Author Topic: CB750 to GL1000 front end conversion UPDATED pics. (Read 27297 times)

Jinxracing · « **on:** December 30, 2006, 11:52:36 AM »

I know that this has been discussed and it's fairly common knowledge that a GL1000 front end will bolt up directly to a CB750, but I wasn't able to find any pictures to that effect here on the forum. So, here are some photos.

The bike is a CB750 K1 (build date 8/70), the trees are from a '75 GL1000, the fork legs are '75-'77 GL1000 pieces and were a freebie from Noel here on the forum...thanks dude!

I installed a set of All Balls tapered bearings at the same time as the swap, and it went without a hitch. Note: Make sure to save some of the balls and the stock lower bearing pieces for measurement when fitting the new bearings or you'll be digging through the trash looking for them with your ass in the air (don't ask me how I know this

). The rubber seal on the lower bearing was particularly impressive; it snaps into the lower race and fits very tightly up into the bottom of the steering head when it's all assembled. Another note: when removing the stock races from the steering head, wedge a rag or something similar up into the steering head alongside the punch/drift to hold it in place. I held it in my fist while rearing back with a hammer like Jimmy Connors returning a serve at Wimbledon...amazingly, my thumb's not broken. However, children wept and birds took flight as a result of the cussing that followed.

The steering stems appear to be identical on the CB750 and GL1000. In the side by side pics, the left stem is the CB750 and the right one is the GL1000. The top view pic really shows the difference in fork leg spacing and diameter. One thought...is it just me or does it look as though the GL1000 trees have signifigantly less trail than the CB750 pieces? I assume that the GL1000 would have more rake to offset this, being a touring bike and all, and I know that the CB750 is already known for having short trail numbers as stock. I'm wondering if I should be shopping for a steering damper before I even put it on the road.

The only small issue is that with the wider front end and different steering stops on the GL1000 combined with my '76 CB750F tank, the fork tubes are hitting the tank. Adding a little meat to the steering stops should fix that just fine. I have no idea if they would hit a stock K tank since the bike didn't come with one.

maksuttt · « **Reply #1 on:** December 30, 2006, 12:47:35 PM »

Looks good. Which wheel & caliper(s) you gonna use? CB or GL?

Jinxracing · « **Reply #2 on:** December 30, 2006, 01:02:31 PM »

I'm going all GL1000...I've got a stock '75 wheel and rotors, and some '76 calipers. Lots of polishing to do first though.

eurban · « **Reply #3 on:** December 30, 2006, 01:38:15 PM »

In 77/78 Honda brought the 750s front fork tubes about 10mm closer in the front to back direction to the steering stem reportedly to improve handling. The GLs seem to incorporate this thinking. Your stock cb750 rotors do not have the same offset (and maybe diameter too . . .I can't remember) as the Gl ones so you should plan on locating a set of Gl ones for your project. As you mention you will certainly be using the GL calipers as the the stock cb750 caliper will not mount up to the GLs fork leg. Even if it could mount up, you really wouldn't want to use a stock leading (caliper in front of fork leg) 750 style caliper / arm assembly as it has a good deal more built in slop than the slightly more modern trailing style GL one. On my 78 750 K with its GL front end, I used a rebuilt CB750f2/f3 style master cylinder (designed for dual discs) in combination with braided brake lines. This setup provides very good braking, vastly superior to the dual disc setups using stock CB750 calipers that I have ridden. Don't spend your time doing this swap unless you use a dual disc sized master cylinder! On my 78K with the stock fat tank and non stock drag bars, the thottle cable connectors at the switch gear would contact the tank with the GL steering stops left stock. I padded out the stops just enough to prevent contact. Turning radius is not particularly good with this setup however. Have fun!

