Tips

on

Spring Service

and

Inspection

3034 N. Fleming Circle, Shelbyville IN 46176317-398-3822

.... <~~::::::--_._.

-. -- '.\ .....

,,

,I,

"~- ..

The leaf spring industry realizes thateverything that benefits the Users of vehicleshaving leaf springs, benefits in the long runthe spring industry. For that reason, wehave compiled the results of the experiencesof prominent neet operators and theopinions of spring engineers, in the beliefthat these will be helpful to those who in­spect or have to do with the preventivemaintenance and servicing of springs.

Page :'

The motoring public has learned thatproper maintenance on their vehicles is es­sential to obtain longer life and economicalservice in this age of rising equipment andfuel costs. In most normal maintenancechecks the spring is sorrly over looked. but aminimum of attention to the springs wouldyield: (a) easier riding, (b) longer and morereliable spring service, (c) better stearingalignments.

When O'Artagnan and other warriorsmade punctures in each other with sharprapiers. the swordsmen liked to test the in­tegrity of their rapiers by bending themalmost double-to make sure the rapierswould not break in actual combat.

By bending the spring farther in thebulldozer. than it would ever go in actualservice; this stresses the metal, on the ten­sion side of the leaves, a little beyond theyield point. This "pre-sets" the spring sothat it will not settle or sag in actual use,and steering alignments will be better main­tained.

It is customary practice, 0 f some leaf springmanufacturers, to test every assembled spr­ing in a "bulldozer." This bends the springfarther than it could ever be bent in actualservice-before the axle makes metal-to­metal contact with the frame. While thisdoes test the spring, and would reveal anyflaws existing in the steel, the real purpose issomething else ...

It is obviously im practical to "pre-set"coil springs in this manner, because the ad­jacent coils of a helical spring make contactwith each other-before the yield point isreached. This would seem to be the reasonwhy coil spring front suspensions frequently

Cf)I­~

ZI­....JoO?~

a......J()

o<l::a..a::w

~Ia..Cf)

I­....Jom,~

Page 0

settle or sag. during the first five or tenthousand miles of use, and then have to bereplaced in order to restore normal steeringalignments.

Semi-Elliptic Spring

Practically all leaf springs, as now usedon cars, buses and trucks are of the semi­elliptic type. Because the semi-elliptic springhas the outstanding advantages of not onlyacting as a spring, to resiliently support thevehicle. but uiso serves the important func­tions of resiliently positioning the axles undof cushioning both driving torque and brukereaction, the simple semi-elliptic type hassuperceded many other kinds of springs, in­cluding cantilever, platform, full elliptic,etc. A semi-elliptic spring gives just as easyriding as the same amount of steel, built intoa cantilever or full elliptic spring.

Q

Full Taper

Athough not new to the market the fulltaper spring is now very popular for suspen­sions systems on light to heavy truckapplication. The major advantages to thistype spring is its superior ride and overallreduction of vehicle weight. which nets greaterrevenue in load miles.

Page 7

The full taper spring although superior insome aspects is not as forgiving as itscounterpart the multi-leaf spring and shouldtherefore be checked on regularly scheduledmaintenance periods.

KEEP V-BOLT NVTS TIGHT!"Tighten-and keep-those U-bolt nuts

really tight" ... is the keynote of goodpreventive maintenance of leaf springs.

Operators of large fleets of trucks andbuses have found that center breakage ofsprings is greatly reduced by "retightening"U-bolt nuts-after the first day'srun-when a spring has been repaired orreplaced. There are a number of surfacesbetween the leaves which bed down a littleduring the first day's operation. Butretightening takes up the resulting slack andthe spring then remains tight for a longerperiod. Just as it is good practice toretighten cylinder head nuts, after theengine has been run a few hundred miles.

When installing U-bolts it is good prac­tice to use torque wrenches to determinewhen U-bolt nuts had been adequatelytightened. Since large torque wrenches arenot yet standard equipment in all shops.neet operators recommend the use of socketwrenches with sockets of length proportIOnedto bolt size, so that the mechaniC can tell bythe "feel" of the pull, or by the sound of the"creak." when the nut has been properlytightened. Fleet operators suggest forwrench handles....

