My left hand bicycle crank has failed. Should I replace it with a different brand/type? (It's a Truvativ Isoflow with square taper bottom bracket)

15
Found 21st Apr 2015
The pedal thread on my left hand crank has failed. Is it best to replace it with the same brand (Truvativ), or should I be looking at other manufacturer's such as Shimano? Also, should I be replacing the other crank too...?

I've never had an issue with square tapered bottom brackets. Is there any reason to switch to GXP or any of the other bottom bracket types out there?
Many thanks

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Original Poster

The crankset is 'Truvativ Isoflow' from a 2006 24 speed Marin Muirwoods. I haven't found an exact matching left hand crank - however, there are various 'Truvativ FiveD' options which look to do the same job;

ebay.co.uk/itm…eb5

amazon.co.uk/Tru…low

ebay.co.uk/itm…81a

Does it make a difference if I buy a 9 speed crankset for an 8 (24) speed bike?

Edited by: "wenttoabetterplace" 21st Apr 2015

as your replacing a none drive side crank there is not so much of a problem.

you just need to make sure the crank is of same length and taper (square, isis, splined etc)
would be worth getting same colour otherwise the bike looks odd though ☺
you might find it cheaper however to upgrade the full chainset with it being 8 speed as your drive ring may need replacing also depending on age.

hope this all helps

matt9511

as your replacing a none drive side crank there is not so much of a … as your replacing a none drive side crank there is not so much of a problem.you just need to make sure the crank is of same length and taper (square, isis, splined etc) would be worth getting same colour otherwise the bike looks odd though ☺you might find it cheaper however to upgrade the full chainset with it being 8 speed as your drive ring may need replacing also depending on age.hope this all helps



forgot to mention changing from square taper does offer benefits such as greater stiffness and moving away from a very ageing technology which is becoming less common.
chainreactioncycles.com is a good place to start looking at upgrades at a eeasonabld price

Original Poster

matt9511

as your replacing a none drive side crank there is not so much of a … as your replacing a none drive side crank there is not so much of a problem.you just need to make sure the crank is of same length and taper (square, isis, splined etc) would be worth getting same colour otherwise the bike looks odd though ☺you might find it cheaper however to upgrade the full chainset with it being 8 speed as your drive ring may need replacing also depending on age.hope this all helps



Thank you for your reply.
The IsoFlow crank has replaceable chain rings, so I'm erring on the side of just replacing the left hand crank and carrying on as normal :). I don't think there was an inherent failing with the crank...the pedal came loose, and I was a long way from home without the tool to fully tighten it. So I think I probably wrecked it !

I've been reading up on the different bottom bracket fittings. You are right about square taper being an aging technology....however, this is a touring bike - and I intend on taking it to some pretty remote places. It seems that square taper is widely available around the world - so I guess it makes sense to stick with it.

Thank you for your reply. I will order that Truvativ left crank from Amazon. The price seems reasonable too.

Do a search for helicoil. You can repair the thread on the crank cheaply and easily.

Thread insert always fail very quickly on square taper due to how they are cnc'd and require pinch resistance to stay tight.
Wenttoabetterplace: glad my advise has helped depending age of bb might be worth replacing at the same time for longevity of use.

Original Poster

matt9511

Thread insert always fail very quickly on square taper due to how they … Thread insert always fail very quickly on square taper due to how they are cnc'd and require pinch resistance to stay tight.Wenttoabetterplace: glad my advise has helped depending age of bb might be worth replacing at the same time for longevity of use.



But surely the thread where the pedal goes is the same on ALL cranks, regardless of whether they are square taper/octalink etc?
(I'm still probably going to buy the replacement left hand square taper crank...unless there is some inherent weakness in the pedal threads on square taper cranks??)
Edited by: "wenttoabetterplace" 22nd Apr 2015

Apologies. I thought the bb end of the arm had gone not the pedal end.
yes pedal end are all more or less the same

Original Poster

matt9511

Apologies. I thought the bb end of the arm had gone not the pedal end.yes … Apologies. I thought the bb end of the arm had gone not the pedal end.yes pedal end are all more or less the same



After further research, it turns out Truvativ IsoFlow cranks are pretty naff (pedal threads stripping is fairly common!).

I have since worked out that I can use a 9 speed triple with the 8 speed system I've got. So that opens up all sorts of options (I'm thinking Shimano Deore/Hollowtech would make sense).

I'll get there in the end :). Thanks for your prior advice though.

Original Poster

matt9511

Apologies. I thought the bb end of the arm had gone not the pedal end.yes … Apologies. I thought the bb end of the arm had gone not the pedal end.yes pedal end are all more or less the same



So, to conclude this little saga

I got the following Deore chainset from Wiggle for £48 delivered + a further 3% cashback from Quidco...and it even includes the bottom bracket.

wiggle.co.uk/shi…et/

(I now know much more than I did about mountain biking groupsets )

Glad you got it all sorted.
mtb cranksets are a mine field.
I run a set of xt on 1 bike and truativ gxp on the other.
the deore cranks are good all rounders.

i would replace the bottom bracket, cranks and chainset - (looks like you did this)
my rationale is:
it is easier,
if one bit is broken probably the other bits are going to break soon,
mixing different components never really works
it is probably cheaper in the long run,
you get nice shiny new components on your bike.

Original Poster

fred box

i would replace the bottom bracket, cranks and chainset - (looks like you … i would replace the bottom bracket, cranks and chainset - (looks like you did this)my rationale is:it is easier,if one bit is broken probably the other bits are going to break soon, mixing different components never really worksit is probably cheaper in the long run, you get nice shiny new components on your bike.



I was under the assumption that it would be expensive to change so many things. But a full Deore chainset, including BB, for ~£45 delivered. It was a no brainer

Original Poster

matt9511

Glad you got it all sorted.mtb cranksets are a mine field.I run a set of … Glad you got it all sorted.mtb cranksets are a mine field.I run a set of xt on 1 bike and truativ gxp on the other.the deore cranks are good all rounders.



It is an absolute minefield! Having said that, I used to own a mountain bike that had a full Deore XT grouspet. It never let me down in the years that I thrashed it up in the Peak District. So I reckon I'll just stick to Shimano Deore or higher from now on. The bottom bracket tech is also highly rated, and widely available - which suits me given that this is a bikepacking tourer that I intend to take to some remote places.

I do wish the companies would standardise around 1 or 2 particular bottom bracket technologies though. Powerspline/GXP/ISIS/Octalink etc etc etc. It's really not helping the consumer
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