Trailing arm install...missing parts?

[john baldwin]

Hi all,
Reinstalling trailing arms after replacing bearings and ran into a snag.
Bentley pg 420-4 shows the arm attached to the body with an M14 bolt, washer and nut. There was no washer when I disassembled.
This diagram also shows two "plates" on either side of the bushings....are these integral to the bushings or separate pieces? If separate, they weren't there either on disassembly.
So, on reattaching the arm to the body with only the nut, after torquing it all down the arm wouldn't pivot up or down....it would slide axially on the bolt suggesting I'm missing something?
Appreciate any feedback here.....
Thanks,
John

[Tigerrat]

My 88 also had no washer. Just the locking nut.
I bought new bushings from host and yes there are plates/discs on the outside of the bushings. When reassembling it was a snug fit going back into the mounting point on the body. Ken

[john baldwin]

Thanks, Ken.
Did your bushings look like this?




It looks as if there is a plate attached to the rubber...or is that just the bushing itself?
Sounds like what you ordered actually had a separate part, that is the plate was a separate piece from the bushing. Is that correct?
Thanks,
John

[Walt Fricke]

You are talking about the inner mount for the aluminum banana arm, right?

The factory design has everything pretty much locked in place, and the rubber deforms to allow the arm to move up and down. Same as with all the other rubber bushings in the suspension, pretty much. And since the motion of the banana is more than just a rotation, the rubber deforms as the axis changes orientation with motion. It is this change which makes hard polyurethane bushings in this location a bad deal, as while they allow the regular up and down motion to happen, acting like a bushing with parts sliding on other parts, they don't deflect to allow the axis change.

Track rats replace these bushings with spherical bearings, which are almost frictionless and allow all needed motions. But at some expense of ride noise and such.

But I gather you had the banana off just to change the wheel bearing, and are reinstalling with all the old stuff in place?

Looking at the Bentley, and a couple of earlier parts diagrams, it looks like there has always been one washer for the through bolt, although whether on the nut end or the bolt end has varied. Porsche also changed the side the bolt is inserted from after realizing it didn't make sense that you should have to remove the transmission just to get the banana off, and got it right some years before your '89. Nut end makes most sense for a washer. But I can't see that part as being essential. And easy enough to get a washer and use it - hardly a critical precision part.

The end caps (plate in the Bentley) seem like they are needed in order to keep the banana end from sliding crosswise, which is what you say is happening. In the catalog for a 2.7, and the one for a 2.4, these plates (called a washer) are not given a part number separate from the rubber bushing part, so replacements could be purchased as a unit. Maybe they fell off somewhere along the line? Did you have a shop replace the axle bearing?

I don't think that upping the torque and distorting the carrier metal which is welded to the torsion tube is the answer. I can't remember if these plates are reused when installing spherical bearings here or not. If not, there should be a supply of them out there in DE/racer's garage junk boxes. Like mine. And maybe a suitably large washer would be a reasonable substitute?

[edit - I see these washers are not still stuck on the ends of the rubber]

[Tigerrat]

Yeah that looks like my old ones. Say 1/8" thick metal disc on top of rubber. It is integral to the bushing. So the axial play you have must just be due to wear. Like Walt says, they move some in all 3 dimensions so that must compress the rubber over time.

[john baldwin]

Thanks, guys...appreciate your responses.

Tigerrat....I'm thinking these plates ARE integral to the bushing...it's mighty tight sliding the arm into the body mount.....

Walt, yes I am referring to the inner mount for the banana arm and yes I was planning to re-install with the old bushing as the many threads I've read on this seem to conclude that that bushing doesn't get the wear everyone expects...plus its a PITA to remove/ install. So I'd rather avoid replacing it!

As for the axial movement, it might be around 0.030"...not a lot and certainly a lot less than what a couple of plates would add. I replaced the bearings, and I kept everything in bags and labelled as it came off the car.

As for movement about the axis, I was under the impression that these arms should be free to swing with minimal friction about the axis of the bolt when the arm is detached from the spring plate. When the arm IS attached to the springplate, I agree the rubber should deform to follow the arc defined by that combination. The rubber deformation you mention should come into play only then...I'm wondering why when I torque the bolt to spec the arm doesn't pivot about the bolt, but tries to deform the rubber in what should be a simple arc.

I guess I forgot what this felt like when disassembling?
Appreciate any continued thoughts.
Best,
John

[Walt Fricke]

I don't think the arm is designed to swing freely around the bolt. That is an ordinary bolt, and the steel insert in the rubber is not the kind of bushing one would use for this purpose. Think of the spring plate rubber bushings - those are not designed for movement other than deformation of the rubber. Same in front with the stock stuff.

I think the plates are designed to hold the rubber in place against the chassis/torsion tube mount. The rubber with its steel jacket is tightly bound to the banana - so tightly that it is a real PITA to remove, and at least when I have done this gets destroyed.

I suggest you get these plates from somewhere or someone. There should be zero sideways play here, at least without the kinds of stress placed on the rubber that cornering and so on does, when it gives a little. You don't want play in suspension joints.

[john baldwin]

Thanks all for your input. Wanted to conclude here to help anyone with this same question in the future.
Confirming with Chuck at ER, the TA when installed is not meant to swing freely about the bolt; the bushing IS meant to deform as the TA moves through the arc within it's range of motion.
The rubber in the bushing is not bonded to the metal...if the range of motion of the rubber is exceeded, it will not rip, but will rotate or slip axially to a new relaxed position.
The "plates" shown in Bentley are not separate items but are actually swaged to the rubber bushings....there are no additional washers or plates between the bushings and the mounting points on the body.
The installation procedure is to attach everything - Springplate, TA and Shock finger tight...then torque down the TA bushing with the Shock in the full droop position.
Hope this helps.
John