How to Change a Bearing In a Reducer Angle Grinder Bosch

Angle grinders (angle grinders, angle grinders) under the German brand Bosch are of high quality, reliability and durability. The main competitive advantage of Bosch angle grinders lies in the widespread use of innovative technologies in the manufacture of the product.

But German quality cannot resist Russian negligence. Improper use of the tool, untimely replacement of grease, carbon brushes, bearings leads to failure of the tool.

In order to repair a Bosch angle grinder, you can go in two ways: give the angle grinder to a service center or repair the Bosch angle grinder with your own hands.

The first option is more expensive and not always high quality. The second option can be implemented only if the consumer has a great desire to figure everything out on his own.

A diagram of the Bosch angle grinder will help you repair yourself.

Bosch angle grinders are conventionally divided into low-power up to 1000 W, and powerful over 1000 W are marked GWS 7-125, GWS 20-230 or others.


The first number of 20 or more indicates a tool power of more than 1000 watts. The second number 230 confirms that this is the maximum diameter of the cutting wheel.

The first digit up to 20 indicates the power of the tool up to 1000 watts, and the second about the maximum diameter of the cutting wheel up to 125 mm.

Design Features of Bosch Angle Grinder

The design feature of the Bosch angle grinder is presented in the gearbox as a thrust bearing of a driven helical gear of a needle bearing. In Bosch rotary hammers, the driven gear is mounted on the spindle shaft by compression.

In Bosch angle grinders of low power, in which spur gears are placed in the gearboxes, the installation of shims is provided. This design allows you to restore the functionality of the contact gears, reducing the thickness of the gasket. Helical gears at high tool speeds wear out significantly less than spur gears.

how to change the bearing in the gearbox Bosch angle grinder

The working environment of grinders is most often a dusty space. Dust is the main danger leading to failure of the power tool, an amorous and angle grinder.

Repair tool required

To repair a Bosch angle grinder, a tool is indispensable. We’ll make a reservation right away, if you have a screwdriver, this will significantly speed up the process of disassembling and assembling the tool.

But you can get by with a set of screwdrivers, preferably with a ratchet mechanism. You can not do without an open-end wrench, with which you will unscrew the nut securing the leading helical gear.

It is better to have a special puller for dismantling the bearings.

Diagnostics of the electrical part can be carried out using a tester or a short circuit detection device.

It is especially useful in that it allows you to determine the malfunction of the rotor or stator without removing the assembly.

The diagram of the Bosch angle grinder will help you carry out repairs yourself, and these instructions will help you adequately cope with any problem.

DIY disassembling Bosch angle grinder

For the owner of a power tool, knowledge of his device and the ability to disassemble is a must.

Knowing the disassembly procedure, the angle grinder allows you to independently perform such tasks as changing grease, changing bearings and carbon brushes.

To disconnect the gear housing pos. 821 from the stator housing pos. 888, it is necessary to disassemble (remove) the handle housing, angle grinder pos. 24.

This operation must be performed to remove the carbon brushes pos.810 holding the rotor manifold.

In the second stage, unscrew the 4 (four) screws pos. 61 that secure the gear housing and stator.

Having pulled out the rotor together with the gearbox, proceed to disassemble the gearbox.

Repair angle Bosch grinder begins with the disassembly of the gear pos.821. Dismantling of the gearbox starts with unscrewing 4 (four) screws pos. 60. As a rule, the screws are screwed into the sealant at the factory. Will have to make some efforts.

Just note! For Bosch low power grinders, the gearbox uses spur gears. For grinders with a power of more than 1000 watts, helical gears are used in the gearboxes.

How to remove the driven gear

After removing the gearbox cover, you can get the helical gear assembly pos. 26.

To remove the gear, you must use a press or puller. But the use of a puller is difficult, because it requires the use of special thin sponges.

Before removing the helical gear, check the gear backlash, tooth integrity, contact spot.

A bearing pos. 50 is pressed onto the spindle shaft, pos. 26. If the bearing has a large backlash, it is noisy when scrolling, the grease has dried, it is preferable to replace it.

