Twinpot Brake upgrade on 78 Skunk

[Rogerlinder]

Sorted, thank you for reminding me.

[salty_monk]

Have messaged you back Mike.

Roger there is a single brake mod thread (much smaller than this one).
do you care if I copy your post over there or do you want to post it?

https://www.thegsresources.com/_forum/forum/technical-forums/performance-tuning-mods/70216-twinpot-brake-upgrade-on-gs550e-gs750c-gs1000c

cheers,
Dan

[kikdrum18]

I definitely want to do this to my 1980 850L. Is there anything extra I need to do besides purchase the kit, rotors and calipers?

[steve murdoch]

Thanks for the detailed report, Roger.
btw, nice looking bike!

[Rogerlinder]

Successfully converted my 1977 GS550. I did things a little different than standard went with a W800 master (12mm bore), MD1124LS 320mm Rotor and an EX500 caliper. The brake master was a bust, but the rotor worked out rather nicely. It’s the No drill original fork option that has been asked after many a time in this thread.

As some of you know salty_monks bracket has been successfully used on single disc GS550 or GS750’s to fit a 310mm 1998-99 CBR900RR rotor. The issue with using this rotor is pad overhang and you must drill it. BCD is correct, but holes are for 6mm hardware and The brake pad needs to be chamfered. The pads will touch each other as they wear. A potential alternative noted during the initial development was a Honda NT 650 or 400 bros rotor is 320mm, has the same BCD, offset, and was intended for M8 hardware like the GS. Not only does it solve the pad overhang issue (https://imgur.com/U91id2G) you don’t have to drill it. The rotor bolts right on and you can even use Hondas bolts (90105-KV0-700); they are same thread as the GS hubs. The only issue is that early speedo shields are too short to use without a rotor spacer, the Hondas rotor bolts felt too short to use with a spacer I reused the bolts I already had. But if you have a later model with a deeper speedo shield you likely won’t have to run the spacer and could use shorter bolts. With spacer, https://imgur.com/nKuejZY, and without https://imgur.com/1Q7RWtm

There are a couple of issues with this rotor, mainly price and availability. As far as I can tell very few NT BROS are in North America, saw one in Vancouver BC classified, couldn’t tell if it was an import or not. It’s very unlikely to find a used rotor. EBC and Metal gear (model number 21-079-A-GL) do make new rotors; I only saw them in Australia or Europe. When I asked an EBC distributor in the states, they said the EBC MD1124LS was discontinued but I neglected to check if that was just for the US, seem to be plenty on eBay at present. Price is going to be the other limiting factor the rotors are $200-300 shipped vs $130 for a single Arashi CBR900RR rotors. You end up spending around $70 to avoid drilling and chamfering pads, if you’re buying new.

Master cylinder was a bit of a bust. I was unable to find a rebuild kit for my master so I wanted something I could get parts for. The W800 and W650 both use a 12mm master, that looks the part, but it just doesn’t push enough fluid for 2 finger braking, pinky and ring finger got in the way. worked ok with 4 fingers but I switched back to the 14mm the bike came with for now. Another annoying feature of this master is a 34mm bolt spacing handlebar clamp, $34 clamp from Kawasaki. Most clamps have 32mm bolt spacing, I ran out of patience trying to find one and jury rigged it with a triple tree handlebar clamp from my bin of spares. Worked well enough to know it wasn’t usable.

Brake caliper came off a EX500, not much of note. If you’re redoing pistons and seals with OEM part look for a Suzuki rebuild set (59100-01831). It’s $75 for both pistons and all the seals vs $190 piecemeal from Kawasaki. The pin and piston seals are about the same price Kawasaki or Suzuki if your pistons aren’t corroded or you’re switching to stainless pistons, it’s not as big of a difference.

As for pads, I just went with a cheap NOS OEM pair I think for a concourse

The new rotor is 3lbs lighter than the original. 6.6lbs vs 3.6lbs

Calipers were both 3lbs.

This is an album of the previous photos:

https://imgur.com/a/gs550-twin-pot-mod-YSguVLJ

[salty_monk]

Looking at your calipers I’d consider replacing them. Plenty of them in good condition here in the US but there must be some ex650 ones in decent shape over there you would think.
they are a different caliper to what you have there. Still Tokico but both pistons are the same size and the mounting bracket is a bit different.

PM back.

