New User looking for advice on Pro Flex 756

[Joao Manuel]

I received a Pro Flex 756 from a friend a few years ago.  I have been riding it for about 5 to 6 years and I get a lot of compliments on the bike.  I don't know much about the Pro Flex and have not seen much information on them until I ran into this group.

Bike Components:
Rear Derailer: Shimano XTR
Front Derailer: Shimano Deore LX
Rear Hub: Shimano Deore LX FH-M565
Front Hub: Shimano Deore LX FH-M565
Rear Rim: Mavic X517
Front Rim: Mavic X517
Cranks: RaceFace
Rear Shock: Girvin GDT
Front Shock: Girvin ODS
Bar Ends: Girvin
 

1) Where can I get full details on what is original versus replaced (not including fenders and rear light)?
2) Haven't seen any 756 with Coil Shocks.
3) The rear shock has no rebound.  Every time i get air born,  I feel and hear the rear spring expand the shock to its max. 


John

 

[shedDY2001]

http://www.bikepedia.com/quickbike/BikeSpecs.aspx?year=1996&brand=ProFlex&model=756

[Joao Manuel]

Thank You.

Now just need to find what I need to do to fix or replace rear shock.

[kiwi]

nice bike you have there sir.The 756 came originally with "friction damped" elastomers.I bought mine brand new in 1996,i will see if i can scrounge up some pics

[shedDY2001]

same colour as 656

[Colin]

It's not unreasonable that the shock would extend fully when airborne and does depend on if you have the correct rate spring for your weight.

Remove the shock and see if it has compression damping to see if it is worn out or not.

Col.

[Joao Manuel]

Thanks for the compliment on the bike.

There is an elastomer around the piston rod but it does do anything.  With the shock completely compressed, there is still at least an 1.155 inch (29.337mm) before the elastomer would be compressed.  See attached picture.

The overall travel is about 0.25" (6.35mm) and there is NO damping in either direction.

What is the 4mm screw on the top of the shock for? It almost looks like a breather hole.

[shedDY2001]

i think your seatpost  is on the wrong way

[w2zero]

I do believe you are correct about that seat post.  Maybe to allow comfort to a short rider? 

The shock probably has no oil left and the nitrogen charge is long gone as well.  A local motorcycle shop might be able to save it or contact this site for new shocks entirely.
 http://shop.noleenj6.com/category.sc?categoryId=7  Expensive but bolt-on and they work.

 Some of the other folks here may have suggestions for other brands as well.

[Spokes]

I think the GTD shock is just filled with oil. It definitely doesn't have nitrogen, that's only the Noleen NR range of shocks. As Col says, takes the spring off and check the damping. It might need refilling and a new oil seal.

Chris

[w2zero]

Digging around in the shop for that GDT and can't find it.  Could have sworn there was a port in the top of that shock.

Wait/What?

From our archives:


         The GDT shock ("Girvin Damping Technology") is a shock that was offered as an Original Equipment item on our 1996 and 1997 bicycles. It uses a similar technology to the Noleen shocks, but does not include an adjustable washer stack or any external adjustments. The GDT, however, utilizes a floating piston and performs well because of this feature. This shock was designed by Girvin engineers to be used on most of our 1997 lineup, but with the late-season purchase of Noleen, was spec'd on only a few bicycles and will not be sold as an aftermarket item.

[Joao Manuel]

The seat post has been turned around for my riding comfort.  Good catch.

There is a port on the top side and not sure what it is for since I can not find any information about the GDT shock.

[Colin]

GDT shocks do use Nitrogen, the "screw" hole in the top is the filler port.

from the K2 1998 FAQ's:
" 6. Why do Noleen shocks and GDT shocks use nitrogen gas? Can't we fill them up with air from another shock pump or from a compressor?  Nitrogen is used instead of gas because it is an inert gas. (Get out your chemistry books...) Nitrogen is not affected by temperature changes the way air is, so it works much better in shocks. Air expands with heat variations, so the pressure inside the shock can actually change with the temperature, varying the damping performance. Air also holds moisture which can adversely affect the movement of the floating piston, and again, affect the damping performance.  Our shocks also require a special filler needle to charge the shocks. Noleens are precision instruments that require exacting tolerances and accurate measurements. Other types of fillers (schrader valves, etc.) do not and cannot provide the accuracy or the tight seal that the Noleen system requires. The end results of the  Noleen system are a longer lasting, more accurate nitrogen pressure as well as less weight. Looking at all the options available, the Noleen charging system is the best for our rigorous demands and exacting tolerances.  If we could have used air in the Noleen shocks and been happy with the performance, we would have. Nitrogen, however, provides the very best performance in our shocks and in charged shocks in general. Ask any motorcycle shop.     "

The MCU is a "bottom-out" protector, so it's unlikley to contact the body, except "in-extremis"!

As I said, remove the shock from the bike, then remove the spring and you should have about 1.8" / 45mm of damped shaft movement on a GDT. You may need a fair bit of weight on it to compress it fully, but if it doesn't move at least an inch then the shock may well be siezed after losing it's oil and nitrogen at some point in the past.

Very little info available on the GDT's as they were only around for a very short time, I've never heard of any maintenance options for them.
Best bet is to look for a Noleen or ODS shock. Then look at Risse maybe............

Col.

[Spokes]

Well don't I stand corrected! Lol. I always thought the GTD was just a simple oil shock the same as the ODS type. Is the GTD more home rebuildable/serviceable than the Noleen is? Obviously the nitrogen charge is a small problem but I do however have the correct nitrogen filling injector tool for Noleen shocks so it should/might fit the GTD.

Chris

[kiwi]

Well don't I stand corrected! Lol. I always thought the GTD was just a simple oil shock the same as the ODS type. Is the GTD more home rebuildable/serviceable than the Noleen is? Obviously the nitrogen charge is a small problem but I do however have the correct nitrogen filling injector tool for Noleen shocks so it should/might fit the GTD.

Chris

dont thinks its any more rebuildable than other shocks,its just a less sophisticated noleen.Not sure of exact details but i think proflex developed the gdt then the opportunity arose to buy/use/whatever noleen so the gdt was superceded in a short time