Fork Oil Capacity

[raychappo]

Hi.
Does anyone know the correct oil capacity for the forks? I've read in the manual that it should be 160ml but that is for the screw in type top of fork.
Mine have the circlip type retaining top and looking through the GT750 forums it suggests anything from 250ml to 266ml per fork. I've been using 160ml in each leg and the forks definitely feel wrong, it under damped and 'noisy'.
Any suggestions?
Thanks
Ray

[timpa136]

Ray,

Actually, RE5 forks are 150cc. I am pretty sure you have 1975 GT-750 forks so I would say go with the GT specs on oil. Low oil can wear the internal slider bushings, too. If I hear the exact cc,s I'll follow up.
Regards
Tim

[raychappo]

Thanks Tim

[wayne]

From the 1975 GT750 owner's manual (forks have a plug with circlip at top):

160 cc of ATF or 10/30 oil.

The genuine RE5 fork works better than the GT of the same year. The difference is quite noticeable but the forks look very similar at a glance.

[ski]

I have never understood why they stated ATF OR 10/30. That's like saying you can mix cement using sand or dirt. ATF has a more consistent viscosity when taking temperature into account than motor oil does. ATF is also lighter than 10/30 so I would have to assume that if you want a stiffer ride, use 10/30.

This is what I have done for years with these bikes, and you can take it with a grain of salt, though I've never had any complaints from RE5 owners. I use actual fork oil. Half the amount is 10W and the other half 15W. It gives great damping and rebound qualities and in the few subsequent tear downs I've performed, I've noticed no abnormal wear. I tend to lean towards a slightly softer, faster responding suspension on all my bikes save for my Bandit which I usually ride like my pants are on fire. I don't want that diving when I corner hard. The easiest thing you can do to tune front forks, is play with the type of oil you're using. Beyond that, you're getting into changing springs, damping set ups and hard part mods. I've only done the latter with my dirt bikes when I was racing in my younger days. It generally turns into too much work which I try to avoid nowadays.

[wayne]

If you think Suzuki's specs sound about as precise as instructions to make cement with either sand or dirt (nice analogy BTW), then you're going to love the advice in my GS750B manual. It specifies a 50:50 mix of 10/30 and ATF. I guess they figured they could cover all bases ?

I personally use ATF in the RE5. I'm advised that it's approximately 15W. With about an inch of preload and the weight of the fairing, it works very well.

However in bikes that I like to personally "tune", I do use actual fork oil, sometimes 10, sometimes 20. I don't go so far as to blend. My arse (ass) isn't that sensitive.

For the rear on the RE5, I use Ikons, there's just about nothing you can do with those originals.

[timpa136]

Aug 28, 2016 4:03:46 GMT -5 raychappo said:

Does anyone know the correct oil capacity for the forks? I've read in the manual that it should be 160ml but that is for the screw in type top of fork.

Mine have the circlip type retaining top and looking through the GT750 forums it suggests anything from 250ml to 266ml per fork. I've been using 160ml in each leg and the forks definitely feel wrong, it under damped and 'noisy'.

Any suggestions?

Thanks

Ray

Just a thought about the noisy, did you recently replace the steering stem bearings? I had one that wasn't fully seated and when I purposely drove over a stretch of "suspension test road" ...it seated and I had a click or noise braking and a readjustment was in order.

Great discussion of fork oils, I had a quart of 5-20 Shell left over from my last RX-8 that I just used for a refill. I will evaluate the forks with it in North Carolina.

I also  noticed while riding different bikes back in the day, the 75 GT750 suspension dampening was softened from previous years and the RE seemed heavily dampened both front and rear in comparison to me. I felt the RE5 was more advanced.

EDIT: After changing my fork oil to Shell 5-20, now, both fork seals are dry after the Wyoming rally where they both were seeping before.
I am very happy with the handling and comfort of the Shell 5-20 oil.  09/2017  Tim

[raychappo]

I'll check the head stock adjustment just in case 😊

[ap951]

"Great discussion of fork oils"

You know I am always learning & I appreciate everyone that contributes to this site.

Thank you!

[timpa136]

Just a follow up after changing to 5-20 motor oil. It seems to work just fine, enough so that I am tempted to try 0-20 motor oil.
I make the comment as my other driver is more jarring or stiffer compression in comparison and I don't remember what oil I used there.

I may take Wayne's advise also and try a 1 inch preload spacer as I have the Suzuki fairing, too.

edit, I changed to 5-20  in the second bike, I'll save experimenting with 0-20 for another time.

[pmcburney]

You know, I reckon there's a reason why dedicated fork oil is single-grade...


Sure, multigrade motor oil isn't subjected to the same temperature extremes in a fork as it would be in an engine, call me paranoid but I'd be more than a little concerned that a multigrade would have different damping characteristics depending on the ambient (and then possibly the 'working') temperature.

You'll always get much more consistent results with a specific, single-grade fork oil than anything else.

Last thing I'd want is NO (or next to NO) damping at low temps, and then harsh, unresponsive damping at higher temps...