Questions on T4 850 Front Dampers & Springs

[Guzzi_Don]

I have pulled the front forks from my T4 850. The RH fork leg as was reported in another thread just came apart when placed on the work bench. It turns out the upper damper unit had unscrewed out of the lower part that is held in the lower fork leg by an 8mm hex bolt.

In the picture below the spring that came out of the fork leg looks to be incorrect. The original parts book shows a two piece spring as original equipment. Any suggestions?



In the picture below the damper rod has a threaded section with a nut on it. As this was already apart when I pulled the forks apart I am not sure if the threaded rod screws ALL the way in to the lower metal part seen below it in the picture and then the locknut tightened up. Also is there any way to make sure the rod does not unscrew in the future?



When I push the damper rod into the unit it can be done with very little effort, but when pulling it out there is much more effort required. When being pulled out it gives a bit and then slows down and then goes again. Is this correct for this type of damper unit?

Any idea what type of damper it is? I don't think it's original.

Is there any way to pull these dampers apart to drain them and refill them with fork oil (maybe 5wt)?



Any more tips on these front forks to make them perform correctly.

How is the top damper, lower damper part it screws into and the spring assembled. I am guessing the damper rod is screwed into the lower part, the spring is slipped over the top of these, the spring is then compressed somehow and the circlip fitted to hold it all in place. Then it is fitted to fork tube from the top and the 8mm bolt is fitted from the bottom to hold it in place.

[Stevex]

Looks like an FAC replacement damper with a Wirth progressive spring.
The piston pushes in easily and pulls out less easily because it's mainly a rebound damper.
The spring does the compression damping.
When you say pulling the damper rod back out gives a bit then slows down, are you doing this with the damper upright; it will have an air gap in it and you need to it upright to work properly.
I don't think they are refillable but someone may put me right on that.
The way you described putting it back together is pretty much spot on.
As far as how much to screw the threaded portion into the bottom rod, I'd go most of the way, leave maybe a thread or so showing, once the lock nut is done up. Probably worth Loctiting it too.
If it was me I'd check the other fork as well. Can you trust who ever fitted the FAC's / springs to have done up that lock nut tight enough?
To compress the spring on rebuild, put a small screwdriver or scriber through one of the holes in the bottom rod and wind  the spring up it until you can get the circlip fitted then wind the spring back down to remove the driver / scriber.

[LeRoy]

I believe that Stevex is correct: you have FAC dampers and progressive springs. That's a good thing if they are in good shape. The progressive springs replace the two-piece springs you were expecting. And, the damper should be upright as you exercise the damping rod in and out. Cycle this a few times and you may find that it's resistance becomes smooth instead of notchy.

The one piece I don't see in your disassembled forks is the cup-shaped piece that goes on the bottom of the assembled damper and spring unit. You fit this over the spring end after you've secured it to the damper rod and extension with the circlip and hat-section metal spacer. This cup has a small protruding tang on the bottom that locates in a notch in the lower end internal surface of the fork leg. This prevents anything from rotating as you tighten the socket head cap screw that secures the damper/spring assembly from under the bottom of the fork leg.

If that cup is missing it just might be possible for the kind of auto-dissassembly that you experienced to happen. Take a look into the bottom of the fork leg. Sometimes the cup remains lodged in there when you take things apart. If it isn't there at all, you need it: it's essential.

[Chuck in Indiana]

To compress the spring on rebuild, put a small screwdriver or scriber through one of the holes in the bottom rod and wind  the spring up it until you can get the circlip fitted then wind the spring back down to remove the driver / scriber.

This is a nice little trick that took me a while to figure out.. duh.. 

[Guzzi_Don]

This is a nice little trick that took me a while to figure out.. duh.. 

Could someone explain this trick to me in plain English please? I don't understand what is being done. I am a bit SLOW!! as well!

[Guzzi_Don]

When you say pulling the damper rod back out gives a bit then slows down, are you doing this with the damper upright; it will have an air gap in it and you need to it upright to work properly.
If it was me I'd check the other fork as well. Can you trust who ever fitted the FAC's / springs to have done up that lock nut tight enough?