Jinxracing · « **Reply #4 on:** December 30, 2006, 01:49:59 PM »

Quote from: eurban on December 30, 2006, 01:38:15 PM

Your stock cb750 rotors do not have the same offset (and maybe diameter too . . .I can't remember) as the Gl ones so you should plan on locating a set of Gl ones for your project. As you mention you will certainly be using the GL calipers as the the stock cb750 caliper will not mount up to the GLs fork leg. Even if it could mount up, you really wouldn't want to use a stock leading (caliper in front of fork leg) 750 style caliper / arm assembly as it has a good deal more built in slop than the slightly more modern trailing style GL one. On my 78 750 K with its GL front end, I used a rebuilt CB750f2/f3 style master cylinder (designed for dual discs) in combination with braided brake lines. This setup provides very good braking, vastly superior to the dual disc setups using stock CB750 calipers that I have ridden. Don't spend your time doing this swap unless you use a dual disc sized master cylinder!

Maybe I wasn't clear in my previous post...The entire front end is all stock early GL1000: master cylinder, trees, forks, calipers, wheel, rotors, valve stem cap, etc.

Noel · « **Reply #5 on:** January 17, 2007, 07:48:02 PM »

Goodonya, mate! You'll be riding it it no time. Coupla years, tops.

Where did you find a replacement top cap for that one fork leg?

xtalon · « **Reply #6 on:** January 31, 2007, 09:53:45 AM »

Jinx, good luck and keep the pictures coming as I am hopefully right behind you on this conversion.

Eurban, thanks for sharing your insight and experience!

--xTalon

ProTeal55 · « **Reply #7 on:** January 31, 2007, 09:56:37 AM »

Looks good - but will look even better when complete

dusterdude · « **Reply #8 on:** January 31, 2007, 10:56:22 AM »

just for informational purposes,the 750 spoked wheel is the same as the 75-76 gw wheel.

Jinxracing · « **Reply #9 on:** January 31, 2007, 12:28:28 PM »

Quote from: Noel on January 17, 2007, 07:48:02 PM

Goodonya, mate! You'll be riding it it no time. Coupla years, tops.

Where did you find a replacement top cap for that one fork leg?

Never did find a replacement cap...going to be turning up a couple on the lathe out of brass.

hahnda · « **Reply #10 on:** January 31, 2007, 02:22:52 PM »

More Offset = Less Trail = Responsive Steering
Less Offset = More Trail = Slower Steering

No need for the dampener since this mod actually increases your trail

Trail =(Tire Radius*(TAN(Rake Angle*PI()/180)))-(Offset/(COS(Rake Angle*PI()/180)))

Jinxracing · « **Reply #11 on:** January 31, 2007, 03:24:46 PM »

Quote from: hahnda on January 31, 2007, 02:22:52 PM

More Offset = Less Trail = Responsive Steering
Less Offset = More Trail = Slower Steering

No need for the dampener since this mod actually increases your trail

Trail =(Tire Radius*(TAN(Rake Angle*PI()/180)))-(Offset/(COS(Rake Angle*PI()/180)))

Ahh, just drew it out on paper and you're right, I had it backwards. That had been bugging me for awhile...now the world makes sense again!

eurban · « **Reply #12 on:** January 31, 2007, 06:02:11 PM »

OK, I give up . . . How do you (Mr JinxRacing) get away with a multitude of large pictures in your original post when I have to shrink down a single picture so small that it is almost useless inorder it meet the file size requirements for posting?

???Maybe I need to be more of a computer Geek??

xtalon · « **Reply #13 on:** January 31, 2007, 07:49:27 PM »

Quote from: dusterdude on January 31, 2007, 10:56:22 AM

just for informational purposes,the 750 spoked wheel is the same as the 75-76 gw wheel.

Dusterdude,

I thought CB750K had a 3.25 x 19 front rim and the GL1000 had a 3.5 x 19 front rim.

--xTalon

hahnda · « **Reply #14 on:** February 01, 2007, 06:34:13 AM »

Quote from: eurban on January 31, 2007, 06:02:11 PM

OK, I give up . . . How do you (Mr JinxRacing) get away with a multitude of large pictures in your original post when I have to shrink down a single picture so small that it is almost useless inorder it meet the file size requirements for posting????Maybe I need to be more of a computer Geek??

