Revised 12/13/01
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
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Introduction
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:
- It is needlessly complex.
- There is no means of replenishing bushing grease without disassembly.
- The thrust bearings are exposed to the elements.
- Servicing requires removing the coil spring, a hazardous operation that requires special tools.
- The parts are now expensive and hard to find, compared to ball joints for a vehicle of similar vintage.
- Few mechanics are familiar with the system.
- Installing new springs is especially tricky, and most spring shops can’t or won’t do it.
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.
- The road wheel, drum (or rotor), wheel bearings, spindle, brake hardware and back plate ultimately all hang on the steering knuckle.
- The bottom of the knuckle attaches to the lower ball joint.
- The thrust bearing sits on a flange on the upper part of the knuckle.
- The bottom of the trunnion rides on the thrust bearing.
- The knuckle pin, or shaft, passes through the bearing and trunnion. The shaft is threaded at the top, and a washer, lock washer and nut holds the assembly together.
- A conical extension, integral with the trunnion, holds the bottom of the coil spring.
- On the side of the trunnion is a horizontal bore, through which a bolt connects the outboard ends of the upper control arms.
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.
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Safety Considerations
The coil spring must be removed in order to access the trunnion. This requires great care and proper tools. Please don’t 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 don’t want to be around when they do it!
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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, it’s 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 doesn’t include those parts with the bearing, you might be able to scrounge them up yourself.
Trunnion
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).
Walter Garson
3900 W. Colorado Ave.
Denver, CO 80219
(303) 934-4788
biggarsod@aol.com
3900 W. Colorado Ave.
Denver, CO 80219
(303) 934-4788
biggarsod@aol.com
Thrust Bearing
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 won’t 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
- Nylon washer: 11/16” ID x 1” OD x 1/16” thick. I haven’t found this size, but if you can get one of the correct thickness but larger OD and smaller ID, it can be drilled and cut (or ground) to size.
- Upper O ring: 3/4” ID x 15/16” OD x 3/32” thick. Standard plumbing size.
- Lower O ring: 11/16” ID x 1” OD x 1/8” thick. Standard plumbing size.
- Steel washer, lock washer and nut
- Plastic dust plug
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Tools
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 it’s safer.
Materials and Basic Construction
- (2) 1/4” x 1 1/8” x 11” steel, drilled at each end, about 9 3/4” center to center, and another hole, slightly offset from the middle.
- (2) 1/4” x 1 1/8” x 3” steel, drilled at each end, about 2 1/4” center to center, and in the middle.
- (4) Flanged studs. Make them yourself or have a shop do it. It’s a lathe-and-die (or weld) job.
The studs are 9/16” OD at the flanges, about 7/16” OD in the milled center. The upper flange is 1/8” thick, the milled part 3/16” and the lower flange 1/16” thick. Threaded end is 7/16”. [Alternatives] - (4) Threaded 5/16” J hooks, about 2 1/2” long, and wing nuts.
Place J hooks through holes in short arms, with hooks on same side as flanged studs. Attach wing nuts.
If you don’t 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 can’t make an endorsement, but the tool does look pretty stout. [More]
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Procedures
Spring Removal and Installation
If using AMC J-7842, Mac CS-21R or equivalent, follow AMC technical service manual instructions:
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The spring is removed by raising the rear end of the car opposite the side from which the front spring is to be removed. Additional compression may be gained by leaning on the fender over the spring. Install hooks in the holes on the ears of the spring seats. The hooks will hold the spring in a compressed position to allow removal from the car. CAUTION: The lip of the lower spring seat MUST engage the seat support to prevent the spring from shifting during operation. The hooks are released from the spring seat by raising the opposite rear end of the car to compress the spring. |
If using homebuilt spring holders modeled on the diagram above, proceed as follows:
- Park on firm, level ground and chock rear wheels securely.
- Place jack under crossmember, near lower control arm pivot but not so close that the jack could slip off the edge.
- Insert flanged studs of spring holding tools inside the upper spring seat “ears.”
- Slowly raise jack until lower flanged studs line up with lower spring seat ears and place them so flanges are hooked into the ears. One side might line up slightly before the other.
- Continue raising just enough to be sure the tools are well seated and secure. Do not raise any further.
- Place J hooks over spring, pivoting cross arms as needed. Tighten wing nuts evenly until the spring is well secured. The idea is for the spring to remain still when the weight is released, not pull over toward one hook.
- Raise jack until spring, seats and holding tools can be removed as a unit, bottom first, toward you. Put spring in a safe place.
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 it’s still properly seated.
Trunnion Removal, Servicing and Installation
- Remove road wheel.
- Support lower control arm and/or restrain bottom of steering knuckle to prevent damage to brake hose when trunnion is disconnected from upper control arm.
- Remove plastic dust plug (carefully if you need to reuse it), nut, lock washer and flat washer from top of trunnion.
- Loosen upper control arm spacer bolt.
- Remove upper control arm to trunnion bolt.
- Tilt trunnion away from upper control arm, being careful not to damage brake hose, and lift trunnion off knuckle shaft.
- Remove old bushings and clean bore surfaces with a brake cylinder hone or rotary wire brush to remove particles of rubber and rust. Take care not to grind off plating.
- Install new bushings. Use special grease if indicated.
- Clean and grease trunnion spindle surfaces and install new bearing kit. The thrust bearing can be packed with ordinary bearing grease as needed. Install small O ring on knuckle first, then the bearing (open side down), then the small O ring, then the nylon washer.
- Replace trunnion, flat washer and lock washer, put thread lock on top nut and torque to 50 ft/lbs.
- Clean dust plug and area where it will fit, and install with silicone glue.
- Put trunnion back between lower control arm ends and replace pivot bolt, washer, lock washer and nut. Torque pivot and spacer bolt nuts to 85 ft/lbs.
Notes
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 bushing’s 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.
I’ve had success heating the sleeve—taking care to keep the flame away from the brake hose—and 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.
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Spring Replacement
Once the spring is compressed, secured and off the car, the factory service manual says:
| Compress the spring by suitable means, arbor press or hydraulic jack and install hooks on spring seats. The spring can then be installed on the front coil spring support. |
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 don’t 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 you’ll need new spring seat cushions and rubber bumpers. It’s a shame to realize you should have bought them while you’re about to compress the new spring.
Unless you’re 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!
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