Fork Oil


CB750 Enthusiast
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Des Moines, IA
So I drained the fork oil last night and replaced it... The manual said 6.5oz each fork, I got just barely over 6oz out of both of them. The bike rides WAY different now!


As a side note, the wife wasn't overly pleased that I used her measuring cup... apparently it's now my measuring cup, and she gets a new one!
As a side note, the wife wasn't overly pleased that I used her measuring cup... apparently it's now my measuring cup, and she gets a new one!
:laugh: Same here, I told her I'd wash it before I put it away, and she said never mind, just keep it. Guess she hadn't missed one of our strainers that I use for sifting blast media.
I used 10W30, manual said to use that or tranny fluid. I also used 1oz of Marvels Mystery Oil in hopes of de-gunking some of the gunk. Plans are to drain/refill in about a month.
Interesting, I thought it had to be Dexron ATF or fork oil :) Almost chickened out of doing mine after seeing some write-ups including removing most of the bar assembly to get to the air fittings. Yikes. Yours doesn't have that air fitting?
10W fork oil is the all around oil. 10-30 will stiffen up the damping a little bit...good for hard riding or heavier loads. I dont like ATF, it can cause fork seal leaks if they were marginal to begin with. It also is on the thin side and can cause really soft suspension compared to a good fork oil. Motor oil can be used but I like actual fork oil because it was designed to be used as a damping fluid and resists foaming better and is more consistent then regular oil.
Mine was easy, remove the caps with a crescent wrench, remove the drain plugs with a 10mm wrench, work the forks til the oil (sludge) stops coming out... I removed the springs and wiped them down, replaced and added the new oil. The caps were under slight spring tension even with the front wheel suspended, a bigger socket would have made getting the caps back on a lot easier.
Folks, please be aware the viscosity of the oil you use makes no difference on how hard bumps are felt. The oil controls how fast the wheel returns to the lower position. As the oil is pulled through the holes in the damper assembly. Your spring is what makes the ride smooth or not. I use a heavier oil as my '76' is a full tourer now. Vetter fairing W/lowers & radios, Lockhart oil cooler, KG Engineering rack, sissy bar, trunk & saddlebags, with a Markland trailer hitch From a GL1100. So with this weight I need a slower recovery time on my front end (12" overstock). FYI I have '81' CB750 SS rear shocks on it for more travel in the back (13.5" long instead of 12", & adjustable dampening). You can get progressively wound springs for these bikes as well.
Please feel feel to ask any CB750 SOHC questions you may have. I have had 30+ of these & still own 10. 2 chopped touring bikes, 1 dual on road off road, 1 cafe racer, 1 9' long chopper, 1 Jammer chopper & the rest are stock models. I just replaced the forks on the bike listed above.
If any one can offer advice it'd be greatly appreciated. I have a 1973 honda cb 750 four.
I have the rims true and balanced with new tires. The forks seals done and have 5 Oz of 15w fork oil. The bike despite my efforts bounces so bad at the front I can't ride it. Really sucks as it's running great.
If any one can offer advice it'd be greatly appreciated. I have a 1973 honda cb 750 four.
I have the rims true and balanced with new tires. The forks seals done and have 5 Oz of 15w fork oil. The bike despite my efforts bounces so bad at the front I can't ride it. Really sucks as it's running great.
You could try a lighter oil. Some use ATF instead of fork oil. Was it doing it before you did the seals? Here is some interesting reading for you from another thread. Confirm that the tires are seated properly on the rims and running true, again.

Forks could be suffering from Stiction... try this.

Method 1

Loosen the front fork hex caps, and then pump the forks with the brake on. That will center the wheel in the forks, if it is out of alignment. Then tighten the fork caps. Then, your triple trees (yokes) can be done, loosen the upper right pinch bolt and lower left, pump the forks again, (re-tighten the bolts) then do the lower right and upper left to take out any misalignment in the trees. Remember to tighten the first two bolts before loosening then other two, or your forks will slip up into your trees... There may be a method to do this in the SOHC manual, also.

Method 2

Start by jacking the bike up so the front wheel is off the ground; a half-inch or so will do it.

If the forks have been removed from the bike:

**1 **Set the stantion tube fork height level with the top of the the upper clamp, and then tighten the pinch bolts in stages to the proper torque. If you're not convinced that the heights are equal, slip the axle into place. If it doesn't glide smoothly through the forks, one leg is higher than the other, so readjust them until the axle slides through them with little or no effort.

2 Install the front fender-but don't tighten the bolts.

3 Install the front wheel and axle. If the axle threads into the fork, thread it in loosely; if it uses a nut, just snug the nut down by hand. Do not tighten the axle pinch bolts.

