tip on using GT550 4LS brake on a GT380?

[jabcb]

Has anyone used a 72 GT550/GT750 4LS front brake on a 72 GT380?

The 72 GT550 & GT380 use the same axle & axle nut.
So this might be doable without a lot of work.

[Alan H]

Check the distance between the forks first.
A friend fitted a 4LS to a T500, but changed the entire front end. Triple tree, forks and wheel.
Is there anywhere for the torque arm to fit on both fork (standard) legs if they are otherwise OK?

[jabcb]

The disk-braked GT380 & GT550 use the same front wheel hub & front axle.
They have different brake rotors & rims.

The drum-braked GT380 uses a torque arm.

The 4LS can be made to fit a T500 front end but that requires some machining of 4LS parts.
(Have seen pics of the 4LS on a T500.)

So its probably a safe bet that you can use a 4LS on a 72 GT380, but the question is how much work is required.

[jabcb]

The GT250 cafe project sits adjacent to my spare wheels. I bought a spare 4LS front wheel something like 4 years ago.
This morning I was working on wiring & my curiosity got the best of me.

So here is a pic of that 4LS wheel fitted to the GT380 tinkering project.


I have another 4LS topic that has info about axle washers Suzuki used on the GT550 & GT750.
The washers are listed in my old printed manual but aren’t listed in the online versions.
That topic: viewtopic.php?f=2&t=12772&p=163800&hili ... ke#p163800

The 4LS brake fits snugly on the GT380 without washers & does not fit with them.

So perhaps the 4LS brake was designed for the GT380/GT550/GT750, with the bigger bikes needing the washers.
And perhaps they decided that made the GT380 too expensive so they went with a 2LS.

[Alan H]

The early GT380 had the GT250 2LS front brake, which was really dire. Suzuki's response was to fit Ferodo linings to the 2LS and then the year after fitted a disc. I understood at the time (1972) that my mate's 380 was the first one done. We went to the Ferodo works in Chapel-en-le-Frith to have the work done to his bike in summer 1972.
The early 550 and 750 had the same 4LS front wheel but with different spacers as the 750's forks were slightly wider - the triple tree was different.
I had a 550J back then and have just started a 550J resto.

[jabcb]

73 was the first year for the GT250 in the US, so it had the disk brake.
The T250 & T350 had the same front drum & the T500 had a larger front drum.

I can just picture some marketing person going…
T350 has 180mm & T500 has 200mm. 380 is only 30 more than 350 so lets go with the 180.
But they should have picked the T500 drum.

The GT380 2LS & GT550 4LS use the same axle & nut. That’s what got me curious about a 4LS on a GT380.

Old parts manuals for the GT550 & GT750 have the same part # for the spacers.
The GT750 manual also lists the spacer as 15.1x30x5
My GT550 cafe project has the 4LS & the spacer is 3mm thick.

Figuring out what you have, and what you should have, is just part of the fun with these old bikes.

The wheels on the GT380 tinkering project were pretty ratty. I already switched to a T500 rear wheel. I’m thinking I should just use the spare 4LS.

Good luck with the GT550J resto. I expect it to turn out sweet.

[Alan H]

If you want a different set of wheels, have a look at the GS500, they shouldn't be far off.
I do love the 4LS though, set up properly it will outstop a disc on the 550, but wasn't up to the weight of the 750.
I'll start a thread on the resto when I get the wheels back - the hubs are polished, but the rims were knackered so getting replaced.

[jabcb]

I’m using Vesrah VB-331 brakes shoes for both 4LS. If you’re interest, several sets are listed on eBay for very reasonable $.

The GT550 project hubs are polished & clear coated. Will be using SS spokes + black Sun rims (F: 2.15x18 & R: 2.75x18).
The GT380 is a low $$$ tinkering project, so I’ll just clean up & service the stock 4LS front wheel.

[Alan H]

Make sure the rims are drilled at the correct angle for the short 4LS spokes.

[jabcb]

I had at one point considered black rims from MikesXS but a bit of reading about redrilling the rim to get the correct spoke angle convinced me otherwise.
Given my skill level, correct spokes+rims from Buchanans is worth the extra $$$.