# Help Please - Shimano TX35 and drivetrain upgrade



## fishrising (Mar 11, 2012)

Cross-posted from the "Drivetrain - shifters, derailleurs, cranks forum," as I thought it might be better here...

All, I just recently purchased a Charge Cooker 24" fat bike for my son. And I already have upgrade-itis for the drivetrain for him, mostly due to (1) poor low gear performance of this rear derailleur and grip shift, and (2) not low enough gearing.

So, the bike has a grip shifter and a Shimano TX35 7 speed rear derailleur. Cassette is 14-24t and front ring is a 36t.

It slips out of 1st gear into 2nd if you even look at the grip shifter. I tried my best to adjust it, to no avail. Also, some hills he is having a tough time climbing, so I want to get him a lower low gear...

So my questions are:

1. Can anyone recommend a quality suitable replacement rear derailleur and shifter? Do I need to go to a downhill setup since this is a 7 speed?

2. Can I go to smaller front ring and/or a new cassette with a large low gear? And if so, what do you recommend?

I am willing to put some more money into this bike for him.


















Yes, I reinforced how he needs to wear his chin strap properly.


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## jestep (Jul 23, 2004)

You basically have 2 options. Go to the M310 7 speed triggers which are decent and you get to keep the rest of the drivetrain. I believe you can still use an 8 sp derailleur with the 7 speed shifters. An older XT or XTR rapid rise works really good for youth bikes. I set my daughter up with one and paired with XT shifters, and it is one of the smoothest setups I've ever used.

Other option is basically to rebuild the wheel with a hub that fits normal 8/9/10 sp cassette. Swap the cassette, derailleur, and shifters to whatever you desire.

I would probably try the first since it's cheaper and should provide an immediate improvement over those grip shifters. The M310's aren't as nice as higher end triggers, but they're a world of improvement over the 7 speed grips.


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## RMCDan (Feb 28, 2008)

fishrising said:


> Cassette is 14-24t and front ring is a 36t.


Man, the drivetrain choices on kid's bikes are baffling sometimes. 36x24 for a low gear = facepalm

This shifter will work with that RD and should work much better than the grip shifter
Amazon.com : Shimano Acera SL-M310 Rapid Fire Shifter, Right (Black, 7-Speed) : Bike Shifters And Parts : Sports & Outdoors

This 13-34 7sp cassette is cheap and will swap right on
Shimano CS HG50 Hyperglide 7 Speed 13 34T MTB Bicycle Cassette | eBay

36x34 is much, much better than 36x24, but still a bit high for a low gear IMO. It looks like the chainring is fixed though, so to go smaller than 36t in the front will require new cranks.


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## fishrising (Mar 11, 2012)

Thank you both! I'll have look at the crank closer when I get home...


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## ETChipotle (Sep 20, 2014)

I have seriously looked at this bike for my girls.
I would start out leaving the rear wheel alone, and just let the bike shop figure out what 7 speed freewheel or cassette goes on there. It might cost 7 dollars more to let them pick it out.

For me the problem can't be solved without addressing the front ring, which means crankset. I think it has a square taper BB but somehow you're going to put a 104 or 94 BCD crank arm on that in the 152 or 155 arm range. So can you buy the new SRAM NX crank in fat bike spindle length yet? or does Trailcraft's crank fit the square taper spindle that the Cooker comes with? I can't find the low cost Spectra cranks I bought last year in 152mm. I think they sold all they had. Mine came in boxes that said 1995 product on it, so there's likely no more of those.


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## fishrising (Mar 11, 2012)

Added two pics of the crank/spindle/chain ring, to help the discussion.


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## RMCDan (Feb 28, 2008)

Yep, definitely a fixed chainring. Square-taper BB, so you're best options for cranks will be Trailcraft or a pair of shortened SRAM S600s from Bikesmith Design

Trailcraft Cycles

SRAM S600 MTB crankarms Shortened


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## fishrising (Mar 11, 2012)

Thanks!


