Slow progress but progress (DIY two seater tadpole trike, 9hp Honda diesel)

[user removed]

Originally Posted by Cobb

williamsburg huh? York Town, Busch Gardens? All about an hour from me. Maybe we can meet up and see this in person?

Sounds good to me.
I can see the coasters at Busch Gardens from the entrance to my neighborhood.

regards
Mech

[user removed]

Originally Posted by kach22i

This looks promising.

I'd love to see the details of steering and turning the wheels when it comes time to reveal.

Are those old style VW Beetle torsion bars up front?

I am thinking about the steering, it does intrude into the passenger compartment. I found a 91 civic at the pick and pull yard with a manual rack and pinion. At this point I think I am going to dump the VW steering box and replace it with the manual rack from the Civic. I can weld mounts to the top torsion tube as close as possible to the shock mounts leaving just enough clearance for the rack ends to clear the shock mounts. I still need to do some measurements to see if the total width of the rack from tie rod end to tie rod end is close to the same as the old VW setup.

This would give me the Honda system including the steering wheel and all necessary parts. It would also give me about 6 inches more leg room and allow the drivers and passengers seats to move forward some.

The VW steering box is clamped to the torsion bar tube so removal is easy and it would also allow me to get rid of the dampner and the mounting bracket for the dampner. It would make the torsion bar tube just in front of where your feet would rest.

regards
Mech

[aerohead]

My Karmann Ghia suffers an uncontrollable wheel shimmy without the damper.Perhaps the rack and pinion counteracts that.Don't know.Just wanted to mention that.

[user removed]

These two pictures show how the tie rods impinge on the place where I would like to put my feet, which is right up to the tubes of the front axle. I think the shimmy is a part of the design of the steering system and the dampner was added to control that.

If the rack is close to the right dimension and close to the same width then the key is that both tie rods are the same length and as close as possible to the same pivot arc as the trailing arms. The closest possible to the top tube on the same plane as the tie rod connecting points on the spindles. It will also make it much easier to seal off the wheels from the passenger compartment.

I also checked and I can buy all of the parts to convert to disc brakes for about $235. I'd rather do that than even try to fix the drum brake system.

regards
Mech

[user removed]

Originally Posted by aerohead

My Karmann Ghia suffers an uncontrollable wheel shimmy without the damper.Perhaps the rack and pinion counteracts that.Don't know.Just wanted to mention that.

I think the shimmy in the stock steering is due to the unequal length of the two tie rods. I'm sure there are some wierd geometry and toe changes from side to side under compression or impact on primarily one wheel. The dampner is a bandaid in my opinion. I know whenever we had a rack that was not perfectly centered you would get some bumpsteer, and you had to correct whatever had the rack misaligned even sometimes replacing the crossmember where the rack was mounted. I always ran the steering wheel lock to lock to make sure the travel was exactly the same from one side to the other. If not then clamp the steering wheel so the rack is perfectly centered, and figure out why (if so) it is not perfectly centered.

I'm not sure if the OE box has a master spline. It it does not then the pittman arm could be off a spline or more and that could be the source of a shimmy, assuming everything else is in specs.

regards
Mech

[Giovanni LiCalsi]

A 1979 MGB front suspension would be perfect for the Tadpole.

[CFECO]

Originally Posted by Giovanni LiCalsi

A 1979 MGB front suspension would be perfect for the Tadpole.

The big advantage of the old VW design, is that all the suspension members are outside of the footwell area, allowing a more forward seating position. No other suspension type can do that except maybe a Model T's leading arm straight axle, or a Ford Twin I-Beam off an old truck. There is a Reason Ford does not use it anymore, crude, heavy, and the geometry is all wrong.

[user removed]

Since the VW design has been made from 1937 until almost today the parts are plentiful and relaitvely cheap. Those who have actually built vehicles understand that the most important thing is to not go backwards with constant revisions without a well thought out plan to minimize wasted effort and increase costs. The steering rack will be super cheap and include everything from the steering wheel to the tie rod ends, at a cost of maybe $50.

The VW front axle beam is also good for collision protection deflecting impact away from the passenger compartment. It also is a highly proven design as far as it's use in dune buggies and other applications where severe impacts are encountered. The later ball joint front axles are the best and with a $235 disc brake conversion and rack and pinion steering everything is where I like it.

regards
Mech

[freebeard]

The dampner was added by VW in the 1960 model year. They added rack and pinion steering in the 1975 model year.

Here's a one-page discussion on retrofitting a rack from thesamba.com:

Rack & Pinion Conversion

There's more:

Search:rack and pinion steering

From a few minutes scan, it looks like stock, 914, VW Polo (not Rabbit), or SACO are options.

[some_other_dave]

N.B.--the 914 and 911 (up through 1988) steering gear are interchangeable, and practically identical. And the VW 411/412 stuff as well. If you're going that direction, at least that'll give you more options.

Bump steer can be a bit of a tricky thing. You can actually fudge it to get toe change that you want during compression or rebound of the suspension, if you're careful. Or at least get something close to what you want. I have seen race car builders spend hours on working out the toe curves of their suspension and fiddling with the tie-rod mounting positions to get specific things to happen...

...Although that is hours that would probably be better spent actually getting the thing on the road, in this case...

-soD