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- Jul 5, 2003
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- Laag Zuthem
- First name
- Renze
Machinery:
1976 5718
1978 5718 35kmh: Work in progress
1967 3011
Because one of the the more frequently asked question on this forum is about brake replacement, here a general basic explanation: If you have questions remaining after reading these basics, feel free to start a topic and ask the more specific questions that may arise on the go !
If you have a cab model, you need a means of hoisting the portals off underneath the cab, like a workshop engine hoist, another tractor with loader, or a forklift. You need to take off the portals, which weigh 100-150kg.
On a cabless version you might be able to get by with a pulley on your shed truss, after removing a mudguard.
Its about a day of work. release the hand brake tensioners on top of the rear axle (underneath a slotted ventilation cover) to make them slide off the drums when you pull the portal.
Before hoisting the portal, "crack" it loose from the rear axle housing and rotate it down to where gravity pulls it, THEN attach the hoist and start pulling it out. This also helps clearing the cab mounts when pulling it out. (dont forget to drain the transmission oil first or it will pour out when you pull it) Mounting goes in opposite order.
Before taking the parking brake assembly apart, get a picture (photography, or a picture in your head) of how the levers run: you need to remember that carefully or a one day repair ends up in a two day repair because you'd have to reverse engineer the mechanism.
When reassembling, make sure you have enough clearance between the brake and drum: The linings are glued to aluminium pads, which expand more than the cast iron drums, when heated. So if you have them too tight, friction will heat them up and push them on harder: Overheating the linings may result in glazing, which makes them ineffective and you replaced them for nothing.. :/
They need about 1 to 2mm play, and should slip on once you have the shoes perfectly aligned on the drum diameter. (usually you need to push them from side to side, together with the brake cylinder pistons, to align) When its fully on, you need to be able to turn the drum with no brake dragging, it may just whisper but not make any grinding noise at all. I once had to use a 13mm drill (ground to a radius head) to drill the recess holes for the brake cylinder pushrods deeper, to get some free play. (the aluminium shoes expand faster when heated, than the cast iron brake drums, so when they drag, the friction heat only pushes them on harder !!)
But before you decide to modify the brake shoes to create more play, first make sure the pistons of the new brake cylinder are fully retracted !
When you have the final drive portal off, there is a C shaped round stock ring that fixates the drum on the diff output shaft. undo that with a screwdriver before you ruin your pulley extractor tool trying to pull the drum off the diff shaft
It is advisable to assemble the hinge pins of the brake shoes with plenty of free play, the aluminium tends to corrode (the white dust) and then they get stuck on the pin. I polish and hone these holes with coarse sandpaper till they have at least 0.3mm free play on the pins so they wobble from side to side a wee bit, and mount with plenty of copper grease (or any other synthetical heat resistant grease)
Common practice when replacing brakes, is to replace the whole package: Service brake shoes, parking brake bands, shaft seals, but also the rubber gaskets between shaft and brake shoe, and O rings. There are three seals: an O ring, a lip seal (take the caps off because they can only be knocked out of their pocket from the inside) and a serrated rubber ring that seals between the brake drum and the shaft itself. (the lip seal runs on the brake drum, the rubber ring seals between the shaft and the drum) When prying a differential output shaft back in the differential, you have a 50% chance of overstretching the old, aged shaft seal and making it leak. Its a days work, dont be cheap and try to save three to five bucks on a shaft seal !!
If you replace the brakes because an oil leak made them ineffective, its usually caused by either the serrated rubber gasket ring that seals the brake drum on the halfshaft, in that case you can see the oil leak marks. A more rare situation is when its caused by a leak from the portal side, so rare that its uncommon to replace this shaft seal precautionary when doing a brake job.
Make sure the difflock coupler on the right hand side is correctly lined up, you can align it after putting the cover back on by finger force, but dont forget to put it back inbetween the yoke if it fell out during disassembly.
Here are some useful Youtube videos to get a general idea of what you're getting into, and how stuff looks on the inside:
View: https://www.youtube.com/watch?v=8dacP1Eqa0w
View: https://www.youtube.com/watch?v=gMYERtVU44M
Just one final word of caution: When you see the brake pipe rotate with the gland nut that pushes it in the brake cylinder, either stop to cut the line (and later reconnect with a standard straight connector from an auto repair shop) or order new brake lines together with the shoes, cylinder and shaft seal. Old gland nuts have a nasty habit of corroding solid on the copper brake line so the line kinks and twists when unscrewing the gland nut.
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The general guideline above, is valid for all UR1 Zetors with drum brakes, however there are some differences in drum diameter on the 2011, the 3011/3511/4712, the 4011/5511, but the shoes of the 4 cylinder 5711/6711 from 1972, and all their successors from 1978 onwards (both 3 and 4 cylinder: 4911-7245) are interchangeable between the mentioned groups.
All models have hydraulic brakes, but from the 12 series (5245-7745) 1984 onwards, the clutch was also hydraulic, using the identical type of master cylinder. If you have any problems regarding master cylinders on the early models, replace the master cylinder entirely and do NOT use a rebuild kit: these cylinders failed ofted due to a bad cylinder coating (the part you NOT replace when putting a rebuild kit in it) The PAL cylinders are bad, the newer ones are supplied by Fragokov.
The 7745 came standard with the disk brakes of the 8011, which was optional on the 7245 in some countries. The same counts for the 6340 and 7340. The Super series of 1997 had disk brakes by Knorr. Those are not within the scope of this basic guideline.
You can also use the site search function on the left top side of the forum, to find a host of brake replacement information on this forum.
As said, if your questions havent been answered by this basic guide, nor by a quick look through old forum topics, feel free to ask !
