Topic: '78 750F brake woes...

[The Dude Abides]

I recently had to take off my front wheel to install a new speedo gear drive. I didn't mess with my brakes at all while the wheel was off....Ever since i reinstalled my wheel, it looks as though  the rotors are sitting crooked when they pass through the brake calipers, and it sounds like rubbing metal when it's rolled. It's almost like my wheel is lopsided now or something. Has anyone had this problem before? all i did was take the wheel off and put it back on! The caliper doesn't scrape/rub all the way around the rotor, it only scrapes/rubs one one portion of the rotors....

I've done some searches in regards to brakes and bleeding the MC, but i thought that since it wasn't messed with i wouldn't need to bleed it, or if that would even help my situation at all......I'm still new to this and would greatly appreciate any input at all you guys have to offer. Thanks!

[madmtnmotors]

Sounds like the axle is not seated properly at the bottom of the fork. Inspect the axle as it sits, then take the axle caps off and inspect for correct orientation. They often have an "F" (front) stamped on them and often an arrow as well. Set the flat side (top) of the axle cap on a flat surface and note that one side is longer... this side goes towards the front and gets torqued down first. The rear cap bolt gets torqued last which sould leave a gap at the rear. Check the axle seat in the lower fork leg and make sure you didn't pinch some flotsam or jetsam in the axle seat.

Keep us posted.

[flybox1]

^ yes!
snap a picture and post it.

[madmtnmotors]

While you're at it, inspect the fork caps at the top of the tree. If one fork was loose it may have slid down in the tree.

[The Dude Abides]

After inspecting the axle caps, there doesn't appear to be ANY sort of gap in them at all....so i must have installed them incorrectly. I'll try and get them apart again this afternoon and look at them closer. Also, can the axle itself be installed backwards? If it's possible to do it....i'm sure i probably did it............

[madmtnmotors]

After inspecting the axle caps, there doesn't appear to be ANY sort of gap in them at all....so i must have installed them incorrectly. I'll try and get them apart again this afternoon and look at them closer. Also, can the axle itself be installed backwards? If it's possible to do it....i'm sure i probably did it............

If you split the gap between the front and the rear of the cap then you might not notice the gap (it's not much) and would not necessarily cause the symtom you describe. Did the speedo drive seat properly? It must engage the drive tangs correctly or you will likely bend them if they don't (they are easily straightened) and could be the source of the "grinding" noise.

It may very well be possible to install the axle backwards. This could possibly affect the wheel offset causing your rotors to drag. I believe the threaded end of the axle (where the axle threaded cap goes) is on the same side as the speedo drive (to the driver's left).

[The Dude Abides]

the speedo drive is seated properly as far as i know, i've been riding it this way for a few weeks and the speedo works fine, the scraping sound is definitlely coming from the rotor/brakes rubbing. If i slowly push it forward, it only rubs at a small spot on the rotor  per every turn of the wheel....

[Pat_at_APE]

Did you use the shim in the left (as you sit on the bike) brake disk to caliper before you tightened the left fork cap/axle bolts?  On the twin disk F model you need adjust spacing between the forks so the brake calipers are spaced correctly to fit the rotor locations.  These instructions are in the "F" only instructions found with factory manuals on this site.

Regards,
Pat at APE
77 CB750F owner

[The Dude Abides]

If you're talking about the shims that go on with the brake pads, i believe i re-installed those correctly. yesterday i noticed one of my axle caps was installed backwards ( arrow pointing to rear of bike) so i fixed it, but still doing the same thing......I'll have to get it back up on the lift this weekend and take it all apart and look at it again. I'm installing a new MC as well. so that may help also. I'll look up the instructions for the fork spacing on the "F" model and check that out as well. Thank you all so much for the help. If it wasn't for this site and my manual, i'm not sure what i would do!

[Pat_at_APE]

Not the shims behind the one brake disk but using a feeler gauge to set clearance. 

On this site there are manuals available.  One is specific to the F and includes special instructions.  Go here (link below) and download the F/F1/F2 Supplement (middle one listed) and read the section on installing the front wheel: 

http://www.sohc4.net/index.php/cb750/cb750f/cb750f-books-manuals/

I hope this explains it for you and solves your issue.  Good luck.

Pat at APE

[The Dude Abides]

Not the shims behind the one brake disk but using a feeler gauge to set clearance. 

On this site there are manuals available.  One is specific to the F and includes special instructions.  Go here (link below) and download the F/F1/F2 Supplement (middle one listed) and read the section on installing the front wheel: 

http://www.sohc4.net/index.php/cb750/cb750f/cb750f-books-manuals/

I hope this explains it for you and solves your issue.  Good luck.

Pat at APE

Thank you for this. I must have missed this my first time looking through the manual. That's exactly what needs to be done, because my rotor is passing through the caliper crooked and not straight on like in the diagram. I guess i need to go pickup a feeler gauge.....

[Pat_at_APE]

You will need those feeler gauges again when you set your valve lash on your next tune up.

Good luck!  I hope it gets you on the road.

Pat at APE