Attack of the Noobie: Fork options/Rotor options (1978)

[Guest]

Hi there! First off, hello and thanks for having such a great site around for a source of all GS knowledge!

I just joined the GS world as of 2 weeks, after picking up a near mint 1979 (ok it may be a 1978 with messed up papers from the MTO) GS750.

Red, with wire wheels, single disc up front etc.

After some digging on this forum and others, it turns out that (as you know) my wheel is already tapped for a second rotor, just neatly concealed by that dust cover over the right hand side of the wheel.

My plan is to convert the bike to dual discs, newer 4 pot calipers (eventually, for now factory dual calipers), and slotted rotors (at least that's the plan - and yes, I intend to do all the other work on the bike, although as I said mint, so there is little to no work to do)

Here are my questions, that I hope you fine folks can answer for me:

1. RE: fork legs. I definitely need some dual disc forks legs (stanchions + legs, to just slide into the current trees). I would like to know, for NON-leading forks (so axle directly in line with the fork leg), what years and models should I be looking for? For example: Can I use 1981 GS750 legs on my 1978? (35mm ones I believe, that I have) OR must I stick to 1970s?

Can I use GS550 legs? GS1000? I am so confused by all this compatibility!

2: Slotted rotors: I can't for the life of me, find used Suzuki GS750 slotted rotors for a 1978. They're all 1982 (which are 10 7/8" across, not 12ish" like the 1978 ones). Am I really stuck using SOLID discs, as opposed to slotted?

3. Are there any NON-suzuki rotors (read as: BIG rotors, since I will be having custom adapters made eventually for modern calipers) that fit up with the GS750 hubs? I remember someone saying CBR900RR rotors... 6 bolt pattern, that works with the hub WITHOUT an adapter, or maybe someone makes a very basic "ring" type adapter to bring a large "flat" rotor away from the hub, closer to the fork leg? (since the factory GS rotors are offset, and a lot of new one aren't, from the 90s and on)

4. How safe will I be using the factory single disc wheel/hub (that 100% sure has 6 threaded holes tapped for a second disc - saving me the effort of finding another spoke wheel!) with a dual disc setup? I am 99% confident it will be fine, but I could be wrong?

I REALLY look forward to your input!

thanks!!

[NoH2Oh]

If you are after better braking rebuilding the MC, caliper, some modern EBC pads and braided lines might just do the trick. Did wonders to my 78.

Use OEM rubber parts...

[lumberjack]

If you are after better braking rebuilding the MC, caliper, some modern EBC pads and braided lines might just do the trick. Did wonders to my 78.

Use OEM rubber parts...

Cool, will bear that in mind. However, I will be honest: I have my heart set on dual discs up front. This bike will be an on going project, and I really would love to have some modern calipers up front, if not "big" rotors.

I might settle on doing a stock dual disc conversion up front (so Gs750 calipers, MC on the GS750 legs and factory smooth rotor (or drilling them)) - just rebuild them as you said, and see how that does.

Even after rebleeding and working on the front brake a bit, I am still not too content with the stopping ability of a single brake.

However, it's a good start, for now, if I can't find the parts I want.

I am still wondering if any of the Honda RC51/CBR600F3 rotors bolt onto the hubs....

[mmattockx]

Are there any NON-suzuki rotors (read as: BIG rotors, since I will be having custom adapters made eventually for modern calipers) that fit up with the GS750 hubs? I remember someone saying CBR900RR rotors... 6 bolt pattern, that works with the hub WITHOUT an adapter, or maybe someone makes a very basic "ring" type adapter to bring a large "flat" rotor away from the hub, closer to the fork leg?

The F3/CBR900 rotors aren't a direct fit. They have a 6 x 6mm x 74mm bolt pattern and most (all?) of the GS's have a 6 x 8mm x 78mm bolt pattern. You can redrill the Honda rotors with the Suzuki pattern, going in between the existing holes but that is as close as it gets from what I know of.

Have a look through this thread: http://www.thegsresources.com/_forum...d.php?t=140253

salty_monk has worked out the easiest brake upgrade going for the GS bikes, selling a simple kit to retrofit Kawasaki twin piston calipers and the F3 rotors onto most of the GS's for a significant improvement in performance. If you want more than that you will have to go it alone and work out bigger rotors and calipers/adapters in your garage. The biggest problem you will find with calipers is that all of the late model 4 and 6 piston calipers are quite wide and they simply don't fit between the rotor and the wheel. The Kawi 2 piston unit doesn't have that problem and fits easily.


