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Compatibilty
#1
Hi All,
This may be a stupid question but.....
I'm trying to basically build a bike or, more accurately, put shiny new parts on an old frame.

I'm trying to go as cheap as possible (I know, not the best idea...) while not buying completely crap parts....

I currently therefore have mix/matched all over the shop which, may or may not have caused some of the problems that I'm having. To this end please can I have some advice on the various compatibilities of things that I have.
Most of the problems are in the gears and shifters but for completeness I'll say most stuff I have.

I have:
Shimano Mega-Range FreeWheel - 14-34
Shimano Front Chainset - 28-38-48
Shimano Rear Derailleur - MTB Acera M360 SGS Long Cage
SRAM PC870 8spd chain
SRAM 3.0 GripShifters

so my current problem is that I cannot make the rear derailleur shift properly. I can hit top and bottom gears fine so the range is not a problem just in between is really hit and miss.
When shifting up I can get maybe 7,5,4,2,1
Then down - 1,2,3,5,7

I've played with it for a couple of hours and got no-where. Am I suffering from incompatibility of shimano / SRAM stuff, or am I bad at setting up a rear-derailleur. If the set-up is a problem does anyone have an idiot-proof, step by step guide to setting up a rear derailleur. I followed the video tutorial initally but couldn't get things to work.
TIA
Dave
  Reply
#2
Dave,
I am just going to throw this in first, is your chain and RD assembly lubed correctly? Next question are you using a 8spd chain on a 7spd cassette/freewheel? On this one I am sure they are not compatible. Atleast a 8spd KMC 8spd chain is not compatible with a Megarange 7spd Freewheel. However that may not be the case with you. I still have the bike and I will check my personal shop records to see if it has the Shimano shifter etc. later.
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
  Reply
#3
Hi Bill,
Quote from chain reaction cycles: (http://www.chainreactioncycles.com/Models.aspx?ModelID=20608)

"compatible with 7 or 8 speed systems"

Quote from SRAM website: (http://www.sram.com/en/srammountain/chains/8speed/index.php)

"compatibility: 8 speed"

if that is the problem what is the best solution? (can I set the derailleur so that it won't make too much of a difference?) do I just need a new chain?
Thanks
Dave
  Reply
#4
If 1 & 7 line up but has problems in-between then check out the derailleur hanger alignment.
Also check the cable for sticking. Remove cable and look for kinks / loose strands.

Shouldn't be a problem with the chain as 8 speed chain is suitable for 7,6 and even 5 speed.
Ride hard or ride home alone!
  Reply
#5
Hi
Thanks for the info about the chain thats a relief
It's not sticking, the cable is new and when I move the shifter it shifts constantly (not randomly like a sticking problem would indicate). It lines up 1 and 7 but in between varies on cable tension, sometimes it can miss 4 sometimes 6 sometimes 3. As if the shifter is not moving the derailleur the correct distance (hence why I ask about compatibility) is there a cheap way to align the hanger or should I get my LBS to do it...
Dave
  Reply
#6
Have a look at shimano's site for compatibility info, but I am pretty sure mega-range needs its own rear changer as there is a big step up to the lowest gear.
  Reply
#7
Ok I do have an apology to make the bike I was referring to did not have the MegaRange on it. However here is sheldon's info on them if it helps... http://www.sheldonbrown.com/mega7/
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
  Reply
#8
hi trevgbb,

I'd be pretty confused if that was the case. The derailleur that I have specifically states that it's range goes up to 34 teeth. So having a large wheel at the back shouldn't be a problem, and it's not, I can easily reach the top and bottom gears, it's just everything in between that is the problem, almost as if the distance that the wire is shifting isn't the same distance as it is designed to shift on the derailleur and freewheel - almost as if they were designed by two totally different companies or something.... Tongue

I've since heard from one or two other places that the shift on a SRAM 3.0 shifter is not equal to the required shift on shimano derailleurs/gears. This doesn't surprise me at all and I have it working roughly okay now so I'm going to stop fussing with it before I make it worse, however if anyone has some certain knowledge to add (exact specs of the stuff or something) I'd be really pleased.

Thanks All
Dave
  Reply
#9
Quote:I've since heard from one or two other places that the shift on a SRAM 3.0 shifter is not equal to the required shift on shimano derailleurs/gears. This doesn't surprise me at all and I have it working roughly okay now so I'm going to stop fussing with it before I make it worse, however if anyone has some certain knowledge to add (exact specs of the stuff or something) I'd be really pleased.

You are right, SRAM shifters will not work with Shimano mechs and vice versa. SRAM uses a "1:1 Actuation Ratio" for their mechs, so the amount of cable pull required to move an SRAM mech one sprocket width is different to the amount needed for Shimano mech.

So if you like twist-grip shifters you'll either have to swap out your mechs for SRAM, if you're not worried about the shifters you could get some Shimano shifters to go with your existing mechs.
  Reply


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