Zetor 3320 brake problem

[geoweaser]

I am new to working on tractors and am dealing with a brake problem on my recently obtained Zetor 3320. Brief background: my clutch stopped working, which lead me to park the tractor. I discovered that the brakes and clutch use the same reservoir, which was completely empty, and after refilling and bleeding the clutch line, it now works. Unfortunately, although the right one brake may be working since there's resistance when I push on that pedal, when I press the left brake pedal there's no resistance. I tried to bleed the brake line losening the bleeder screw but found that it never gets pressurized by pumping the break pedal (for the first few presses on the pedal, I didn't have a hose running from the bleeder screw to a bottle of brake fluid; I realized I should have done that and eventually did so). When I press on the pedal, I sometimes hear a "squishy" sort of sound coming from where I think the master cylinder is.

Clearly there's a problem somewhere in the system since the reservoir was completely empty. Can anyone help me diagnose and -- Lord willing -- fix the problem with my brakes?

 

[MTGreen]

How are you trying to bleed? 2 person pedal pumping?
Suggest trying suction bleeding or bleeding by pressurizing the reservoir

 

[geoweaser]

The last thing I tried was by myself: attach hose to bleeder screw, then hold brake fluid bottle (half filled) with hose in it while sitting in seat and pumping brakes. I first filled the hose with fluid using a pipette.

Thanks for the suggestion. I'll have to look into suction bleeding and pressurizing the reservoir. Maybe I can get at least one of those strategies working using my shopvac.

 

[MTGreen]

The last thing I tried was by myself: attach hose to bleeder screw, then hold brake fluid bottle (half filled) with hose in it while sitting in seat and pumping brakes. I first filled the hose with fluid using a pipette.

Thanks for the suggestion. I'll have to look into suction bleeding and pressurizing the reservoir. Maybe I can get at least one of those strategies working using my shopvac.

That rarely works unless you have a one-way valve in your tubing. Suggest you look into 2 person brake bleeding where you open and close the bleeder on each stroke

 

[geoweaser]

Thanks. I'll give it a shot.

 

[JackDaniels1982]

I would have to say that you likely have a leak in your brake system somewhere. Further speculation would be that it is in your left side. In theory as you bleed it you should find a leak somewhere. (even sitting it may/should leak - cardboard underneath may give you a clue) In my experience brake leaks rarely get better on their own and you will be doing a lot of bleeding! I can't talk much as mine leak somewhere on the back on a 7745 for both sides and except for emergencies I only use the mechanical parking brake now.

 

[geoweaser]

I did the two-person bleeding for more than 30 minutes: pump breaks several times, open valve and let air escape, close value, repeat.... We worked mostly on the left brake (bleeder valve), but also on the right. Through the process, we nearly drained the reservoir twice, collecting what seems to be half or so of the brake fluid in a pan beneath the tractor. The clutch remains good and the right brake, which already had good pressure, also remains good but may be even slightly better. The left break unfortunately remains squishy, with no pressure. I didn't hear any air come out whenever I opened the right brake bleeder value, but air came out each time I opened the left valve.

Any ideas where the problem may be? Master cylinder?

There is a leak somewhere, but it's relatively slow and I haven't tracked it down yet. Thus, I don't think this leak is related to the problem but I could be wrong!

 

[MTGreen]

Squishy brakes come from compressible air in a system designed for relatively non-compressible brake/hydraulic fluid. It can also come from inadequate seals in the master cylinder piston creating bypass. Are the brakes on your model outside the rear transaxle or inside? If you have outside brakes and a fast leak you would see it leaking out when you step hard on the pedal. If you have a slow leak you would get a nice firm pedal for a short period of time.
Applying Occam's law of parsimony here, it's most likely inadequate bleeding on that side possibly due to poor design with high spots in the system. I would try pressure bleeding or vacuum bleeding first.
After giving that a boy scout try with no results, I would replace the seals in the master cylinder piston on that side

 

[geoweaser]

I don't know if "squishy" is the best description. The phenomenon I meant to describe is that the only resistance the brake pedal exerts when pushed is from the spring. I'm not sure where the brakes are (gulp), but as I've learned, they are dry disc brakes. I've not seen any leaking out whenever I step hard on the pedal.

I'll see if I can get the pressure bleeding technique you suggested to work. Thanks.

 

[geoweaser]

With some help, I was able to get the brakes working. I had to replace the lefthand master cylinder. Bleeding the lines at that point was a challenge. Ultimately, it was probably taking the master cylinder back off and doing a bench-bleed that made the difference. I followed this by a bit of suction on the bleeder screw and then two-man bleeding. It became fully pressurized.

Thanks for all the input.