shimano positron 400

[andy q]

HI can anyone help please i have a very old raliegh hybrid with shimano positron 400 derailleur of which the springs have seen better days as the unit is almost kissing the cogs can i purchase new springs or do i need a new unit.If the latter what would be compatible by the way it is a 5 speed many thanks Andy.

 

[Drago]

I got a Positron 400 mech in VGC I could sell you.

 

[RecordAceFromNew]

Aside from Drago's offer above, you could also get a modern replacement. Assuming your Positron is like this (i.e. the hanger is integral with the mech, rather than the mech bolting on to a separate hanger which in turn bolts on to the frame), then you could pick something like this or its minor variance. They are perfectly serviceable, and have wider range capacity in case you would like a wide range freewheel one day.

If on the other hand your Positron does not have an integral hanger then your rear mech choice will be much greater. Alternatively you can achieve that by getting a universal bolt on hanger.

You should pick based on what change if any you would like make to the bike in future and how much you would like to spend.

I am assuming you are running friction shifter, because the Positron seems to predate SIS indexed shifting.

 

[TheDoctor]

Positron used a rigid wire IIRC - it pushed and pulled the mech. Sort of like a forerunner of SIS, and utterly incompatible with any modern day levers or mechs.
I doubt you'll fine any spare parts these days - it came out in '82 or so.

 

[RecordAceFromNew]

Positron used a rigid wire IIRC - it pushed and pulled the mech. Sort of like a forerunner of SIS, and utterly incompatible with any modern day levers or mechs.
I doubt you'll fine any spare parts these days - it came out in '82 or so.

You are right according to this - well caught Doc!

That being the case, unless there is sentimental/historic value, if I were the OP I would change the shifter as well as the mech to something modern.

 

[TheDoctor]

Tourney rear mech and a cheap gripshifter or some such should do the trick.
Having said that, I'm not sure that the springs have gone, as I don't think the Positron had springs....

 

[andy q]

Tourney rear mech and a cheap gripshifter or some such should do the trick.
Having said that, I'm not sure that the springs have gone, as I don't think the Positron had springs....

Thankyou all for replying so quickly the tourney seems to be the way to go but can i use the lever that is on the bike already or do i have to get a grip type there is a main spring that holds the unit down away from the gears or should do after changeing gears with light finger pressure i am able to push it down.
I do have an old mountain bike with 18 gears is there any chance i can use this derailleur another thought my unit is short would i need alonger chain a lot of questions i know but i bow to your superior knowledge.This needs to be done as the rear wheel locked up on me last week the bike stopped but i did not again many thanks Andy.

 

[TheDoctor]

You'll need a new gear lever too - the Positron won't be compatable with a modern rear mech.
I suggested a gripshifter as I know these are available in 5 speed - having said that, thumbshifters come in 5 speed too, so I'd go with whatever you prefer or whatever is closest to what you have on the bike already. Getting a new chain will mean a new freewheel and probably chainring(s) too, at which point it all gets a bit pricey.
Ever fancied a singlespeed? That's the cheapest way of getting mobile again...

 

[andy q]

You'll need a new gear lever too - the Positron won't be compatable with a modern rear mech.
I suggested a gripshifter as I know these are available in 5 speed - having said that, thumbshifters come in 5 speed too, so I'd go with whatever you prefer or whatever is closest to what you have on the bike already. Getting a new chain will mean a new freewheel and probably chainring(s) too, at which point it all gets a bit pricey.
Ever fancied a singlespeed? That's the cheapest way of getting mobile again...

Thanks for your reply i would like to keep to 5 speed so will go with tourney and 5 speed thumb shift chain and gears if needed or Dragos mech have you got a price please!

 

[Drago]

£15 posted if you want it. I could post up a pic later. It's VGC. I'd bought it for a resto, but sold the bike on instead. Had stripped the mech, decreased the lot, reassembled the jockey wheels with fresh grease etc.