Front Suspension

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1950 to 1963 early American suspension. If you are not redirected there automatically click the link above.

June, 2007

The early American front suspension is a very old Nash design. Complete with actual Nash parts; this sort of makes the 1963 Rambler American the newest-oldest American car made, as far as I know. It's a nice and simple double A-arm system, but has chronic problems that were resolved in later designs.

First, it has a trunnion top and bottom. Now everyone hates trunnions outright and thinks ball joints are somehow superior, but I disagree. When done right, and maintained even poorly, they are reliable and last nearly forever; the upper trunnions in my 1963 Rambler Classic are original, with likely 350,000 miles on them.

However the American trunnion system is a holdover from the Nash days, literally. Frank Swygert says that they interchange with 50-55 Nash, I don't doubt it.

The lower trunnion isn't too bad, and if you lube it at all, it lasts just fine. Problem is some people don't do any maintenance, like zero, nada, none; with no lube metal grinds metal and the steering knuckle can exit the trunnion in extreme cases. Ouch. There was a 'late' TYPE 2 part that added a pass-through stud, castle nut and pin. Mine's the early design, but it was somehow lubricated and it's perfectly fine. The original parts are going back in the car.

The upper trunnion while very strong safe and reliable has a severe lubrication problem. The upper A-arms have a pass-through pivot bolt that is attached to the arms with jam-thread force, and the threaded bolt pivots within the threaded iron casting. The problem is that as the grease ages and thickens it becomes impossible to force new lube in to push out the old. The end result is that after a decade or two the bolt freezes into the casting, such that instead of the arm-bolt-arm pivoting within the casting, the bolt freezes into the casting, causing the arms to pivot on the bolt, which wears the thin metal very fast. Because all the parts are threaded with a bolt head and nut nothing comes apart, so it remains safe; it simply ruins all the parts.

In my case the bolt was utterly and completely frozen into the trunnion casting. Since all of these cars are this way used parts are rarely better, and rebuilt-used run $350 per side. Ouch. I nearly adapted 'big car' (10 80 series) upper trunnion system parts, but the arms would require shortening, which is beyond my welding capabilities, though that would be a real solution otherwise.

[9 Sep 2007 NOTE: Hey! Revisit that 80-10 upper arm biz! While the 01 arm is shorter, there is a big spacer between the perch forging and the chassis! It appears to be the same as the arm length difference. However, this would affect the A-arm geometry, but it might be OK. Needs checking.]

Instead of shelling out big bucks for more flawed parts, I worked out a real solution that's safe, cheap, reliable, and lubricatable. The trick part could be applied as a modification to replacement stock parts.

The fundamental problem is the inability to lubricate the long trunnion threads. Even the factory recognized this, and reduced the outside of the trunnion bolt to .590" (it's a 5/8-11 UNC thread of otherwise standard dimensions). The bolt is additionally drilled lengthwise, with a Zerk fitting in the head and a cross-drilled hole approximately half-way down it's length. The problem being that no amount of pressure can force grease back through 1.5" of thread!.

My solution is to replace the bolt with a chrome-moly threaded stud, flatted on two sides, a single hole cross-drilled in the center, which aligns with a new hole drilled in the trunnion casting which then has a zerk fitted. Grease applied through the Zerk in the casting can now flow down the two flats and exit at the arms, under the O-ring. There is still a portion of thread that bears load and does not receive direct lubrication, but now has fresh grease on either side of it which is swept by suspension motion. This vastly improves overall lubrication.

I chose rod because fully-threaded bolts of sufficient length are not available, and because it allows easy alignment of the new grease hole before application of the locknuts on the arms. The same could be done with a stock trunnion bolt, but it would need to be dry assembled first to locate the place to drill the new grease hole to match the casting; the bolt would then only match that one arm pair.

I didn't take photos of the greasy suspension on the car, or in parts. It was spectacularly caked with hardened grease mixed with rust. What else is new. Took hours to scrape it off and prep for hot-tanking, photos of nice clean parts below.

Disassembly and removal from the car was pretty easy; it's a very lightweight and modular system, typical of AMC's excellent design work.

However not illustrated here is the unbelievable disaster the upper trunnion bolts caused. Basically I sheared off one nut, and both heads, leaving the upper arms stuck on the casting. (It's not obvious but the hole in the stamped upper arms is threaded. The broken bolt stub holds the arms onto the casting; you can't spin the arms relative to the casting to remove because the arms hit the spring seat. Forcing it would ruin the upper arm.)

