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Discussion Starter #1
Im rebuilding a 1978 Honda CB400A that has a cracked sleeve. I want to build and add a side car. It was suggested that I stiffen the front forks maybe swap the rear shocks to a set form a 750. I not smart enough to swap forks out so Im thinking of rebuilding my forks and adding 20 weight oil instead of ATF .Any thoughts suggestions . Help needed.

Will the bolt hole centers from the 750 shocks match the 400a or should I look for something else . Im going to modify the shock mount for the rear mount of the side car at least thats the plan now. Thoughts?

Bill
 

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20W fork oil is way stiff, probably too stiff. I suggest most of the time to go to 10W, 15W if the bike is being ridden fast and hard. Springs would be the first thing I'd change rather than oil. Oil serves to dampen the spring oscillations and you need heavier springs for the load of the side car, then figure out which weight oil works best with the spring rate.
Rear shocks on the CB400A are clevis to clevis type, hard to find. I've used this company for rears, they might have some suggestions or be able to change the spring https://www.tecbikepartsusa.com/Classic_Japanese_Motorcycle_Shocks_s/1829.htm
You might contact Race Tech Street and Progressive https://www.progressivesuspension.com/products/metric and ask for suggestions as well.
 

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I ran the stock shocks from my 73 CB750K on my 81 CM400C with 12 weight fork oil and no air added to the air-forks. With the 120 width rear tire, it was the best handling bike I've owned.
 

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Discussion Starter #4
Thanks Jim and Allen Havent bought any thing yet still in the planing stage. Since Im working on the bike motor I thought I would make the changes on the bike before laying out the side car.

Will have to see about mounting points. Found a front wheel from an 81 400t but dont know if the center is to high for the floor of the side car or it I will have to drop the frame lower .

Im thinking that all three wheels are the same plane maybe the weight of the car would be to high from center? Getting there.

Had a computer nerd look at my computer . After he stopped laughing he wanted to know why I was use a model t computer. Soon as I talk my wife into thinking its her idea Ill pick up a new computer then maybe I can post some photos when I start the build.

Bill
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You jogged my memory Mike, I also added 3/4" preload spacers to my forks mentioned below.
 

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I'm not sure if you need to increase the spring compression rate. Build it first and then worry about spring rates. Many sidecar rigs have the car pinned to the bike so it can be quickly removed for normal use. Most of the sidecar weight would be split between the sidehack wheel and rear wheel of the bike. The bike was setup from the factory to be capable of passenger carrying. What is the GVW of the bike before and after the modification? To the question of the sidecar wheel, the question is, should the rig have a third wheel brake or not? How does the control of the brake integrate into the rest of the bike brake system. How much braking power should the wheel have?
 

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Discussion Starter #8
Thanks for the info. Some more information . The side car will not be much more than a frame . Maybe a small storage box for whatever. Will weigh about 1/3 of the bike weight or about 130 pounds. Lost the use of my left leg so a 400a so I dont have to shift gears and a third wheel for balance. I will not carry passengers. All good points to consider. I will rebuild the forks because they need it but will stay with the ATF oil. may add the washer.but will think about. I dont plan on adding third brake .The 400a will probably not exceed 70 mph and with smart riding I should be ok except for actions from other people. Thinking of mounting points at the down tube just below the coils, extend the down tube for lower mount, rear shock mount ,and the rear foot peg. The platform will be lower than the center line of the wheels to lower the center of gravity . None of this is set in stone. I will be grateful for all thoughts and suggestions.

Bill
 

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I would start with about 9 inches of wheel lead and 1/2 inch of toe in. You may need to adjust the mounts to lean the bike away from the chair a few degrees to get it where it goes down the road without pulling to one side or the other. Put at least 50 pounds of ballast in the car while you're learning to drive it(VERY important).
 

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Had a computer nerd look at my computer . After he stopped laughing he wanted to know why I was use a model t computer. Soon as I talk my wife into thinking its her idea Ill pick up a new computer then maybe I can post some photos when I start the build.

Bill
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Are you running MS-DOS, Win 3.1 or Win 95? Those are the antiques :lol::lol::lol::lol::lol:
 
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