Topic: GL1000 to CB750 front end swap

[fredmalito4]

I saw mentioned that a GL1000 front end can swap on to a CB750 to give it a modern braking system. Does everything interchange, I.E. GL steering stem and bearings fits CB neck, CB fender fits GL forks, CB handlebars and instruments fit GL upper tree, same length tubes, etc.

If so, I'll need the wheel, brake hoses/tee, calipers, trees, forks, and... anything else? Thanks!


Fred

[seanbarney41]

yup, you got it.  I don't know if I would call the GL brakes "modern" but they are certainly better than a cb750.  The cb fender does not fit the gl forks.  Also, you will have some fine tuning to do to get back proper handling.  The springs for the gl are too stiff for the cb and the fork legs are about 2" too long.  If you can, grab the gl wheels, as they have nice aluminum rims.  The front wheel bolts right up with an identical hub.  The rear will lace right up to the cb750 hub using the gl spokes.

[fredmalito4]

I was considering the ‘78 front end, but the length would be an issue. I want this to be a stealth upgrade. I want this to look as stock as possible.

Any other dual disc options? What about DOHC 750 Front ends?

[seanbarney41]

What are you trying to gain by a front end swap?  If it is better brakes, basically every Japanese company had better brakes than Honda by about 1975.  But suspension was basically inferior to Honda, except maybe Suzuki.  Just about any front end can be swapped with the right bearings and possibly a steering stem change.

[fredmalito4]

I’m looking for better braking options with caliper mounted to slides like a car, not the nonsensicle adjutable bracket caliper on my 78 K model. I want it to look like it should be there, except to those really in the know, as this is a restoration/restomod project.

[seanbarney41]

The easiest thing to do is to get your stock front brakes working as good or better than new.  It can be done.  Thousands of do it your-selfers have done it.  If you can't get the stock parts to work properly, complicated parts swaps are just gonna make matters worse.

Once you get the stock stuff working properly we can talk about improvements.

There just is not any easy or cost effective swaps that look stock for these bikes imo...I am assuming you are not gonna be happy with running cast wheels and you are relatively inexperienced motorcycle mechanic.

[fredmalito4]

I  am a very experienced mechanic, at least in the automotive world. That may be why I hate the stock setup, as they are such a foolish design.

[fredmalito4]

 I’m also not concerned about cost, I’m more concerned about fitment.

[seanbarney41]

The difference between modding bikes and modding cars is mainly one of production numbers.  There is not a large enough demand for bolt on set ups, so you will have to do more research, design, and fabrication yourself. 

Let's go back to the "simple" gl1000 swap.  First you have to find a donor front end, which of course, is also 40+ years old at this point, and will need total rebuild, from fork internals to brake seals.  It is also more complex(lots more parts to replace than a cb750), so you are gonna spend about $400 to get that frontend working as a stock gl1000 front end on a cb750.  Brakes will be much improved.  Suspension will be very hard unless you weigh more than 250lbs, and your bike will turn very slowly due to the excessive fork length or slide the tubes up in the trees and your losing too much suspension travel and it looks like crap.  Also several other problems such as fender fitment and getting some gauges mounted and reasonable amount of turning radius without hitting the tank.  Of course, all of this can be fixed, but will it look stock enough for you? and will require a few hundred more $$$

If I were you, I would look at other swaps...maybe from a Suzuki GS750?...most of the really good ones make the use of a spoked wheel either very difficult or expensive or both

Another option would be adapting better calipers to the stock rotors and fork legs.  Got access to a vertical mill?  Your gonna be looking at a lot of vintage road race bikes for ideas and info here.  Fortunately, you will have a few more options available that would not meet vintage class rules.

And I am not trying to insult you here, but at the end of the day, and reading your other current thread, you have not managed to get the stock stone axe simple brakes working properly on your own bike...

[Bankerdanny]

IDK, the design is pretty straight forward. I upgraded my 550 with a thinned and drilled rotor and braided hose. I found the feel and function to be much improved.

But if money isn't an issue then just swap in modern upside down forks. Cognito Moto sells triples and a hub that will allow you to use a spoked rim with the modern fork and braked.

