Bosch 11236VS hammer drill doesn't hammer

[slantsix]

Someone gave me a Bosch 11236VS hammer drill that has lost its hammering ability. This unit has seen lots of hard pro use. Looking at the exploded diagrams, my guess is that its general means of function is that the "arm" on the "eccentric" pulls the piston rearward, compressing the main spring (pulling from the front of the spring thru linkage coming through the spring from the rear), and at a certain point in the rotation of the assembly, the piston is released, striking the rear of the striker pin, which is linked to the chuck holding the bit. The only other mechanism I can imagine is that the "eccentric arm" merely plunges the piston forward against the rear of the spring (and thru linkage to the chuck), but it seems to me that this would supply an insufficient force for the impact function. I have disassembled the unit (quite a greasy mess), and can see no broken or obviously worn parts. I could NOT see some of the forward parts which, if my memory serves me correctly -- it's been perhaps a year -- were hidden inside the impact mechanism housing, which seemed a more formidable task than I was ready to tackle without knowing more. Anyone know what part or parts are worn or broken and need replacement? (Yes, I managed to reassemble with no leftover parts, and previous drill-only functionality is restored.) Anyone know if my idea of how it functions is correct? Close?

[cmoorejack]

Hey slantsix.
the most common hammering problem with this tool is a worn o-ring on the striker..the striker moves inside the hammer piston and creates a pneumatic percussion to give more power to the hit..with a worn out o-ring and sometimes hammer piston[or chamber] the punch almost doesn't exist..also a dried out hammer piston and you have a striker that doesn't move..
try replacing the o-ring and lightly grease..[you should should have some resistence when you reinsert the striker
hope this is helpful..
Craig

[slantsix]

I never would have thought of that. Thanks very much. That really makes sense the more I think about it -- it still hammers, but with almost no effective impact. Is that a special O-ring I need to order from the supplier, or will a generic do? Am I close on how the thing functions? I.e., does the main spring's sudden release from compression provide the impact, or does it serve instead to push the striker back into the "strike-ready" position? (Or something else?)

[cmoorejack]

The o-ring is kinda special..better to purchase the correct one..1-610-210-121 ..
The area between the piston and the striker is where the air pressure is built up allowing for the extra punch..[the piston doesn't actually hit the striker..the striker hits the impact bolt that actually makes contact with the bit..!]
Craig

[slantsix]

OK, I've got the O-ring. I've disassembled the unit. There seems to be plenty of grease in the gearbox and on the striker, cylinder, and O-ring. The striker came out with considerable resistance (does that mean the problem is somewhere besides the O-ring?), and appears to be undamaged, other than perhaps a seemingly insignificant small nick near the outer perimeter. I've wiped the grease from these 3 parts where they contact one another. I'll replace the O-ring anyway, but I'm wondering if I should order more grease, or just collect grease from other parts in the gearbox, or use a readily-available generic grease. I happen to have a multi-purpose all-season lithium grease, "highly water resistant, high melting point, suitable for chassis, wheel bearings, water pumps, ball and roller bearings." It's even purple, like the Bosch stuff. Should I orfer the Bosch factory stuff anyway? (# 1615430005, as I found on another post of yours.)

[cmoorejack]

Considerable resistance could also mean it was stuck....It is best to use the Bosch grease..you can also put a little air tool oil on the o-ring ..keep the grease out of the striker chamber.[the striker needs to glide somewhat and not be pushing grease].. .new grease is always better than old grease...
Craig

[slantsix]

OK, I got everything working. I was curious about whether the problem had been with the O-ring, or whether it was because of too much grease in and around the cylinders. So I decided to reassemble with the old O-ring. The striker seemed awufully sticky with just the air tool oil, so I added a thin layer of the gear grease -- much better. I wasn't sure how far to initially "load" the striker into the cylinder, so I just pushed it in to about the O-ring. I reassembled, and everything works fine -- with one exception. In the hammer-only position, the bit turns slowly (I can stop it by holding the chisel bit with my hand), instead of being stationary. I have tried the "vario-lock" feature, but I can't seem to get the chuck locked so it doesn't turn. Did I reassemble something wrong? I find the most difficult part of reassembly to be getting and keeping the selector switch inner linkage aligned as you reinsert the gear assembly into the housing, and then properly reinstalling the selector switch.

Also, the gear grease, part# 1-615-430-005, is not purple (did they change it because too many people were eating it?). It looks more like the grease used on the bit shanks. The vendor assured me it's the right stuff. By the way, how much grease should I pack into the thing?

[cmoorejack]

Hey slantsix,
It sounds like you still may have an issue with the selector..it may be misaligned a little or tweaked..and it may correct itself over time..as far as the grease..there should be a thin film inside the chamber and the rest outside..[if you have too much grease or oil in the chamber the striker cannot move as freely] if ya get back in there you might as well put the new o-ring on..just because..
congrats so far on your repair..!
cmoorejack