4 Spin the wheel as vigorously as you can and abruptly clamp on the brake. Holding the brake lever on, tighten the front axle

**5 **Lower the bike onto the ground, and, while holding the front brake, gently pump the forks a few times. You did remember to tighten those upper pinch bolts didn't you?

6 Tighten the lower clamp's pinch bolts, followed by the axle pinch bolts.

7 Tighten the fender bolts.

That's it bub, the forks are now aligned, but wait: there's more.

If you suspect the forks are tweaked but don't want to go through the whole shebang, there's a short cut.

Support the weight of the bike on the jack or center stand, and loosen the front axle. Remove the lock nut, and then try to slide the axle out of the fork. If it comes away with little effort, the forks are in alignment. If the axle has to be pounded out, it's a safe bet the forks are slightly tweaked. Of course that presumes the axle hasn't been rusted into place.

To correct a slight misalignment, loosen everything but the top clamp pinch bolts (you don't have to remove anything), and start at Step #3. Anytime the wheel is removed, perform steps #4 and #5: that'll center the wheel in the fork and provide better suspension and braking action.

Method 3

Here’s how to remedy. Keep in mind that the sequence and order of this procedure is very critical:

1. Start with the bike on a level concrete floor on the centerstand. Put a small floor jack under the front of the engine (with a very thin board to protect the engine). Jack up the bike just enough so that the weight is off the front tire. Warning: jacking beyond the point that the rear tire contacts the ground will lever the bike off the centerstand and cause a nasty spill.

2. For extra safety, run 2 tie-down straps down from the ceiling to the handlebars.

3. Loosen all of the following in this order but do not remove:

• Left side, front axle cap pinch nuts (left as viewed by the rider). There are 4 of these. Make sure you’ve loosened these 4 nuts enough so that pressure is off the retainer and the left fork lower (“slider”) is free to “float” relative to the axle. Test to make sure the slider can move side-to-side relative to the axle.

• All 6 of the bolts that secure the fender

• Top fork stanchion Allen bolts (secure the fork tubes to the upper triple clamp).

• Fork caps (just loosen slightly)

• Lower fork stanchion attach bolts (secure the fork tubes to the lower triple clamp).

4. Next, remove the fork caps to relieve the pressure from the fork springs.

5. Carefully lower the front of the bike with the jack until the fork is fully compressed. Be sure you have enough slack in the safety tie-downs to allow full compression. As the front end is lowered, carefully observe the action of the brake hoses and speedo cable to make sure they are not put into jeopardy by this extreme compression.

6. Tap the lower and upper triple clamps (stanchions) in several spots with a soft mallet.

7. Carefully tighten all of the fasteners in the following order. Very important: be sure the fork tubes are at the same relative height inside the triple clamps. Normally, they should be flush with the top of the upper triple clamp.

• Lower triple clamp pinch bolts

• Top triple clamp pinch bolts

• Left side axle pinch nuts

• Fender attach bolts.

8. This is a good time to make sure your fork oil is at the correct level. With the fork fully compressed and the fork springs removed, I run 160mm of free air space above the oil. This is a more accurate level of filling the forks than the factory suggests in the manual. Their method is approximately 6 oz when you drain the forks… 6.8 oz when you do a complete overhaul.

9. Raise the bike and replace the front springs. Loosen the top triple clamp pinch bolts again to reinsert and tighten the fork caps. Re-tighten the top pinch bolts.
I like all the good advice, but one important thing hasn't been mentioned. Have you had the front wheel spin balanced? If not, your hop could be right there. If the front tire is out of balance it will hop @ a particular speed. Take front wheel off & pull the axle & take to a bike shop with a spin balancer, not bubble. It should be under $20.00. The shop I worked @ had a nice Snap-on one.
Well, it didn't work. I replaced the oil with 10w. Followed option 3 from above post. It's still extremely bouncing in the front. I'm at a loss. I know the complete history of the bike as my dad bought it new. No layover, hard hits or accdents. Very frustrating as it use to be super smooth to ride.
How stiff do the front forks feel? What type of 10 weight did you use? I use a 5w fork oil in mine. When they balanced your tire were they able to spin it up to speed a bit to see how smooth it runs? Where in BC do you live?
I would take my forks apart and clean them. If your front suspension is simply bouncing up and down, it sounds to me like your fork fluid isn't traveling between the chambers like it is supposed to, and hence you have no dampening, leaving your springs to do all the work. And as a result, you are bouncing up and down.
My two cents.