Progressive springs not so stiff..

Ok, I know its been covered a million times, from a million angles but I am still at a loss to grasp this.

I just rebuilt the forks on my 1983 R100(RT) and installed a set of Progressive springs from Bob's. The length appears to be a tad shorter than the OEM ones I removed, but adds up to the same when I cut the pre-load spacer to the Progressive recommendation for my bike (year and model).

Today, at a friends house, as I saddled up to leave he noticed that the front-end travels nearly all the way down (compressed). I was also mentioning to him, that braking somewhat sharply, particularly in downhill turns (like coming to an intersection), it feels rubbery.

I also have a San Jose fork brace and an aluminum CNC'd triple tree. The break rotors are partially responsible for it, I think but the compression is puzzling. I am not a small guy (225lbs), but it wasn't doing it before I rebuilt the forks during the RT conversion.

Does this sound like too much preload? An over tight steeringhead bearing? Wrong springs? Fork oil weight (I used 7.5)?

Stumped.

too much preload would lead to limitation of compresion action, not an increase.
steering head bearing adjustment impacts L/R action, not up/down.
Even brake rotors should not really impact compression all that much.

I'm first voting for insufficient fork fluid, next is too light a fluid mix (tho 7.5 is a pretty good blend #) and 3rd is too light a spring. Did you go with anti-dive springs or spacer/bumper at bottom of fork leg?

Tony -

A bu** load of information here...sounds to me like you have too much sag.

http://mysite.verizon.net/vze4dp63/bmwmotorcycleparts/forks1.html

might sound silly, but did you put the oil in...

bikerfish1100 said:

too much preload would lead to limitation of compresion action, not an increase.

Click to expand...

....so perhaps too little preload then?

bikerfish1100 said:

steering head bearing adjustment impacts L/R action, not up/down.
Even brake rotors should not really impact compression all that much.

Click to expand...

Gotcha, but I mostly notice the rubberishness hard breaking or in a slowspeed turn.

bikerfish1100 said:

I'm first voting for insufficient fork fluid, next is too light a fluid mix (tho 7.5 is a pretty good blend #) and 3rd is too light a spring. Did you go with anti-dive springs or spacer/bumper at bottom of fork leg?

Click to expand...

I put in 225cc's of 7.5 weight per Clymer's spec for 1983 R100/RS/RT/CS. I recall a discrepancy (and I think I posted about it, I'll check) between Clymers and Progressive's method of measuring. Progressive's instructions say to measure the distance from the fluid top to the top of the fork tube. Clymer's strictly a volume measurement and I went with that.

I'm not sure I know what an anti-dive spring looks like. I bought the only Progressive that Bob's BMW keeps in stock. It's all spring, no spacer at the bottom and has two separate windings, abotu 4" tightly wound, followed by a long section not wound as tight, and then another 4" tight section. The OEM springs I took out (and might put back in) had a white cap on each end.

20774 said:

Tony -
A bu** load of information here...sounds to me like you have too much sag.

Click to expand...

Thanks Kurt. Too much sag with brand new springs? So, I'd read that as I need MORE preload to take up the slack?

Boy, I'm starting to really appreciate those dialable Ducati forks!

kgadley01 said:

might sound silly, but did you put the oil in...

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Not silly at all, I did say I'm stumped. Anyway, yes I did (with the drain plugs in and everything).

I read Progessive's instructions as an either/or and decided that the quantity specified by BMW (Clymer) met the fluid minimum required. I went to a heavier oil as I did not like the dive when braking. 7.5 was to light for me. I'm much happier with the 10 wt. The spacer length was straight from Progressive instructions. It worked for me. For me, using the measurement from the top of the fork per Progressive , was too much oil.

Sagging Progressive Springs Update

Ok, I am not 100% sure how I did it, but I managed to cut the spacer to the recommended size from Progressive's instructions and I was still 3/4" short just getting to the length of the stock springs. Anyway, I think I've corrected.

In the meantime took a friend's recommendation to use a light coating of Hylomar Universal Blue Sealant along the threads to prevent any leakage through the pinch slot on the aluminum top clamp. Prior to applying the Hylomar, I cleaned the threads with a toothbrush and couple squirts of brake cleaner.

I used Schedule 40 PVC (3/4" ID) for the spacers and a piece of 9/16" for the guide tool to apply enough downward pressure to get the threads to bite. I have the front wheel about 1/2" off the ground to do this. The spacers are 1-3/4" to account for the difference in spring length, the delta between the OEM top clamp and the aluminum clamp and a bit more to accommodate for my weight. 1-1/2" would have made them the same length as the OEM springs. Masking tape to protect the aluminum top clamp getting mangled by the socket face.

Thanks for everyone's help figuring this out. Here are a few pictures.

Eery situation is different and one size does not fit all.
The best way to figure this out is to measure and adjust your suspension's "sag".

Just Google it. Instructions are averywhere.

i had the same problem when i first got the ST. under hard braking the engine would actually bang into the front fender. the po had put progressive springs in. adding just 15-20 ml of oil to each stanchion made a world of difference. i know it's not a particularly "scientific" way of going about things, but it was effective and no leaks from over filling resulted.