To compress the spring on rebuild, put a small screwdriver or scriber through one of the holes in the bottom rod and wind  the spring up it until you can get the circlip fitted then wind the spring back down to remove the driver / scriber.

Thanks Steve for the valuable info. Yes I did have the damper horizontal on the bench when I did the test. I will try it upright when I get home from work.

I do plan to do the other fork leg as well. Someone mentioned that there is a piece missing from my setup that goes in the bottom of the lower fork leg. I will have to check on this when I get home as well.

I am not understanding about winding the spring up, etc. Could you explain more thoroughly for me please?

Thanks

[Chuck in Indiana]

Think of it as a screw thread. When you put a pin in the hole and rotate the spring, the spring compresses and relaxes, depending on which direction it is rotated. Got it?

[Guzzi_Don]

I seem to be missing the alloy part that goes in the base of the lower leg. See picture below which shows all there was at the bottom of the spring and lower rod when I pulled it apart.



When I have the spring and damper assembled as pictured below the portion of the lower damper rod that takes the circlip is a good 1" up inside the spring. So I am waiting for suggestions on how to assemble this setup successfully.

I am thinking that the setup with progressive springs and FAC dampers was longer than the original setup and therefore the alloy spacer/thingo in the bottom of the fork leg was left out -- just a thought.



These next two pics show a close up of the lower rod inside the spring.





BTW I checked out the damper by holding it vertical and pumping the plunger and the action improved by 100%. Feels really good now. Problem solved.

Thanks for all the help so far.

I might have to disassemble the LH fork leg now to see if it is assembled correctly with the alloy piece under the spring in the lower leg.

Thanks

[Guzzi_Don]

Think of it as a screw thread. When you put a pin in the hole and rotate the spring, the spring compresses and relaxes, depending on which direction it is rotated. Got it?

THANKS Chuck. I get it now.

[LeRoy]

I seem to be missing the alloy part that goes in the base of the lower leg. See picture below which shows all there was at the bottom of the spring and lower rod when I pulled it apart.

The piece you are  looking for is not an alloy bit, It's a steel cup fabricated from a stamped end piece and a bit of tube. It looks (and costs)like this:

http://www.mgcycle.com/index.php?main_page=product_info&cPath=197_199&products_id=4478

The little protruding tang at about 4 o'clock on the end of the cup is the important element as it engages with a slot in the bottom inner fork leg to prevent the spring/damper assembly from rotating as you try to tighten the bolt from the bottom to fasten the whole thing in place in the fork leg.

[Guzzi_Don]

The piece you are  looking for is not an alloy bit, It's a steel cup fabricated from a stamped end piece and a bit of tube. It looks (and costs)like this:

http://www.mgcycle.com/index.php?main_page=product_info&cPath=197_199&products_id=4478

The little protruding tang at about 4 o'clock on the end of the cup is the important element as it engages with a slot in the bottom inner fork leg to prevent the spring/damper assembly from rotating as you try to tighten the bolt from the bottom to fasten the whole thing in place in the fork leg.

Thanks Bob for your help so far. I have no doubt that as I go along further on this trail I will need more help.

My BAD thinking it was an alloy part when it was steel. How expensive are they though; they work out to be $47 ea. for me with the exchange rate at .72 to the US dollar. So that would be $94 for 2 of them plus the exorbitant postage costs from the US which would be at least $30.

In hindsight I reckon I was lucky to get the bottom 10mm hex screw out without the lower damper rod turning with the bolt as I tried to undo it.

[Stevex]

Where are you located Don?
I've just been on the Stein-Dinse web site and they're 23 Euros each.

[Guzzi_Don]

Hi Steve,

I am in Australia.

Thanks

[Guzzi_Don]

My present problem seems to be that on the LH fork leg the steel piece that sits in the bottom to locate the lower damper rod to stop it from turning is stuck in the bottom of the lower leg. I have managed to get a long screwdriver between one edge and lever it over a bit. So it is now cocked over to one side a bit. Now I cannot get it to move to come out.

Any suggestions? I left it sitting upright in a tin of petrol last night hoping that when I get home from work this afternoon it may have dissolved some muck in there and allowed it to loosen up a bit. Any other ideas to get it out? Heat, tipping boiling water into the leg, etc. All suggestions welcome.

