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Help requested. OLD Bosch SB 400-2 dismantling/service advice...

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I have an OLD, that's bought in the early 80's old, apparently Swiss built Bosch SB 400-2 hammer drill. It has worked perfectly every time I've used it and I've never had a moment's problem with it, until now. It seems to have lost a gear tooth in the reduction mechanism, at least that's what I think is the problem, I pull the trigger, it turns for a second and then the chuck stops spinning and there's a horrible grind-y noise from somewhere inside - just about behind the chuck and after the motor, hence the suspicion of the reduction gear.

I'm trying to open the thing to confirm my diagnosisi and assay the possibility of a repair but I'm falling at the first fence, I can't open it. I've undone all the screws I can find to open the case and it sort of splits open from the chuck to the handle but there's something still attached at the top/back that's stopping it from coming apart.

It's a REALLY good drill, the prospect of finding a replacement of similar quality is unnervingly expensive, I really want to try and repair it if at all possible but not being able to get into it is making that possibility remote.

Anyone here a guru to the old, good, Bosch stuff?
 

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guineafowl21

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Check for a screw hidden under a label - if you run your fingernail along it, you’ll find the dip where it is.

Sometimes screws are hidden behind plastic plugs, which you have to lever out.

Failing that, there may be a clip holding the clamshell together - try to see in with a torch and release it, or do what I do sometimes - get frustrated by manufacturers’ trickery and bust the final fixing apart.
 

AES

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Also, there COULD be a ring (metal probably) around the collar of the body between where the drive shaft exits the main case and the back of the chuck. If that IS the case then you'll need probably to remove the chuck which MAY be held in by a bolt whose head you will only see deep down inside the chuck with the jaws fully open.

Good luck
 

Noel

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I have an OLD, that's bought in the early 80's old, apparently Swiss built Bosch SB 400-2 hammer drill. It has worked perfectly every time I've used it and I've never had a moment's problem with it, until now. It seems to have lost a gear tooth in the reduction mechanism, at least that's what I think is the problem, I pull the trigger, it turns for a second and then the chuck stops spinning and there's a horrible grind-y noise from somewhere inside - just about behind the chuck and after the motor, hence the suspicion of the reduction gear.

I'm trying to open the thing to confirm my diagnosisi and assay the possibility of a repair but I'm falling at the first fence, I can't open it. I've undone all the screws I can find to open the case and it sort of splits open from the chuck to the handle but there's something still attached at the top/back that's stopping it from coming apart.

It's a REALLY good drill, the prospect of finding a replacement of similar quality is unnervingly expensive, I really want to try and repair it if at all possible but not being able to get into it is making that possibility remote.

Anyone here a guru to the old, good, Bosch stuff?
I used to have a Bosch similar or the same. As far as I recall there should be nothing other than the 5/6 screws holding the top half of the case on. No need to remove chuck. Perhaps it just needs a little prising apart?
 
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flying haggis

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take all the screws out there should be about 8 then if there is a label bridging the two halves run a knife through the middle where the join is, then prise apart. the were well made in those days so the fit is a tight one (ooh matron!) the metal plate on the bottom can sometimes hold it together due to the crud getting round it
or if all else fails
 
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Thanks for the swift replys guys. I'll give all of them consideration as soon as I get back to the drill - life is getting in the way just now. I'll post an update and some more pictures in a bit.
 

Phill05

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I have the CSB 480 RE and the PSB 680 RE both impact drills and both will open after taking out 7 or 8 screws.
 
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Ok, here's a couple more pictures of my currently foiled attempts at getting this drill open.

I've checked for screws under the labels - nope.

I Googled for drawings and schematics and the best I could find was not at a high enough resolution to show anything I'd missed.

The only screws in the sticking area are out, it's like it's been glued or something. Which, on reflection, is just about conceivable as I've run the thing in a vice a couple of times but I tried to be careful about it. I'll be gutted if I've accidentally friction welded the sides together.

Anyway, I'm afraid I'm losing a bit of hope here. brute force is becoming an option but the kicker with brute force is that it tends to break things beyond repair in the effort. Ironic in the extreme.

20210408_081211.jpg
 

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flying haggis

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very similiar to my drill i took apart to re do the brushes. mine was very tight to get apart. use a wide bladed screwdriver and work along the seam. from the pics nothing appears strange so perseverance should pay off.
 

Jacob

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It doesn't have an automatic clutch does it? My Bosch SDS and my Hilti both have a protective clutch which you don't discover until something jams and you get an alarming noise like a self destructing gear box.
 

flying haggis

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slice through that label next to the trigger, It's not helping. Then, as has been said, wide blade screwdriver, or old chisel and go steady.
if it is like mine that label is actually a metal plate so difficult to slice through but it just sits in a slot so should come out. might be stuck with cr*p
 

bourbon

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if it is like mine that label is actually a metal plate so difficult to slice through but it just sits in a slot so should come out. might be stuck with cr*p
I see that now that it is metal, but it has moved (there is a gap at the bottom of the label) looking at it again, It seems to be tight around the bottom of the trigger, so concentrate around that area. It will come free, they were made to go together so they should come apart
 
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It doesn't have an automatic clutch does it? My Bosch SDS and my Hilti both have a protective clutch which you don't discover until something jams and you get an alarming noise like a self destructing gear box.
I'm not sure what an automatic clutch would be like before, but the noise is definitely in the self destructing gearbox league. It's possible, but what would that mean for the disassembly?
 
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Well, I bit the bullet and went for brute force. It worked and it would appear that I actually had no option.

Something has melted at the brushes end of the rotor allowing a lot of play in the system. Nothing seems to have broken and all of the gears (all metal, I'm pleased to note) are intact. If I can find a decent metal shim or something that will fit in the play space I will be might be able to fix it.

A smidgen of phosphor bronze maybe? It's going to have to take a lot of friction/heat wear, but that leads to the possibility of melting the case again. Anyone got any suggestions? Graphite? Molybdenum?
 

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AES

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Hmmmmmm! If I were you I'd like to know (if you can find out, no disrespect intended) just why all that heat has occurred there. Is it possible that the rear bearing has at least "semi-seized" onto the main shaft, thereby causing the bearing to rotate on the shaft within it's outer case locator, so heating up the housing to "melting/semi-melting" point? Looks a bit that way to me. What does the surface of the main shaft look like where it runs through the rear bearing?

Purely guesswork at this end please note.
 

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