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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.
 

Keith 66

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As above, the rear bearing has seized or partly so through lack of lubrication & the outer race has spun in its housing melting it. I had exactly the same thing happen to an ancient wolf power planer a few months back, it started making a shrieking noise & i found it before it had done much damage, Washed the bearings out & oiled them & it a runner again. That Wolf is early 70's so one of the newer ones!
 
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I think the "bearing" was in fact a single ball bearing like at the front of the main shaft. You can see the front bearing has a ball and behind the ball a couple of plates. If you look closely (I'm not sure the photo will bear the zooming in required) you can see the rear plates squished in to the melted bit. The shiny part of the commutator - where the brushes have polished it - exactly matches the amount of play. I believe the noises were from the fan turbine scraping the green housing - close inspection shows the wear marks on the fan blades and the housing which contact when the shaft is at the rear of the play distance.

I don't know where the rear ball bearing has gone but that may be all it needs. The wear marks at the rear housing only happen if the shaft is allowed to fall back; I really wish I know what happened to the ball bearing, it's kinda key to the whole failure/problems. It's quite a simple but elegant design so I'm hopeful it can be fixed because I *really* like this drill.
 

AES

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I'm really NOT trying to be a "smart buttocks", 'onest, but your naming of parts is confusing me. Are you saying the rear bearing has lost a single ball (almost impossible without a HUGE amount of damage, surely?) or are you saying the whole of the rear bearing is missing?

Just to be clear on the naming of parts, the "bear bearing" will consist of an inner "race" (that's a ring, the inside hole of which should be a sliding fit over the central (main) shaft (that's also got the commutator and the cooling fan fixed to it. That same rear bearing (let's call it a "bearing assembly" if you like) then has a number of steel balls - at least 9, probably more - which "run" around a semi-circular groove cut into the outer face of that inner race. In turn those balls are held in place by the "outer race". That's another ring whose inside diameter will be just a bit smaller than the overall diameter of the circle made by the steel balls running around the groove in the inner race. The outer race also has a semi-circular groove cut into it, but this time, the groove is on the inside of the outer race (i.e. the opposite side to the groove on the inner race).

That lot, in order - inner race - then balls - then outer race - are all held together because during manufacture, the maker has "forced" the outer race "over the top" of the balls and inner race. You can imagine the force required to do that (that's not quite how it's done really, but that picture will suffice here), so unless the whole steel bearing assembly has "exploded" with VERY obvious destructive effects on the plastic casing, a ball/s just cannot "be missing" as you say.

Equally the whole "rear bearing assembly" can't just be missing either. Have you accidentally dropped the whole thing on the floor, under the bench (such things happen to me frequently)!

Anyway you do need to find that whole rear bearing assembly (it can't have disappeared completely) because marked (usually) on one face of the outer race will be a series of numbers. Amongst other things, those will tell you the inner and outer diameters of that bearing assembly and it's thickness (front to back) and also, probably if it's a sealed bearing or not (it probably isn't BTW).

It MAY be that Bosch will still have that bearing in stock (bearings are standard items) even though the drill is old, but even if not, if you find those numbers you can easily get a replacement on "the open market". Many here can tell you how/where.

But you must find that missing bearing assembly first - you're looking for something that's probably a bit blackened (should be a dull silver originally) made of 2 rings, one inside the other, and about (VERY roughly) an inch in diameter and half an inch thick. And as it was built, that rear bearing assembly just "sat" in the case in a "holder" moulded into each case half.

Sorry to make this sound complicated, it isn't really, and I promise I'm not "extracting the urine" but sorry again, your explanation above just doesn't make sense.

When you've found the bearing let us know and we'll go the next steps, easy. But make no mistake, without a "rear bearing assembly" as I've described above, that drill will not run again, no matter what you do in the way of spacers, etc.

But
 
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