Rubber mount softail

Like it says above.
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blb350
NewB
Posts: 5
Joined: Mon Jun 04, 2012 3:47 pm
SELF INTRODUCTION: Enthusiast who has built motorcycles for 40 years, and is a great proponent of this original website! Two years ago I built a rubber mounted softail that has not failed. There have been many failures with these due to the poor design (extremely high forces) of the rear shock travel. Motor/trans mounting dimensions came from this website, and I couldn't have done it w/o CH Forum input.

Rubber mount softail

Post by blb350 »

Rubber mount Evo softail in a Paughco Twin Cam frame (no center downtube). I just wrote up a long complete description but lost it when I went to preview it, and found out that I couldn't go back to add more pics without losing everything (lacking serious PC abilities!). If you are interested I will talk more about it. For the present I will just post it, and can explain later if anyone is interested. I have 5000 miles on it currently.
Attachments
Cradle dimensions
Cradle dimensions
Rbr Mnt Cradle small.jpg (253.11 KiB) Viewed 4739 times
Front Motor Mount
Front Motor Mount
Front motor mnt.jpg (218.19 KiB) Viewed 4739 times
RH view cradle
RH view cradle
Cradle RH view.jpg (95.03 KiB) Viewed 4739 times
LH view cradle
LH view cradle
Cradle LH view.jpg (96.84 KiB) Viewed 4739 times
Cradle & TC frame
Cradle & TC frame
Cradle & TC frame.jpg (101.23 KiB) Viewed 4739 times
Death Valley
Death Valley
DthVly2 small.jpg (91.26 KiB) Viewed 4739 times
hansgoudzwaard
Contributor
Posts: 804
Joined: Wed Oct 26, 2011 10:43 pm
SELF INTRODUCTION: I was on the last board as bonustoolkit. I have changed that to my given name.
I started a project build there " File and Fit." I paln to continue that when I go back home in Dec. 2011. I first joined the board when Gary W had it in the year 2005. That was the time I really gained an interest in building chops. I have a long way to go, compared to some here.

Re: Rubber mount softail

Post by hansgoudzwaard »

I am interested. Thanks for posting.
blb350
NewB
Posts: 5
Joined: Mon Jun 04, 2012 3:47 pm
SELF INTRODUCTION: Enthusiast who has built motorcycles for 40 years, and is a great proponent of this original website! Two years ago I built a rubber mounted softail that has not failed. There have been many failures with these due to the poor design (extremely high forces) of the rear shock travel. Motor/trans mounting dimensions came from this website, and I couldn't have done it w/o CH Forum input.

Re: Rubber mount softail

Post by blb350 »

One of the main challenges in building this was due to the relativley poor rear suspension design that a softail has. Because the rear shocks are located underneath the eng/trans, the attachment point for the shocks to the swing arm is very close to the pivot point of the swing arm, something like 8" or 9" (23cm). On a "normal" rear suspension, that distance might be on the order of two feet (61cm). Because of this, the shock springs must be much more stiff (higher spring constant), on the order of three times greater than "normal" rear shocks (for the same amount of return force). The downside of this, is that those high spring forces will be applied the rubber mount system. This is the primary reason that other rubber mount softails out there have had difficulties with their life cycle (failed). The two stiff rear springs will just eventually mash the rubber in one direction, failing it in the worst case, or minimizing it's effectiveness in the best case. My rear bushings are polyuerathane with a DUR A rating of 70 (too high for my liking). They were sourced from automotive, and were designed to be used on the leaf springs for an older model Ford Mustang. I did not modify the size of the holes in the frame where the swing arm pivot axle goes through, so there is 1/16" inch clearance that allows for poly bushing movement, and acts as a maximum allowed bushing displacement. (The stock swing arm setup has some steel bushing that passes through the frame.) See crosssection. More, later, thx for responding!
blb350
NewB
Posts: 5
Joined: Mon Jun 04, 2012 3:47 pm
SELF INTRODUCTION: Enthusiast who has built motorcycles for 40 years, and is a great proponent of this original website! Two years ago I built a rubber mounted softail that has not failed. There have been many failures with these due to the poor design (extremely high forces) of the rear shock travel. Motor/trans mounting dimensions came from this website, and I couldn't have done it w/o CH Forum input.

Re: Rubber mount softail

Post by blb350 »

Nore pics
Attachments
Front motor mount uses Dyna bushing
Front motor mount uses Dyna bushing
Rbr Mnt front small.jpg (241.61 KiB) Viewed 4712 times
Crossection w/ stock on left and modified on RHS
Crossection w/ stock on left and modified on RHS
Rbr Mnt section view small.jpg (251.15 KiB) Viewed 4712 times
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