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Adjusting old Simplex derailleur?

Old 10-14-07, 09:01 AM
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Adjusting old Simplex derailleur?

Hi, I'm really new to bikes (so my general understanding, and terminology, is probably off a bit), but want to see if I can get an old bike fixed up that I got for a song at a yard sale. It's a Motorbécane Mirage.

The first thing I've done s far is replace the cable for the rear derailleur, the old cable was broken. It's a Simplex derailleur. I found a few old posts in this forum, most say "get a new derailleur" Maybe I'll end up doing that but my goal in this project is to learn by some experience and frustration about bike repair and maintainence. I.e. i'd rather spend time than money in this case.

After putting on the new cable, the pulleys on the derailleur were too close to the sprocket, i.e. it was dragging on it in the lowest gear. After searching in vain for the nonexistant B screw adjustment, I studied it more closely and tried twisting the larger nut that's behind the derailleur (thin, between the pulleys and the derailleur body), which fixed the angle. But now there's poor tension on the chain and the chain slips. Maybe I screwed it up, or loosened the other end (where it attaches the hanger).

Anyway, my question is, anyone know what the correct way to adjust the angle is? Are there any resources out there for this bike/these parts, or French parts in general, maybe a site that has some of the manuals/instructions?

Thanks!
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Old 10-14-07, 09:38 AM
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How many teeth on your biggest rear cog?

As I remember, that Simplex derailleur was designed for no more than 28 teeth. If you have a freewneel with a 34 tooth big cog, as was common in those days, it probably isn't going to work.

The big issue with those Simplex derailleurs was the plastic derailleur body. As a general rule they'd only last a couple of years before the plastic would wear at the pivots and they'd get all sloppy. I'm kind of surpsised to hear of one lasting this long. The common period replacement was a Suntour VGT. It'll handle a 34 tooth big cog too.
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Old 10-14-07, 09:47 AM
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Simplex der repair sequence- Loosen large bolt holding der to dropout, dip derailleur once in trash can, replace derailleur

In addition to Retro Grouch's excellent advice, I believe that Simplex ders just didn't work very well, even when new, because they were not true parralelogram derailluers. If you had a straight block FW (one tooth difference between cogs) you could get them to work, but otherwise, they were sketchy.
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Old 10-14-07, 03:30 PM
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Assuming that your derailer is not damaged or worn out, it should work perfectly well. The only adjustments are to the high and low limit screws. The condition you describe sounds like the derailer is not mounted correctly on the hanger. You're not getting any spring tension.

The common period upgrade was the Suntour VGT, but the common period replacement was another Simplex. They were very inexpensive and meant to be discarded and replaced when they wore out. You can still find new ones for $5-$10.

This may help you. Ignore the indexing part.
http://www.sheldonbrown.com/derailer-adjustment.html
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Old 10-14-07, 04:10 PM
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Originally Posted by Retro Grouch View Post
The big issue with those Simplex derailleurs was the plastic derailleur body. As a general rule they'd only last a couple of years before the plastic would wear at the pivots and they'd get all sloppy. I'm kind of surpsised to hear of one lasting this long. The common period replacement was a Suntour VGT. It'll handle a 34 tooth big cog too.
Confirm on both counts.
I replaced the Simplex RD that came on my Atala sometime during the Watergate hearings.
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Old 04-05-08, 03:21 AM
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Sorry to revive this old thread but in playing around with a Simplex Prestige, Simplex Criterium, and Simplex SX100, I think I have the answer.

The top of these derailleurs have a bolt which which controls the tension of a spring shown at "A" in the photo. This bolt takes a 5 mm Allen wrench. The backside at "B" has a special nut that takes a 14 mm box wrench to loosen. Loosen the nut at "B", then use the Allen wrench at "A" to adjust the spring tension which pulls the pulleys away from the cogs. When the tension is correct, tighten the nut. Not the same as a "B" adjustment screw and requires some dexterity to hold the Allen wrench at the right spot while tightening the nut but it does work.

If rotating the Allen wrench does not feel like tension can be increased, there is a chance that the spring behind the bolt is broken. That was the case with this unit. The bolt and spring are shown in the third photo. The spring tip on the right should come out at 90 degrees to the spring body and engage a hole(s) in the back of the plastic body. This spring has about a 45 tip which in another thread, I did not realize was broken. The broken spring scratched out the bottom of the Delrin body of the derailleur as shown in the fourth photo.
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Old 04-06-08, 06:13 PM
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how is the derailuer meant to sit on the bike ? this is how i have it but think it looks odd[IMG][/IMG]
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Old 04-06-08, 06:24 PM
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Originally Posted by suhinaffy View Post
how is the derailuer meant to sit on the bike ? this is how i have it but think it looks odd]
Agreed.

The body of the derailleur in that gear should be ~ 4 o'clock position, the picture shows at ~7 o'clock.
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Old 04-07-08, 01:53 AM
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how do i adjust it to the 4 oclock position ?
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Old 04-07-08, 12:53 PM
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The procedure is described in my last post, but before you do that, I would suggest you read this article by the late Sheldon Brown. The 4 o' clock position is approximate. This article explains how and why this angle is about 4 o' clock. The actual angle will depend on the size of your largest rear sprocket.

http://www.sheldonbrown.com/derailer-adjustment.html
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Old 01-15-13, 10:34 AM
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Later that same century.... I finally got the broken jockey pulley changed on my Criterium, & gave everything a good cleaning & lube. It looks just about like new now, other than that foilcal thingy, that says Simplex, being slightly mutilated (I got it that way, honest). Not having a 14mm box wrench, I just used my secret weapon needle-nosed vice-grips.
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Old 09-02-14, 06:44 AM
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Better late than never, I guess. I got these Simplex "Prestige" manual images at www.retropeugeot.com.

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Old 11-20-19, 03:04 PM
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Originally Posted by trhouse View Post
Sorry to revive this old thread but in playing around with a Simplex Prestige, Simplex Criterium, and Simplex SX100, I think I have the answer.

The top of these derailleurs have a bolt which which controls the tension of a spring shown at "A" in the photo. This bolt takes a 5 mm Allen wrench. The backside at "B" has a special nut that takes a 14 mm box wrench to loosen. Loosen the nut at "B", then use the Allen wrench at "A" to adjust the spring tension which pulls the pulleys away from the cogs. When the tension is correct, tighten the nut. Not the same as a "B" adjustment screw and requires some dexterity to hold the Allen wrench at the right spot while tightening the nut but it does work.

If rotating the Allen wrench does not feel like tension can be increased, there is a chance that the spring behind the bolt is broken. That was the case with this unit. The bolt and spring are shown in the third photo. The spring tip on the right should come out at 90 degrees to the spring body and engage a hole(s) in the back of the plastic body. This spring has about a 45 tip which in another thread, I did not realize was broken. The broken spring scratched out the bottom of the Delrin body of the derailleur as shown in the fourth photo.
Thanks, just what I was looking for. Pulley was dragging on the freewheel and the tightening of the spring, along with straightening other bits saved a Suntour GT for another project.
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Old 11-22-19, 10:13 AM
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Thread started 12 years ago, last (zombie) post 5 years ago.

FWIW, back in the day I set up new bikes that had these RDs. They were c**p then. Get a different derailleur.
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