Fork oil...

[robertklee]

Ok. Just completely rebuilt front forks on my 60/5. Everything new but springs. What's best product to fill them with and how much for reasonably soft action? Thanks.

:usa

[shire2000]

Obviously it is Fork Oil you will want. As to what brand and weight? well, a lot of that is personal preference. If you want the absolute stock ride, then you would use what BMW recomended back when your bike was built. Most likely 5 weight. Lots of people experiment to find just the right setup for their particular riding style and feel. Some mix 2 different weights to get to what they want, while others add a little bit more at a time till they get to what they want. Trial and error.

An couple of examples:
1. On my 1980 R45, BMW recommended 5 weight, I use 7.5 weight and add 10cc more than stock. Gives me the handling I like on that bike.
2. On my 1981 R100RT, BMW recommended 5 weight. I use 7.5 weight and add an additional 20cc. Gives me just the right stiffness for my style of riding.

In both instances, I use BelRay Fork Oil. There are lots of different brands out there. Most are pretty good. I would not use BMW branded oil as they do not even make thier own, it is relabeled from a large well known manufacturer.

So, check your manual, see what weight they recomend. Figure out your riding style. If it is a bit agressive, I would suggest moving up one level in oil weight and putting in the stock amount. If it isn't stiff enough, it is pretty easy to add a little more at a time.

[GregFeeler]

Ok. Just completely rebuilt front forks on my 60/5. Everything new but springs. What's best product to fill them with and how much for reasonably soft action? Thanks.

:usa

Unless you modified your forks (like filling in one of the dampening rod holes), my experience with /5 forks says you'll have no problem achieving a "soft action". :) Rather, the problem would be too much dive under hard braking.

I would suggest you change the fork springs unless you are dead certain they are five years old or less. Thirty-five year old fork springs are not going to give you the performance of new ones and it's just about impossible to tune other parameters to compensate. I'd buy the BMW HD springs - or maybe Progressives. The Progressives typically give a firmer ride than the HDs, and the HD's are firmer than stock. Given you'd like a softer ride, I think the HD's would be where I'd start. Remember that the /5 was noted as having a under-dampened ride ("gummy cow") and a wee bit firmer spring rate with better dampening gives a more stable ride for most folks.

For fork oil BMW recommended Shell Aero 9000 (or some such) which was a very light aircraft hydraulic fluid - about 5wt or less. BMW makes a 7.5w and you can mix your own from 5 and 10wt if you'd rather use BelRay or another handy brand. I'd do this in two stages. First, experiment with different weights in the stock amounts until you have the dampening (ride going down the road) performance you want. Then add more quantity until you have improved the braking dive. You'll never really reduce it significantly without modifying the forks, but with new springs and 10 to 30cc's more fluid you can make some very nice improvements.

[PMonk]

I had a very stiff front end on the /6 I bought last year.
Bike had progressive springs. I was considering changing them out but when I drained fork oil it was obvious the problem was either the weight was too thick or had just gotten old. I flushed the forks and replaced with 5w and now ride is much improved. Not too much dive but they do ride a lot smoother.

Wilbers makes progressive springs for our bike as well as progressive.

Anyone ride on Wilbers?

[PGlaves]

The oil specified when /5 bikes were new was Aeroshell in what amounted to a 3 wt. oil. Most of us went to 5 wt. or slightly heavier. Those are long travel, cushy forks for enjoying your ride over cobblestones or something.

Progressively wound springs do help a lot. So will increasing the volume of oil by 10 to 20 cc. The reduced air column above the oil compresses more rapidly, limiting dive. The heavier wt. oil provides the increased rebound damping required by the combination of a heavier spring and the reduced air column.

It will likely take some trial and error to get it the way you like it.

[Boxerkuh]

I agree with the previous posts. I think this is based on a lot of trail and error. 10cc in each leg did do a lot more than I thought. I believe going up in 10cc increments is important with plenty of riding in between. I ended up going from 7.5 weight oil in stock cc to 5.0 weight oil with 20 cc more in each leg. I believe it is much better that way, but that could just be my belief only. That is why I saying; you need to try different things and stick with it when you find it the way you like it. I think it is also important that you keep the weight of the bike the same; i.e. if you are cruising around town, highway, touring, curves, etc. Remember it is all about compromises.

[Penforhire]

I would lean toward the heavier wt oils. Like the others said, you should have no problem with getting soft action. I found mine, freshly rebuilt, way too soft at 5 wt with a by-the-book fill level.

[Polarbear]

We used to use red automatic tranny fluid in our forks all the time and I have used it in my BMW's too, without any issues. Unknown weight, but it works perfectly. A cheaper than BelRay option, but cheap is not always what folks want. The tranny oil is a good one, though. I learned the tranny oil thing, racing dirt bikes a long time ago. Randy:thumb

[jforgo]

FWIW Honda recommended tranny fluid for mid70's 4 cylinder bikes.

[Polarbear]

I thought it was Honda too. It works fine, I know that:)Randy:thumb

[PGlaves]

We used to use red automatic tranny fluid in our forks all the time and I have used it in my BMW's too, without any issues. Unknown weight, but it works perfectly. A cheaper than BelRay option, but cheap is not always what folks want. The tranny oil is a good one, though. I learned the tranny oil thing, racing dirt bikes a long time ago. Randy:thumb

Absolutely - in the /5 vintage bikes manufactured to use 3wt oil which is approximately the viscosity of ATF.

My experience in the later bikes spec'd at 7.5 wt is that ATF is too thin in these.

[robertklee]

I appreciate all the replies. Thanks.

:usa