Mark

[lumberjack]

The F3/CBR900 rotors aren't a direct fit. They have a 6 x 6mm x 74mm bolt pattern and most (all?) of the GS's have a 6 x 8mm x 78mm bolt pattern. You can redrill the Honda rotors with the Suzuki pattern, going in between the existing holes but that is as close as it gets from what I know of.

Have a look through this thread: http://www.thegsresources.com/_forum...d.php?t=140253

salty_monk has worked out the easiest brake upgrade going for the GS bikes, selling a simple kit to retrofit Kawasaki twin piston calipers and the F3 rotors onto most of the GS's for a significant improvement in performance. If you want more than that you will have to go it alone and work out bigger rotors and calipers/adapters in your garage. The biggest problem you will find with calipers is that all of the late model 4 and 6 piston calipers are quite wide and they simply don't fit between the rotor and the wheel. The Kawi 2 piston unit doesn't have that problem and fits easily.


Mark

I noticed that kit, but I have NO idea of how much it costs, or the details (for example which year rotors I need to buy, what the newest calipers/MC I can buy off ebay for that kit).

If the kit he sells wasn't too pricey, it wouldn't be too bad of an option, since it would be ready to go and not some "DIY garage engineering project".

Ideally, I WOULD like larger rotors and calipers, but as you said, fitment may be an issue and I don't really have the means with which I can experiment (time, money, space, tools etc)

Do you by any chance recall the price on the F3 rotor and 4 pot caliper conversion kit, by Dan? (I think that's his name, right?)

[lumberjack]

The F3/CBR900 rotors aren't a direct fit. They have a 6 x 6mm x 74mm bolt pattern and most (all?) of the GS's have a 6 x 8mm x 78mm bolt pattern. You can redrill the Honda rotors with the Suzuki pattern, going in between the existing holes but that is as close as it gets from what I know of.

Have a look through this thread: http://www.thegsresources.com/_forum...d.php?t=140253

salty_monk has worked out the easiest brake upgrade going for the GS bikes, selling a simple kit to retrofit Kawasaki twin piston calipers and the F3 rotors onto most of the GS's for a significant improvement in performance. If you want more than that you will have to go it alone and work out bigger rotors and calipers/adapters in your garage. The biggest problem you will find with calipers is that all of the late model 4 and 6 piston calipers are quite wide and they simply don't fit between the rotor and the wheel. The Kawi 2 piston unit doesn't have that problem and fits easily.


Mark

Hey, so I looked into this a little bit and seems the following is what I've discovered:

GS750: 78mm 6 X 8mm
VFR800 (up to 05) and CBR900RN: 78mm - 6 X 6.5

Seems it would be a matter of just drilling those holes out a little bigger, rather than "in between" The spacing seems a direct match, just a matter of hole size

Now, if I will be needing a spacer (to distance from the wheel) or not, that's the question, but it seems the rotor should bolt up once the holes are enlarged, no?

Example of some cheapo rotor for CBR's

[Big T]

Read thru the Salty Monk thread until you find the CBR 600 (I think F2) which bolt right on

Cost?

I got my twinpots with hoses and pads for about $50. I used a Suzuki rotor and got the lower legs from someone here (you only need the two lowers). You're probably looking at $2-300 to convert. More when you swap the rubber for braided lines.

If you want massive braking, you can use a bandit or 90s Katana front end and retro fit your wheel



My experience is that the stock parts will allow you to lock the front wheel at 35 mph. Don't know if you need more than that

[mmattockx]

Do you by any chance recall the price on the F3 rotor and 4 pot caliper conversion kit, by Dan? (I think that's his name, right?)

I bought my rotors off ebay years ago, don't remember what they cost. Same for the kit, I bought it from Dan when he was still making them from aluminum. If you read through that thread I posted the price may be in there or you could PM Dan and see what he says.

