Cat 936F brakes

[Bala]

Its been a while since I have been on here. I have been back on the tools for a year now, apart from 3 months off with a broken collarbone.

Mostly working on trucks but the company also has some other misc gear and as I have experience other than trucks I am tending to get to do a bit of the work on the odd stuff, which is all good by me.

Anyway, there are two Cat 936F loaders, one is overflowing the brake oil reservoirs. They have oil not brake fluid.

I havent looked into the problem, it will probably get a good work over in the coming wet season, but wondering if anyone knows of a common cause for this brake problem.

Cheers

 

[Nige]

There are 2 brake oil reservoirs, one for front brakes, one for rear brakes. Is it just overflowing one reservoir or both..?

 

[Bala]

thanks for the reply Nige.

I am pretty sure it is only one that is a problem, it is the outer one on the left hand side. But I cant remember if that is the front or rear.

 

[Mark250]

Hi Bala
The early f series loaders had weak diffs the side washers used to fail and the contamination would-take out the brake seals because they had inboard brakes
Check the diff oil for visible metal
Regards
Mark

 

[Bala]

Thanks Mark,

Will check it out. These loaders are quite neglected so anything is possible.

 

[Mobiltech]

I have always found that when the brake seals fail the brake oil goes into the diff not the other way around, sounds odd that it would go the other way.

 

[Nige]

I have always found that when the brake seals fail the brake oil goes into the diff not the other way around, sounds odd that it would go the other way.

There should be almost no pressure in the differential housing (unless there is a breather that's blocked maybe?) so I don't see how a failed brake piston seal could push oil back through the system to the reservoir.

I was thinking something in the air side might be the root cause seeing as the brakes are air-over-hydraulic.

Bala, If you want a copy of the brake system operation document drop me a PM with your email address and the loader Serial Number.

 

[kshansen]

Well not on a 936F or even a Cat machine but where I worked we had a Komatsu WA600. But it still had about the same set-up for brakes. Pistons and multi-plates in wheels with air over oil master cylinders. Right from new it would gain oil in the reservoir oil tank. Dealer said this was "normal" said the brake piston seals would let a little axle oil leak past when they released. So we just kept draining off the extra oil at each service. Probably less than a quart in 300 hours work. Strange thing is after a couple years the oil level stopped going up and stayed right in the center of the sight gauge for years!

 

[Bala]

I have always found that when the brake seals fail the brake oil goes into the diff not the other way around, sounds odd that it would go the other way.

I have had backhoes and tractors where the the brakes seals have gone and the brake oil has leaked into the diff.

There should be almost no pressure in the differential housing (unless there is a breather that's blocked maybe?) so I don't see how a failed brake piston seal could push oil back through the system to the reservoir.

I was thinking something in the air side might be the root cause seeing as the brakes are air-over-hydraulic.

Bala, If you want a copy of the brake system operation document drop me a PM with your email address and the loader Serial Number.

Thanks Nige, There is parts manual at work, there may be a shop manual, if not I may take you up on your offer.

Well not on a 936F or even a Cat machine but where I worked we had a Komatsu WA600. But it still had about the same set-up for brakes. Pistons and multi-plates in wheels with air over oil master cylinders. Right from new it would gain oil in the reservoir oil tank. Dealer said this was "normal" said the brake piston seals would let a little axle oil leak past when they released. So we just kept draining off the extra oil at each service. Probably less than a quart in 300 hours work. Strange thing is after a couple years the oil level stopped going up and stayed right in the center of the sight gauge for years!

It is making oil not just pushing air into the reservoir and making it over flow. I was just driving thinking that it may be sucking up from the diff rather than pushing up from the diff. just as kshansen has suggested. The compressor unloader is not working, it is just blowing off the tank safety valve!. So it is quite probable that the two problems are tied together.

 

[Nige]

Thanks Nige, There is parts manual at work, there may be a shop manual, if not I may take you up on your offer.

No worries, just PM me with an email address if you need it.

