Marzocchi Monster T – Fork Seals / Rebuild

I recently picked up a used 2004 Morzocchi Monster T. This is an awesome downhill fork – if maybe just a little bit on the heavy side. It was one of the first 40mm stanchion mountain bike forks and as such is super beefy and very plush. It is a great fork and I look forward to many fun miles riding on it. I installed it as part of a Rocky Mountain RMX 2.0 downhill rig but not suprisingly the seals wept oil. This is pretty common on older forks and I have replaced seals several times before on other bikes so I was no stranger to the symptoms or the remedy.

Installed Enduro seals - Looking good!

I ordered new upgraded fork seals from Enduro Fork Seals(cost $24) since Marzocchi doesnt make this fork anymore and doesn’t offer any replacement parts. Enduro seals have gotten great reviews online. Without furher ado – what follows is the basic step by step for replacing the seals on the 2004 Marzocchi Monster T fork. Tools you will need: – An assortment of hex wrenches (4mm, 5mm, 6mm, 8mm) – a 28mm socket or large crescent wrench – a 10mm wrench – Something to hold the fork (I used a bike clamp) – 1 liter of 7.5 wt fork oil (430ml for each leg) – Cleaning supplies – Super Slick Grease (or other greasy product,this stuff from Rock n Roll is highly recommended)

One stanchion with the lower triple clamp still attached.

1. Remove the front wheel, handlebars, brakes etc. 2. Remove the fork from the bike by sliding the upper triple clamp off and sliding the fork out of the headset. Remove the lower triple clamp by sliding it off the fork lowers and then remove the fork brace (shaped like an M) 3. select one of the fork tubes and place it in the fork hodler (bike clamp for me) 4. Remove the 1.5mm air bleed bold at the top of the fork tube. 5. Loosen the 28mm fork cap on the top of the fork tube. It will come apart from the fork tube but still be attached to the cartridge. 6. Push spring and the preload tube down so you can reach locknut with the 10mm wrench.

The top cap is removed from the stanchion but still heald in place by the cartridge rod. A 10mm wrench and a 28mm wrench must be used in tandem.

7. Holding locknut with the 10mm wrench, use the 28mm socket to unscrew the fork cap. This is a pretty complicated task with only two hands. I recommend asking for some help to save yourself from a lot of frustration. 8. Remove the preload tube and spring. Drain the oil from the fork tube. move the cartridge rod up and down a few times to drain extra oil out.

8mm allen on the bottom of the fork stanchion to remove the cartridge

9. Turn the fork leg upside down and with an 8mm Allen wrench remove the bottom screw complete with O-ring.The bottom screw didnt come out super easily for me (i had to grab it with plyers and pull it out once I had released the cartridge completely) but your experience may vary. In any case pull the complete cartridge off the fork leg and set it aside to leak oil. 10. Remove the dust seal from its seat using a small flat-tip screwdriver. Also remove the metal stop ring that is wedged into the groove holding the fork seal in place. I used a 1.5mm allen wrench for this but a small screw driver would work too. Just pull that metal ring out being careful not to damage the fork tube or the metal wring (you will be using all this stuff again)

If the old seal doesnt come out...

11. Pull stanchion out of slider, to separate these two elements you will have to pull hard. Typically with this operation the fork seal, the spring cup and the top guide bushwill be removed from the lower fork slider. However, in my case the fork seal didnt come out when I pulled the upper tube out. After a lot of swearing, frustration, and an internet search, I hit the fork seal with WD40 and then heated the assemnly up with a heat gun. Small amounts of heat did not work – I had to wait until the WD40 started smoking. Then, wearing gloves to avoid getting burned and being very careful not to scratch the inside of the lower fork tool, I was able to pry the fork seal out with a screw driver. A plastic tire lever may also work – and be safer for your fork – up to you. 12. You can inspect all the bushings to make sure they are still in good condition, but honestl, with the age of this fork, I am not sure that you would be able to find repalcements even if they were too worn. Mine looked fine so I didnt bother removing the bushings from the upper fork tube. 13. The old fork seal ring and dust seal are not used again – this is the whole reason we are doing this: To replace these seals! So toss those suckers.

All of the pieces: From bottom to top - Lower stanchion, upper tube, cartridge, spring, preload spacer
The order of things. 4:Stanchion 3: upper tube 7: top guide bushing 6: spring cub 5: Fork seal. Also shown: stop ring, dust seal.

14. Clean everything with a good degreaser. My fork stanchions had all kinds of nasty stuff inside. Make sure everything is good and dry before putting it back together. 15. Smear the dust seal and the sealing ring with lots of grease. Also put grease on the mating surface in the fork lower. 16. Insert the following components in the stanchion tube in this order: top guide bushing, spring cup, sealing ring, stop ring, and dust seal. 17. If everything is greased up properly the dust seal should slide in fairly easily. I used a heavy cardboard tube cut down to size to use as a fork seal insert tool. Lots of people use pvc cut to size (I didnt have any lying around – but I did have the cardboard) and I am sure you can find a 40mm seating tool if you look on the internet too.

Highly specialized fork seal seating tool
New seal in place with metal lock ring in the groove.

18. Once the seal is in place replace the metal wring. It should fit into the groove on the inside of the fork lower stanchion perfectly. If it doesnt, then the fork seal is not seated all the way and you will need to press it further in. 19. Insert the dust seal in its seat using the same special tool you made for the seal. This was particularly difficult for me, but with some broot force and the aid of some careful manipulation with channel lock plyers – I got the dust seal on. It should fit nice and tight against the fork lower stanchion. 20. Insert the cartridge into the stanchion. 21. With an 8mm Allen wrench, tighten the bottom screw complete with O-ring (the recommended tightening torque is 25 Nm) into the cartridge. Before you put the screw in lube the O-ring with a bit of fork oil so you dont damage the O-ring with friction when screwing it in.

8mm allen bolt holding the cartridgre into the stanchion.

22. Once the bottom of the stanchion is sealed up we can add oil. The book recommends 430ml of 7.5wt. Thats what I used. Your preference of oil, volume, and weight may vary depending on experience. I dont know enough to change those paramters.

Carefully measured oil coming nearly to the top of the upper tube. The cartridge rod is in the center.

23. Measure out the oil first into a measuring cup and then pour the oil into the stanchion using a funnel. Move the cartridge rod up and down a few times about half way through the pour to be sure air bubbles arent getting stuck in the cartrdige. 24. Insert spring and the preload tube. 25. Screw lock cap down on the cartridge rod. 26. Screw down lock cap onto the stanchion.

27. Do the same for the other side. Keep in mind some of the parts are different for each side, so keep each sides pieces separate if doing them simultaneously. 28. Put everything back together! Thats it!

Spring and preload tube in place
Everything back together!

And back on the bike!

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