% inch U-bolt nuts-handle 3 feet long.J!4 inch U-bolt nuts-handle 4 feet long.7/~ inch and I inch U-bolts. handle 6 feetlong.

Page.: X Page 9

HANDLE

sioned. Practical mechanics tell us that theyuse the "creak" of a bolt, as the nut givesproper tension. Since the U-bolts of truckand trailer springs may be 10 to 20 incheslong, then 20 times .003 inch is .060 which,with 16 threads per inch, would almostequal one full turn of the nut-after the nuthad been seated solidly.

Length of Wrench Handle Should be inProportion to Bolt Size.

But torque wrenches and long handledwrenches, like micrometer calipers, are onlyas good as the mechanic who uses them.Instances have occurred where, due to insu f­ficient length of threads or badly cutthreads, torque wrenches have merelymeasured the "pull around" of the nut onthe U-bolt, rather than the "pull together"of the spring and axle pad. Not only shouldthreads be a correct fit, but both threads andcontacting surface of nut should belubricated with a mixture of graphite and600-W oil or cup grease.

When in doubt as to whether the U-boltnuts are really clamping parts togethertightly, a sharp "rap" with a hammer willsound the answer. Just as railroad car wheelinspectors rap car wheels, before each longtri p.

Further retightening, of new or repairedsprings, is suggested at th~ end of the first1,000 miles. after 3,000 miles and at each 5,­000 miles thereafter.

"Army Ordinance," official U. S. Armypublication, stated "bolts should be tighten­ed, until they have stretched .003 inch perinch of length," and suggested thatmechanics should practice-until they getthe "feel" of a bolt that is properly ten-

Although the afore mentioned methods oftightening are excellent rules of thumb youmust consider the U-bolt material being us­ed. Basic bolt grading are Grade 2 lowest,Grage 5 and Grade 8 highest or best.

The chart below shows the Maxi mumSuggested Torque-Fine ThreadSeries-On U-bolts

MAXIMUM SUGGESTED TORQUEFINE THREAD SERIES

Dia. Size Max. Yieldand Torque Strength

Threads/Inch Grade Ft.-Lbs. P.S.!.% - 20 2 36 36,000

5 92 92,0008 129 130,000

9/'5 - 18 2 51 36,0005 131 92,0008 185 130,000

% - 18 2 71 36,0005 181 92,0008 256 130,000

34 - 16 2 124 36,0005 316 92,0008 446 130,000

~8 - 14 2 197 36,0005 502 92,0008 710 130,000

- 12 2 293 36,0005 748 92,0008 1,057 130,000

1%-12 2 422 36,0005 949 81,0008 1,522 130,000

P,lgc 10

1't4 - 12 2 584 36.0005 1,313 81.0008 2,107 130,000

1% - 12 2 782 36,0005 1,760 81,0008 2,825 130,000

1'12 - 12 2 1,022 36.0005 2,299 81.0008 3.690 130.000

• The C-l045 hot rolled steel cold bentmeets the SAE standard of Grade 2 and isgenerally used in small Ola. U-bolts withlight applications.

The SA E-1541 cold drawn, stress relievedmaterial lends itself very well to those springshops which have installed U-bolt bendingequipment capable of forming threaded rodinto the formed V-bolt in the cold state. Theultimate tensile strength, yield strength,elongation, reduction in area and hardnessmeet the specifications for the mechanicalproperties of Grade 7 and the material hasbeen accepted by several Original Equip­ment manufacturers for truck V-boltapplication. However, this material issomewhat questionable as to its impactresistance at low temperatures. To the bestof our knowledge, impact resistance is asomewhat vague criterion as to how itaffects the overall performance of thisspecific product and its intended use. Wecan find no reference to it as it relates to thevarious grades of fasteners ..

The SAE-4140 material, fully heattreated after forming, fulfills all of the re­quirements of Grade 8 specifications andhas superior impact resistance properties.For this reason we strongly suggest the useof SAE-4140, fully heat treated U-bolts fordiameters of %" and up.