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## GrayJay (May 16, 2011)

The rear wheel looks to me as if it is most likely a threaded freewheel and not a cassette, not too surprising at that price point. Freewheels are a bit heavier but will work fine for kid weight rider. Verify that it is a FW and look for another 7-speed freewheel with a larger low cog, most any 7-speed FW made in the last 30 years should interchange, just avoid an older pre-index era freewheel which may not shift as well. 

Check that the low gear limit screw on the rear derailler is not too tight, might be why it pops out of 1st gear so easy. If not, I would try replacing the shifter first before replacing the RD. Most any shimano 7-speed or 8-speed shifter will be compatible with the 7-speed freewheel spacing. 

Most every MTB crank spindle made is JIS taper, you would have to look really hard to try to find a square taper kids size MTB crank with anything other than JIS taper. 

I am curious if the frame is remotely lightweight. Any indication if it is CrMo tubing or just plain hi-tensile (gaspipe)? $350 is a decent price for the frame and fat 24" tires & wheels IF the frame is not walmart level garbage.


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## Steve-XtC (Feb 7, 2016)

GrayJay said:


> The rear wheel looks to me as if it is most likely a threaded freewheel and not a cassette, not too surprising at that price point. Freewheels are a bit heavier but will work fine for kid weight rider. Verify that it is a FW and look for another 7-speed freewheel with a larger low cog, most any 7-speed FW made in the last 30 years should interchange, just avoid an older pre-index era freewheel which may not shift as well.
> 
> Check that the low gear limit screw on the rear derailler is not too tight, might be why it pops out of 1st gear so easy. If not, I would try replacing the shifter first before replacing the RD. Most any shimano 7-speed or 8-speed shifter will be compatible with the 7-speed freewheel spacing.
> 
> ...


Welding *looks* more CroMo than aluminium alloy


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## Steve-XtC (Feb 7, 2016)

jestep said:


> You basically have 2 options. Go to the M310 7 speed triggers which are decent and you get to keep the rest of the drivetrain. I believe you can still use an 8 sp derailleur with the 7 speed shifters. An older XT or XTR rapid rise works really good for youth bikes. I set my daughter up with one and paired with XT shifters, and it is one of the smoothest setups I've ever used.
> 
> Other option is basically to rebuild the wheel with a hub that fits normal 8/9/10 sp cassette. Swap the cassette, derailleur, and shifters to whatever you desire.
> 
> I would probably try the first since it's cheaper and should provide an immediate improvement over those grip shifters. The M310's aren't as nice as higher end triggers, but they're a world of improvement over the 7 speed grips.


First consideration is to think about the frame and if you want to spend on that frame. It looks like CroMo not alu alloy.... (just from the welding) but ...

Then the main choice is swap the backwheel/hub for a cassette or not .... the 7sp makes it 90% probably its a freewheel. 
After that the choices line up....

Swapping the wheel for a hub with Cassettes is likely difficult (non fat disc brake wheels in 24" are hard enough!) *In other words its likely a wheel build....*
eBay/pinkbike etc. might be your friend and you might want to just find ANY replacement rear wheel for now then rebuild the one from the bike?

Sticking with a freewheel then leaves *some options like Sunrace who do make a 9sp freewheel*... never tried one personally....

Cranks .... if you have a decent set of tools (vice being probably the most important) then shortening S600 cranks turns out to be really easy. (Or at least a lot easier than I expected it to be) .... main things you need are a decent drill - good speed control and no wobble (I used a rechargable but good quality one) and drill slowly, I drilled 5,9,13 mm .. the main thing is slow or you melt the aluminium ... tapping for the pedals took 15 mins.... I just put lots of grease in and 3 forwards, 1 back... (just like I learned at school decades ago)

Once you do that you have the choice of 104 BCD and I went for a 30T narrow wide...(on the back is a 11-36)

*Depending what you end up on the rear will determine your choice on the front...