Hey, so I looked into this a little bit and seems the following is what I've discovered:

GS750: 78mm 6 X 8mm
VFR800 (up to 05) and CBR900RN: 78mm - 6 X 6.5

Seems it would be a matter of just drilling those holes out a little bigger, rather than "in between" The spacing seems a direct match, just a matter of hole size

Those should fit after drilling the holes out to 8mm. The center hole on the GS is 56mm, how do the Honda rotors stack up there?


Mark

[lumberjack]

I bought my rotors off ebay years ago, don't remember what they cost. Same for the kit, I bought it from Dan when he was still making them from aluminum. If you read through that thread I posted the price may be in there or you could PM Dan and see what he says.



Those should fit after drilling the holes out to 8mm. The center hole on the GS is 56mm, how do the Honda rotors stack up there?


Mark

I'll need to read into that, the center hole size, but I can't imagine that being too much of an issue (either they're going to be bigger, or a smidgeon smaller which can be lapped out by a shop)

From what I can tell, it's 58mm on the inside diameter. 17mm offset, if I am looking at the right ones. With the GS being 56 (or 52 in the 1980s one), then we're good by 2mm or more

I don't mean to be a d*ck, since I am new here, and Dan did a HUGE service to the community by making those adapters.... but is there any other type of caliper out there that would work, that wouldn't (and I apologize here) look so ugly with a HUGE adapter like that?

Is there any way to make that adapter smaller/skeletonized?

I mean, I saw something like this while scouring the web and just thought "WOW now THAT is clean" --> Using RC51 rotors and much nicer calipers:



The issue with RC51 rotors is that the spacing is 94mm, so you'd need adapter for the rotors themselves (which is evident in the photo I think - you can see the central adapter with the 78mm pattern bolts, and then the 94mm RC51 bolts mounted to that - costly probably, but my god it's sexier!)

And then I saw this one, GT750 hub, CBR rotors and SV650 calipers, but since there was no adapter shown, I can only imagine this person used Dan's style one, since it's essentially the same setup (and I WILL ADMIT that based on your evidence that the brakes are plenty powerful with the below setup, then I'd be happy, I just need an adapter that isn't so bulky!):

[mmattockx]

I don't mean to be a d*ck, since I am new here, and Dan did a HUGE service to the community by making those adapters.... but is there any other type of caliper out there that would work, that wouldn't (and I apologize here) look so ugly with a HUGE adapter like that?

Is there any way to make that adapter smaller/skeletonized?

The adapter is pretty small in your hand. Anything else is untested and you have to figure out the bits yourself. If you don't have cheap access to machine tools and the skill to run them then the price gets out of hand pretty fast when you are tinkering away in the garage.

I mean, I saw something like this while scouring the web and just thought "WOW now THAT is clean" --> Using RC51 rotors and much nicer calipers:

That caliper would be pretty tough to fit, there really isn't much room between the rotor and the wheel spokes. You would have to space the rotor out as close to the fork lower as you could get it without interference and mount the caliper to suit.

As a random test, I took a set of Nissin 4 piston calipers that I have and test fit them over the OEM rotor on my 1100E and there is 2-3mm of interference with the wheel spokes. There is about 5-6mm of clearance between the rotor and the fork lower, so it might just work if the rotor was spaced out to within 1mm or so of the fork lower.

The issue with RC51 rotors is that the spacing is 94mm, so you'd need adapter for the rotors themselves (which is evident in the photo I think - you can see the central adapter with the 78mm pattern bolts, and then the 94mm RC51 bolts mounted to that - costly probably, but my god it's sexier!)

The good thing about needing an adapter is you can build in the rotor offset you need. If you are willing to make an adapter then there are lots of 320mm rotors available on ebay.

TBH, since you are wanting a project bike with fancy brakes and no ugly adapters you may well be getting into the money range of doing a front end conversion from a modern bike. You get bigger fork tubes, better suspension performance, much better brakes and 17" wheels with radial tires all in one package.


Mark

[Steve]

I am going to back up a bit and answer a few of your original questions.

1. RE: fork legs. I definitely need some dual disc forks legs (stanchions + legs, to just slide into the current trees). I would like to know, for NON-leading forks (so axle directly in line with the fork leg), what years and models should I be looking for? For example: Can I use 1981 GS750 legs on my 1978? (35mm ones I believe, that I have) OR must I stick to 1970s?

Can I use GS550 legs? GS1000? I am so confused by all this compatibility!

