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Im thinking of rebuilding my front forks because I've noticed that the rebound from it is quite slow when i compress them down. I have no experience with the function of r75/5 forks. Only think i can compare to functional front fork is from my fathers Harley which has good rebound. Also i should mention the bike was sitting for quite a while, say 15 years.
Also i have checked for the fork alignment and they seem pretty straight, not to mention the front axle goes in smoothly with no binding.

It is very possible that the bottom bumpers have dissolved, which might be clogging up an orifice, but you might be able to get away with just changing the fork fluid for now. If you have lots of things to deal with to bring this bike back to riding condition after sitting for all this time, you might want to try just the fluid change first.

How did you "check for fork alignment?" Axle going in smoothly is good, but you should check that they are in the same plane with a piece of glass on the fork tubes (like all forks can be checked) along with checking the distance between the tubes at top and bottom (which you don't have to worry about on most "normal" forks which have top triple clamps).

Go to my website for the article on forks.

i read on snowbums website that the spacers are 5/8" long. I took mine off and found them to be 1 1/2". Also i measured the springs and there stock length. Something doesn't add up, and i was wondering if this could be a cause to why my forks seems stiff

Those are not factors in stiff forks. I suggest that you keep on reading until you are comfortable with understanding just how they work, or what you should care about in putting them together.

Did you perform the simple tests to measure stiction? Start with the basics and follow the steps to measure things.

As Duane said, that wouldn't stiffen your forks (if the springs are also stock strength). Taller spacers raise ride height but do not change the stiffness of the spring. They also may prevent the fork from bottoming (by providing more travel before bottoming) but only if they don't make the springs coil-bind before you've used all your suspension travel.

Major Softie wrote:As Duane said, that wouldn't stiffen your forks (if the springs are also stock strength). Taller spacers raise ride height but do not change the stiffness of the spring. They also may prevent the fork from bottoming (by providing more travel before bottoming) but only if they don't make the springs coil-bind before you've used all your suspension travel.

What is stiff?
Back in a minute

OK, I think we have different ideas on what stiff means. I once tried some spacers, maybe 25mm long, as well as 15 wt. oil. That was stiff!
Take out the spacers lelocp, try 7.5 or 10 wt. oil and see what you think.
The slow rebound is a concern that could be a result of crud in the system as the Major says.
1-1/2" spacer is too long.

i found out they were bmw hd springs but regardless of the springs i was wondering what size spacer should i use, i only weigh 145lbs. Im also gonna check for stiction as Duane mentioned.

None of this is useful if the forks aren't aligned. Most forks on these old BMWs aren't aligned. With alignment and decent parts, they are good forks for that era.

lelocp wrote:i found out they were bmw hd springs but regardless of the springs i was wondering what size spacer should i use, i only weigh 145lbs. Im also gonna check for stiction as Duane mentioned.

Spacers may not be needed at all. Start from a base and see what is/is not needed.