Author Topic: GDT Spring help!! (Read 5343 times)

Nightowl · « **on:** August 27, 2006, 09:57:35 pm »

Hey all,
I just recentlry purchased 3 brand new GDT shocks off of ebay(had to buy all three)My problem is is that they came without springs. i was wondering what the length and diameter should be. also, would a spring off of a noleen shock fit? If anyone has any advice to offer, or even better, a spring they would consider selling, it would be greatly apreciated. I'd really like to get one of the GDT's mounted.
Thanks guys,
Matt B

orange · « **Reply #1 on:** August 28, 2006, 12:01:34 am »

I've used a spring off my Noleen NR-2 on my GDS - do you mean ODS or GDT as I think they are different.

Colin · « **Reply #2 on:** August 28, 2006, 12:45:43 am »

Aaaah, you bought them!

http://cgi.ebay.co.uk/3-GIRVIN-Shock-from-K2-full-suspension-NEW_W0QQitemZ170020031465QQihZ007QQ

I was considering getting them as spares for my ODS equipped bike, but at that price I'd be liable for import duty on them..........

(From Girvin publicity at the time)
GDT shocks
"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."

Never used them myself, but they were designed to be used with coil springs so "should" be better than ODS units.......
All 3 of these are rear units but don't have the bottom coller for mounting the spring on.....
Just measure the diameter of the piston body and the diameter of the spring coller to give you the spring sizes that will fit, then you need the length between the collars.
On an ODS unit the measurments are:
piston body = 27mm diameter
collar size = 45mm diameter
Spring length = 89mm

Never heard of GDS Maybe it means "Girvin Damping Shock" but I've never heard the company use that term, just "GDT Shock"

Nightowl · « **Reply #3 on:** August 28, 2006, 01:36:15 am »

Yep, Im sure they are GDT, they are the same shock that are in the link colin posted above, but from a different auction, aparently this seller had (has) quite a few of these, as this is the third batch of three ive seen sold. The auction i won ended on the 13th of august and another set of three just ended yesterday. Its great to see all these proflex parts still around, the problem is i want to buy everything i see!!!
Matt B

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=006&item=160015444677&rd=1&sspagename=STRK%3AMEWN%3AIT&rd=1

knuckledragger · « **Reply #4 on:** August 29, 2006, 06:45:39 am »

This is my first post. I just recently discovered this site and I am very happy I did. I have a ProFlex Beast GDT I bought new in 1996 (I think). It is a 16" frame and I added a Rock Ring, TWP brake levers, Tektro brake boosters, Azonic high rise handle bars and a few other miscellaneous items. It came with the GDT shock in the rear and what appears to be the ODS in the front (unmarked). Both front and rear came with coil springs. They are yellow and the front is marked 250 and the rear is marked 300. I stopped riding for a few years and am now just getting back into it. I still love this bike. Unfortunately, I have gained about 50lbs from my riding days and the rear spring just isn't doing it any longer. I too am looking for a source for a spring (heavier) for the GDT shock. I have removed the shock and spring and have measured the spring. It appears that the spring is ~100mm long, ~46mm wide and has an inside diameter of ~32mm. I e-mailed Rapid Descent but no reply yet.

orange · « **Reply #5 on:** August 29, 2006, 09:08:19 am »

hang in there for rapid descent - they'll sort you.

knuckledragger · « **Reply #6 on:** September 01, 2006, 12:21:49 pm »

Well, no such luck from Rapid Descent. They do not have springs for the GDT shocks. Any other ideas? It seems that there has to be springs that fit these. Is this an odd size or something? I seem to remember that you could get Speed Springs for these at one time.

kiwi · « **Reply #7 on:** September 01, 2006, 06:54:57 pm »

i would think a noleen spring would fit.Otherwise take your shock to a spring manufacturer and get one made,its a well know science.I think you could use the same rates as suggested by K2/proflex for your bike/weight.

shovelon · « **Reply #8 on:** September 02, 2006, 03:10:51 am »

What did Rapid Descent say about his cor springs not fitting? Was it the shock body diameter?

I just obtained an 856 frameset that has that same type of shock with a spring(red). Now that I think of it, I had a 97 beast that I had blown the noleen shock. The dealer sold me a GDT with a yellow spring, and it fit perfectly.

Renton makes titanium springs.