Personally if the compressor unloader is not working I'd fix that first before moving on to the brakes. You never know what weird things the additional air pressure in the system might be doing.

 

[Bala]

I have managed to confuse myself as I had to swap out parts on the two 936 loaders we have. The one with the major brake oil problem does not have an air problem.

I may see this one as early as this week or may not. I dont decide what gets done when where I now work, which is a nice change.

It may no be any time soon but if the problem gets solved I will report the findings.

 

[Mark250]

I have always found that when the brake seals fail the brake oil goes into the diff not the other way around, sounds odd that it would go the other way.

hi al,l these diffs don't have a breather as such and run slightly pressurised with a small relief valve that looks like cut off grease nipple



years ago when the F series came out the early machines (970F) used automotive brake fluid in the brake reservoirs this was later changed to SAE 10 however the brake reservoirs were the same only with the addition of a small sticker to indicate the change, as a result we had a lot of machines that had the wrong fluid added to these reservoirs and caused a lot of brake seal issues.
so if the diff side thrust washers haven't failed and the relief valve has not seized closed, it is possible that some one has added brake fluid instead of oil and damaged the seals. the residual diff pressure will push the oil back into the brake reservoirs
Regards
Mark

 

[Bala]

Thanks Mark, for the effort on the info.

I am assuming there is no air running into the diff housing and that it is just the air in the housing expanding as it gets warm and rather than having a breather open to atmosphere they have the small relief valve to maintain pressure in the housing.

And then why? To stop water getting in?

If so is there any reason I could not just take the relief out and run the breather higher like I do on my landcruiser.

Then if the seals are bad I will see a loss of brake oil into the diff.

Cheer

Max

 

[Mark250]

hi Bala,I am unsure why it is slightly pressurised but I assume your right with the water and also to expand the lip seal on the pinion shaft ????
usually you can smell the brake oil at the reservoir and get an idea what it is. As the diff and the brakes are the only items mechanically connected there really is no where else where it can come from. you could also isolate each side and operate for a while to tell which side is leaking if you wanted
At the end of the day you will probably have to pull the axle assy and strip and reseal/ rebuild as required
they are quite straighti forward to repair
Regards
Mark

 

[Bala]

The oil in the reservoir is goes black, I have no doubt you are correct and it is pushing oil up from the diff.

I dont know what will get done and when, as I said I dont make that call.

But at least i now know I need to check the diff oil for metal for possible diff failure, and that we have a seal problem.

I have done brake seals on a JCB backhoe and a new holland tractor so I would think this is similar just a little bigger.

Thanks to all for the feedback.

 

[Nige]

Those relief valves in the diff housing are well known to stick closed and thus generate pressure inside the axle. Generally the factory mount them on a flat surface which then gets covered in dirt and buries the breather which then sticks shut - great design ....... So the first thing I would check is that the breather is not buried and even if by some remote chance it's in clear air, is it stuck closed..?

On larger loaders we had good luck with removing those relief valves completely and then using pipe fittings and ran a length of hose up through the machine frame to a suitable location where we mounted an atmospheric breather. Later Cat came out with a new model range which basically copied what we'd already done .......

 

[Bala]

We actually did one of these loaders. Mainly because the oil that overflows out of the reservoir spills onto the turbo so the boss was worried about it catching fire. We pressure tested them with air and the rear held nothing and vented through the diff breather hole, which is what I expected as there was no oil in the reservoir when it came in. The seal in the rear were very perished.

The front held 30psi, but this was the one that was overflowing the reservoir.

The seals in the front were not perished at all, but about 2" of one had a fold in the back up ring inwards. This explains how the pressure from a blocked breather was pushing oil into the reservoir but the seal could hold under braking pressure.

I modified the breathers so they are open, rather than pressurised.

All in all a perfect result.

I have done these style of brakes on backhoes and tractors but never had an overflowing reservoir problem. So another thing to put in the memory bank.

Thanks again to all those who helped.

 

[Nige]

Always nice to hear a success story .....