To make things just a bit more fun, the trunnion bolt isn't Grade 8 or anything, it's hardened. I mean, like a wrench. Good files slid over the surface; new Starrett hacksaw blades were like a butterknife over glass. I immediately ruined an "import quality" (sic) but sharp 1/2" drill bit (1 HP motor) without even .125" penetration. Hard.

(There are 63 Ambassador parts mixed in here.)

These are the Ambassador parts (same as Classic), 10 and 80 series. It also is a trunnion system, but a good one, that I documented here. I worked up a very simple scheme to fit these well-designed, long-lasting parts to the American, but I'm not that good a welder [see NOTE above]. The second photo is a side by side comparison. It's easier than it looks to adapt!

Though everything is clean, things aren't as good as they seem. The upper arms remain attached to the upper casting by virtue (sic) of the spectacularly frozen trunnion bolts. Not shown are the hours spent heating the front section of the casting dull-red, plunging into cold water, repeated 10 times; welded a nut on and worked it with a wrench the 3 degrees it would move; applying AeroKroil (cold, hot); drilling a hole to insert Kroil; I did not try sacrificing chickens but I considered that.

Commercial "tap disintegration" I priced at around $150 per side. It would have worked though.

eBay to the rescue: I bought a packet of three 17/32" carbide drill bits and simply ground the suckers out. The original bolt is drilled lengthwise, thankfully, providing a convenient pilot hole. Luckily I have a small Jet mill, and the casting has nice flats perpendicular to the trunnion bolt hole. I clamped the hell out of it and turned the stuck bolt into dust -- almost literally, as you can see. I got out only a 1/2" section of the bolt intact, which was useful actually as it let me check the diameter which turned out to be reduced (thanks to John Elle for spotting that).

I actually got the miserable things out. And I found an excellent tool for picking out threads from inside the casting: a 3/8" wood paddle bit! The V-shaped tip has a groove that leaves a perfect hook for reaching into the 60-degree threads and hooking the end of the remaining thread. As you can see I had to pick out nearly everything in 1/8" sections. They were locked in place with hardened grease and rust. The stuckest bolts I've ever removed!

All this work did very little damage to the threads, of which there are plenty, anyways. Ran a tap through it just the same.

With the crap out of the hole I cogitated for a few weeks on a solution, the aforementioned double-flatted, cross-drilled headless bolt.

Assembly/fabrication notes

The new bolt is made from chrome moly 5/8-11 threaded stock from MSC Direct (see shopping list below). I turned the OD down to .590, matching the original; it's a lot of length, this decreases friction and increases likelyhood of lubrication. I flatted it on my mill, one side full length so that I can more easily align it during assembly (turns out to be unnecessary).

[9 Sep 2007 note: After final assembly, with the milled flats the reduced diameter is NOT necessary.]

The nuts are Grade 8 nuts from MSC also. I decided that I'd replace the seals and O-rings with stock parts, that seems fine, and vastly cheaper and better than NOS parts.

Drilled the face of the trunnion over the long trunnion thread for a Zerk grease fitting; this hole will match up with the hole in the new trunnion bolt.

Front of the flatted trunnion bolt. The full-length flatting turns out to be unnecessary.

The "back" side of the new bolt.

The new clearance for grease flow path visible (front shown).

Here's the hole and flat alignments relative to the trunnion casting.


I take it back -- it is hard to assemble, unlike the big car suspension.

Prepping the upper trunnion for assembly. I installed drive-in zerks, easy, as I could not find the right tap (1/16" pipe I think)...

The thrust bushings were worn out, almost immovable, but luckily I had a new set I'd bought for the 63 Classic, which turned out to be indentical with these. I bought them from some AMC supplier, who ingeniously ground off the markings so I wouldn't notice they were a commonly available part! Here's the part number of the original.

Assembling the upper trunnion and arms was easy. I pressed on new bushings. ESPO provides one part number for upper and lower; the originals are different parts, the uppers have stamped ribs to set insertion depth. When using "lower" bushings on the upper arm, you simply have to carefully measure insertion depth as shown in the TSM.

The arm halves went on the pivot/perch, and the spring stop bolts in. This sets the width for the trunnion on the outer end. Assembly consists of inserting the trunnion bolt on through one side (don't forget the O-rings or seals) and manually positioning the cat trunnion more or less centered as the bolt passes through. The bolt threads "ought to" line up with the threads on the other arm half, you can loosen the spring stop bolt to allow a bit of give to get it started.

The grease seals are so simple I used generic parts I got from instead of OEM replacements. It ain't rocket science here. I used a pair of O-rings each side, they seal out dust and water and allow grease to exit. (Grease will exit using the modified bolt!)

