Seat post does not hold adjustment
 

The culprit is a Simplex SX 1500.

https://farm9.staticflickr.com/8535/...883010d16a.jpg

It does not hold the saddle adjustment. No matter how tight I make it, the saddle inevitably ends up nose tilted up.

Anyone else experience this and do you have a solution?

Does it happen with different kinds of saddles? Just wanting to rule out that it's not somehow a saddle rail diameter problem.

Check that the two clamp halves are not bottoming out.
I have found steel rails are a must.
Not Campagnolo secure, but French and lighter.

My vote is to check it with other saddles. I've had similar problems with new saddles on vintage seatposts.

Might be a bit tough as about the only thing I ride is Brooks Pro. I do have an Idéale that I can try. Thanks for the suggestion. Here's hoping my butt likes the Idéale. It's a 2000

I have a post that's similar to that, maybe a slightly different model. I eventually replaced the lateral bolt with the axle bolt of a Razor Scooter. I know, I know. You kinda have to muscle your way past the gag reflex sometimes. But it worked.

I am pretty sure CV-6's seatpost uses two bolts, the nuts are inside and face each other.
To get mine sharpie pen tell tale secure, I had to lubricate the threads and really really torque down on the bolts.

I had some issues like this as well, the paste that's used for installing carbon posts/stems/bars did the trick.

Compared with your Pro's ?
Ugh. The 2000 is a hatchet, IMO.

+1 on bottoming out. Make a couple passes with a file on the flats, this ensure that clamp is pulling tight, to bottoming out and without the need to over torque the bolt which will inevitable end with if failing in the middle of ride on the hottest day of the year.

But, if the clamp has been slipping, it's probably toast. The lands are most likely worn from the friction and won't make a good purchase anymore.

Ideale 90.
Unfortunately with one eBay seller who plastered the search with expensive ones, everyone now believes they are worth a fortune.

NOS post. Will try the filing. I like my Pros.

Oh, right! That's different from the one I have.

For what it's worth, I've found some Idéale saddles used thinner rails than Brooks, so when mounting an Idéale I sometimes have to wrap something around the rail to get the clamp tight. That's not the same problem as OP is having, but perhaps related?

An alternative to filing is to add a something like a washer to take up extra space and grip, such as a disk of coarse sandpaper.

Photo below of the seat clamp.

https://c1.staticflickr.com/9/8402/8...de25fb3d25.jpg

I do have a Simplex post that is as you describe. It works fine.

And a correction. The saddle is a 2001. Not that it makes much difference for the issue.

+1. It has gotten out of hand.

RARE Vintage Ideale Rebour 90 Speciale Competition Saddle with Flat Alloy Rails | eBay

IIRC, the mod. 2000 was just the plain plastic shell, like the old Unicanitor saddles. I have a mod. 2003, which is based on the same shell but with a layer of padding and leather cover. It really didn't agree with my butt, which is accustomed to Brooks Professionals. YMMV, of course. OTOH, I have an Ideale mod. 90 and a mod. 92, both of which are leather saddles like the Brooks and both work fine for me.

CV-6-

I have exactly that post on a newly restored Bertin C 37 and it is equipped with a 1970s Brooks Professional. I weigh 185 lbs and have no slippage problem. The seat rails are a tight fit but the whole thing snugged down and stayed that way. Is there sufficient friction between the riveted on cradle halves and the post itself? Perhaps roughing up with coarse sandpaper? RE: Ideale 2000, 2001, 2003 etc. Don't. If you fit a Pro and are comfortable, you will experience severe discomfort with the plastic Ideale variants. The leather ones should be fine as I have done both. Just say no to plastic.

I would try some double-sided sandpaper "washers" between the clamp/post interface, or maybe on either side of that center spacer. That looks like the post on my '82 PX10, but I haven't had any issues.

And I don't mind the 2001 saddle attached to that bike :)

Try some carbon assembly paste and loctite on the threads.

Alternatively, once you have the saddle positioned like you want, you could cut some sort of plug (wood, rubber) to fill in the slot below the bolt and jam 'em in.

I have not followed the later versions of Simplex seat post, I can see how that design would be easier to assemble but less effective.
The assembly really depends on the center spacer to transmit the counter force from the bolt, and the nut potentially might just dig in more rather than keep the system tight….
I would consider a brass shim washer to provide a tight fit for the hourglass shaped spacer, maybe even going as far as to dress the inside of the clamps to increase their surface area in contact with the "hourglass". And a grade 8 metric allen head cap screw in place of that OEM bolt.
Or, locate an earlier Simplex post
Or, admit defeat and go Campagnolo.

Right now it is a Campagnolo post on the bike. But I am wanting to go "tout Français". The shim idea gave me an idea, but I don't know if it is feasible. A star washer if it is thin enough. This along the line of ExPres' idea of folded sand paper. Will play around with it later. Looks like this weekend may be a washout.

Just a bad design on Simplex's part.......
Sure, slots at the clamp going north/south = a big invitation for it to eventually slip with road shock. Just replace it with a nice JPR two bolt, micro adjust post and it will never slip!

assembly paste on the contact surfaces, and I wouldn't go for loctite, at least not the locking kind. Just normal assembly grease is probably better.