Brakes on 7341

[boxersoft]

I acquired a Zetor 7341 recently. It didn't have any use over the winter and when I next drove it, the brakes failed - they felt spongy at first and after a few presses on the pedal they gave up completely.

I noticed that some fluid had leaked from one of the front wheel hubs onto the wheel - I assumed at first that it was brake fluid and a seal or pipe of some sort had blown. There seems to be plenty in the reservoir though and the leak doesn't seem to have affected the paint on the wheel, so perhaps it's oil and may may not even be related. The handbrake still works OK.

I've done some work on cars before but I'm completely new to tractors. Can anyone suggest where I should start looking to trace the fault?

 

[ixer0]

Hi Steve

The fluid on the front wheel will be hub oil. (Don't let it run short as it only holds about a litre.)
The first thing to try is bleed the brakes as it sounds like the master cylinders are letting air in. There are probably 7 bleed screws (Depending on tractor spec.) One on each rear wheel cyl on top of the axle, 2 on the air valve under the cab R/H side, one on the trailer brake valve (if fitted) and one on each front hub. Front hub ones need air in the air system to operate.
Try that lot and see how long they last before you lose them again.

Good luck

Mike

 

[boxersoft]

Thanks Mike.

Front hub ones need air in the air system to operate.[/]
That's interesting. I tried to use the tractor's compressor to inflate a car tyre recently but I couldn't get any air out of it at all. I understand that you have to release air from the tank to stir the compressor into life, but when I tried that it seemed empty (no hiss). I don't know if this would explain the complete lack of braking if only the fronts depend on the air system, but it doesn't sound like it's a coincidence. I guess under the circumstances I should investigate the air system (assuming that it does[/] sound like a fault) before bleeding the brakes. Any suggestions?

Apologies for the delay in responding, by the way. I had requested e-mail notification of posts but didn't get any so I didn't notice your reply.


Steve.

 

[ixer0]

Hi Steve

It's only the front brakes that need the air system working. You need the air going to operate the 4WD and Diff-lock also. Start with the pipe from the relief valve to the tank - they crack regularly so no air pressure builds up. New pipes are rubber.

Regards

Mike

 

[boxersoft]

It's only the front brakes that need the air system working. [/]
Whatever's causing this problem is affecting more than just the front brakes - there's absolutely no braking whatsoever from the foot brake. The Operator's Manual (which uses "interesting" translations into English!) says something about "Front driving axle brakes are controlled by air-liquid amplifier depending upon pressure in the rear brake circuit", which I thought would mean that both front and rear had a common system, but perhaps not.

You need the air going to operate the 4WD and Diff-lock also. Start with the pipe from the relief valve to the tank - they crack regularly so no air pressure builds up. New pipes are rubber.[/]
I'm not sure what the "relief valve" is - is itthe bit between the compressor and the tank that includes the the tyre-inflator take-off? If so the hose from there to te tank certainly does look cracked. I thought it was surface cracks onl, but I guess it's worth replacing anyway. But... shouldn't I still be getting air out of the tyre inflator hose when that's connected anyway?

Thanks,

Steve.

 

[ixer0]

Hi Steve

You are correct as to which valve we are talking about. I think the airline uses "system pressure" so if there is a bad leak it doesn't have any pressure.

Regards

Mike

 

[boxersoft]

Curiouser and curiouser...

I had assumed the air tank was empty because the drain valve isn't venting air, but throwing the 4wd switch a number of times evidently caused a valve in the regulator to operate and start delivering air to the tyre hose. Presumably this happened because engaging 4wd repeatedly reduces the air pressure in the tank, and yet the drain valve doesn't. Is the drain valve prone to blocking, by any chance?

I also noticed that the operator's manual refers to pulling [/]the ring to drain the tank. Mine seems only to move when I push[/] the pin, not when I pull it. Don't know whether this is significant or just a change in design.

Steve.

 

[boxersoft]

The first thing to try is bleed the brakes as it sounds like the master cylinders are letting air in. There are probably 7 bleed screws (Depending on tractor spec.) One on each rear wheel cyl on top of the axle, 2 on the air valve under the cab R/H side, one on the trailer brake valve (if fitted) and one on each front hub

Well, I tried, but all I could find to bleed was a single nipple on a part under the RHS of the cab and the two front hubs. That has made a difference, with the right brakes working to some degree. The left is dead though, with a bit of resistance only if pumped. Any recognition tips for the ones I've missed? I thought I'd at least be able to spot the ones on the rear axle but evidently not

By the way, I have a Gunson "Eezi-Bleed" device that I have used on car brakes to allow bleeding without an assistant (it pressurises the system so it's like constant pressure on the brake pedal). It didn't seem to work on the Zetor though - is the brake system incompatible with such devices?

Regards,

SteveR.

 

[ixer0]

Hi Steve

There is a bleed screw on each rear wheel cylinder. Look on top of the axle at each side under the cab. (Follow the brake pipe to locate them) If you have hydraulic trailer brakes there is a small bleed screw on the brake valve. (Under the cab at the front left hand side) Where you found the bleed screw under the R/h side of the cab there are normally 2 together. For bleeding the front brakes make sure you have plenty of air in the tank and press both pedals together.
I've used an eezi-bleed on them with no problems.

Regards

Mike