sidecar mounting question

[mark59]

I have a 1980 4 speed frame with a 1958 style swing arm and a 1946 LE car frame. i am fabricating a rigid to frame rear mount rearward enough to be able to kickstart a U model flathead. my question is what is the preference a swing arm mount or a rigid mount? seems to me a rigid mount would be more stable. my rearward mount will be just in front of the rear shock, similar to the 1979 rear mount but farther back. another question is the vertical height of that mount, i have the 1958 rear mounting hardware and am using that as a location to fabricate my rigid mount, seems the axle heights are the same for bike and hack with no preload on the shocks, i am building into my design an inch of vertical adjustment, how critical is this dimension? any thoughts from the forums seasoned hack riders would be appreciated.

[Chris Haynes]

Why not simply use the '58 mount? Don't try to reinvent it.

[T. Cotten]

Why not simply use the '58 mount? Don't try to reinvent it.

Wouldn't his '80 frame have a square swing-arm, sans hack mount hole, Chris?

Its too modern for me... Maybe just a square swingarm mount would do.

And Mark!

Although the '80 rear frame connection was relatively solid, the earlier swingarm connections were rubber-bushed. Even the 'gland nut' ball joint connections, front and rear, and even the top mount beneath the neck stock was meant to have *some* flexibility.

My '65 with hack bent two swingarms (not hard to straighten), but my buddy with an '80 could do stunts constantly.

.....Cotten

[Rubone]

Wouldn't his '80 frame have a square swing-arm, sans hack mount hole, Chris?

Probably not since he said in his first post it was a '58 type...
I agree with Chris, why change things needlessly. When using the '79 style mount the factory chopped the early casting apart and bolted a mount on. Doing so will destroy the value of the 46LE frame.

[T. Cotten]

Sorry, Folks.

The original square swingarm had a different width apparently, so only mocking it up would tell if a round swingarm mount would still allow toe-in correctly to the rest of the frame.

You never know until you try...

...Cotten

[Rubone]

The entire geometry of a 1980 4 speed frame is identical to a '58, only the shape of a couple tubes differs. Adding a '58 swingarm to a '80 frame makes all the dimensions identical to a '58. No mock up is necessary as all OEM parts will bolt up and 'toe in" is the same as using a '58 frame....

[ryan]

Front upper mount connects right above lower gas tank mounts. Front lower mount 10.75" below bottom edge of upper safety bar bracket to top edge of lower mount. Use rear mount 87197-58 that connects to the round swing arm.

Then change manual brakes to hydraulic brakes if you desire to use a brake on your sidecar. Use 1958-1975 parts. You can use a 1958-62 bike complete rear brake set up for this. You need a star hub wheel, a piece of 1" tubing 11/16" long for a spacer and a 87433-36 axle. You will also need rubber sidecar too bike rubber hose 87778-58A, it is 7" tip to tip.

I gave you enough to get started. Have fun and good luck.

[mark59]

thanks for the input folks, a few things to clear up on my project. the 46le frame required quite a bit of work to bring back to oem specs, the cross tube that the mechanical brake rod passes thru had already be cut off at casting, this is where i have milled a piece of round stock inserted into that tube to support my new rear mount. so no radical change to frame,original mount will stay intact. the original design 1936 was rigid mounted to the frame until 58, considering 58 thru 64 still needed clearance for kick starter, this also was done with the 73 swing arm until 79, now we are back to rigid mounting. i simply want a rigid mount and room to kick start the U model flathead motor on this build. moving the mount to just in front of the rear shock meets my needs well. i have ridden shovels all my life and have broken the frames a few times, the swing arms take a pounding and dont need any more stress on them. i have spoken to several folks who have had hacks for many years and they all agree that a rigid car frame is better than swing arm mounted design.
58 and 73 rear mounts differ from each other compensating for swing differences, other than shock mount locations both swing arms are the same dimensions, pivot, axle, etc. 20170515_154950_resized.jpg i have built in an inch of vertical adjustment and using the 79 style ball which is threaded i can set my toe in easily.

