Stacey

I've just rebuilt my Marzocchi XC400 air over oil suspension fork.

In talking to the tech dude at Marzocchi they recommend 7.5 wt fork oil. I've heard that using Automatic Transmission Fluid will offer better fork performance.

Truth or fiction? Opinions please.

mx_599

personally, i would use a 5w fork oil from a motorcycle store. i like Honda oil in a black bottle. you don't have to use 7.5w. you can experiment with other weights for different characteristics and/or bw.

i would think the additives to a tranny fluid would be different than that of suspension fluid. but i am not sure. some of the auto gurus here probably know.

HP Fork Oil 5W
Friction-modified formula specifically engineered for the latest in suspension technology from Showa™ and KYB®.
Minimizes stiction and cavitation, providing optimum performance for all Honda inverted-fork suspension systems.

cryptid01

What is "better fork performance", exactly?

I'm pretty sure that when the Marzocchi engineers designed the fork, they used 7.5 wt., so I have no reason to doubt that it's optimally tuned for same. ATF might work just as well, but I doubt it works any "better".

Michigander

I kept an old crappy fork going by dumping 10W30 into it for all of the last michigander. One 5' or so jump blew it out completely, and being an old manitou, it certainly isn't about to get rebuilt, no parts available. I'm still a poor college student so the fork has yet to be replaced. My theory is that for older forks, add oil as needed, and see what happens. Probably doesn't matter a whole lot what kind. Older forks won't work nearly as well as a modern one, regardless of how well they are functioning.

Hopper

When rebuilding forks I usually want to have some 5wt and 10wt around, depending on how it was performing change the oil weight. Keep the oil level the same as before (you can adjust it by a couple mL) but you can also adjust the performance of the bike by changing the oil weight. You can do mixtures such as 1:1 for 5wt:10wt and this will give the equivalent of 7.5wt. By changing the ratio you can change the feel of the fork.

Stacey

Thanks for the replies guys. I understand the weak points of this fork, as compared to a modern 32mm stancion fork with 6-8 inches of travel. It came equipped on a $10 thrift store rescue bike that I'd just like to get up and running decently. For my intended usage and the fact that I'm an oncology patient on disability somewhat precludes a replacement/upgrade at this time.

Hopper, the fork was sacked when I got the bike, more oil covering the outside of the sliders than contained within and not holding an air charge for more than an hour or two. So, I have no baseline performance standard to evaluate the need for any change in set up.

Gotta hand it to Marzocchi on this one. The fork was the subject of a crown recall which had not been done on the bike. I called them, confirmed that this was indeed a recall fork crown and they issued a RMA with no hesatation. Not bad for a 14 year old fork.

Svr

A very rough, generic estimate of viscosity for ATF is 10wt... which is a bit thick for the operating temperature of a bicycle suspension fork. It should work ok, but the fork might feel a bit overdamped and sluggish.

RIC0

Go with some synthetic fork oil if you want the best. I use Amsoil in my rockshox. I'm also a Amsoil dealer if you would want some let me know.

Hopper

From your description I would first get new seals and overhaul the fork and as a basleline use 7.5wt oil. Each time you rebuild the fork work out what you want. If it is over dampenedmake it a bit mor viscous (use more 5wt) if it feels to soft and springy use more 10wt.

Stacey

Done already, thanks.

New seals and o-rings throughout. Just need to add oil and put the stancion plugs back in and charge it with air. Waiting on a replacement crown from Marzocchi, as the old crown was the subject of a recall.

So, it sounds like the 7.5 wt is the way to go and adjust as necessary. Cool!

mx_599

your body weight is a consideration as i already mentioned. are you light, heavy, or average?

Stacey

Last I weighed myself around 185.

mx_599

yeah, okay. stick with the recommended 7.5

AfterThisNap

OT, but my old girlfriend had a rex rat named Max that she adored. Even I still miss that little guy from time to time.

sbenne

Hey Stacey,

I know you wrote this a long time ago but I'm trying to rebuild my XC400 and I'm having trouble figuring out how to get the oil seal out. Do you remember how you did it?

... I've downloaded the manual (missing some pages) from Marzocchi's web site and have removed the seals inside the stanchions but still can't get the stanchion out of the tube and/or get at the main seal. I'm assuming there's a retaining ring atop the slider tube that holds the seal and the stanchion in place -- just can't figure out how to remove it.

Steve

Cheeto

Well since people are saying ATF will work, Ill fess up,
I didnt have any oil in my fork from it not working right, I toped it off with ATF and now it works just fine.