[onionhead]

Hey all,

I'm just pulling my old '05 Transition Preston out of storage and going through it. I came upon an old problem.

In the middle few gears of the cassette, I'm getting a nasty slip-and-grab when I crank hard or simply stand hard on one pedal. I actually shinned myself goofing around a few years ago and had to get stitches from it. The slip-grab is a nasty deep pop-crunch sound from out back. A lot like I am between gears, but deeper.

First thing, I figure it was the chain jumping gears. I tested and tuned the derailleur repeatedly, and it's tuned well. I thought maybe my shifter cable was getting hung up on the frame or suspension pieces when I crank hard - its not. I checked the pivots for the rear suspension - all are tight. I checked the rear hanger - it was a little tweaked, but after a vice-job, it's straight again. I've spun and inspected the cassette a hundred times looking for bent teeth or bent rings, but nothing.

I'm wondering now - would a bad freewheel cause nasty slip/grab too?

Can anyone offer any advice on how to troubleshoot this further?

The freewheel spins and buzzes like it always has. The bike has pretty low hours on it, and I ride like a powder puff. More XC than anything.

I'm a bit perplexed that it only happens in the middle few gears. Perhaps those gears are delivering more torque to the freewheel vs the higher gears... and it's not slipping in the lower gears because I quickly pass through the meat of the pedal stroke. Not sure - just grasping here.

I'm running a combo of SRAM X5 and X7 hardware. I forget the cassette honestly, but it's SRAM too. I'm running Funn wheelsets. It was all ordered as a package deal.

Thanks!

 

[eaterofdog]

Freehub is dying. Pawls are slipping.

 

[sanjuro]

Freehub is dying. Pawls are slipping.

I wouldn't assume that, particularly if it only occurs in a few gears.

Keep in mind on a new drivetrain, all cog/chainring teeth and chain pins are exactly 1/2 inch apart.

Now fast forward 7 years. Probably the chain has been replaced 3-5 times, the cassette once, maybe the big and middle chainring too.

The chainring teeth are 5/8" apart (except the small which is almost 3/4"), the cassette 9/16", and the chain is 17/32". Not exactly compatible.

You could bust out a very precise ruler and measure all the widths and see how much variance you have from the 1/2" pitch.

You could also replace parts, starting with the freehub, assuming it is a Shimano, probably for about $25. If it ain't that, then you need to think about a complete drivetrain overhaul, because replacing piece-by-piece will result in worse incompatibility.

 

[onionhead]

Thanks guys!

All parts are original and in great looking condition. I have a vernier caliper, and can measure things up tonight. I don't suspect parts are worn, but I could be wrong. I've got a 12 year old XC bike that I ride the wheels off of, and it's all on original drivetrain hardware.

I think it is a Shimano out back. Its been years since I've been into biking - its all fuzzy.

 

[slimshady]

I'd check those middle gears for excessive wear, and also the chain for excessive stretching... I bet you a beer that's where the problem resides... As Sanjuro stated, a minimal excessive wear there could drive you crazy. I also bet this is happening in the middle gears because that's when the combination of the force you put in the pedals combined with the inertia and friction your rear tire puts against the terrain. In the lower gears, your pedal strength outcomes the friction, and in the upper ones, you simply don't think of putting that much pressure over the pedals.

 

[onionhead]

I took a very quick look last night, but didn't measure anything up.

I did a quick test I'd perform on a motorcycle or dirtbike. You grap one of the pins or links in the chain where it is wrapping around the rear sprocket, and try to pull it off or away from the sprocket. It shouldn't lift much.

In my bicycles case, I chose the largest gear out back. I could reveal almost a complete tooth on the sprocket. That's bad on a motorcycle. How is it on a bicycle?

Is there a better way to measure things up?

The gears 'look' fine, but I'm not sure if they are. I'm more familiar with motorcycles and dirtbikes. It's obvious when something is bad in their case.

It'd be nice if it's just the chain, or cassette. I'd feel like a real rider... actually wearing parts out...

 

[slimshady]

Sounds like your chain is way too stretched... You might go to your LBS and ask them to check it with a chain stretch tool, such as the one from Park Tool. I'd ask them to check the whole transmission, since this a rather old bike...

 

[BIGHITR]

I was always told, replace the chain and cassette at the same time. Not doing that I got bad results in the woods just like you're talking about. Also jumping chain over cassette teeth I had too and the moment I bought a new chain and cassette it went away. Considering how much pricepoint offers last years Sram cassettes for, for about $70 bucks you can replace both with a $20 Sram chain and a Sram cassette for about $45 or so. Just my experience with what you're describing.

By the way, one time I found the jumping chain to be a split cable end where it mounted into the rear derailer. I had to get new cable housing and it fixed it. Just had that happen last August 9 months ago.