Mountech RD seized - overhaul
 

I had been thinking about posting a picture of my bike with the Mountech RD & asking how long I would have before it exploded on me, but that ship has sailed.

I was out on a ride this morning when I felt some grinding when pedaling. I looked down & the chain was bouncing something fierce! I tried trimming the rear derailer as I could see the front was fine, but no improvement. I hopped off to see if something was caught in the chain or RD. Nothing. Back on & same thing! Hopped off again to check the RD. Lower pulley moves fine, upper barely budges...

Phone call for a pick up.

Later in the day I found some time to take a look. I didn't debate long in trying to overhaul despite the bad reputation. Since I was away from home & didn't have a backup RD or store nearby to pick something up the options were repair or no bike rides.

Anyway, here're my picture notes for reassembly:

https://cimg6.ibsrv.net/gimg/bikefor...3cfbba87de.jpg
Above: position after first spring is unwound.


https://cimg6.ibsrv.net/gimg/bikefor...50261681a7.jpg
Above: position of second spring under tension.

https://cimg6.ibsrv.net/gimg/bikefor...ff8b3804ce.jpgAbove: position of second spring when unwound.

https://cimg1.ibsrv.net/gimg/bikefor...6ebadc6651.jpg
Above: RD reinstalled & shifting through all five speeds just fine.

I had to take it apart twice as the first time I didn't wind the second spring up quite right & the chain would get pinched between the derailer & largest sprocket. Second time was the charm, but the real test will be tomorrow when I actually get it out for a ride.

After having seen the insides of the Mountech, I see how it earned it's reputation. Way too easy for dirt to get in & way too time consuming to routinely clean. It's really a wonder it got approval for production.

I guess that ship is back at anchor; so how long have I got before it raises a ruckus again?

Thanks for taking me down memory lane to 1985 or so, working on my 1984 Stumpjumper Sport.

I too found the easy entry of dirt into the pulley bushing most troublesome, especially as the involved rubbing surfaces were abnormally huge, creating massive friction after riding in wet conditions in upstate NY.

I cleaned out and loaded mine up with white grease, then rode it for perhaps another year or three until finally upgrading the drivetrain to some 6s SIS combination.

I have one of these awaiting overhaul. Do you actually remove the spring or just flush out the dirt?

Why?

There's 9 million and twenty seven decent derailleurs in the world, out of that there's a few hundred that are really good and out of that there's still 94 that are REALLY good. Why play ****-**** games with the biggest failure ever conceived by any bicycle manufacturing company?

If you want a Mountech- use the 2nd generation- it's much less problematic- it gets rid of the captive pulley and mechanics, but is still stuck with that triple pivot design that really doesn't solve any issues.

That looks something like an 84 Stumpjumper Sport- if you want something dominant and Suntour from around the same era- go with an XC. (not XC Sport or anything, just plain ol "XC"). If you really want a triple pivot, go with a Le Tech, but it's going to be more fragile and problematic and no better than a dual pivot. If you want unique, go with an XC triple pulley- significantly more robust, it works flawlessly and it's a hit at parties.

"Hey Bob, the Vikings are looking to turn the corner at any... SAY... is that a triple pulley derailleur on you Stumpjumper?"

"Why yes it is, Phil..."

Friends don't let friends ride 1st gen Mountechs.

The upper pulley spring is the Achilles heel of the Mountech derailleur. I wonder how well it would work without the spring? The Huret Duopar, for example, manages that second articulation without the need for a spring. I may have to scrounge up a Mountech and give it a try…

Huret uses a second parallelogram for the floating cage. It relies on chain tension to move the cage up and down. Suntour uses a spring to help move the cage. Shift advantage? Tall toothed pulleys will help too.

I removed the spring, it wasn't that difficult & there was lots of gummy old grease.

I mainly cleaned it out so I could continue riding while out of town, but it was cool to see the inside & how little it takes to stop the upper pulley.

I'd love to run a 3 pulley XC! Got an extra?

PS: nailed it regarding the Stump jumper Sport.

I'm going to hang on to mine for a while yet-

It's funny- I have an 84 Stumpjumper Sport- it came to me mostly stock from the original owner. The only thing changed out was a 1993-ish XT derailleur and an LX hub with a Weinmann rim from around 1993... that seems to suggest that the Mountech blew up and took the wheel with it in 1993.

Finally got the rear derailer I was looking for:

https://cimg4.ibsrv.net/gimg/bikefor...bbbaf7323a.jpg

Haven't had a chance to ride it yet because of the Tomaselli brakes - they used motorcycle cables & housing. I'm not sure if the smaller cable end will work in the larger brake or if I have to get actual motorcycle cables & housing.

score!!!

My ‘83 Stumpjumper Sport still sports a first gen Mountech. When I purchased it, I overhauled it. That was over a thousand miles ago. It’s now a dingle-speed so I still have Mountech mounted. Why? Men like me like to live on the edge!

Nice! But, all the same, I'll leave the edge life for you!

I hope you have a backup plan. When mine went out, it was like a flip was switched. It was working fine when I stopped to look around, but when I hopped back on, I heard a kind of grinding sound. It took me a little bit to figure out it was the chain sliding over the stuck pulley.

Indeed. Worst case scenario I shorten the chain and turn it into a true single speed.

Love the triple pulley!

Did the Shimano Superplate ever do this like the Mountech? Same design, with concentric pulley and the extra pivot arm. I toured for some months on a Superplate and never had a problem, but now I'm wondering if I was just lucky.

Not familiar with the Superplate, You can see the abnormally huge rubbing surfaces on the upper pulley below:

https://cimg3.ibsrv.net/gimg/bikefor...06093e4e3e.jpg