GT750 single disc setup

MotoMartin · Post by **MotoMartin** » Wed Dec 09, 2009 10:25 pm

My "76 GT750 has a single front rotor setup. At one point in the bike's life it was either a race bike or a "boy racer". One of the modifications was to remove one of the front rotors, and connect both brake lines to one caliper. At the moment the braking power is akin to pressing two wood blocks against the rotor. I have bleed the lines, roughed up the brake pads, cleaned off the rotor but it is still has very poor performance. My question is: Was the single disc set up with two brake lines to one caliper ever a viable setup or should it be converted back?

Post by **Suzsmokeyallan** » Wed Dec 09, 2009 10:38 pm

Thats not a good setup, youd be better off blocking off one of the outlets at the splitter on the lower tree and removing that extra hose.
However the brakes need all the help they can get so put back the other disc and caliper.
You should really rebuild the whole brake setup if you didnt or dont know its internal condition.

tz375 · Post by **tz375** » Fri Dec 11, 2009 3:33 pm

Removing one side is an old drag race trick to reduce weight and is usually a fashion statement gone wrong.

The answer to the question comes in many parts.

Firstly, as Allan alluded to, the original performance wasn't outstanding by modern standards, so reducing it is unlikely to be a winning solution.

Two hoses to one caliper is almost the same as a single hose, but more hose length to bulge and distort and lose effective pressure.

Secondly there's the issue of master cylinder to slave cylinder ratios which has just changed from about 12:1 which is barely workable to 6:1 or so which is so hard to squeeze that basically it's a non event.

You could try a variety of solutions depending on how original you want it to look.

You could replace the one caliper with a single EX500/SV650 twin piston caliper an a suitable master cylinder.

You could do that and replace the disk with a modern disk. My favorite is CBR600F2 which is as close to a bolt on as it gets. Or get a new replacement disk from EWBC who list them for that application

You could do a pair of the above

Or you could get a complete stock set up. I have pairs of disks I would never use on a bike and someone must have calipers to sell. Lots of choices.

MotoMartin · Post by **MotoMartin** » Fri Dec 11, 2009 11:16 pm

Thanks for the input.
Yes it is hard to squeeze with little feel or movement in the lever.
I'll look for a used rotor and caliper on Ebay.

CJF · Post by **CJF** » Sat Dec 12, 2009 1:51 pm

What type of modifications are required when fitting a SV650 caliper to the stock fork and rotor? I wouldn't mind upgrading my GT500 front caliper. Do you need to make up a new mounting bracket?

tz375 wrote:Removing one side is an old drag race trick to reduce weight and is usually a fashion statement gone wrong.

The answer to the question comes in many parts.

Firstly, as Allan alluded to, the original performance wasn't outstanding by modern standards, so reducing it is unlikely to be a winning solution.

Two hoses to one caliper is almost the same as a single hose, but more hose length to bulge and distort and lose effective pressure.

Secondly there's the issue of master cylinder to slave cylinder ratios which has just changed from about 12:1 which is barely workable to 6:1 or so which is so hard to squeeze that basically it's a non event.

You could try a variety of solutions depending on how original you want it to look.

You could replace the one caliper with a single EX500/SV650 twin piston caliper an a suitable master cylinder.

You could do that and replace the disk with a modern disk. My favorite is CBR600F2 which is as close to a bolt on as it gets. Or get a new replacement disk from EWBC who list them for that application

You could do a pair of the above

Or you could get a complete stock set up. I have pairs of disks I would never use on a bike and someone must have calipers to sell. Lots of choices.

Suzukidave · Post by **Suzukidave** » Sat Dec 12, 2009 4:06 pm

If you really want to upgrade the front on the GT500 swap out the whole front end from a GS like Jug head did .. then you have better forks and brakes

MotoMartin · Post by **MotoMartin** » Sun Dec 20, 2009 12:54 am

I did not even notice until I saw "oldjapanesebikes" website, my forks had been reversed so that the caliper is behind the fork leg (like every other bike) any chance that this has made my brake less effective if it was designed to go the other way?

Post by **oldjapanesebikes** » Sun Dec 20, 2009 10:13 am

Perhaps you could post a few photos of your setup showing both sides ? I'm wondering if you don't already have GS (or some other) forks installed rather than GT.

MotoMartin · Post by **MotoMartin** » Sun Dec 20, 2009 10:58 am

Here are photos of each side.
Today I am removing the brake line that was for the missing left caliper that was also joined to the right caliper. I'll see if that makes any improvement.

tz375 · Post by **tz375** » Sun Dec 20, 2009 2:56 pm

It looks to me as if they are stock forks rotated so that the calipers are behind and drain screws at the front

fender appears to be a 77 or maybe a GS and the caliper looks like a GS or something later, but it isn't a Gt caliper.

And of course the legs are painted and should be clear over brushed aluminum.
Tt calipers to rebuild for a stock look or those SV calipers or EX500 calipers for an almost stock look but much better brakes. Both need a simple adapter.

MotoMartin · Post by **MotoMartin** » Sun Dec 20, 2009 3:31 pm

Front brake works quite a bit better with the extra hose removed.
Front fender(mudguard) is from an XS1100 Special.

Post by **oldjapanesebikes** » Sun Dec 20, 2009 3:36 pm

tz375 wrote: ....but it isn't a Gt caliper.

Agreed - not even sure it is Suzuki.

Post by **oldjapanesebikes** » Sun Dec 20, 2009 3:43 pm

MotoMartin wrote:Front brake works quite a bit better with the extra hose removed.
Front fender(mudguard) is from an XS1100 Special.

I'm wondering if that calliper might not be off an XS1100 also ?

MotoMartin · Post by **MotoMartin** » Sun Dec 20, 2009 4:14 pm

[/quote] Agreed - not even sure it is Suzuki.[/quote]

If it helps it says "Aisin Jap" on the back.
The pads are Aisin JB CX FF, not round like stock pads.
The brackets look factory does not look shop fabricated.
Not the same as my XS1100 brakes.

tz375 · Post by **tz375** » Sun Dec 20, 2009 4:33 pm

They look similar to a late RD400F or maybe an XS650 from the late seventies.