Sheared rear shock attachment piece

AbramClark

Active Member
Discovered this was broken yesterday as soon as I carried the bike outside and put it down. Now I'm wondering where to get a replacement piece. I assume it's just a plate of spring steel?

2018-05-13_broken-frame-piece.jpeg
 

telephd

Guru
I think it is titanium Abram. I might have one in the parts box. Ill check when I get home. Another possible source might be Robert or Jonathan at Rose City Recumbents.
 

super slim

Zen MBB Master
Have a look at this link, as the circular rear fork top, needs to have a flat radiused section 10 mm radius, starting 10 mm from the CL of the nearest fork clamp bolts, in the front so the Titanium spring bends around a flat profile!

Look at the Cad drawing in the link below.
http://cruzbike.com/forum/threads/broken-titanium-rear-spring-2.2132/

Cruzbike should have a spare titanium spring, but if not a out of spring steel 110 by 30 1.0 mm thick.
The 30 mm width has to be a tight fit to the the clamps, as this is what holds the top of the fork from moving sideways.
The long edges need to be radiused and finely sanded to stop any fatigue cracks.
silvio rear spring 110  by 30.jpg
 

3WHELZ

Guru
Concur, I would recommend contacting Robert. I had purchased a spare just in case this occurred during a ride. I included in the sale of my Silvio 1.0; otherwise, I would have gladly given it to you
 

AbramClark

Active Member
I might have one in the parts box.

If you don't still have an older Silvio to match the part, I'd be happy to buy it. I just emailed Robert too.

Have a look at this link

How many miles have you put on your super slim <.5mm stainless version? If you've tested it well, it sounds like the answer to this issue may well be to go thinner / more flexible.

Thanks for the drawings too, I have a friend who could machine me a suitable replacement :).
 

benphyr

Guru-me-not
This tribe is awesome. You know you are a CruzBiker when you get this kind of help from other members of the tribe: broken piece posted on the forum results in several suggestions of where a discontinued piece may be found, how one could be made from scratch including diagrams, replacement part sent from other member of the tribe, all within a four days!
 
Last edited:

super slim

Zen MBB Master
0.47 mm thick plate bent into S shape.jpg
If you don't still have an older Silvio to match the part, I'd be happy to buy it. I just emailed Robert too.

How many miles have you put on your super slim <.5mm stainless version? If you've tested it well, it sounds like the answer to this issue may well be to go thinner / more flexible.

Thanks for the drawings too, I have a friend who could machine me a suitable replacement :).
3,500 Km with a 25 mm travel air bag rear suspension.
No 1.6 mm thick titanium plates left, as the two I bought broke when trying to deflect 25 mm + 10 mm initial (for the inflated length of the air bag)
1.6 mm thick suspension plate with little deflection

side view 48 mm high .JPG

0.47 mm plate bent into an S curve by the initial deflection.
I have now added restraining straps, so I can increase the pressure, and create a preload.
 
Last edited:

bladderhead

Zen MBB Master
That air spring is clever. Where did you get it? Is it totally sealed or do you pump it, like the front one? How long before the rubber deteriorates?
 

AbramClark

Active Member
The thing I'm concerned about is that if I want to upgrade to a custom air shock like "super slim" did, I'm concerned the thicker Ti connector won't be flexible enough and will shear quickly. If I do this I think the best option would be to make my own version like they did that's thinner. But I'm not a mechanical engineer!
 

super slim

Zen MBB Master
The thing I'm concerned about is that if I want to upgrade to a custom air shock like "super slim" did, I'm concerned the thicker Ti connector won't be flexible enough and will shear quickly. If I do this I think the best option would be to make my own version like they did that's thinner. But I'm not a mechanical engineer!
the 1.6 mm thick spring will DEFINITELY break if using an air spring!! as the two I tried, lasted 5 Km and the first large bump! When fitting the second 1.6 mm spring, I did the big bump test outside my house!
The 0.47 mm thick spring has lasted 3,500 Km, and holds the rear fork from rotating sideways, and resists the rear brake load!
 
Top