Which Works With What?

[1FJEF]

How do you figure which shifter works with your rear gears? I'm getting conflicting answers from local shops.
Here's the facts:
Unknown origin used bike. It's been tampered with extensively so I don't have a reference to what it came with.
Daily commuter (10 miles) fat cruiser tires.
1 front chainring.
7 speed freewheel (not freehub/cassette). Looks like it says Shimano HG 37 on it.
SRAM twist grip style shifter, I could try & read the faded white model # on it if needed. The cable seems proper & appropriate.
The derailleur says 7SIS on it.

Here's the issues:
Somethings broken or missing in the grip shifter, the bobby pin lookin' spring that rests in the gear detents wont stay still, it slides around the interior rim of the shifter with a good 1/2 inch of travel.
It upshifts fairly well, but doesn't like to downshift, you have to go a few gears past to get it to go just one. Doesn't want to go into or stay in 1st. Will upshift when you ride over rough surfaces. The derailleur will move freely from 1st to 7th if you grab it & operate it by hand (hi-low screws are OK).
The freewheel makes sounds like two skeletons humpin' on a tin roof (clattering ensues from within), especially if you apply a little side pressue to the derailleur while pedaling.

SO, How do I know which shifter to buy to go with a new 7 speed freewheel. Do I just assume it'll be ok with my derailleur or a future derailler upgrade?
I'd like another twist shifter, but would a thumb shifter, or combination thumb shifter/brake lever work?
Should I get another identical shimano freewheel (the ratios seem fine)?
If I upgrade the rear wheel to 7speed freehub/cassette will the same shifter/derailleur/cable work? (Spacing between the cogs on the existing freewheel is about 3.12mm, except from 6th to 7th which is a bit more). Cog spacing on two of my other bikes that have 7spd Shimano Freehub/cassettes is also about 3.12mm, but for every gear.
Local bike shops give conflicting answers.
Oh, by the way, I'll get a new chain of course. I was thinking a KMC x8.99. It's 7.3mm wide, has a masterlink & is reasonably priced. Shimano chains seem to rust at an alarming rate, for me at least.

[JohnV]

Sounds very similar to what I have on my hybrid. You should be able to use a SRAM MRX 7 speed grip shifter on it if you are still going to stay with grip shifters. Here is a link for them at Amazon.Com

[DaveM]

I'm pretty sure shimano 7 speed spacing is the same for casette and freewheel. For cassette, it is 5.0 mm center to center between cogs (measure ctc, not the spacer thickness. see: http://sheldonbrown.com/cribsheet-spacing.html)

Any 7 speed "shimano compatible" shifter will work. I think all SRAM 7 speed is shimano compatible, but not 100% sure about that. Any style of shifter will work as long as it is 7 spd shimano compatible. The twist shifters in general seems to be sloppier shifting and cheaper quality. But there's not a huge amount of choice in 7 speed anymore.

I don't think you need to change your freewheel unless there's a problem. But if you do, change the chain as well. (I prefer SRAM chains to shimano)

[nfmisso]

Hi Jeff;

So many choices.

1st do not consider upgrading to a 7 speed cassette system - too much $$$; if you insist on going to a cassette; go to 8/9 speed freehub and cassette.

Freewheel and cassette spacing are the same for Shimano. Currently; I have three bikes operational; all have seven speed; two are cassette (blue and tandem) one is a freewheel (red). All three have Shimano rear derailleurs.

You need to replace your shifter. Under heavy load, no top normal (95+ % of all rear derailleurs), down shift well, all need a touch extra cable pull, but not a full position, less than half a position.

Shifter choices - here are a few that will work with your 7 speed Shimano system:

SRAM MRX (twist grip) and TRX (trigger) only will work with Shimano. All Sunlite, Sunrace and DNP are Shimano compatible.

* this is what I put on my blue bike:
http://www.ebay.com/itm/SHIMANO-SIS-SL-TY-22-7-SP-BIKE-SHIFTER-LEVER-RIGHT-NEW-/380369267565?pt=Cycling_Parts_Accessories&hash=item588fc66b6d

* this is what I have on the red bike and the tandem:
http://www.amazon.com/SRAM-Bicycle-Twist-Shifter-7-Speed/dp/B0017YX2OO/

* here are some other choices:
http://www.amazon.com/Shimano-Acera-Altus-ST-EF51-Shifter/dp/B003ZMBNMY/
http://www.amazon.com/SRAM-Mountain-Trigger-Shifter-7-Speed/dp/B000VT2GHA/
http://www.amazon.com/Shimano-Tourney-7-Speed-Revo-Shift-Optical/dp/B001OO0LIC/
http://www.amazon.com/Sunlite-Twist-Shifter-Set-7-Speed/dp/B004NTPZXQ/
http://www.amazon.com/Shimano-SL-TX50-TOURNEY-Speed-Shifter/dp/B001RI5MCU/
http://www.amazon.com/Shimano-SL-TX30-TOURNEY-Speed-Shifter/dp/B001NVAI7U/
http://www.amazon.com/Shimano-Handlebar-Mount-speed-Shifter/dp/B001L5Y1GC/
http://www.amazon.com/SunRace-Sunrace-speed-shifter-Black/dp/B001GSMSBO/

I hope that this helps, and does not add further confusion.

[1FJEF]

As usual, your answers are practical & detailed, thanks, especially to Nigel.

What the heck is the + button for? Shifting up? Fine tuning?

[nfmisso]

(09-25-2011, 11:37 AM)1FJEF Wrote:  As usual, your answers are practical & detailed, thanks, especially to Nigel.

What the heck is the + button for? Shifting up? Fine tuning?

Thank you

I have no idea - I have never handled those shifters....

[nameused]

(09-25-2011, 02:44 PM)nfmisso Wrote:  

(09-25-2011, 11:37 AM)1FJEF Wrote:  As usual, your answers are practical & detailed, thanks, especially to Nigel.

What the heck is the + button for? Shifting up? Fine tuning?

Thank you

I have no idea - I have never handled those shifters....

If I remember right we had a bike with those shifters come in the other day for a flat change. I believe the plus button did the same as upshifting so you could either use that or the lever.

[1FJEF]

It seems clever, to keep the shifter compact. Stab with your thumb to upshift, hook with the index finger to down shift. I guess it didn't catch on, I know I've never seen it on a bike.

[Joe_W]

Also note that there is no group marking visible, so it was at the lower end of Shimano's component hierarchy. Nice idea nonetheless and probably simple to realise (tech already in place in higher end groups). Makes those shifters much more convenient than without the button.