[fredmalito4]

Sean, the reason that this was an idea in the first place is because I am going to have to rebuild the front end on this bike anyway,  so if I could instead source a replacement that would serve me better that would be in my best interest. Also, it appears that the problem with the front brake has been solved; someone at one point prior to me owning this bike put the fender mount between the fork and the brake bracket, and that apparently that is not the way it supposed to be mounted. That is probably going to solve all my woes, and I can’t for the life of me  figure out why asking a question about a bike that I have never owned in stock format would lead anyone to believe I wouldn’t know what I’m doing. I am used to these as a chopper, where everything is hand fabricated  and stock stuff gets thrown up on eBay.

Danny,  thank you for that suggestion, I will look into it.

So if the GL front end is not a direct swap, what about the later DOHC CB750s? Will their forks work?

[seanbarney41]

Sorry Fred.  As mentioned before, I was not trying to insult. The internet is full of misinformation and I don't know you personally.  Working on cars can be much different.  I worked on cars before I got into bikes also, and found the learning curve to be steep.  Just remember a car missing a wheel still has three, a bike missing a wheel?...!  I know, too obvious.

later DOHC bikes should have some easy swaps but it will be difficult to run a spoked wheel as they all came with Comstars

also, if money is not an issue, I think the gl1000 swap is a good one.  I have done one myself, and I just wanted to point out that it isn't as easy as it sounds and the results may not look very stock.  It was a lot of work and cost more than I thought it would, but I feel the results were worth it.
DSCN1081 by Sean Barney, on Flickrthis bike is the most dialed cb750 I have ever ridden, and that is a lot of cb750's

[slikwilli420]

Sean's bike is a classic example of a nicely done GL swap. Take his advice and if you wanted to go even further with braking performance, you could adapt some early 2 piston calipers from Grimeca, Lockheed, etc and have period-racing-grade braking power up front and would be a very far cry from the stock parts you started with. The GL forks need to be set up correctly then you will have a very nice front end.

[gschuld]

The gl1000 front end is a good option, been done plenty of times.

I considered it myself, and did my research and acquired a compete 76 gl front end for the swap.  One main thing that discouraged me was the extra bulkiness all around.

As mentioned earlier, the trees are wider spaced, the fork legs are 2” longer, the fork legs are beefier, and the calipers looked huge by comparison.

I personally prefer a more stock looking (perhaps OEM style sleeper) bike.  I just couldn’t justify the extra beefiness of the GL1000 front end.  FWIW, the stock GL1000 front end is also noticeably heavier(I don’t have my notes on hand, sorry)

For a road racer where you benefit from the extra fork tube/slider rigidity and big brakes and don’t mind dealing with the heftier looks and alterations needed to make it work, it’s proven and works just fine.

Same for a street bike of course.  But considering that many of the cb750 road racers run with factory forks and dual disc factory type brakes/rotors(or vintage dual piston calipers), it’s hard to argue that a GL1000 front end is needed for most applications.

If you are happy with the handling and condition of your current front end, I’d consider converting it to a dual disc front with factory parts, or go further and upgrade to dual piston calipers.

George

[fredmalito4]

One way or  the other I’m going into this front end to rebuild it. Adding a second disk andcaliper sounds fine to me. What year and model bike do I need to look for those parts from?

[Bankerdanny]

You want 750 parts and I believe that pretty much any year SOHC4 will do. There is a guy in Wisconsin who has a business called Godffrey's Garage (I'm trying to find the link to his online store) who will sell you the complete package plus a modified speedometer drive that is necessary when you add the 2nd disk.

The thinned and drilled rotor on my 550 came from him and I drove up to his place and picked it up in person. I highly recommend him. I know that Sean got parts for the dual disk setup on his 750F, which has a stock front end, from him.

[slikwilli420]

George makes some good points. The GL front end is heftier than a stock, by how much, I don't know. I went to some great lengths to shed weight off the front end of my race bike with GL forks, like cutting down the other brake caliper lug (only one caliper allowed), hollow 20mm axle and aluminum damping rods. They are heavier but you cannot beat the stiffness of that front end. Its made for a 660lb touring bike and the wide axle clamps make for a very rigid front end.

