Trunnion and Front Spring Service
1964-69 Series 01
1964-68 American, 1969 Rambler and SC/Rambler
1968-69 Series 30, 70
Javelin and AMX
American Motors, innovative in many ways, lagged behind in suspension technology in the second half of the 1960s. While other makers had already converted to an all-ball joint system, AMC was still using upper trunnions, a mere step above the kingpins introduced on horseless carriages early in the century.
This discussion and what follows is limited to the 1964-68 American, 1969 Rambler and SC/Rambler, and 1968-69 Javelin and AMX models.
The system is evil for several reasons:
How It Works
In the interest of keeping peace with Daimler-Chrysler Corp., I will not reproduce illustrations from the AMC technical service manual (TSM). The following knee-bone-connects-to-the-leg-bone narrative is meant to supplement, not replace, that resource.
OEM trunnion bushings are steel and artificial rubber. The vertical bushing allows the knuckle shaft to pivot in the trunnion and absorbs some vibration and shock. The horizontal bushing allows the upper control arms to pivot in the trunnion and absorbs some vibration and shock. The bushings are designed not to bear weight, but to allow rotary motion while maintaining proper alignment of the parts.
Bushing failure often results when the steel inner sleeve rusts to the knuckle shaft or control arm bolt. This applies torsion to the outer rubber wall and causes it to wear. The rubber can also dry out or otherwise break down from age, thermal-cycle stress and physical wear from exposure to water, dirt, salt and other chemicals.
When the bushings wear out, alignment in the vertical and longitudinal axes is compromised, and side loads are applied to the trunnion, thrust bearing and knuckle, further hastening wear. This will eventually affect the camber, and the coil spring will develop a characteristic bend. Front-end play might also be apparent on bumps, turns and stops.
The coil spring must be removed in order to access the trunnion. This requires great care and proper tools. Please dont trust your life to bailing wire, cheap turnbuckles, cast iron brackets, etc. I have known people to use bent threaded rod to hold the spring, but I sure as heck dont want to be around when they do it!
Parts and Sources
Note: Though some of the parts might not look so bad, consider swapping them all out at once anyhow. How old are they? Original? And how excited will you be to pull those springs out again in six months or a year?
Even if the thrust bearing looks OK, its a safe bet that the O rings and nylon washer will be fried. These parts (some vendors now call them an installation kit) are included in the AMC thrust bearing package. If your vendor doesnt include those parts with the bearing, you might be able to scrounge them up yourself.
The TRW number is 10234 (rebuilt, thrust bearing not included); NAPA lists it as NCP 2801499.
At a swap meet or from an OEM vendor, get AMC Group 10.042-2, Part 318-4708 (thrust bearing not included).
Walt Garson manufactures replacement bushings you can install yourself if your trunnion is in good shape. He also sells rebuilt, greaseable trunnions and greaseable replacement thrust bearings (not OEM, but very likely better).
3900 W. Colorado Ave.
Denver, CO 80219
Kit: At a swap meet or from an OEM vendor, get AMC 320-4934 (includes ancillary parts).
Bearing only: AMC 316-3284, Hoover 3061-R, Nice 608V, 7480 or 5210W. You can also substitute a common D7 type bearing, available from many industrial supply houses. This bearing is not sealed like the OEM unit and probably wont last as long out in the elements, but should be OK for a show car. Walt Garson (see above) offers sealed, greaseable versions of these.
Thrust Bearing Ancillary Parts
You will need a torque wrench, a good hydraulic jack, sockets and combination wrenches (1/2 through 3/4) normal hand tools and shop supplies. You might need a torch (a small butane or propane unit will do) and a big pipe wrench and/or giant Channel Lock pliers. A factory technical service manual (TSM) is strongly recommend.
Most of all, you will need a pair of spring holders: AMC (Kent-Moore) J-7842, Mac CS-21R or homebuilt.
Homebuilt Spring Holders (two required per spring)
These tools hold the compressed front coil spring in place so that it can be removed from the vehicle. They are about 2 1/2 longer than the Kent-Moore and Mac designs, so there is less tensile stress on the tools and spring support ears. This changes the removal and installation procedure slightly, but I think its safer.
Materials and Basic Construction
Place J hooks through holes in short arms, with hooks on same side as flanged studs. Attach wing nuts.
If you dont want to make your own spring-holding tool, you can buy one from Garrett Jacob, who has begun making them for Americans and also for the big cars (Classic, etc.). Not having used one, I cant make an endorsement, but the tool does look pretty stout. [More]
Spring Removal and Installation
If using AMC J-7842, Mac CS-21R or equivalent, follow AMC technical service manual instructions:
If using homebuilt spring holders modeled on the diagram above, proceed as follows:
CAUTION: Take care that the lip of the lower spring seat just overlaps the top of the trunnion. The spring seat can shift, so add weight gradually and watch carefully.
Once enough weight is on the spring that the holding tools flanged studs are clear of the ear edges, remove the hooks and tools. Slowly load the rest of the weight on the spring and make sure its still properly seated.
Trunnion Removal, Servicing and Installation
One thing to prepare for (aside from the usual risk of death or dismemberment from removing and installing the coil spring) is that the vertical bushings steel sleeve sometimes seizes to the knuckle shaft. After you work the trunnion off the spindle, the sleeve, with bits of rubber stuck to it, remains.
Ive had success heating the sleevetaking care to keep the flame away from the brake hoseand cranking it with a big pipe wrench until it breaks free. Then you can twist it back and forth with giant Channel Lock pliers while working it up the shaft. Be careful not to yank on the brake hose, and try not to scratch the knuckle shaft. The new bushing will need to ride smoothly on it.
Once the spring is compressed, secured and off the car, the factory service manual says:
That leaves out the first half of the job: Squeezing the compressed spring until the holders can be removed, then uncompressing it.
First, you will have to find a suitable press. It must have a long throw, or you could end up with the spring only partially uncompressed when the press is fully retracted.
Make sure the bottom of the spring is well secured to the press bed. The springs tend to be a bit off kilter (the result of worn bushings) when they come off, and you really, really dont want the bottom to skid off the press. Try to visualize which way it would go if it let loose, and keep yourself out of that path.
Try to determine ahead of time whether youll need new spring seat cushions and rubber bumpers. Its a shame to realize you should have bought them while youre about to compress the new spring.
Unless youre lucky enough to have a very well-equipped garage, leave time for two trips to the machine shop, one for each wheel. Or make two pairs of holding tools!