19 jan 2021
new 2005
This information is intended to help assemble or diagnose Rambler trunnion front suspensions, and assumes you have a factory Technical Service Manual (TSM) or you're just winging it (heh heh) and that you have basic mechanical competence. This isn't a how-to for beginners. Though it's specifically for a 1963-1964 Ambassadors or Classics it applies in general to all of the "big chassis" cars (eg. 10, 80 series) until the 1970's when they switched to a ball joint on the upper arm.
All of the photos and procedures were worked out on my 1963 Classic wagon. It was stock except as noted here.
There is a separate document for the early Ramber American suspension.
While most manufacturers had switched to ball joints by the 1950's, even, Rambler hung on to them for a long time; maybe they had a barn full of the things out back. Trunnions work well; even poorly maintained they last nearly forever (at the time of this writing mine are 40 years old and still in fine condition) but are subtle to install, and the information is not in the technical service manual.
(Though they do require some maintenance! They're not magic! Wayne Lamothe inherited a '63 Classic that someone had managed to apparently never grease. It takes a close look to see that the threads on the trunnion are worn down to where the cap simply slides off! (The driver was never in any danger as the arms with spacer holds the assembly together by itself.)
The Rambler front suspension works great -- when i good condition. Technically sweet, strong, very light, and you can bolt 1980's disk brakes to it. Once you have them sorted out, they work great, last a long time and are reliable. Mostly people whine about them because they don't understand them.
The two big gotchas with this suspension are:
I've worked out safe and repeatable solutions to these problems. Each has a section below.
I strongly suggest thoroughly cleaning all of the suspension components. You will not get the trunnion assembly process right if the parts are encrusted with old grease and grit. It is not easy to get all the hardened grease and dirt out.
The procedure below requires the trunnion cap insides to be completely free of old grease and grit. You will probably have to pick it out with a sharp tool, wash in solvent, and repeat more than once. In the how-to sequence below the "dirty" parts below we tight enough to torque loose the cap from the arm. It must turn freely. The one below doesn't seem all that bad here; I assure you that cap required mechanical force to assemble.
This three-second video, though it shows a different (small car) trunnion, is how clean and free it must be. The caps here are identical to the big-car trunnion caps. This is how clean these parts are when first assembled at the factory. If it is not this clean and free, it may bind, and loosen the caps from the arm.
The how-to sequence shows unlubricated parts. You should apply new, clean grease to all trunnion parts (except cap-into-arm) before assembly.
The previous 2005 version of the assembly sequence follows the new one below.
BEGIN: These are the basic components of the upper control arm trunnion system. The bushings should be installed first (not installed here).
STEP 1: Thread each trunnion cap into each arm, and torque to XX ft/lbs. This will be the final assembly and torquing of the trunnion caps. Note that the underside of the cap "head" is cleanly flush with the arm metal -- no gap. If it is not square, the arm shallow threads are stripped and the arm must be replaced. It is all too easy to cross-thread the nut into the arm. Go slow, hold it square to the arm, and try to install by hand. If tools are required to start it, be extra careful.
STEP 2: Now ready to assemble the two arm-plus-caps and center trunnion casting into the control arm. This trunnion is too dirty to use in a car, for the record.
Do What I Say Not What I Do Department: Install grease seals onto the trunnion arms before assembly. Grease seals, fat O-rings are as good/better than the factory seals, will not be shown in this sequence. I left them off here so that you can see what is going on.
STEP 3: Install the trunnion casting into one arm (doesn't matter, they are identical) and just run it down. If the inside of the cap is not clean, it will bind. Don't "tighten" it, just take up all the slack.
STEP 4: Add the remaining arm half to the trunnion. Thread it on a couple of turns.
STEP 5: This would be best shown on a video, but I don't feel like making videos, and in 20 years this HTML will persist, whereas Youtube and TikTok, who knows, so now's a great time to practice visualization (lol). The two arm halfs are free to rotate on the trunnion center portion, any part can move.