[fredmalito4]

I looked up Godfrey’s garage, I found a number, and gave him a call. That is exactly what I was looking for! I am sending him my whole front end minus the wheel and he is going to shave and drill my rotors, modify the calipers for banjo bolt, set me up for the second caliper bracket for the right side, rebuild the forks because I’m too lazy to do it, and provide a source for braided hoses to match the mods. He also mentioned that he likes ditching the adjustment screw completely as it is unnecessary.

 Should’ve asked him if he had a source for new headlight mounting ears too…

 Thank you all for your assistance,  I truly appreciate it.

[slikwilli420]

I looked up Godfrey’s garage, I found a number, and gave him a call. That is exactly what I was looking for! I am sending him my whole front end minus the wheel and he is going to shave and drill my rotors, modify the calipers for banjo bolt, set me up for the second caliper bracket for the right side, rebuild the forks because I’m too lazy to do it, and provide a source for braided hoses to match the mods. He also mentioned that he likes ditching the adjustment screw completely as it is unnecessary.

 Should’ve asked him if he had a source for new headlight mounting ears too…

 Thank you all for your assistance,  I truly appreciate it.

So... no swap to something that will be superior in every way?

[M.Henry]

Can you PM the number for Goddfry's garage? The modification from Goddfry's garage sounds right along the lines of what I may be interested in doing to my bike too. To bad I likely won't get to drive up personally to pick it up though. Looks like a nice garage of work.

[RJ CB450]

If you are not concerned about single pot calipers, I highly recommend first year Nighthawk parts.  Still CB chassis, but with a beefed up suspension and brakes.  Dual rotor, two piston calipers.  And still the CB chassis so hopefully rake is still similar.

Drawback is you would be going to comstars.

[fredmalito4]

https://www.linkedin.com/in/jeff-stephens-6050721a

[M.Henry]

If you are not concerned about single pot calipers, I highly recommend first year Nighthawk parts.  Still CB chassis, but with a beefed up suspension and brakes.  Dual rotor, two piston calipers.  And still the CB chassis so hopefully rake is still similar.

Drawback is you would be going to comstars.

What suspension changes are present that make sit beefed up? That braking set-up does sound great though.

[RJ CB450]

Not sure the details on the 750, but to compare in terms of the SOHC 650, the 650SC (Nighthawk) front forks are 2mm larger diameter, and the brake MC is also a bigger bore.  I have the 650 nighthawk, is what brought me here and how I learned about this as it can create problems since many cb650 parts do not account for SC variations.

I did a lookul over lunch here to check out the nighthawk 750s.  I didnt compare all parts, but they look to use a similar build to the CB750f.  Same rebuild parts, seals, etc.  Similar, but not exactly same part number.

I am actually reminded of a few added variations as well involving both the nighthawks and the gl1000.

You gotta be careful getting used GL1000 if you ride lots!

My friend is a 1000 enthusiast and restorer.  The lower fork housings dont have a secondary slide bushing.  Single slide so bottom tubes can wear bad, essentially can lead to forks not being rebuildable.  So could end up buying forks that are scrap, but you do get wire spoke wheels.

The nighthawk as I said shares with the 750f but has an extra I forgot.  Take a peek and compare the schematics.  The CB750SC (82,83) have extra parts.  They have anti dive dampening for front fork tubes whereas the 750fs had sportier forks, but did not have the anti dive.

Alas weather is till ugly here.  It would be interesting to see if could run the GL wheel in the dualcammer 750 forks.  I could measure my friends gl1000 rotor bolt pattern, axle and spacing.  When riding, I often run into a guy when I stop for coffee who rides an 82 750sc.  Dont have his contact though.

EDIT:  GL1000 clarification.  What I meant, if I remember right, is that because it only has the one slide bushing, it is a permanent part of the upper tube and not replaceable.  So upper tube needs to be replaced.  Again, memory thinking back, but hopefully sort of get what I am getting at.  I can get the full details if you want.

[Bankerdanny]

The fork tubes are wider, which will make for a stiffer front end, but I don't think that the difference will be noticeable for the vast majority of riders. If you live in a place with lots of curving roads or if you want to build your bike into a tourer with a big Vetter on the front then there is a definite advantage, but otherwise a decent fork brace and adding a 2nd disk to the existing fork gets you all the upgrade you can really take advantage of.

As far as the master cylinder goes, that is easily replaceable without going to the effort and expense of replacing the entire front end.