2: Slotted rotors: I can't for the life of me, find used Suzuki GS750 slotted rotors for a 1978. They're all 1982 (which are 10 7/8" across, not 12ish" like the 1978 ones). Am I really stuck using SOLID discs, as opposed to slotted?

3. Are there any NON-suzuki rotors (read as: BIG rotors, since I will be having custom adapters made eventually for modern calipers) that fit up with the GS750 hubs? I remember someone saying CBR900RR rotors... 6 bolt pattern, that works with the hub WITHOUT an adapter, or maybe someone makes a very basic "ring" type adapter to bring a large "flat" rotor away from the hub, closer to the fork leg? (since the factory GS rotors are offset, and a lot of new one aren't, from the 90s and on)

4. How safe will I be using the factory single disc wheel/hub (that 100% sure has 6 threaded holes tapped for a second disc - saving me the effort of finding another spoke wheel!) with a dual disc setup? I am 99% confident it will be fine, but I could be wrong?

1. As a general rule, the L models will have the leading axle. The exceptions to that are the '80-'81 750E and 1100E.

That means that you can NOT use the '81 forks in your '79, at least not unless you change the triples, too, but then you would likely dent your tank when you turn the wheel to full lock.

2. The reason you can't find slotted rotors for your '78 is because Suzuki did not offer them until the '80 model year.

There were different sizes (and offsets) for single- vs dual-disk bikes and also for the rear, but I don't have any of those specifics.

3. I can't help you there, but apparently there are some who can.

4. You should be OK with your current wire wheel and two disks.

.

[lumberjack]

I am going to back up a bit and answer a few of your original questions.

1. As a general rule, the L models will have the leading axle. The exceptions to that are the '80-'81 750E and 1100E.

That means that you can NOT use the '81 forks in your '79, at least not unless you change the triples, too, but then you would likely dent your tank when you turn the wheel to full lock.

2. The reason you can't find slotted rotors for your '78 is because Suzuki did not offer them until the '80 model year.

There were different sizes (and offsets) for single- vs dual-disk bikes and also for the rear, but I don't have any of those specifics.

3. I can't help you there, but apparently there are some who can.

4. You should be OK with your current wire wheel and two disks.

.

Appreciate the concise reply from a fellow Canuck (and #4 is encouraging )

[lumberjack]

The adapter is pretty small in your hand. Anything else is untested and you have to figure out the bits yourself.

True, very true. Always go with the path of least resistance, yes?

As a random test, I took a set of Nissin 4 piston calipers that I have and test fit them over the OEM rotor on my 1100E and there is 2-3mm of interference with the wheel spokes. There is about 5-6mm of clearance between the rotor and the fork lower, so it might just work if the rotor was spaced out to within 1mm or so of the fork lower.

Holy moly, we're getting into "thickness of a hair" territory here!

Curious: Using the CBR 78mm bolt pattern, 296mm rotors with a 17/17.5mm Offset.. will I STILL be needing a spacer? Or are those a direct bolt on without need to distance them from the hub face?

The good thing about needing an adapter is you can build in the rotor offset you need. If you are willing to make an adapter then there are lots of 320mm rotors available on ebay.

See, I like the way you think ... haha I love unique one off stuff, getting to use bigger, scarier brakes ! HOWEVER... the cost is what frightens me the most. A lot, in fact. I am afraid a machine shop would charge like $300 just for adapters - I remember a family friend telling me he'd have to charge me $100 just to make a muzzle brake for a rifle, and that was AT COST as a favour....

TBH, since you are wanting a project bike with fancy brakes and no ugly adapters you may well be getting into the money range of doing a front end conversion from a modern bike. You get bigger fork tubes, better suspension performance, much better brakes and 17" wheels with radial tires all in one package.

I am stuck on, and stubborn to use those wire wheels. This is going to be a cafe project/brat bike eventually, and I really would like to get those big brakes on a wire wheel.

I HAVE heard of people getting a Bandit 600/1200 front end, and just adapting the hub bearings to accomodate a larger axle (since it's pretty standard stuff), however at that point, I have no idea how the conversion goes... I mean, do you have to do anything to your headtube? (I assume the steerer needs modding, etc)

I would think the Bandit front end is wider and has space for larger calipers with dual sided pistons

Also, in that photo I posted with the RC51 rotor and ZX6 caliper (the silver setup), apparently those are TITANIUM adapters... $$$$

It sure does look good, though...