The grease hole in the bolt must line up with the new zerk on the casting. To do this, simply measure the distance from the end of the bolt to the hole; then insert the bolt to this depth, as shown. Make sure the bolt is installed such that when the upper A-arm is level, the flat is perpendicular (hole aligned with) the added zerk.

The uppers are only slightly annoying to assemble; the lower arm is just bizarre. I pressed in the bushings and fitted the trunnion nuts into the arms. To the lower trunnion I added the new O-rings, greased the threaded journals, and assembled the trunnion and lower arms, adjusting it so that the shock absorber mount/spacer just fit. This sets the spacing at the trunnion end of the arm.

Then I clamped one arm of this sub-assembly in the vise so that the inner pivot will be vertical. Of course you can't put the pivot bar in; so now take the trunnion nut (1-1/8") out of the top (unclamped) arm, put the inner cup washers and pivot bar in place, then the arm, and inserted the shock spacers with the bolt very loose.

Now comes the tricky part -- getting that last trunnion nut on. As assembled in the vise, the threaded end of the trunnion is protruding from the arm. This part is all feel and judgement and danger. The trunnion nut threads onto the trunnion, but at some point it contacts the arm. The nut's external threads are really broad and shallow an thread into the arm. Cross-thread this, and you ruin the arm. But you have to thread two different-pitch threads at once! And in doing so maintain the exact spacing between the arms for the shock spacer.

Basically I pull up and pushed down on the arm (slight flex) to feel the start of the external thread. Once caught, it goes OK. Caught wrong, it wants to cross-thread.

I got it right but it pretty much defies explanation. The nice thing is, the whole suspension except spring can be assembled on the bench, it weighs about 20 lbs without the brakes, and bolts into the car with four bolts! That part is sweet.

Somehow it all works, and it's very pretty when done. It's a very spare and elegant design in it's own way. The inability to lube the thing is the only serious problem, and I think I fixed that.

I neglected to take pictures of the lower arm assembly, sorry.

That lower arm is a design problem, period. Right where the heaviest load is, force in all three planes!, is a non-positive fastener. Non-positive meaning no retaining locknut, just the threads of the trunnion nut engaging the sheet metal arm. It's weak by design.

Big brakes and modern fat tires would make this much worse. You could apply forces to that lower trunnion that would have been impossible in 1963. 9x2 brakes and 6.00 tires, there's your force limiting!

Since the front shocks are mostly unavailable (though Kanter Auto Parts and Galvin's AMC Rambler Parts have some) I took the opportunity to add some stiffness to the lower arm. The original shock lower mount is a 0.75" diameter spacer; I replaced that with a 1.5" diameter spacer as shown. (Length is 1.475"). This should significantly increase lower arm stiffness.

One nice thing about these nice modular suspensions is that you can build them entirely on the bench, and install as a unit. Very convenient for doing careful work!

Now here's something you'll not see on a factory American suspension -- grease flowing out the back of the upper trunnion!


The original front shock absorbers are completely unavailable in the aftermarket, the stocks are reduced to NOS parts. The problem is that the lower shock mount is a very oversized eye, shared by no other car, ever. It's 100% unique to this car.

Knowing this, I turned the lower shock mount into an opportunity to stiffen the lower arm further, and used two extra holes in the lower arm to make a new mount. I used some 2" x 3/16" steel scrap to make the new mounts. I basically cut-and-fit the pieces by trial and error on the assembled and installed lower arm. It's not rocket science, basically I made the bolt-on tabs first, then fabricated the cross piece to fit, marked it with a sharpie to approximate the angle, tack welded it, double-checked it, then welded it up.

Now all I need is, umm, shocks. Using the online PDF Gabriel catalog, which in Reference F lists shock extended and collapsed lengths (aargh, in part number order, essentially random!) I found some candidate shocks from cars of similar mass. In these "classic" shocks there is no variable valving or ride-heigh-specific valving. I ended up with 68-69 AMX rear shocks! Gabriel 82069, which cross to (notice I did not state 'the same as') NAPA/Monroe 5819.

(KYB lists KG5521 for premium (69 AMX rear) Gas-A-Just.)

Here are front, and rear, shock data, for the record:





Original front



measured by me

Original rear



from catalog; Gabriel 82155

Using my new front mounts, which only increase shock length requirement very slightly, I am using:





Fabbed front



Gabriel 82069

Fabbed front



NAPA/Monroe 5819

Note that NAPA substitutes their 5819 part for the Gabriel 82069 and 82004 (71-80 Pinto, another candidate shock) even though Gabriel lists two separate parts, with different lengths. I'll let you know how that works out...

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