1961 rambler roadster, new axle and trans...

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you are correct, and i welcome your comments! i totally agree with your observation, though i think my margins will be OK here. i welcome your ideas though.

actually the lower bolts are single shear, too. the lowers are 5/8" uppers 1/2". all are grade 8. the 1/2" bolts are the limiting item of course.

there's two sets of forces i tried to consider; normal operating and hard curb-whacks, or crashes, eg. "none of the above".

here's my logic: i'll state it as if it's fact, it's easier to write. if you smell a turd, yell! lol

the engine makes 200 ft/lbs torque, in first (3.1) and this axle (2.73) that's some 1700 ft/lbs at the axle. let's say i rev it up and dump the clutch (haven't done that for 40 years!), what with the flywheel and mass, twice that? say 3500 ft/lbs. the distance between the heims is about half a foot, so double again, 7000 lbs of force, best/worse case operating. assuming the tires would grip that much, doubtful.

there's four grade-8 bolts in shear, two are 1/2" so they are the limiting case. from what i read a 1/2" grade 8 bolt has a shear strength of 17,000 lbs. there's four of them, but assuming two are loose/uneven forces/bad geometry, even two of them should have enough margin.

the heim is spaced off the bracket by 1/4" spacer. the angle isn't 90 degrees either.

but i think the ear they are bolted to will deform first, before the bolt fails.

i think i'm talking myself into making them double shear, lol. now's the time.

the "none of the above" crash/curb-whack i think is more a worry. i've seen especially front end parts catastrophically fail "for no reason" that later examination shows a very old (corroded) crack in an arm, etc. i assume from an older crash that was repaired. that's more my worry.

i also have the road experience of a much simpler, weaker, system -- no bolts in shear though -- that was simply two 1.25" DOM .120" wall tubes with a boxed end that clamped to the factory leaf spring perch on the axle tube. that simple system took all the operating torque. i had no way to measure "windup" flex but there was zero static deformation after most of a year of operation.

with a big motor and serious tires and gears i think this system would need a different implementation.

and this is my first time using heims. obviously they work, but i can see how easy it is to mis-use them. eg. my forces are not at 90 degrees (15 deg off) so that adds to the complication... and there's nothing compliant in the system except the tires.
today i got the axle back under the car, squared it to the chassis, and added the front heim to the front tip of the wishbone. couldn't do that until i got the "final" rear assembly in place, setup wheelbase correctly and got it square-ish. with the wishbone in place i was able to get the rear positioned much more closely to correct -- wheelbase within 1/4", but adjustable, but most importantly, square to the chassis.

i'm not real happy with my chassis references but i think i have a final solution to that. later.

this pic shows the position of the wishbone tip to the transmission yoke. yoke inserted, no driveshaft yet. in this pic the wishbone is at full droop. at full squat (air springs bottomed) it's parallel. that end of course doesn't move much, it's a loooong lever!


man, it's like Ford made this axle to be retrofit to ramblers. the shock mounts are in the right place, as-is. there's a hole in the 4-link arm support to which was bolted an adapter for a little yoke for the shock bottom. once removed, the hole accepts a shock stud, the kind that sometimes comes with OEM replacement shocks and that i had in my junkbox. inserted into the hole, the AMC shocks bolt into place, perfectly.

OK! busy week. i sent off the clutch from the car, plus two old cores i'd scrounged in the last decade (these clutches are rare and not valuable, so no one has any). they're on their way back from from Tennessee Clutch & Supply. i had two good clutches made from the three cores, so i have one for the shelf.

got a lot of parts in and things are falling together. axles are in the housing, brakes affixed, panhard bracket problem solved and fabricated, got the chassis end of the panhard solved and half built. found a really great brake line problem-solver part, a "banjo union", more on that later.

all of the heims are now in double-shear. thanks OldIron. (i'll pick up the correct hardware next week.)


turns out the 1998 Mustang e-brake cable system is pretty much the same as the Rambler system, from 1958, go figure. all i have to do is modify the yoke that accepts the front end of the cables (we'll see if that's true when the 2nd cable arrives from RockAuto). Rambler uses an intermediate lever to translate stroke from dash to rear brakes so if the leverage is wrong (likely, since OEM was 9x2 Bendix drums) i have an easy fix there.

got the axle assembly back in the car and positioned it precisely -- i modified a couple of Zerk fittings to accept a tape measure tip, since that's literally the bottom center of the virtual "kingpin", and screwed one into each front lower control arm's lower trunnion. it's a perfect reference. with that info i was able to measure the driveshaft.

worked out the U-joint situation -- to make a long boring story short, the driveshaft that was installed on this chassis uses an odd, ting U-joint, 2.25" across, not 1200 series even, just some strange Nash part. it looks like a big steering joint. but in my iron pile i had a couple of "AMC" driveshafts from the 60's and 70's, six-cyl cars. those take ordinary Spicer 1310 U-joints. The Mustang uses a 1330 U-joint.

with all this i figured i'd take one of the driveshaft-donors to get shortened but i was pleasantly surprised to find one was almost perfect. i moved the axle back 3/8" and there's now 1" of yoke stickout.

the axle panhard mount was a PITA. the panhard has to be about 6" rearward to clear brakes, shocks, rear cover. it is in line with axle center, horizontally. this put the side to side force at a 45 degree angle to the tube. a big fat two-ended bracket just barely leaves room for shock install.


so the axle assembly is complete, minus brake lines and e-brake cables. those parts should come next week, as should the clutch.



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