What you need to do is find a place besides this site to upload them to. I like photobucket. Its free, its fairly easy to organize, and it gives you the link to drop directly into a message to see the pics. If you upload direct from your computer to the sohc site you will be limited to the amount and size of pics.

Jinxracing · « **Reply #15 on:** February 01, 2007, 07:51:53 AM »

Quote from: eurban on January 31, 2007, 06:02:11 PM

OK, I give up . . . How do you (Mr JinxRacing) get away with a multitude of large pictures in your original post when I have to shrink down a single picture so small that it is almost useless inorder it meet the file size requirements for posting????Maybe I need to be more of a computer Geek??

I use PhotoBucket (www.photobucket.com) to host the images, then when creating a post use the "insert image" button. Works like a champ!

Regarding the front rims...I haven't pulled the tires off yet, but aside from the big difference of the GL1000 rims being aluminum, it does look to be a tad bit wider. I'll measure the fronts and rears once the tires come off and post here.

Jinx

xtalon · « **Reply #16 on:** February 01, 2007, 10:05:23 AM »

Quote from: Jinxracing on February 01, 2007, 07:51:53 AM

Regarding the front rims...I haven't pulled the tires off yet, but aside from the big difference of the GL1000 rims being aluminum, it does look to be a tad bit wider. I'll measure the fronts and rears once the tires come off and post here.

I think what Dusterdude said is correct if you have a '77-78 CB750K, but not if you have a '70-76 CB750K.

Can you or someone else confirm that the GL1000 forks are indeed 37mm diameter. I read it one place, but wanted to make double sure before I ordered additional parts.

Thanks in advance!

--xTalon

dusterdude · « **Reply #17 on:** February 01, 2007, 11:16:48 AM »

when i looked at parts fiche,the hub number is the same for both.

bill440cars · « **Reply #18 on:** February 01, 2007, 12:28:45 PM »

"Can you or someone else confirm that the GL1000 forks are indeed 37mm diameter. I read it one place, but wanted to make double sure before I ordered additional parts.
Thanks in advance!"

--xTalon

Quote

Hey xTalon, if you'll check out ohiocaferacers.com, you'll find a list of fork tube sizes for lots of different bikes of different years. It a good reference point. LOL

Later on, Bill

dusterdude · « **Reply #19 on:** February 01, 2007, 01:31:45 PM »

they most definetly are 37mm

Jinxracing · « **Reply #20 on:** February 01, 2007, 01:54:25 PM »

Yes, they're definitely 37mm. I've measured them about a dozen times over the past week while machining up some headlight bracket shims.

Jinx

xtalon · « **Reply #21 on:** February 01, 2007, 06:39:26 PM »

Guys, thanks for the info on the GL fork diameter. I must have spent 1/2 day trying to find the answer yesterday and searched everywhere with no luck.... here, google, everywhere. I should have just asked here, but I didn't want to get jumped on for something that's probably common knowledge to everyone here.

Bill, thanks to the link to the site. Cool site and some cool bikes. Love the gas tanks.

--xTalon

Noel · « **Reply #22 on:** April 10, 2007, 10:52:04 PM »

How about some updates? Or did you finally come to your senses?

Jinxracing · « **Reply #23 on:** April 11, 2007, 12:41:40 AM »

Updates? Well, let's see...

I ditched the CB750F tank in favor of something a little cooler, got the GL1000 front end on so it's up on its wheels, the metric thread gauge arrived in the mail the other day and the brass is on order so I can get those fork tube caps made, I trimmed down a stock GL1000 fender to look a bit more sporty and it came out surprisingly well, motor's cleaned up and just about ready for its maiden fitment into the frame, and lots more. I'll post some pics later this week.

Cold beers are in the fridge whenever you feel like dropping by Noel!

Jinx

eurban · « **Reply #24 on:** April 11, 2007, 06:59:51 PM »

Here's a older shot of my 78K showing off its Gl front end including swiss cheese drilled rotors and stock Gl whale tale fender.

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Author Topic: CB750 to GL1000 front end conversion *UPDATED* pics. (Read 27297 times)

Author Topic: CB750 to GL1000 front end conversion UPDATED pics. (Read 27297 times)