Page II

We have emphasized U-bolt nut tightnessbecause, when the middle of the spring isclamped solidly against the axle pad, as in avise; then the middle of the spring cannotbend and, if it cannot bend, then it also can­not break at this point. Because the middleof the spring is the place of greatest hazard,it is necessary to clamp it securely to pre­vent breakage at this point.

It is possible for worn or improperlyfitted axle pads to be a contributing cause ofcenter spring breakage. Since many modernsprings are flat, under normal full load,pads for such springs should also be flat,and only slightly rounded at the ends. Wearof spring pads can only be caused by move­ment of the spri ng on the pads. If the V­bolts have been holding the spring so tightlyto the pad that no movement occurs, therecan be little wear.

U-BOLT SPACER PAD

I':' ,t IiJ :'T iT':'"

! , .II

I

~~I

L......- J- -----, -----.\ 'Y

I ~

Don't Omit U-Bolt Spacer.The U-bolt spacer plate is important for

two reasons: (a) It maintains the V-boltsdirectly in the line of pull and parellel witheach other. When this spacer plate isomitted, the long U-bolts may be pulled upat a slight angle and apparently tight. Butwhen the vehicle flexes the spring, the U­bolts will gradually slide over to their trueposition and may loosen enough to causemiddle spring breakage. (b) Because thespacer plates are shaped to fit the contour of

Page 12

the U-bolts, the U-bolts may be drawn upmore solidly and more securely.

The center bolt assists in assembling,shipping and handling of the spring-beforethe spring is pi aced on the vehicle. After thespring is installed, the center bolt assist inpreventing: (a) the lengthwise shifting of theleaves, (b) the fanning out of the leaves, (c)acts as an indicator to show the spring iscorrectly pi aced on ax Ie. I n all of these fu nc­tions, it is only an assistant and, when acenter bolt is bent or broken, the U -boltsshould be suspected 0 f having failed in thei rfull duty of clamping the spring to the axle.

Spring eyes should be a free­running-but not a loose fit on the shacklebolts. Except when rubber bushings are usedin the spring eyes, as in some applications,the spring shackle bolts shou Id be regularlylubricated with chassis lubricant, to preventfreezing or binding of the spring eyes on thebolt. This might cause opening up of theeye, or "straight across" breakage of themain leaf near the eye.

