Struts, bump-stops, suspension, oh-my...

[Mike]

This was submitted to the mailing list by our resident pro, Carl Beck.

see http://www.zhome.com/ZCMnL/tech/MacPhersonStrut.htm

Aircraft type landing gear - aka "struts" - were redesigned and

applied to automotive use by an Engineer working for Ford of England

in the early 50's - Mr. Earl F. MacPherson.

In that sense of the term - an Automotive "MacPherson Strut" or

"strut" is actually comprised of a shock absorber with a coil spring

mounted above it. The "strut" is attached to the auto structure at

the top of the coil spring and the wheel hub is attached at the

bottom - the bottom of the assembly is located by a lateral link and

anti-roll bar (al la TR-7) - or by a lower Transverse Link and

Tension Compression Rod (al la Z).

On our Z's the MacPherson "strut" is comprised of: (without regard to

how the Japanese translated it in their Part Manuals;-)

1. Strut Tube: - the "shock absorber tube" with a spring perch or

seat welded on the outside of the tube near the top.. the spring sits

on this perch/seat. The front axle is located at the bottom. The

combined Strut Tube and Shock Absorber are referred to as the "Strut

Assembly".

2. Shock Absorber: -the "shock absorber" built into the inside the

strut tube (normally replace by a cartridge insert). The shock

absorber "piston rod" moves in and out of the tube/cartridge and is

damped in it's movements via oil flowing through very small valves

attached to the lower part or bottom of the piston rod.

3. Coil Spring: - the "coil spring" mounted near the top the strut

tube, sitting on the spring perch - the perch is welded to the

outside of the strut tube.

4. Spring Seat: - that holds a slightly compressed spring, at the

top end of the shock absorber piston rod. The top end of the shock

absorber piston rod is threaded - so a nut/washer holds the spring

seat in place there. The "bump stops" sit on the top of the shock

absorber tube - held in place because they surround the shock

absorber piston rod. Under full compression of the coil spring -

they stop the spring seat - from bumping the top of the shock

absorber tube.

5. Mounting Insulator: - the mounting insulator is bolted to the car

with three bolts at the top.

6. Strut Bearing: - The mounting insulator rides on the "strut

bearing" thus allowing the Strut Assembly to turn right/left.

If you shorten the springs, shorten the travel or length of the shock

absorber piston rod (as happens with all to many cartridge type

replacements), overload the car - - you increase the possibility that

the suspension will "bottom out" - - - - - meaning it hits and

compresses the bump stops. For this reason you almost always want to

replace the bump stops when you change shocks.. cheap insurance....

A farther modification of the design of the Automotive Strut was done

by Colin Chapman of Lotus to adapt it to the rear suspension.... Mr.

Chapman located the strut via the use to two links at the bottom to

restrict lateral and longitudinal movement.

Thus our Z's use MacPherson Struts on the front suspension and

Chapman Struts on the rear.

So What Does Nissan Call The Parts in the Front Strut?

1. Strut Assembly = Assy. Strut Front Suspension (assy includes the

tube, the axle & shock)

2. Shock Absorber = Assy. Shock Absorber

3. Coil Spring = Spring Front

4. Spring Seat= , Assy. Bumper Bound

5. Mounting Insulator: = Assy. Insulator Strut Mounting

6. Strut Bearing = Bearing - Strut Mounting

So .. you can't find "Bump Stops" - in the Parts Manual because they

are part of the "Assy. Bumper Bound - but you can buy them in the

after-market.

BTW - Later year Z's used a dust cover over the shock absorber piston

- to help keep dust/dirt off the piston and out of the seals that

surround it... thus lengthing the life of the shocks... not a bad

addition to the older Z's while your at it...

More than you wanted to know....

FWIW,

Carl

Carl Beck

Clearwater, FL USA

IZCC #260