Rotate (thread) the most recently added arm further onto the trunnion, and every full turn, flop it down onto the table and measure the distance between the inner edges of the bushing ends of the arm.
The only dimension to worry about at this step is that measurement between the inner tips of the bushing ends of the arm. Each full turn is about 1/4".
IF YOU CANNOT GET EXACTLY 8.25 INCHES: STOP. There is something wrong. Do not proceed, and absolutely do not install this on a car, it will self-disassemble. Parts may be bent, the caps not seated squarely in the arms, etc.
Insert the spacer/stiffener between the flats on the small end of the arm and torque to XX ft/lbs (not shown here).
If you get 8.25" between the arm tips, and with the spacer/stiffener installed and torqued the trunnion will not turn freely in it's space between the arms, Something Is Wrong. It may be that the arm ends are bent, caps not square in the arm ends, or the inside of the trunnion caps are dirty. This must be fixed before this assembly can be used in the car.
STEP 6: Now go back and look at the trunnion end. The trunnion wants to be centered, but is probably not. Simply rotate the trunnion center casting in half-turn increments until it is close to exact, within 1/16" of centered. (Any remaining error will be adjusted out when you subsequently align the suspension.)
STEP 7: This is the trunnion, centered in the arm, of course sans seals for the photo sequence.
This is another one of those things left out of the TSM.
The upper A-arm pivot bushings, the ones that the caster and camber adjusting eccentrics run through, should have a dished washer placed or crimped over the inner sleeve, where it faces the chassis, on the inside of the upper A-arm (see first photo).
The problem is that most replacement press-fit bushings are not exactly correct; the rubber is brought out flush with the end of the inner sleeve. Unfortunately on the early cars this doesn't work right; the inner sleeve works its way into the chassis pivot hole and eats away at the end of the sleeve and elongates the hole. The solution is to cut away the rubber, as shown in the photo, and install the dished washer as it should be. The washer not only transmits the (small, but non-zero) side forces evenly, but the dished shape helps installation.
The trunnion consists of a cast steel center cross with bronze bushing, two doubly-threaded cap nuts, a thrust bearing and assorted hardware; the steering knuckle is shown at the top of the photo. If lubricated at all, there is very little to wear out; recommended interval is 30,000 miles, and you need to remove the vent plug to grease it (RTFM).
The thrust bearing carries the downward suspension force and eventually wears, reasonably gently, and in a fail-safe manner. In 2020/2021 the part is readily available, Nice (brand) bearing 608V, available on Amazon, even. There were two outer-diameter bearings used in trunnion suspensions; the smaller diameter used on the early (63-64) cars are made of unobtanium, but allegedly you can simply install the larger one and let the dust-cap ding on the A-arm, the race is supposedly the correct size and only the dust cover is larger. I haven't tried this, but eventually I'll have to. My thrust bearings were still good at 190,000 miles (take that! late-model cars). They were in good shape when I disassembled for initial inspection when I first got the car, at 87,000 miles.
When you first look at the trunnion system, you may find the design to be somewhat baffling (I did). That's because there's actual subtlety in the design. It's rather clever in fact.
A trunnion is essentially a U-joint, and works the same as one in a drive shaft. The steering knuckle runs through the bronze bush, vertically, and allows the wheels to turn. That part is as simple as it appears to be.
It's the upper "A" arm assembly with the two doubly-threaded caps that is a bit of a puzzle, at first. The caps thread into each A-arm half with a weird shallow thread and simultaneously threads onto the trunnion itself. If all five parts (two arm halves, two caps, one trunnion) are not threaded together exactly correctly you'll stress the hell out of the parts and ruin them driving. The width of the wide end of the A-arm assembly (that fits into the chassis) depends on correct trunnion assembly too, and will ruin the press-fit rubber bushings if they rub on the chassis. The TSM is utterly silent on these little details.
