81 Katana 1100.
They retained that design on the Katana's and GSX's right through until the mid-eighties.

There will be no discernible difference with the orientation of the forks - the caliper will work as well (or not) no matter which way around it is.
But, as previously mentioned, with only one disc connected to a dual-disc M/C the hydraulic ratio will be all wrong.

IMHO, the later calipers work significantly better, especially when combined with later discs.
The brakes on the aforementioned Katana are a vast improvement over my GT's brakes, with much the same size discs and very similar caliper design and swept area.

Discs and calipers are pretty easy to come by. If it were my bike I'd be trying to track down an identical (RH) caliper and disc and re-plumbing the second brake line back to it.

Your brakes should then work much better.

Good luck
Paul

tz375 · Post by **tz375** » Mon Dec 21, 2009 9:53 pm

Paul,

That's really useful info for all of us looking for a low cost brake upgrade that looks close to stock.

Do you happen to know hos close the Kat caliper bolt spacing is to the GT? In other words, can they just slide on or do they need an adapter?

pjmcburney · Post by **pjmcburney** » Mon Dec 21, 2009 11:18 pm

tz375 wrote:Paul,

That's really useful info for all of us looking for a low cost brake upgrade that looks close to stock.

Do you happen to know hos close the Kat caliper bolt spacing is to the GT? In other words, can they just slide on or do they need an adapter?

AFAIK, straight swap over

Not only is the caliper bolt-spacing identical, the disc offset and sweep area is the very much the same if not identical. You should be able to use the Katana/GSX calipers on either GT discs or Katana/GSX discs.

I know for a fact the front hubs are completely identical - you can lace up a GT hub, bolt on Katana discs and fit it straight into a Katana front-end, spacers, speedo drive and all...

What I don't understand is exactly why the later caliper works so much better. It's still a single-piston, floating design, and the pads aren't that much bigger. The hydraulic ratio is the same (I think), but it just, well, works.
I was unfortunate enough to have been involved in a rear-ender (on my 1100 Kat at the time) some years ago.
A dumbass ahead of me couldn't decide what lane he wanted to be in and ended up just propping in front of me instead. I grabbed a fistful of front brake at 60 km/h and the front wheel locked solid (much to my surprise I might add) and I slid straight into his tailgate.

The impact converted the Kat's forks into bananas... I survived with nary a scratch but the bike was off the road for ages, I had to get the frame straightened as well

.
Thankfully it was a company vehicle and their insurance payed up.

Here's a pic of the Kat caliper -

Pretty sure it's one of those.

Cheers
Paul

Suzukidave · Post by **Suzukidave** » Mon Dec 21, 2009 11:45 pm

http://cgi.ebay.com/ebaymotors/82-83-Su ... 27acef7b72

MotoMartin · Post by **MotoMartin** » Tue Dec 22, 2009 7:55 pm

Yes, my caliper looks alot like the GS1100 ones shown. As you can see from the Ebay photos the pads are larger than stock and rectangular and not round. Amazing that the bolt spacing on the fork legs would be the same.

tz375 · Post by **tz375** » Tue Dec 22, 2009 10:34 pm

You have options now and thanks to all the guys that contributed, the pool of knowledge just got a little deeper

MotoMartin · Post by **MotoMartin** » Sat Dec 26, 2009 5:35 pm

The calipers of the late 70's and early 80's GS 550 thru 1100 look similar, but they all have different part numbers. The mounting brackets are different. The 1980 GS550E looks the most similar in terms of bolt spacing, I'll try to verify the measurements.

MotoMartin · Post by **MotoMartin** » Thu Jan 14, 2010 6:17 pm

Just for closure, the caliper and bracket were from a 1980 GS 550 E, and bolt right on.
The brakes work much, much better now.
Thanks All.

Post by **oldjapanesebikes** » Thu Jan 14, 2010 6:44 pm

Being able to stop can be a good thing !

GT750 single disc setup

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