Forks don't rebound

[dswassy]

Hi all, I am hoping for some fresh suggestions. I have an R80/7 with stock forks that I recently rebuilt. For the life of me, I cannot get them to work properly. I have actually rebuilt them multiple times with new parts, fresh fluid, etc. No matter what I do, I cannot get them to rebound as they should. Basically, I can push down on them and get them stay down, or lift up on the front end and they'll stay up. I have aligned them, even replaced the tubes in case they were bent, same result. Thinner fork oil didn't solve the issue either. I have also conducted the stiction test before adding oil and installing the springs, and they move and down freely so I know the fender brace is not the issue.

At this point, I'm starting to believe this is how they are supposed to behave. The only thing left that I can think of is replacing the springs, or maybe the damper rod is too tight (I installed new rings) but it is still difficult to pull in and out in the tube by hand when first installing.

Any tips would be much appreciated before I give up!

Happy riding

[barryh]

The thing most likely to prevent the forks rebounding against spring pressure is stiction due to misalignment. I suppose hydraulic lock could do that as well but I can't envisage how that could happen. Draining the oil would soon eliminate it as a possibility.

I would remove the wheel and spindle then test each leg individually to make sure both legs are free to move.

[dswassy]

Thanks for the response.

Everything moves freely without oil but once I pour the fork oil in, they stiffen up.

[Rob Frankham]

So, let's restate this...

1) When the forks are assembled (completely ?) without fork oil, they compress and extend freely without any sign of problems

2) When the correct amount of oil is put into the forks, they will compress but rebound to the normal position is restricted and they will extend but again returning to the normal position doesn't happen. (I take it as, in both cases, they can be returned to the normal position by manual pressure...)

(1) above tends to argue against stiction due to tight seals or mislaigned forks...

(2) above argues against hydraulic lock

About the only thing I can think of is that oil is not able to moive properly through the damper assembly, which argues either that fluid ports in the dampers are blocked or that the damper assemblies are incorrectly reassembled... best I can do I'm afraid...

Rob

[dswassy]

You have it bang on. That is all correct. I was hoping it was as simple as the dampers being blocked or incorrectly assembled but I have taken them apart and reassembled correctly again and again, and they are both clean and correct.

[barryh]

Hydraulic lock is hard to envisage due to the compression damping as the holes in the damper rod are quite large, certainly too large to get blocked by sediment. The rebound damping oil hole is much smaller and together with the damper valve is a more likely culprit.
Is it a given that you are filling with the correct quantity of oil ?

I would want to envisage the oil flow through the forks but to do that we need to know the year of manufacture because an R80/7 spanned two different designs of fork internals.

[dswassy]

Yes I am filling with 250cc. It is a 1980 model.