[bill_face]

salty_monk thanks for the info. The chap at the local motorbike is struggling with that info. I've PMed you

[salty_monk]

That caliper is from an old 80’s Ninja, and EX500 or a Concourse.
also came on the Suzuki Dl650 and SV650. Plenty of bikes.
The last of them were used on the Ninja 250’s and Concourses up to about 2006.

There is a more modern caliper set off an Ex650 that will also fit if you have the later version of the bracket.

good luck! English weather and roads are brutal!

[bill_face]

Hey. I did this upgrade a while back and my brakes have seized up. Gonna do a caliper rebuild. Trouble is I can't remember what calipers (or rotors) I got from salty_monk

Old PMs seem to have vanished from the system.

Could anyone identify from the photo?

[salty_monk]

Pull that rotor off and make sure the back of it is flat. I usually kiss the holes with a countersink and then run it on some paper on a flat surface. You need the mounting surface to be totally flat.
In my experience that’s been more common cause of pulsing than a warped rotor.

thanks for doing all the weighing and math!

[hookemdevils22]

Add my 82 650G to the list. Just finished this evening: CBR600F4 rotors, EX650 calipers and master cylinder. I wasn't able to do much testing because the left side CB rotor was warped.

I weighed all parts and shaved 946g (2.09 lb) off the front, all of which is unsprung and most of which is in the rotors (664g/1.46lb less rotating mass including salty spacers). That also includes the 641g (including the additional pair of M10-1.25x40mm bolts + nuts needed) for salty's spacers and bracket.

I also picked up calipers from a Concours ZG1000 (140g heavier each as compared to EX650, 160g each lighter than stock) and radial masters from an 05+ R6 (16mm bore) and Kawasaki Concours 14 (11/16" bore) for further testing. I'll have a separate write-up with hydraulic ratios, a calculator, full weights, and more.

[salty_monk]

Your assembly is wrong. The drive dust cover goes on the OUTSIDE of the rotor. You have it on the inside against the wheel.

also some general comments to your PM follows (before I saw picture)

The kit won’t affect the way the Speedo drive interacts with the wheel. Whatever you had before should be exactly the same after.
what does happen is that when you tighten the axle the Speedo drive itself binds on the dust cover. It’s pretty easy to see and feel if you’re looking for it (the wheel won’t spin easily by hand although you may be able to force it around).
not all dust covers need cutting back, usually the pre 1980 ones are ok and the post 1980 ones need trimming but it’s not a hard and fast rule as lots of parts have been swapped around on these old bikes over the last 40 odd years.

Cheers,

Dan

[garyS-NJ]

Finally bolting up the salty monk twin pot upgrade on my 1979 gs1000e and I see the speedo drive dust seal (#10 in parts Fischer metal shield with 6 holes for rotor bolts) extends about 4mm past the wheel hub. I don't see why I should trim the dust seal in fact I think it should be longer to further envelope thd speedo drive. Now I'm wondering if I trimmed it before powder coating. I remember in this post with directions there was something about trimming the dust seal and just read that was for some later bikes. So I laid the wheel up the speedo drive and see that the drive fits into the dust seal and there's a ledge on the drive so the seal extends around the drive and that ledge on the drive is sbout that same 4mm.
this is where I'm scratching my head because the tabs on the speedo drive only extend about 0.030" into the hub notches barely giving much drive surface. But the speedo drive itself laid up against the hub hits home to the wheel bearing inner so even with the old stock rotor, or untrimmed dust seal (if I did trim it), I would not have deeper contact between the speedo drive tabs and the hub notches. This is looking like I should trim the speedo drive itself so the drive tabs extend deeper into the wheel but that don't make sense because I'm sure the drive inner is flush with the wheel bearing inner acting like a spacer in which case the only way I'd have more tab contact area would be to use a different speedo drive (or tab washer which is removable with a snap ring.
now I know I'm sounding like an idiot because even with just 0.030" tab to hub notch contact, the wheel does drive the speedo. All that said, the dust shield definately isn't holding the speedo drive out so I'm thinking I should bolt it up because it will be how it was with the old rotors

[salty_monk]

Hi Neil - I just got back from there, could have bought you a set of brackets over... I do still have some on my shelf. I'll PM you. Dan

[Jofka]

Good afternoon,

i have had my 1983 gsx 1100es for several years and have recently become aware i would perhaps like to stop a little sooner, old age and reaction times perhaps, bit of a long shot but you wouldnt happen to have an adaption kit and list of parts for a 1983 GSX 1100 es? im in the uk.

regards Neill