SRAM MRX shifter replacement

[underarock]

Hello, all. I'm wondering if an SRAM MRX Classic shifter will be OK as a replacement for an SRAM MRX 204-705. (That doesn't match anything I see on the SRAM web site, but I figure it's older or only sold with big-box bikes or something like that. It's the only number on the unit.)

Details.... I bought my son a used Magna mountain bike--knowing it was a cheap brand, that might need some work, but everything seemed mostly OK. My biggest concern was that the right grip shift was really tight to turn out of 7th gear. I thought I could fix this with some simple adjustment.

My first thought was the rear derailleur, which seemed very tight & had a rusty spring. Sure enough, with some lubrication, it moved much easier, and the shifter could now be turned. But... it wouldn't stay. It would go straight back down to 7.

So I took the shifter apart (wondering if this bike was a mistake....) and discovered that the spring is missing! With nothing to press into the ratchet notches, no wonder it wouldn't stay anywhere but the highest gear.

I figure for the cost of the MRX Classic, I might as well replace the whole thing rather than try to dig up a spring. I'd appreciate any advice you have.

[trevgbb]

I would consider replacing with almost any type of thumb shifters, much easier to operate in my opinion, you can get a basic set for very little, there is much less to go wrong and cable replacement is much easier, and you will have the full length of the grips to hold.
And keep an eye on the rear wheel, the hubs don't last long on these!!

[underarock]

Hmm, thanks, that's probably worthwhile... I checked around and the low-end choices that I found seem to be SRAM TRX and Shimano ST-EF50 (combo brake & shifter). Do I need to worry about sizing & compatibility with the existing cassette etc.?

[Bill]

Pretty enough easy way to remember is if the derailler shifts 7 then the shifter should shift 7 . Not sure about the brake/shifter combo but only part I would find hard is installation but do able.

[JonathanSG]

SRAM Twist shifts are a nightmare to replace cables and impossible to adjust or repair if they go wrong, it's a sealed unit. I just overhauled my kids 6 speed 20" MTB as she goes in the terrain park these days and the cup and cone wheel bearings and external bearing BB don't last more than a few rides.

New wheels and replacing the crankset to a cartridge types were simplicity itself but the SRAM twist Shift; it took me 3 hours to get the cable through, I had to plead, beg, cajole, curse, swear, force the thing round 2 90' turns in the housing. I was looking for a suitable six speed thumb shifter but cannot find any of these around these days any one any ideas?

[X-RAY]

somebody with more knowledge help me out here, but i believe some srams use a different cable pull ratio that isn't compatible with shimano. the 1:1 versus 2:1 thing. as i said, someone who knows can help you more than me, but its a question that needs answered before you buy a shifter you cant use.

[JonathanSG]

(09-12-2010, 07:03 AM)X-RAY Wrote:  srams use a different cable pull ratio that isn't compatible with shimano. the 1:1 versus 2:1 thing.

I am 99% sure that SRAM do not make any 2:1 ratio rear derailleurs so you are correct SRAM rear derailleurs are all 1:1 cable pull ratio and SRAM 1:1 shifters have to be used. All SRAM shifters are 1:1 except rocket attack, MRX and TRX which are 2:1 and will work with Shimano rear derailleurs - these will not work with any current SRAM rear derailleur.

As your Twist Shift was MRX the bike will have 2:1 rear derailleur probably shimano or other - you therefore need a 2:1 Shifter. SRAM TRX or Attack 7 speed Trigger shifters or MRX Pro Twist Shifts. You could also use Shimano Shifters - I think Acera and Altus are their cheap 7 speed ranges. Maybe you could post the derailleur make and model number

As far as I know there are no compatibility issues between SRAM and Shimano Front Derailleurs except maybe the top end stuff.