To remove the bearing, it is necessary to remove the gear wheel, circlip and dismantle the bearing. If the bearing remains in the gear housing while removing the rotor shaft assembly, the bearing is removed using a hammer and a soft tip.

How to remove pinion Bosch angle grinder

Leading gear pos. 27 is removed from the rotor shaft in the following sequence:

  • hold the rotor by hand and use the open-end wrench to unscrew the nut pos. 45 counterclockwise;
  • remove the washer pos. 59.;
  • pull out the helical gear, key 27.

Check visually the integrity of the gear teeth, contact spot.

If the gears are very worn (licked), there are chipped teeth, then they must be replaced. over, the replacement of gears is always done in pairs.

In low-power Bosch angle grinders, a needle bearing is used as a support bearing in the gearbox.

Do-it-yourself repair of the bosch uhm follow the strictly enclosed instructions. If you need to remove the needle bearing from the housing, quick thinking is indispensable. Its dismantling is carried out only at destruction.

To get the destroyed bearing race, you can use the proven method.

Video: How to Change a Bearing In a Reducer Angle Grinder Bosch

A tap is selected with a diameter slightly larger than the inner diameter of the cage of the destroyed needle bearing. The tap is fixed in the screwdriver’s chuck and screwed carefully at low speeds into the clip. When the tap reaches the bottom of the gear housing, it will begin to raise the clip.

In addition to the spindle shaft needle bearing, Bosch angle grinders also use two more bearings mounted on the rotor shaft.

How to remove bearings from a rotor Bosch angle grinder

To remove the bearings from the rotor, pos. 803, Bosch angle grinders are recommended to use pullers.

The bearing pos.15 near the collector is easily removed, but to remove the bearing pos.14 from the impeller side, it is complicated by the fact that a number of preparatory operations are necessary.

The bearing pos.15 is closed by a soft rubber socket. A similar rubber protection pos.33 also covers the bearing pos.14.

To remove the bearing pos. 14, unscrew the nut pos. 45, remove the spur gear pos. 17 and the plastic protection pos. 33. Using a puller, you can easily remove the bearing from the rotor shaft.

And if there is no puller? A vice, two metal strips and a hammer with a soft metal extension will come to the rescue.

Dismantling Bosch angle grinder

Possible electrical problems

Faults in the electrical part of the Bosch angle grinder can be divided into simple and complex.

Simple electrical faults Bosch angle grinder

If you turned on the angle grinder and it refuses to work, start looking for a malfunction with a broken power supply wire. Most often, a wire break appears at the entrance to the angle grinder or to the fork. Avoid twisting; this will cause a short circuit in the tool.

To determine such a malfunction, it is necessary to open the handle covers of the angle grinder. In Bosch angle grinders up to 1000 W, the cover is fastened with one screw at the end. For Bosch grinders over 1000 W, the handle cover is secured with several screws.

Using the tester, ring the power circuits from the input plug, pos. 5, to the switch. With the whole circuit, proceed to check the operation of the switch. Bosch angle grinders use simple switches controlled by a switch lever.

But the electrical contacts of the switch burn up and become the cause of the failure of the angle grinder. It is impractical to restore the contacts of the plastic switch, it is necessary to replace it with a new one.

If the switch is intact, use a tester to check for the presence of a chain from each pin of the plug to each carbon brush. For whole chains, the angle grinder should turn on. If it does not rotate, then the malfunction is mechanical. Jamming of gears or destruction of bearings is possible.

Motor check

If your Bosch angle grinder is gaining momentum regardless of you, it starts to get very hot, sparkle, you need to pay attention to the integrity of the rotor windings, stator windings.

An involuntary set of revolutions of the ear indicates a malfunction of the stator windings. The integrity of the windings is checked by a tester, and the short circuit between the turns is checked by a special device.

How to identify rotor failure

Rotor repair is a complex process available to foremen with straight arms.

A rotor malfunction is indicated by a drop in engine speed, the appearance of a long sparkling trace on one of the brushes. This is the first sign of a short circuit in the turns of the armature winding.

Repair of the rotor is preferably carried out in special workshops. And you can rewind yourself, if you decide to repair the Bosch angle grinder yourself.