Terry

P.S. the GDT worked as well as the Noleen.

knuckledragger · « **Reply #9 on:** September 02, 2006, 07:38:24 am »

Here is the response from Rapid Descent:
"the springs you've got are going to outperform anything else. If you really want to change the shocks for, say, a stratos strata air shock or a risse then you are looking at big money and should possibly be looking at a new bike or frame instead!

set the preload up a bit and this should stiffen up the rear shock for the
time being.

our cor springs are specifically for those with the broken MCU shocks."

No mention of why they would not work. What are the dimensions of the COR springs?

shovelon · « **Reply #10 on:** September 02, 2006, 10:49:57 am »

Quote

Here is the response from Rapid Descent:
"the springs you've got are going to outperform anything else. If you really want to change the shocks for, say, a stratos strata air shock or a risse then you are looking at big money and should possibly be looking at a new bike or frame instead!

set the preload up a bit and this should stiffen up the rear shock for the
time being.

our cor springs are specifically for those with the broken MCU shocks."

No mention of why they would not work. What are the dimensions of the COR springs?

I just looked at the RDS site. His kit included a spring collar that fits the spring to the shock body. I think that is why he is not recommending his kit.

Unless you have the means to fab an adapter, you may mess up the shock. You have the old preloaders, right?

I don't agree with the notion that the money for a Risse shock is wasted. They are reeeeely good. I have one now, and used to own Jeffhop's Astro 5.

Any hoodle, just up the faith and keep prodding us. Something will come up.

Terry

shovelon · « **Reply #11 on:** September 02, 2006, 10:57:48 am »

On second thought, go to your LBS and ask for a Manitou spring. They cost about $30. They are being made by the gadzillions.

Terry

kiwi · « **Reply #12 on:** September 02, 2006, 12:38:07 pm »

the COR spring is made to fit the ODS damper.

Colin · « **Reply #13 on:** September 03, 2006, 10:22:09 pm »

I don't see what the issue is here, GDT's were designed to work with springs so fitting one onto these should present no problem, if (Big IF) you have the original spring collars...............But..... from the photo (link above) the bottom collars are definately absent, also maybe the top ones, (if GDT's had top collars) Anyone got one and can comment? (see below).

Spring rate woudl be the same for ODS or GDT, so the only other issue is the spring length. I think COR's are 90mm long. Knuckledragger says his original one is 100mm, so as long ast the preload can take up 10mm of slack you're fine, (probably).
Hey Knuckledragger, get us a good close up picture of that GDT!

I'd have thought the bottom collar from a RDS kit would be fine. The top one (if needed) would definately be different. If you don't need a top one and the pre-load collar bears directly onto the spring then your fine! In the eBay item photo's, the GDT's appear to have a coil seating recess on the preload screw so that would confirm it.

I've just looked at my March '97 MTB PRO Bike Test of the 657 (856 with GDT) and I'm pretty sure from the photo's in there, that there is no upper collar and the pre-load screws directly down onto the spring.
There is a bottom collar, it's very thin, but I guess would have a "seat" to locate the spring centrally, I reckon a RDS one will be identical.

What are the black bits on the piston shaft? are they MCU "bottom out" bumpers? Or are they part of the metal body of the shock? In the Bike test photo's these appear to be absent or very small........

Anyone got a good photo of a GDT to confirm this?

Tell you what, send me a GDT and I'll experiment!

Col.

knuckledragger · « **Reply #14 on:** September 04, 2006, 04:19:10 am »

I can get a pic of the shock and its associated pieces, but I am not very computer savvy and do not know how to post it!

In my case the GDT shock has the screw-down pre-load adjuster threaded on the shock body (like in the e-bay pictures). It is shaped like a top-hat and has a raised collar on the bottom, around the center hole, to keep the spring centered. It does bear directly on the spring and there is no separate collar or "plate" at the top of the spring. The shock also has a bottom plate with the same raised area to center the spring. I am not sure how many mm the adjuster could "take up" but judging from what I see it looks like it would be better to go slightly longer than shorter. I will look closer when I get home. The "black bits" on the shaft are hard rubber-type bumpers. I assume they help some if/when you bottom it out.

I do not know what the RDS "collar" units look like or what size shaft they are designed to go over. Do the ODS and GDT have the same shock shaft diameter? Do the RDS springs come in a variety of "weights"?

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Author Topic: GDT Spring help!! (Read 5343 times)