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Discussion Starter · #1 ·
I have read somewhere here in the past that some people have used synthetic motor oil or ATF in their forks for rebuilds instead of fork oil. Can anyone chime in? I have an Mx Pro that needs an immediate R&R and I don't have a sufficient amount of oil to do the job and the local shops aren't open for the holidays (some time constraints exist as well).

I have heard someone use syntec 5w50 motor oil, which I also suspect 5w30 is going to give much the same result. Incidentally, I use 10wt.

Also, it goes with reason ATF will work, but I don't know what the viscosity estimates are for the Dexron/Mercon types vs the thicker type F and the Mopar. Anyone chime in?
 

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ATF can be used, but the biggest drawback is the loose viscosity requirements. One bottle of brand x atf might be equivilent of 10 weight, while another bottle of brand y might be 15 weight. Once in a pinch, I used the Wal Mart brand of power steering fluid in my bomber for about a month.

Motor oil? I don't think it would hurt anything, but it's not really intended to be used as a hydraulic oil like ATF or PS fluid.
 

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Discussion Starter · #3 ·
Well, ATF types are supposed to be within a certain viscosity range per type, as named above. Were you looking into the same type across the different brands?

As far as power steering fluid goes, many of them are ATF types with some differences, usually the viscosity. There are others that more closely resemble motor oil with anti foam agents.

Motor oil is used as a hydraulic fluid in modern engines. Hydraulic lifters/tappets use motor oil under pressure. Some variable valve timing equipment uses motor oil in the actuators. I don't know how resistant it is to foaming, although I think it may be decent, especially on the outlet of a turbo, where the return oil is a foam and must release the bubbles as it makes its way back to the pan.

Thanks for the input. Hopefully we can shed some more light on this issue. Supposedly the damper side gets very dirty and the motor oil stays cleaner.
 

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Jerk_Chicken said:
Well, ATF types are supposed to be within a certain viscosity range per type, as named above. Were you looking into the same type across the different brands?

Motor oil is used as a hydraulic fluid in modern engines. Hydraulic lifters/tappets use motor oil under pressure. Some variable valve timing equipment uses motor oil in the actuators. I don't know how resistant it is to foaming, although I think it may be decent, especially on the outlet of a turbo, where the return oil is a foam and must release the bubbles as it makes its way back to the pan.

Thanks for the input. Hopefully we can shed some more light on this issue. Supposedly the damper side gets very dirty and the motor oil stays cleaner.
Yes, the cSt of various types of ATF can vary from batch to batch.

Motor oil does see hydraulic duty in piston engines, not only as you've described but also to float the crank and cams off their bearings, still, if it was superior in this respect, you'd think it would be used in auto transmissions and dampers.

I don't see how motor oil would stay cleaner in a suspension system. It's not exposed to high temps or the byproducts of burning a petro based fuel.
 

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Motor oil can't compress enough to work in a fork. ATF varies significantly in viscosity from brand to brand. Not to mention ATF will eat away your seals. Just pony up and buy the suspension fluid... It's a few bucks for a big huge bottle. Golden Spectro or Bel-Ray.
 

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what about moto fork oil?

I would guess that the local Kragen would carry Motorcycle fork oil, which is the same thing as bicycle fork oil.

...and yes, some liquids compress a small amount. That's why oil won't make waves that last for any length of time. They absorb the shock, unlike water.
 

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XSL_WiLL said:
Motor oil can't compress enough to work in a fork. ATF varies significantly in viscosity from brand to brand. Not to mention ATF will eat away your seals. Just pony up and buy the suspension fluid... It's a few bucks for a big huge bottle. Golden Spectro or Bel-Ray.
Err.... I don't quite understand the seal compatability phobia that exists in the bicycle community. What kind of seals are used in an automatic transmission? Magic seals? ;)
 

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pimpbot said:
I would guess that the local Kragen would carry Motorcycle fork oil, which is the same thing as bicycle fork oil.

...and yes, some liquids compress a small amount. That's why oil won't make waves that last for any length of time. They absorb the shock, unlike water.
Yes liquids do compress a small amount. Do some googling for the modulus of water and see what you get. It takes a horrendous amount of pressure to compress a little.

But that has nothing to do with waves in a fluid. That is relative to the viscosity and density, not compressibility.

As for ATF in marzocchis. Zanetti is making a lot of sense at the moment. I have used it in many forks (incl some marzocchi) with good results. The brands I used feel a little thicker than the standard 7.5wt.

I have also tried using hydraulic oil, but found that the viscosity changes a lot with temperature (as you'd expect really).

I wouldn't use motor-oil in a damper.

I have heard there is a difference in noise between using motor-oil and ATF in gearboxes, I suspect the ATF is noisier.
 