[mark59]

20170514_104600_resized.jpg20170507_231937_resized.jpgthe front curved section had been cut off and angled downward several degrees along with the stabilizer bar being cut and angled to fit who know what back in the day. so this is not a pristine piece of history being cut up. pics show the repair to bring the front mount back into spec, since it is brazed it took some creativity to put it back together, a piece of round stock was turned to fit inside the main tube and threaded into tube at casting, this allowed plug welds for about 12 inches past the brazed casting, threaded section then had a section of steel threaded onto the rod then the curved section was also threaded on, the curved section was tigged to the steel collar, curved section was also plug welded and then the whole assembly was brazed. hole in casting allowed threaded section to be brazed.20170505_175530_resized.jpg

[ryan]

"the cross tube that the mechanical brake rod passes thru had already be cut off at casting, this is where i have milled a piece of round stock inserted into that tube to support my new rear mount" this quote from your next to to last post kind of baffles me because the rear mount is above this piece for the rigid frame bikes, the round swing arm bikes and the square swing arm bikes. Using a later shovel frame with an earlier round swing arm should give you enough room to kick start your bike even with a U motor.
Someone probably cut the mechanical brake tube for a juice conversion for a 1958 and newer bike. The side car geometry is the same from 1936-1984 for the 4 speed only bikes. The rear mount was cut off in 1979 for a bolt on rear mount that bolted to the passenger foot beg.

Yes your frame is for a rigid frame bike, but the mounting location did not change on your frame whether it is for a rigid frame bike or a swing arm bike. You should still have room to kick start your bike no matter the set up if your tranny is still in the correct location and you have the correct length kick starter. Oh, and yes I know the difference between the between all rear mounts, but again the location on the sidecar, itself, has not changed until 1979.
Re
So my question is this: Are you running a stock style four or three speed in the original location on your frame? Something else had to be changed for you not to be able to have clearance for a kicker because, again, the rear mount on sidecar has not moved until 1979.

[ryan]

Ok after all my typing and info, there are no issues with your mounting, you just simply want it to be a rigid mount. The info you first gave sent some of us to consider something was wrong somewhere when there is simply nothing wrong. I do not understand why you want to re-invent something that has worked for years on thousands of bikes, but it is your project.

So for you to run rigid mounting with your frame, you may need to add a gusset on your frame if you do not already have one. It would be like this part number originally for a left frame repair part# 47261-68. I pretty sure you will not need it, but I gave it just in case.

[mark59]

the gusset is in place, i do the right side gusset on all 4 speed frames after having several crack at the cast steel/ tube joint. also a large gusset has been added to the seat tube post at the base. this frame has had all the oem welds touched up with tig welding. tig for low heat, penetration, and control mig for general welds and stick for high stress like the lower mount for side car.

[mark59]

running a standard 4 speed trans,
" this quote from your next to to last post kind of baffles me because the rear mount is above this piece for the rigid frame bikes, the round swing arm bikes and the square swing arm bikes." .....my new mount retains this same offset, look at the pics, the 58 mount is in place and is being used as a reference point to fab new mount, using the lower cross tube only requires an inch and a quarter difference in height to match the 58 mount, i know the oem mounts will clear the kicker, just dont like tugging on the swing arm.

[mark59]

Cotton, the swing arm mounts for 58 and 73 have a different offset, the short pivoting part with the rubber bushing this compensates for the width difference between the square and round swing arms

[T. Cotten]

Cotton, the swing arm mounts for 58 and 73 have a different offset, the short pivoting part with the rubber bushing this compensates for the width difference between the square and round swing arms

I know, Mark!

Attached is a comparison of the square swingarm mount on the right, and a round swingarm mount on the left (new reproduction).
Note that not only is the offset different, so is the height of the balljoint above the stud, and the length of the stud as well.

That's exactly why I posted that only an attempt at assembly would tell if there is a toe-in problem (and perhaps a camber issue as well) .
Even with a proper round swingarm mount, it took quite a bit of effort to properly set up a '71 hack upon my '65s. There is a reason the forward brace is adjustable!

Ironically, with a rigid rear mount, the same hack frame then hooked up to my '49 frame perfectly. So either something was different with the Shovel frame geometry that the hack was originally set up for, or it was botched badly by the dealership.

....Cotten