If you stick with a freewheel you have Shimano 7/8 speed OR you could go Sunrace 9 speed (SRAM might have other 7/8 options) BUT you likely end up in only half decent shifter/rear mechs... on 7/8 speed

Get to a cassette and you can choose 9/10/11 

I went for the cassette and ended up with 10 speed. 
You could look for a Sunrace freewheel and go 9 speed cheaper....

We are currently running SLX a rear brake with a 160mm rotor and XT 78x front brake (again 160mm rotor) and shifter with a XT shadow + rear mech.

SLX/XT is just better.. it shifts better, is more adjustable for smaller hands ... needs less pressure to shift and is lighter.

The brakes took some finding cheap (weeks on ebay) but actually shifters and rear mech are not THAT much more expensive than cheaper kit.*


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## RMCDan (Feb 28, 2008)

GrayJay said:


> The rear wheel looks to me as if it is most likely a threaded freewheel and not a cassette


Good catch. FW options aren't great unfortunately

Freewheels 7 Speed | Jenson USA

Of those^^^, it it were my money I'd probably get this one.
DNP Epoch 7 Speed Freewheel > Components > Drivetrain > Freewheels | Jenson USA


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## fishrising (Mar 11, 2012)

Thanks again all! I've ordered a bunch of parts and will update this post once everything is installed.


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## fishrising (Mar 11, 2012)

Got all the parts!!!

Got the cranks installed this evening, so my son now has on the crank up front 2 front rings (no front derailleur) 32x14-24t or 22x14-24t, as I bought a 2x front crank. What a world of difference from 36x14-24t.

Next up, rear freewheel and I found out I don't have the right tools to swap free wheels. So, I ordered them. Coming next we are replacing the 14-24t rear freewheel to a 14-34t freewheel. This will be like a new bike to him shortly! Oh, and my old SLX hydraulic brakes from my fat bike since I bought new XTs!

Then lastly a new trigger shifter instead of the grip-shift.


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## ETChipotle (Sep 20, 2014)

Good job! Keep up the good work and thanks for the update! By coincidence I just hopped over to this thread to see if you had any news.


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## fishrising (Mar 11, 2012)

Ok, so I installed the new crank and freewheel! But I am concerned with the chain line. It lines up almost perfectly when in the highest gear (smallest rear cog), but seems quite bit off when in the lowest gear (largest rear cog). Tough to see in the pics. It shifts and pedals fine.

Is this a concern? Do I need to get the cranks seated closer to the frame? Or for an 8 year old, good enough?





































New shifter and brakes will come after I solve this.


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## Steve-XtC (Feb 7, 2016)

fishrising said:


> Ok, so I installed the new crank and freewheel! But I am concerned with the chain line. It lines up almost perfectly when in the highest gear (smallest rear cog), but seems quite bit off when in the lowest gear (largest rear cog). Tough to see in the pics. It shifts and pedals fine.
> 
> Is this a concern? Do I need to get the cranks seated closer to the frame? Or for an 8 year old, good enough?
> 
> ...


You could try for a shorter bottom bracket which is quite cheap (UN55) but if it's working ... and pedalling ok I'd be tempted to leave t for now and see how it goes?


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## fishrising (Mar 11, 2012)

UPDATE: So, I've decided to just let my son ride it as is for now and he is having a blast! No chain drop issues. And the gearing is so much better for him.

We went from 36x14-24T to:

Dirt: 22x14-34T
Road: 32x14-34T

This is on a 2 ring crank set, but with no front derailleur, we will simply manually move the chain when he wants to. Which he has not wanted to do yet.

So far, in addition to the $349 for the bike, this setup has cost me (minus tax and some shipping):

Trailcraft Cranks 2x Option $79.99
Shimano MF-TZ31 7 Speed Freewheel 14-34T $9.99
- Park Tool FR-7 Falcon Freewheel Install/Removal Tool $8.37
- Park Tool FR-1.2 Shimano Freewheel Install/Removal Tool $8.50

And next up are:

Shimano Altus M310 7-Speed Right Shifter $12.95
Hand me down Shimano SLX Hydraulic Disc Brakes


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