RTV900 rear brake cylinders do not return to free

[Luckystars]

Has anyone seen this where you start to go either direction and it feels like the brake is on? I hardly ever use the brake but it seems to apply itself. There are 2 cylinders on the back and when it wants to drag these "wheel" cylinders are extended some. I use a screw driver like a pry bar, I don't think anyone use a screw driver for screws, and I can slowly push the plunger to the rear. This frees it up It'll be good for an hour or several days.
When it does this the brake pedal is hard.
I'm thinking bad master cylinder or maybe bad hose. Is there a check valve in the lines somewhere?
The Master is not over filled and when I remove the cap it is normal, no pressure or build up.
Lifting the pedal doesn't help.
Next time it does this I'll have a wrench to fit the bleeder with me and see if opening the bleeder allows them to release.
Any thoughts or experience is appreciated.

 

[PoTreeBoy]

Is the brake pedal return spring missing, or anything preventing the master cylinder from fully retracting? If this is like most disc brake systems, there is a relief port right at the end of the stroke that prevents trapping fluid in the line.

 

[Captain13]

You might just need to lube the caliper pins. Also, check for corrosion on the pressure side of the caliper to make sure that corrosion is stopping the caliper to release fully.

 

[whitetiger]

You need to spray a good penetrant on the shafts where they enter the transaxle and work the shaft back and forth some. It is very common since people rarely use the brakes. It gets moisture and rusts between the shaft and housing. A little soaking and moving the shaft will free it back up.
You might go ahead and do the diff lock and front axle engage shafts also while you are at it.

 

[Luckystars]

Is the brake pedal return spring missing, or anything preventing the master cylinder from fully retracting? If this is like most disc brake systems, there is a relief port right at the end of the stroke that prevents trapping fluid in the line.

I am working on the rear so no calipers but I like the idea that the pedal may not be returning to 'vent' off the pressure. I'll check that this afternoon. Maybe the rod is adjustable and can be shortened. Last night it did it again and I cracked the bleeders in the back. These was no pressure just a few drops. I did the screwdriver push them back again and they went in easier. I 'think' my issue is in the front but I'll keep looking. Maybe a bent line underneath? I'll look more this afternoon. Also check the freeness of the levers and look at return springs. Thanks everyone.

 

[Pau7220]

Not knowing the age or condition of the machine... is it possible someone put hydraulic (or any petroleum) oil, or DOT 5 brake fluid in the master cylinder? It really does sound like contaminated fluid. Take a sample from the master and put it in a bottle with water..... it should be completely water soluble... nothing floating.
If contamination is found, every hydraulic component with rubber in it needs to be replaced.

 

[lugbolt]

inside the master cylinder there is a vent port. Brake fluid is one of those things nobody ever thinks about until something like this happens, then OMG, we need to do something. What I saw a lot of-particularly with motorcycles and ATV's, is that the fluid never got changed (ever) or flushed (...ever), and it sucks moisture out of the air, which causes the fluid to get congealed, and that semi-jelly like fluid tends to plug up the vent inside the master cylinder. Typically when this happens, you can apply the brake one day but it won't return, and the lever/pedal is rock hard--because it won't vent pressurized fluid back to the master cylinder.

With that, I have never run into this on RTV's-ever. Doesn't mean it don't happen, I just never saw it. Brakes on RTV's were something that were quite rare to have to work on at the little dealer I worked at. I had to adjust them sometimes (rears) and flush fluid if a customer wanted a full service, but that was it.

 

[GeoHorn]

You might wish to inspect your parking brake mechanism to be certain it isn’t setting the brakes and is fully releasing.

 

[Luckystars]

What I have done this morning (before reading these great ideas) was I checked for slack in the parking cables. It has some. Loosened each side wheel cylinder about 1 turn, just so I'd have more travel in the pedal. Checked the pedal to make sure it wasn't topping out and t does not. And the last thing is a return spring on the drivers side that goes from a clevis off the brake arm to a lever that pulls forward and must be pushing a bypass port in the rear transaxle. This spring was loose but not off. I adjusted this last to 1/2 turn from having tension. It was about 4 turns from tension. I assume it bypasses fluid to prevent 4 wheel launches?
I do have more pedal travel and they have released in my quick test drive. I'll know more this evening after I water everything.
Thank you all.

 

[whitetiger]

a return spring on the drivers side that goes from a clevis off the brake arm to a lever that pulls forward and must be pushing a bypass port in the rear transaxle. This spring was loose but not off. I adjusted this last to 1/2 turn from having tension. It was about 4 turns from tension. I assume it bypasses fluid to prevent 4 wheel launches?

That is the pressure dump valve so you can change gears. When you depress the brake, the hydro pressure is dumped so there is no pull on the transmission and you can shift gears with the oil cold.

 

[Luckystars]

That is the pressure dump valve so you can change gears. When you depress the brake, the hydro pressure is dumped so there is no pull on the transmission and you can shift gears with the oil cold.

Thank you for that. I have never tried to switch gears when moving. It slows so quickly when I let off the throttle pedal.
By loosening the brake adjusters it seems the problem has been neutralized. I say that because when parking in the Florida sun the wheel cylinders will not stay bottomed out. They creep out about 3/16". Putting 5/16" slack still leaves some room for free wheeling and the brake pedal is still very high. It has become a non issue. It's working but doesn't feel like I fixed it.
Thank you everyone for the help and ideas.