I have a 2004 Sportsman 700 that was purchased for me as a Father's Day gift this year. While playing with it the first few days I noticed that the brake master cylinder (the little box attached to the grip on the left handlebar) was leaking. Soon thereafter I took the machine to the local Polaris dealer and had them go through it stem-to-stern since I didn't know what the previous owner might have done with/to it. One of the things they did was replace the brake master cylinder, which didn't surprise me since I had noticed it leaking.

Everything worked well for a couple of months, but the machine wasn't really stressed much. Mostly easy-going trail rides and some brush work.

Today I took the machine out for its first really intense ride. Some serious hill climbs, rut bouncing, etc. Halfway through the ride, I noticed the brake master cylinder is leaking again!!! WTF?!? Two separate master cylinders and they both fail in precisely the same way?

I plan to take it right back to the same dealer, but in the meantime I'm wondering if this is commonplace. Perhaps there's a known design problem on the master cylinders? Anyone else experience this?

Thanks!

 

Yeah, I have a 2004.5 700 efi and noticed that mine is wet all the way around the top where it seals. It's not dripping or anything but just made it wet from the seal down about 1/4". Was yours worse than that or just enough to notice like mine?

 

I have an 03, same problem. I used a little RTV sealant(blue) around the edge(very small amt) no more leaks. take the cover off and u will see the edge I'm talking about.

 

Polaris has redesigned the master cylinder completely for 2007. When you take it back request the revised model. Before this revision they were notorious for leaking. One problem I found was that fluid trapped above the gasket would leak as the gasket is only designed to seal the reservoir. How it gets there we do not know but after I diassembled and cleaned that out I had no more leaks on my 05 800. Get the 07 piece if you can.

 

Mine was, and is, leaking enough to drip down onto the front body piece and the left footwell. The footwell plastic does NOT like brake fluid, BTW.

It's also lost enough that the little "eye" shows low when the machine bounces a bit.

I'll talk to the dealer about the 2007 version and see if it can be retrofitted.

I guess it's good to know this is a "known" problem. That may make it easier to resolve with the dealer.

Thanks for the feedback!

 

Got the word back from the dealer. It turns out they replaced just the LID (with its o-ring) when they serviced my machine a couple of months ago. Since it's still leaking, they believe the body itself is probably distorted and thus not sealing. They're giving me credit for the lid I already purchased and not charging me labor to install a whole new master cylinder. Cost is still around $135, though.

I asked about using silicone around the lid and the tech said there is a small vent port on the lid that must not be closed. You are not supposed to have a perfectly air-tight seal there. He said he's silicone it if I wanted but that he wouldn't recommend it. Naturally they're in the business to sell services but he seemed pretty honest about it.

I also asked about retrofitting a 2007 cylinder. He said it was possible, but that the brake line banjo bolt fitting was different. They'd have to replace the entire brake line along with the cylinder, something he described as "cost prohibitive". BikeBandit shows the 2004 brake line costing $52; they don't have 2007 data yet but I bet the combination of the 2007 cylinder and 2007 brake line won't be any cheaper than the 2004 versions so it would probably be well north of $200+ to retrofit the 2007 brake cylinder. No thanks.

I asked what they think is going on here, and the tech confirmed they do see a lot of this - "We've probably replaced 30 or 40 of these in the last year." They try an intermediate fix by replacing just the lid/o-ring, but when that doesn't work they have to replace the entire assembly. I asked what he thinks is going on and his theory - unconfirmed by Polaris - is that the cast aluminum fluid tanks are sometimes slightly warped. If true, they'd have to be warped quite a bit to not be sealed by an o-ring.

I confirmed that the replacement cylinder will be warranted, and I suspect after the history I've had they'll take care of me even if it's a little past the warranty period. Brakes are pretty important so I'm spending the $130 to make it right. I'm not thrilled but it does seem like the dealer is doing what they can to take care of me.

 

i hope your problem is fixed after you spend the money. if it does not fix it go buy some rtv sealant and seal all the way around the lid like i did and your problem will be solved.

 

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I don't understand why it shouldn't be an air tight seal. If not, then air (with moisture) is going to enter and that means rust. Plus, I imagine some dust would get in--I mean, have you ever taken anything off your machine that didn't have dust in it?

I would first try making sure there was no fluid around seal. Next, I would consider a new seal (if yours has one). Last, I would use silicone. I had a leaking problem, too, but several tries at "first" worked for me.

GJRonK

 

I agree, the idea of a vent into a master cylinder - when they give you all those warnings about how brake fluid attracts water - struck me as a little odd. However, they've installed a new unit and so I'm now committed to that course of action.

If it leaks again, I'm going the silicone route.

 

As I understand it you must have the tiny vent in these systems for two main reasons. One is that brake fluid expands as it is heated and once expanding the slight amount of air above the fluid in the reservoir would have no where to go and pressure would build up back through the system causing all sorts of havoc. Also, as the fluid heats up it expells moisture that may be in the fluid by vaporization although the extent of such would depend on the amount of heat introduced into the system by use of the brake, ambient heat from the motor, etc..