The dark color of the rotor winding and burnt collector lamellas indicate a short circuit in the rotor circuits. The malfunction is eliminated only by replacing with a new rotor.

Stator Repair

Bosch angle grinder repair includes stator restoration. The main sign of stator failure is a spontaneous increase in the speed of the working angle grinder, which cannot be reduced by adjustments. A burned stator winding changes color, becomes darker. The stator core also darkens from high temperature.

The stator is easier to rewind, although here you must follow certain rules and sequence.

If you removed the stator housing cover, carefully inspect the condition of the carbon brushes and rotor manifold lamellas.

The length of the carbon brushes should not be less than 8 mm. By the way, in Bosch angle grinders, carbon brushes with a “shot” are used, a device that stops the operation of the angle grinder with a minimum length of the carbon brush.

The collector lamellas must not show any deposits or wear. Carbon deposits are easily removed with cotton wool soaked in alcohol.

Stator overheating and rotor short circuit

Speed ​​control malfunctions

In angle grinders of the Bosch series, especially of low power, speed controllers are installed. Access to the speed controller is carried out by opening the handle of the stator housing, which is held on one end screw.

The speed range of the controller can be set with a potentiometer hidden in the handle panel.

It is quite easy to remove a faulty regulator, since it is mounted only on the guide.

Repair of the UMM speed controller is a complex process, the implementation of which requires not only special knowledge, but also tools and equipment.

If the speed controller is out of order, but there is no new one, then disconnect the supply wires and install a jumper.

Red shows the jumper installed when the speed regulator fails.

Mechanical damage

Bosch angle grinder is designed for cutting, grinding, polishing work. The operation of the tool in dust at high loads is particularly detrimental to the durability of the gearbox, namely its gears.

In addition to wear and tear of gear teeth, mechanical failures include the destruction of bearings and the housing. Repair of the Bosch angle grinder in terms of replacing failed bearings and rebuilding the housing is not difficult if there is a desire and need.

Assembly angle grinder

The assembly of the angle grinder begins with the examination of all parts, assemblies, bearings, gears.

Pre-prepare the workplace with proper and good lighting, lay tools, lubricants, wipes.

What grease to use for a Bosch angle grinder

Repair to Bosch ears will not be of high quality if you do not change the grease during its execution. For high-quality lubrication of components, Bosch angle grinder is recommended to use those lubricants that are offered by the tool manufacturer. But their high price makes us look for another way, and there is one.

Domestic lubricant manufacturers have developed special lubricants for gearboxes and grinder assemblies.

In terms of quality, they are in no way inferior to foreign lubricants, but are much cheaper. The only negative, our lubricants require a more frequent change.

Rotor assembly

The assembly of the rotor consists in mounting bearings on it, installing the impeller. Lubricated bearings are pressed onto the shaft using a wooden extension. The bearing near the collector is closed with rubber protection. This is a general rotor shaft assembly algorithm.

In some models, the Bosch angle grinder has its own characteristics.

Gear assembly

The assembly of the gearbox begins with the installation of a rotor shaft in its housing. When the shaft is inserted into the housing, the drive gear, washer, and lock nut are put on the shaft. The gear housing with the inserted shaft must be placed in the stator housing.

When you insert the collector bearing into the socket, push the gear housing to the stator housing. Check the ease of rotation of the rotor in the bearings.

A spindle assembly with a mounted bearing and gear is mounted in the gear housing cover.

It remains to insert the cover into place and check the quality of rotation of the spindle shaft. If the shaft rotates easily by hand, it is fashionable to tighten the screws securing the rotor housing cover. The screws are pre-lubricated with sealant.

This is a general gearbox assembly algorithm. On some models, the repair of the gearbox Bosch angle grinder is slightly different.


  • Knowing the general scheme of Bosch grinders, you can safely take on the dismantling of a tool for lubrication;
  • The ability to repair a Bosch angle grinder with your own hands will extend the life of the tool, independently replace the grease, carbon brushes;
  • Observing the operating mode and technological maintenance of the tool, you will extend its trouble-free operation for many years.