Typical Eyes of Springs.

~~~UP-TURNED EYE

BERLIN EYE

REINFORCED EYE

Page IJ

The military or full loose wrapperslengthwise clearance allows relativelengthwise freedom of the main and secondleaves. But if the eye of the main leaf shouldbreak, the spring is retained in place by thewrapper eye of the second leaf and the vehi­cle can still be safely driven.

MILITARY WRAPPER

EYE CASTING

PLAIN END MOUNTING

Heavy-Duty Spring Eyes.

Page I~

Add .l leaf') Adding a leaf. to increase theload-carrying caracity or a spring seems soeasy we should think twice before doing so.A properly designed spring is a balancedspring, with leaves so graded or "stepped"in length. with regard to the other leaves,that each leaf carries its fair share of theload. As a result, the strength is in propor­tion to the stress. throughout the length ofthe spring.

Realizing the importance of proper leafstepping. it may be preferable to add two oreven three leaves of thinner cross section. inorder that the proper form of the springOlav be more nearly maintained. If the spr­ing' has endured long service and has beenrepaired more than once. it may be better tohave a new spring built that is properlyengineered to carry the additional load.

When only one leaf is added. especiallyon vehicles having the Hotchkiss drive; it isusually the second leaf. The second leafassists the main leaf in resisting the ad­ditional torque and braking strains, due tothe overload. Also, the second leaf carriesmore metal, and more metal does morework. In any case, it is well to consult thespring manufacturers, before makingradical changes in the springs.

A-SECOND PLATE TOO SHORT

Page 15

c-s JSTEPPI~GCorrect stepping equalizes stress

between all plates.

SPRING alPS

When a truck wheel hits a bump, themain leaf of the spring is strongly assistedby all the shorter leaves of the spring inresisting the shock. But, after the bump hasbeen passed, the main leaf would ordinarilyhave to absorb most of the rebound-all byitself-if the main leaf was not assisted inabsorbing the rebound by the other leaves,attached to the main leaf by means ofrebound clips.

Spring clips prevent break due to fanning.

The secondary function of the reboundclips is to prevent spreading or "fanningout" of the leaves, which might result ineventual breakage. For these two reasons, itis obviously important that broken reboundclips be replaced by "properly adjusted"rebound clips.

Page 16

LEAF WIDTH

Proper Clip Clearances.

While these rebound clips should controlthe leaves, they should not bind the ends ofthe leaves against lengthwise motion oneach other. The width of the clip, should beIllh inch or more over the nominal width ofthe spring. The spacer tube, over the springclip bolt, maintains this clearance.

There should also be clearance, betweenthe spacer tube of the clip, and the main leafof the spring to: (a) allow the "twist" to bedistributed over a greater length of the mai~

leaf, when one wheel goes over a bump 01

drops in a rut, thus placing the axle at anangle. Clips near the ends of the springshould have the greater clearance. (b)Clearance prevents rubbing of spacer tubeon and consequent wear and weakening ofmain leaf, due to notched stick effect.

Clip bolts should be assembled with thehead of the bolt away from the tire, so thatif a nut should loosen and the clip bolt comepartly out, it will not cut the tire.

INSPECTIONBecause springs usually give such trouble-

Page 17

free performance, they are apt to be entirelyneglected-until trouble actually occurs.However, since springs are both workingparts and structural parts, they will wellrepay the small amount of inspection andpreventive maintenance service necessary tokeep them in safest operating condition.Such spring inspection may be divided into:(a) Checking the performance of thesprings, as shown by vehicle. (b) Checkingthe springs themselves by actual inspection.

Visual Inspection.Before a vehicle starts out, experienced

mechanics can often spot a sagged coil spr­ing by the low appearance of the frontfenders. But a more reliable method is tocheck the clearance between the chassisframe and the shop floor. Of course the tireinflation must be considered, for greater ac­curacy. Or the distance between floor andwheel rim can be checked. Any tilting or un­eveness of the vehicle body should alert theserviceman to the possibility of saggedsprings.

EQUAL ON BOTH SIDES

~O;;~:Z~Distance from Fixed Shackle Bolt toCenterbolt should be equal on both sidesof vehicle. Distances "x" and "y" shouldbe equal.

On trucks or trailers having helpersprings, it is easy to notice the distancebetween the ends of the helper springs andtheir pads, when the vehicle is empty. Thisdistance, and the percentage of full load, atwhich the ends of the helper springs contacttheir pads varies with different makes andmodels of vehicles. But on one popular

\

I

Page 18

make of trailer, the helper springs contacttheir pads at 40% of normal full load.

When the vehicle is empty, the distancebetween the rear end of the helper springand its pad may be as much as 1/4 inchgreater than the distance at the front end ofthe helper spring. That's because, as thevehicle is loaded, the chassis frame pivotsaround the front axle, so that there is moremotion towards the rear.

Now that we know the causes and curesfor possible spring troubles, let's make ourspring check in this, or some othersystematic manner, because, by followingthe same order each time, we are less apt tomiss anything.

