790 Brakes Overflowing/Overheating?

[DWCox]

Hi,

I have a JD 790 and was compacting soil on a steep hill. This required me going up the hill, pushing in the clutch, and then rolling back down the hill with the brakes on. I had to do this repeatedly on a rather large area of hill. Needless to say, this produced considerable heat in the brakes and I could hear the brakes squeal and also smell them after a while.

Yesterday, I finished this compacting procedure and noticed the smell was rather strong. Later I also noticed a black fluid on the floor of the garage. I inspected under the tractor and there was black fluid oozing out of what appears to be overflow holes on each side of the rear axle. The fluid had the strong burnt smell of the brakes.

What is this fluid? The best that I can figure is that the outside of the brake drums are bathed in fluid to keep things cool. Was this fluid superheated and overflowing out the axle after the drum became very hot? If so, should I replace this fluid somehow?

Thanks in advance.

 

[crashz]

The 770 and 790 are almost the same tractor. They share nearly everything. But I'm not sure about the brakes. My 770 has dry shoes. So if they are the same, my thought is that you could have toasted the axle seals.

 

[DWCox]

Thanks for the reply. I went out to JD online and checked the parts diagram, and it appears you may be correct--the brakes are dry and there is in fact a seal directly behind the drums. The drums must have heated to the point of compromising the seal. I never thought that would be possible.

I will open it up and and check it out tomorrow.

 

[Willl]

Next time use a low gear to maintain down hill speed.

 

[DWCox]

Next time use a low gear to maintain down hill speed.

Thanks. I actually started putting it in reverse the next day when I realized that the brake smell wasn't going away. I was compacting clay material inside the basin and sides of a large pond. Even driving up the side and then using the brakes in a controlled reverse descent took a a great deal of time. Changing gears in the middle compounded the time.

This would have been an ideal situation for a hydrostatic transmission.

 

[DWCox]

I pulled the brake covers yesterday and, interestingly, the seals behind brake shoes were fine. Evidently the excessive brake heat had turned the small amounts of grease behind the brake drum into liquid, where it mixed with brake dust at the bottom and flowed out the hole. So, I cleaned everything up real well, broke the glaze on the brake shoes and drums, and added small amounts of high temp grease where needed. It works find now.

 

[RoyJackson]

I'm late on this thread...sounds like your fluid got hot and expanded...which would result in some fluid venting.
Since the 790 has dry brakes, you wouldn't see any fluid from them.
I strongly recommend you use the low range reverse gear (with MFWD engaged and a low RPM) for your work. That would provide the most engine braking and reduce the load on your brakes. Also, this would reduce wear on that dual stage clutch (which isn't cheap to replace!!).

Freewheeling down a slope is not the safest thing to do. Sooner or later, you'd take a joyride down...which could have disastrous results.

 

[Willl]

your fluid got hot

What fluid you talking about Roy ?

 

[RoyJackson]

What fluid you talking about Roy ?

Hydraulic Fluid in your transmission.

 

[DWCox]

No leak from the transmission fluid--and no free-wheeling in reverse (hence the use of the brakes). My original post was premised on the thought that these were wet brakes, but they turned out to be dry. I have used this packing procedure for ponds in the past with Case backhoes and larger tractors. The 790 is a fine little tractor, but I will be more careful not to push it in ways I have larger tractors.

 

[Willl]

Hydraulic Fluid in your transmission.

Still don't follow ya Roy. How would hydraulic fluid come anywhere near the brake shoes and ooze out of the holes the OP was talking about ?

 

[irwin]

I pulled the brake covers yesterday and, interestingly, the seals behind brake shoes were fine. Evidently the excessive brake heat had turned the small amounts of grease behind the brake drum into liquid, where it mixed with brake dust at the bottom and flowed out the hole. So, I cleaned everything up real well, broke the glaze on the brake shoes and drums, and added small amounts of high temp grease where needed. It works find now.

Well okay, sounds good. Not very many complaints about the solid little 790.

Glad all's well....

 

[RoyJackson]

Still don't follow ya Roy. How would hydraulic fluid come anywhere near the brake shoes and ooze out of the holes the OP was talking about ?

First post described fluid coming out of what appeared to be overflow holes on the rear axle. There are a couple holes back there (close to the transmission housing). The fluid could also have been coming out of the hydraulic tank and flowed down the casting...hard to say, really,without actually seeing it. But the only fluid in that area of the tractor is hydraulic fluid. BTW, the brakes on the 790 are inboard, just outboard the differential.
Of course, this could also be grease...but I'd never seen bearing grease get hot enough to get that liquidy.