[mmattockx]

True, very true. Always go with the path of least resistance, yes?

Well, that depends. I am a mechanical engineer and have access to machine tools and other specialized things so there are times I may take the hard road in order to get exactly what I want. If you don't have the time and resources to do that then taking the established road is probably the better option. At least you know where you will end up when it is finished.

Holy moly, we're getting into "thickness of a hair" territory here!

Yes, I wasn't kidding when I said there isn't much room. Your spoked wheels may be worse, too, because the spokes take more space than cast wheels do.

Curious: Using the CBR 78mm bolt pattern, 296mm rotors with a 17/17.5mm Offset.. will I STILL be needing a spacer? Or are those a direct bolt on without need to distance them from the hub face?

That depends, how are you measuring the offset? The F3 rotors I have measure 17mm from the mounting face on the hub to the outside face of the rotor. Dan's kit supplies an additional 4mm thick spacer that is needed to line everything up properly for the Kawasaki calipers.

See, I like the way you think ... haha I love unique one off stuff, getting to use bigger, scarier brakes ! HOWEVER... the cost is what frightens me the most. A lot, in fact. I am afraid a machine shop would charge like $300 just for adapters - I remember a family friend telling me he'd have to charge me $100 just to make a muzzle brake for a rifle, and that was AT COST as a favour....

If you can't do the machining yourself or have buddies that will do it for beer money then it is a very expensive proposition to do these things.

I am stuck on, and stubborn to use those wire wheels. This is going to be a cafe project/brat bike eventually, and I really would like to get those big brakes on a wire wheel.

In that case I would buy Dan's kit as a first step and know that it will work with no extra screwing around. Once you have it done and your bike is running then you can decide if it really bothers you and if you feel like investing the time, effort and $$$ it would take to go your own way.

I HAVE heard of people getting a Bandit 600/1200 front end, and just adapting the hub bearings to accomodate a larger axle (since it's pretty standard stuff), however at that point, I have no idea how the conversion goes... I mean, do you have to do anything to your headtube? (I assume the steerer needs modding, etc)

There are threads around about many of these swaps, but they are never a straight bolt up. You always end up needing spacers or adapters of some sort.

I would think the Bandit front end is wider and has space for larger calipers with dual sided pistons

Yes, that is one of the big advantages of the new front ends, they are intended to have wide tires, big brakes and the rest and are spaced accordingly. I have an early 2000's GSXR600 fork here and the tubes are spaced at 215mm instead of the 185mm that my 1100E uses. Even with the bigger tubes sizes on the GSXR fork that leaves almost 1" of extra space to fit calipers in without hitting the wheel.


Mark

[salty_monk]

The kit from me is about $85 snail mail to Canada. There are some reasons the kit is the way it is - most of these relate to cost (which seems to be important to you), ease of fitting & a large factor of safety.

The kit I currently have fitted is a little different but the factor of safety, specific parts required & amount of work do not make it practical as a forum wide solution.

The kits are now steel (cheaper, thinner / slightly smaller so less obtrusive & allow use of the stock bolts - finding metric bolts is not so easy here in the US).

There is info posted on all the rotor & caliper options or I can email them to you if necessary.

The newest calipers you will find that fit are 2006. (ZG1000 calipers - both sides or 250 caliper - buy two & use the parts to fit to an older left side from an EX500, ZG1000 or Ninja).

The newer Ninja / V strom, SV650 etc 2 piston brakes would fit from a thickness of caliper perspective but it is a much more complex bracket - time versus cost! Also those have two pistons the same size and are not such a nice caliper as the older one. The older one has 2 different size pistons & give a better lever feel.

There are some rotors that only need the bolts enlarging - that is true but they are generally rarer & again more expensive than the F3 ones and still need a ring behind them (the ring acts as a template/drilling jib to re-drill the F3 ones anyway). The cheaper Chinese ones weren't about at the time.

I have seen 4 piston brakes fitted. You need to space the rotor very close to the fork leg & put the bolts in from the back. The bracket is different - I wasn't happy with the setup I saw.
If you got Blackbird rotors or the very rare 320mm rotor you may get slightly more room but I still think it would be extremely tight.