(One of the subtleties is the weird double-threading. It's for safety, basically. The upper A-arm is held together not only by the obvious grade 8 bolt and spacer, but by the five threaded trunnion components. The trunnion would work just fine, in the normal case, if the caps simply threaded into each A-arm half and the trunnion had plain bearings, but would catastrophically disassemble should upper or lower arm components fail, such as in an accident (or worse, be pre-stressed into later unexpected failure by a an earlier survived accident). As the suspension moves up and down, the steering knuckle moves fore and aft, due to the threads. It's just a small amount, but normal. Good engineers design for the worst case, not the best case!)
This is another one of those things left out of the TSM.
The upper A-arm pivot bushings, the ones that the caster and camber adjusting eccentrics run through, should have a dished washer placed or crimped over the inner sleeve, where it faces the chassis, on the inside of the upper A-arm (see first photo).
The problem is that most replacement press-fit bushings are not exactly correct; the rubber is brought out flush with the end of the inner sleeve. Unfortunately on the early cars this doesn't work right; the inner sleeve works its way into the chassis pivot hole and eats away at the end of the sleeve and elongates the hole. The solution is to cut away the rubber, as shown in the photo, and install the dished washer as it should be. The washer not only transmits the (small, but non-zero) side forces evenly, but the dished shape helps installation.
This is the original 2005 version. It was lacking clarity on some details hopefully fixed above, but I keep it here for completeness.
Thread a cap into each A-arm half. Tighten by hand at this point just to take up slack.
Install the grease seal onto the threaded trunnion arms (wide end out) and thread the trunnion onto one of the arms. Just run it down, do not tighten.
now do the same with the other arm. it now begins to look like an A-arm.
the following steps take advantage of the fact that the trunnion threads into the caps. NOTE: this pic shows the arm assembled, with spacer and bolt tightened. the bolt isn't inserted until these steps are complete. i didn't take enough pictures, sorry. what i wanted to show is essentially the previous image but held as shown here.
STEP 1: place the A-arm on a flat table and set the spacer in place. it probably won't fit right the first try, likely too loose (a gap) or too tight (requires force, pushes the arms apart).
STEP 2: to adjust, hold one arm-half in one hand, rotate the other arm-half; counter-clockwise to increase the spacer's gap, or clockwise to close the gap. at this step, do not worry if the trunnion isn't centered between the arm ends. that's done later.
repeat until the spacer fits snugly but without any force or gap. when you have it correct, insert the bolt through the arms and spacer and tighten it. if you have it correct, with the spacer-bolt tight, the trunnion will turn freely in it's place between the arms. if it binds, you have it wrong, remove the bolt and repeat the three steps.
As a further check, measure the distance between the outer, wide part of the A-arm assembly. It should be 8.25" inside to inside. With the upper arm bushings pressed in, the A-arm assembly should *just fit* into the chassis. If you've assembled the trunnion wrong, it will either scrape on the inside of the chassis (trunnion caps too far apart) or jam onto the chassis inwards (trunnion caps too far apart). If you've got the spacing correct, the trunnion will pivot freely and the A-arm will fit nicely into place in the chassis. If it doesn't just fall into place it's not right!
at this point the A-arm looks like an A-arm; however the trunnion itself is probably not centered, closer to one arm or the other. now we fix that, again taking advantage of the threadded trunnion. the A-arm assembly is symmetrical; there isn't a top and bottom or left and right. simply turn the trunnion 180 degrees and check again. when centered, the side with the threads for the spring perch is "up". done!
Once you've got the A-arm assembled right, the rest is easy. The steering knuckle simply runs vertically through the thrust bearing and trunnion; don't forget the O-ring grease seals. The castellated nut (with washer) on top should just be run down with your fingers; there's no need for preload here at all. I finger assemble and move to the nearest hole for the fattest cotter pin I can find (a steel pin would be better). You can see the nut and pin in the image to the right, where it lives under the spring perch, not yet installed.