Thanx

[John A]

Wiggle it with your long screw driver and it should drop right out.

[charlie b]

If it is cocked sideways then get a long rod and shove it through the hole on the bottom of the leg.  That should knock it loose.

[Guzzi_Don]

Thanks guys,

A quick update: I managed to remove the stuck cup in the lower fork leg by putting a thin drift in through the 6mm drain hole and tapping it out that way.

I managed to find a guy in Perth, Western Australia who supplied me with new cups as mine were buggered (the side lug was damaged on both of them).

I have now reassembled one fork leg and fitted, torqued up the 10mm allen bolt than holds the damper in place from the bottom (under where the axle goes through). I could not find any info on fitting that bolt so I used 243 Loctite on it and torqued it to 32 lb ft with new alloy washer in place. Was this ok.

One more to do.

Oh!! I have also refitted the steering head with new tapered roller bearings as well.

Thanks.

[Stevex]

I have now reassembled one fork leg and fitted, torqued up the 10mm allen bolt than holds the damper in place from the bottom (under where the axle goes through). I could not find any info on fitting that bolt so I used 243 Loctite on it and torqued it to 32 lb ft with new alloy washer in place. Was this ok.

Just checking Don...you put some ATF in there for lube didn't you?

[Guzzi_Don]

Just checking Don...you put some ATF in there for lube didn't you?

Hi Steve, I haven't put any ATF in the fork leg yet although I did use some during assembly. I have only screwed the top nut in a few threads at this stage as I am having trouble finding info on the exact amount of ATF to go in these forks (T4). Some say 70cc, others 80cc, any ideas, does it really matter?

I have a syringe and will fill the fork leg using that through an extremely small gap when the top nut is released once I know the correct amount.

Thanks

[jvb]

The Haynes Workshop manual recommends 0.060 (60cc) of a litre of atf for each leg for the T3 which is the same as the T4 (Have not seen any manuals for the T4).

My T4 still has the fairing, and to be honest,  I've put about 60-70cc of whatever fork oil I have about, as viscosity does not effect the damping function and is purely for lubrication and to limit fork travel.

When reinstalling the forks, Guzziology recommends dropping the forks 10mm in the yokes to quicken up the steering.

[charlie b]

FWIW, the T5 is listed as 60cc as well so you should be good there.  I just use ATF since the manual calls for it and it's cheap.  :)

PS well partly correct.  The owners manual lists the fork fluid capacity as 60cc of ATF.  In the maintenance section it says to refill with 100cc of ATF. 

[Guzzi_Don]

My T4 still has the fairing,

Hi, glad you chimed in. What country are you in? I've read somewhere that they didn't have the T4 in the US so guessing you don't come from there.

Maybe it was just for Australia and Europe (maybe NZ as well).

The T3 Owners Handbook I have says 0.070L. or in my parlance 70mm.

[Bazil]

Interested to read this thread. I have a Mark IV LeMans which also had the damper rod flopping around unattached to the slider.  ( Maybe it's an Australian thing - I'm in Victoria) It has FAC dampers and a progressively wound spring ( I think Moto Speciale?)  However the construction is a little different from the T4.

The damper rod screw has a locknut on the threaded end which then screws into an alloy spacer to secure the spring ( and this is where it came undone) The alloy spacer is notched at 9 o'clock and 3 o'clock. There is a nylon spacer which fits around this but is not secured. It has notches to match those on the spacer and slides snugly down the slider.  There are no tabs on any of this. The nylon spacer had some damage caused by the fork drain screw tunnelling into it, which I've cleaned up with a Dremel.

I've re-assembled the damper/spring assembly using Loctite on on threads to hopefully stop it undoing again

It looks to me that the only thing stopping the assembly rotating is by aligning the notches in both the alloy and nylon spacers with the fork drain plug screw, which protrudes into the fork. There does not seem to be an easy way to ensure that the notches in the alloy spacer and nylon spacer are correctly aligned both with respect to each other and the fork drain screw.

Is this correct ?