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Zanetti said:
Err.... I don't quite understand the seal compatability phobia that exists in the bicycle community. What kind of seals are used in an automatic transmission? Magic seals? ;)
It is the fact the ATF has a tendency to swell seals. Not so good on a suspension fork. I used to know a mechanic that used ATF as a temp fix on Mazda RX7 main seals.... Smoked like something out of a James Bond movie for about 1/2 hour, but it would swell the seals enough to stop leaking for a while longer until the customer could afford to have the problem fixed properly. Plus, ATF isn't really known as a lubricant either, which is something your fork needs.

Do yourself a favor and get some proper fluid...

Brian
 

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Moto fork fluids are the same as bicycle just you get more volume for the same or less money.
There is no standards for oil weights, manufactures can claim there product is any weight they wish.
:)
 

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Brian Peterson said:
It is the fact the ATF has a tendency to swell seals. Not so good on a suspension fork. I used to know a mechanic that used ATF as a temp fix on Mazda RX7 main seals.... Smoked like something out of a James Bond movie for about 1/2 hour, but it would swell the seals enough to stop leaking for a while longer until the customer could afford to have the problem fixed properly. Plus, ATF isn't really known as a lubricant either, which is something your fork needs.

Do yourself a favor and get some proper fluid...

Brian
What elastomer material are the main seals of Marzocchi forks made of?

ATF not a lubricant? Please tell me you're kidding. Are the internals of auto transmissions frictionless?
 

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"El Whatever"
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dogonfr said:
There is no standards for oil weights, manufactures can claim there product is any weight they wish.
:)
Was it DGC who posted a test of some oils?? He found that there are inconsistencies from brand to brand. The oil wt variated in a given range of cst's.

But... there are standards for oil weights. ISO VG and SAE come to my mind. If I require ISO VG 32 for, say, my lube oil system on a gas turbine, I can expect it to be inside some range of viscosity and make a claim against the manufacturer if its oil does not accomplish it.

However, it's an industry standard not to mix oils from different brands because the manufacturing differences (additives, viscosities, etc). If you are going to use other brand, generally (rule of thumb, not a written one) you dump the old oil completely and put in the new oil. Otherwise, depending on oil cleanliness grade (there are cleanliness grades too) you may just add more oil of the same brand.
 

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"El Whatever"
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Zanetti said:
What elastomer material are the main seals of Marzocchi forks made of?

ATF not a lubricant? Please tell me you're kidding. Are the internals of auto transmissions frictionless?
Oil pumps for power steering aren't frictionless either. Most are gear-pumps... that need lubication. So, power-steering fluid might work too (if it doesn't have any nocive additives).

Sorry for my ignorance... is ATF used in all the transmission?? Because in one part of the tranny the oil is just used to activate valves and power transmission (works like a turbine, AFAIK, with two rotors that do not touch each other) but the other part has the gear which has a lot of friction.
 

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Zanetti said:
What elastomer material are the main seals of Marzocchi forks made of?

ATF not a lubricant? Please tell me you're kidding. Are the internals of auto transmissions frictionless?
The seals are rubber...

And I would love to hear the apples to oranges comparison on the internals workings of a telescopic bicycle suspension fork vs. an automatic transmission....

Brian
 

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Zanetti said:
Err.... I don't quite understand the seal compatability phobia that exists in the bicycle community. What kind of seals are used in an automatic transmission? Magic seals? ;)
There are different type of seals made out of different materials. DOT fluid is very corrosive. Mineral oil is not. If you look at the two seals from a say.. A Magura or Shimano brake and compare it to a Hayes brake, it's different.

Most ATF contains a seal sweller, this also dissolves rubber. But if you just take a chunk of rubber and throw it in a jar full of ATF it'll eventually dissolve.

Same thing with forks, it'll work for a while, but eventually, it will eat through the seals and it'll start with some seeping, and it'll get worse and worse.

And to whoever that said fluids don't compress. That's wrong. Fluids do compress, not much, but they do.
 

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Jerk_Chicken said:
Fluids don't compress, period Will. You make mistakes like this a lot.
Whatever. Put motor oil in a fork, you'll see what I mean. And I've never made that statement before. Atleast not that I can recall.
 

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Warp2003 said:
Was it DGC who posted a test of some oils?? He found that there are inconsistencies from brand to brand. The oil wt variated in a given range of cst's.

But... there are standards for oil weights. ISO VG and SAE come to my mind. If I require ISO VG 32 for, say, my lube oil system on a gas turbine, I can expect it to be inside some range of viscosity and make a claim against the manufacturer if its oil does not accomplish it.
I work at a moto dealership & went to change the fork oil in a Suzuki & the manual said use #10 fork oil. When i called Suzuki to find out what weight #10 is they could not say. The person i spoke with had a very nice chart, unfortunatly i missplaced it, that showed a comparison of different manufactures weight numbers & what they would be equal to. You can go to a moto dealer & check out the fork fluids & spin your head all day, SS7 ,SS8, #5, #10, Soft, Heavy, 2.5wt, 7wt the list is long. Another good one is Hypoid 80wt, 80wt gear oil. 80wt gear oil is equal to 30wt motor oil aproximatly. ;)
 
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