GT500 rear brake

rbond · Post by **rbond** » Mon Jul 27, 2009 9:39 am

Has anyone done or know of, a rear disc brake conversion for a GT500? At speed the rear drum is useless, at a crawl it will slow and stop. Good thing I have had a lot of practice using the front as a main brake..... Not the best method, but on T/GT500's it's the only game in town.

rngdng · Post by **rngdng** » Mon Jul 27, 2009 11:09 am

Interesting; my GT500's rear brake worked very well. I never understood why the 750's brake didn't work as well.

Lane

rbond · Post by **rbond** » Mon Jul 27, 2009 11:44 am

If I remember the parts breakdown, the same shoes fit the 500, 750, and the GS400. Worked good on the 400, (rod actutated) not so good 500 (cable), 750 I can't say. I have not had the pleasure of riding a GT750 or any of the triples really. My loss. I did read where the shoes were re-lined at a truck shop and they then worked great with little wear. May have to try that, but I think it would be an interesting 'upgrade' to do a disc conversion. Any thoughts?

Post by **Suzsmokeyallan** » Mon Jul 27, 2009 1:54 pm

The rr brake on the 750 wont win any prizes but its not all that bad, it works for a few repeated stops before it gets a bit vague.
The 500 is a lot lighter so it should work a bit better at least. A lot of stuff needs to be checked to get the most out of the rr brake, most important of all is that the shoes are of a serviceable limit and that the lever arm is positioned so its not pulling past the effective angle.

rbond · Post by **rbond** » Mon Jul 27, 2009 2:26 pm

(The rr brake on the 750 wont win any prizes but its not all that bad, it works for a few repeated stops before it gets a bit vague.
The 500 is a lot lighter so it should work a bit better at least. A lot of stuff needs to be checked to get the most out of the rr brake, most important of all is that the shoes are of a serviceable limit and that the lever arm is positioned so its not pulling past the effective angle.) Agree whole heartedly with your statement. I put new shoes, the arm is on the shaft so as to engage as far as possible to the end of the cable. I have put about 2k on the bike since, so the shoes should be bedded in, adjusted cable as needed. I have to use the rear no matter what because the brake light switch works everytime unlike the front switch. I replaced the contact, spring, and plunger it helped for a while. The contact plate with the wires is the culprit, have not had the opportunity to replace that yet. I have some EBC shoes, but they are 10mm too wide. When it cools a little here, I will put them in a vise and do a little surgery then put 'em on the backing plate. Maybe the compound on those will do better. I have had plenty of experience dragging a disc in the rain, so having to deal with front and back discs will not be anything new.

tz375 · Post by **tz375** » Mon Jul 27, 2009 2:41 pm

Most of the braking is done by the front - anything from 70% to 100% unless the surface is wet or slippy. That means that the front brake (disk ?) has to be operating efficiently.

You ahev probably done all teh usual things like making sure the caliper slides easily and teh hoses are not bulging and wasting effort etc. The grade of stainless is not the best in terms of coefficient of friction, and if you are not concerned about originality, a change of disk from a modern bike and a matching SV650/EX500 type caliper really makes a difference.

At the rear end, Allan covered most of the issues, but if it still isn't any good, talk to Vintage Brake and get new linings. Allan's point about lever angles is spot and and often brakes are at angles that just don't work. Sounds like you have that part covered.

Make sure that all the pivots are as smooth and friction free as possible.

rbond · Post by **rbond** » Mon Jul 27, 2009 4:02 pm

The front brake is still original, except fluid, I changed that when I first got the bike. It works just fine, still have a good amount of pad left. From others postings, and vintage road tests, all agree the rear does a poor job. I was hoping the EBC shoes have better friction material than stock on some aftermarket shoes, they are just too wide. But I feel safe in assuming that the main reason is simply a design flaw in the T/GT rear brakes that does not allow them to function properly. There are too many other models and makes that have and still use cables to operate rear brakes that work fine. So I was curious if anyone had done a conversion to disc even for racing purposes. It seems that there is little problem with swapping wheel assemblies, spacers, etc. to get dual front or even just newer discs on older bikes, so a rear wheel conversion may not be difficult. I have access to a large supply of junked bikes (literally in the forest) where I could find parts to adapt.... I suppose what I am asking is for a little educated guessing in what parts from what model bike(s) might work.

tz375 · Post by **tz375** » Mon Jul 27, 2009 5:28 pm

Just a crazy, off the wall thought, but have you looked at a twin leading shoe front brake assembly or modify your to 2LS with linkages from a front brake.

T500 is wide and may be the right size. CB72 would work but the chain is on the wrong side and flipping it makes it twin trailing shoes - but that could be modified too.

diamondj · Post by **diamondj** » Mon Jul 27, 2009 5:32 pm

If you're staying with spoked wheels, part of your problem is finding a rear hub that includes a cush drive and a disc brake assembly and is narrow enough to fit into the T500 swing arm. The first year GS1000 and GS750 had them but the assemblies are too wide for a T500 hub. Same deal with the Kawasaki Z1000. I think a couple of the CB Hondas had spokes and a disc as well but I don't recall which....

What about a different rear drum? Pick up an XS650 rear and you'll gain an aluminum rim as well. Vintage Brake likes the CB72/77 front hubs - perhaps the rear drums are good as well?

I know the RD400 had a rear disc but the wheel is an aluminum cast seven spoke. You'd probably be better off trying to bolt up the full rear suspension off the RD as the caliper stay is a weird set-up. One of the T500 race frames I have had an RD400 rear suspension bolted in and I still have the swing-arm out of it so I know it will fit the T500 frame.

So why do you need a stronger rear brake on your GT500? I've found the rear drum on the T500/GT500 adequate for trail braking and holding the bike in place at stop lights which is almost all you'd want to do with the rear brake anyway.... Are you sure your rear drum is adjusted correctly? I have a link to a full factory service manual in the "Links to cool sites" section and they cover rear brake adjustment there....

Jim

johnakay · Post by **johnakay** » Tue Jul 28, 2009 3:52 am

the rear brake on my old T500 was far better than the front.

rbond · Post by **rbond** » Tue Jul 28, 2009 8:14 am

Well mine came with the, I assume, original shoes with a little over 9k miles on it. After I brought the bike home, I found out it does not have the original tank, (blue), but has a painted over red tank. I have no idea what the previous owner(s) did to this bike. It was not ridden that much, but must have been thrashed hard when it was, to have to replace the tank already. So anyway, the rear has never worked that good, my GS400 worked real good, so I was a little disappointed that the GT brake was very weak. I got new shoes (Parts-n-More), they were no better than stock. The EBC's don't fit, yet, so I am exploring my options. I am no machinist or welder, but I think I can cut and drill some aluminum plate to fabricate mounting brackets for a master cylinder, and a mount for a caliper...... If it comes down to finding a more suitable replacement lining, I will do that, I kept the old shoes just for that idea. I prefer to keep it as stock as possible, but sometimes a little modifying, modernizing is necessary. Every bike, even those numerically in sequence from the factory has it's own unique 'personallity', that is a good as any explanation why your brakes work good, mine suck, someone else's is in between, etc. It's a crazy world. These challanges keep us busy.