Any thoughts from your collective wisdom appreciated.

Bazil

[redrider90]

Those look like Wirth progressive springs as they are longer. You'll find out when you go to put it back together as they will fit very snuggly and getting the cap and c clamp in place can be a challenge. It has been awhile since I put mine in but I figured out a way to compress the springs and hold it in place while putting the cap and clamp back on. I am sure someone here has a method: I just cannot remember what I used. When they were new the Wirth's were quite strong difficult compress.
I cheat and subtract about 25% ATF and add STP. The mixture is very slick and the STP adds just a bit of viscosity to reduce the chance of leakage by the fork seals.
Now before someone goes yelling at me about how stupid an idea that is, I have put 40K miles on the front end with that mixture. I replaced the seals a couple of years ago only because  my stock Mille stanchion tubes had pitted and rusted and needed to be replaced.  Mille stanchions where notorious for rusting.

I just reread the thread and sure enough someone had posted the trick. Now I remember how I did it. But it took me awhile to figure it out. I won't say how long awhile is so as not to embarrass myself. 

[redrider90]

Hi Steve, I haven't put any ATF in the fork leg yet although I did use some during assembly. I have only screwed the top nut in a few threads at this stage as I am having trouble finding info on the exact amount of ATF to go in these forks (T4). Some say 70cc, others 80cc, any ideas, does it really matter?

I have a syringe and will fill the fork leg using that through an extremely small gap when the top nut is released once I know the correct amount.

Thanks

[Groover]

I believe those lowers are the same as the SP1 fork lowers and late G5 models. If so, the shop manual calls for:

2oz (0.0080) - G5 models (but I think this may be the earlier G5 fork lowers with the guzzi/bird emblem stamped on the lowers)
3oz (0.0090) - SP models (in my opinion, this would be applicable to the later G5 & T4 models that don't have the eagle stamp on the forks)

Since I think the late G5 forks, your T4 and SP1 forks are all the same, then I'd go with the 3oz. I went with 2.5 to be in the middle on my 81 G5 because I wasn't 100% sure and somewhere something isn't documented properly. I got the above measurements from the G5, SP1000 workshop manual.

Hope that helps.

[LeRoy]

I believe those lowers are the same as the SP1 fork lowers and late G5 models. If so, the shop manual calls for:

2oz (0.0080) - G5 models (but I think this may be the earlier G5 fork lowers with the guzzi/bird emblem stamped on the lowers)
3oz (0.0090) - SP models (in my opinion, this would be applicable to the later G5 & T4 models that don't have the eagle stamp on the forks)

Since I think the late G5 forks, your T4 and SP1 forks are all the same, then I'd go with the 3oz. I went with 2.5 to be in the middle on my 81 G5 because I wasn't 100% sure and somewhere something isn't documented properly. I got the above measurements from the G5, SP1000 workshop manual.

Hope that helps.

Ease your mind. The oil in these forks has a very non-critical job and it has _nothing_ to do with the damping. That's the job of the sealed damper units. The fork oil simply keeps the innards wet and oily. This prevents internal corrosion and keeps the seals a bit lubricated as it generally slops around. So, it scarcely matters whether the amount used is 2 oz. or 3 oz. Both are approximate translations from the original metric units of measure. The kind and weight of the oil is also not terribly important. You want to avoid things that will damage the seals. An oil that's extremely low viscosity may leak out too readily while too heavy an oil won't easily reach the upper area to lubricate the seals. ATF works fine. So would most any reasonably light weight fork oil.

[jvb]

Ease your mind. The oil in these forks has a very non-critical job and it has _nothing_ to do with the damping. That's the job of the sealed damper units. The fork oil simply keeps the innards wet and oily. This prevents internal corrosion and keeps the seals a bit lubricated as it generally slops around. So, it scarcely matters whether the amount used is 2 oz. or 3 oz. Both are approximate translations from the original metric units of measure. The kind and weight of the oil is also not terribly important. You want to avoid things that will damage the seals. An oil that's extremely low viscosity may leak out too readily while too heavy an oil won't easily reach the upper area to lubricate the seals. ATF works fine. So would most any reasonably light weight fork oil.