l. Check leaves. (a) for displacement outof position, (b) for checks or cracks or ac­tual breakage of individual leaves, (c) forwear, due to rubbing of spring clips on mainleaf, (d) for sagging or bent leaves.

2. Center bolt (a) should be equidistantbetween two U-bolts, (b) should not be bent,loose or broken.

3. Check U-bolt nuts for tightness. Rapwith hammer, if necessary to check forthightness. Tighten securely, with wrenchhandle of adequate length. Check springseats for wear, if U-bolt' nuts have beenloose.

4. Check spring clips. (a) for free fitbet\leen clips and edges 0 f leaves, (b) shou Idbe I/I~ inch clearance between main leaf andclip bolts nearest ends of spring, to allow fortwist. Less clearance is needed for clip boltsnearer center of spring.

5. Check spring eyes for (a) opening up

Page 19

or cracks, (b) for free but not a sloppy lit onspring shackle bolts, (c) for lubrication.

6. Check spring shackle bolts for: (a)wear, (b) tightness.

7. Check radius rods or other relatedparts of spring suspension, if any.

8. Check shock absorbers, as defectiveshock absorbers will definitely shorten spr­ing life.

[t is important to remember that nearlyall leaf spring fractures are of theprogressive type-they start small. Thisgives the inspector a chance to locate smallchecks and cracks-before they becomelarge fractures. Since steel is stronger incompression than in tension, most fracturesstart at the ou ter edge of the tension sides ofthe leaves.

Building codes give a laminated woodbeam a much higher safety rating than abeam of solid wood. The laminations(plates) of a leaf spring also give the leafspring a higher safety rating-because it isvery seldom that more than one leaf breaksat a time. The breakage of one leaf usuallygives "warning" by (a) by the feel of theride, (b) by the position of the vehicle body.This gives ample time to replace it, beforeother leaves are damaged by the overload.

j'.\ge 20

U-BOLTS

-?TIGHT NUT

BUTLOOSE BOLT "':....~---

Nuts may be tight while bolts are loose.

However, let's not overwork this safetyfactor. but use reasonably careful driving tofinish the day's run and then replace thebroken leaf-before any other leaves aredamaged by the "concentration" of stre~s

over the edge of the broken leaf. However, Ifthe main leaf is broken (unless the secondleaf is of the "wrapper" type, or there is amilitary wrap of the spring eye) it may.bepreferable to tow the vehicle to the servicestation. With either the military wrap of thesecond leaf around the eye of the main leaf,or the wrapper type of second leaf, the vehi­cle may usually proceed under its ownpower.

On the road. A tendency to "strike bot­tom" or hit the rubber bumpers may resultfrom: (a) excessive overload, (b) saggedsprings, due to speed too great for load androad.

Springs of modern design are usuallynearly flat-"nder normal full load con­ditions. When springs are nearly flat, they

Page 21

are in a hd~er position to endure constantflexing. and they also tend to act as straightradius rods and so maintain axle positionsand steering alignments more accurately.Consequently, when such modern springshave "reverse camber," the vehicle may besuspected of: (a) overloading of vehicle, (b)sagged springs. (Springs of earlier designsoften had more "arch" or camber and somay not have reverse camber, even whenoverloaded or sagged.)

Position of shackles should be noted, tosee if the angles of these shackles on the twosides of the vehicle are the same. Moderndesign of spring shackles, places the shackleat an angle which places the main leaf incompression-rather than in tension. Thisslows down the oscillation rate, or rate ofbounce. and so gives a more comfortableride. The shackle angle, for that particularvehicle, should be used as a guide. Wrongshackle angle may indicate a spring that istoo long or too short for that vehicle. Alsosome present designs are in reverse camberunder full load and are not overstressed inthis position.

Inspecting springs for quality andworkmanship.

I. Center hole. If made with good dies, itwill be clean-cut. A poor center hole may setup additional strains in the steel, which maycause premature breakage.

2. Trim points. Must be done with goodequipment, to avoid cracking, chipping andrough edges.

J. Clips. Must be right size and shape tofit properly.

4. Eyes. Must be: (a) Tight. (b) Accurate-

:i

Iv sited. If eye is too small, bushing may be~rushed when forced in. tr eye is too large,bushing will be loose. (c) Must be paralleland st~raight, to avoid setting up excessstrains in the main leal'.

5. Fitting of leaves must be accurate, toavoid setting up excess stresses in steel andcausing premature breakage.

6. Leaves must be fitted side to side, aswell as surface to surface.

7. Proper heat treatment.

DRIVING TIPSEngineers evaluate the factors

determining the life of springs somewhatroughly in this manner.

Design. When vehicles operate underspecial conditions, special design may con­siderably reduce spring costs per mile. Vehi­cle manufacturers produce for average con­ditions. Under special conditions, redesignmay be necessary to secure improved per­formance.

Steel. Spring companies generally usesteel ofSAE specification 5160 or 51B60which are developed for leaf spring use.

Processing. The manufac ure of springsincludes the forming and the heat-treatingof the steel to temper and toughen it, and isequally as important as the steel itself.Heating and forming of heat treated steelwill greatly reduce the strength of the steelby loss of proper heat treating andrepresents a serious safety hazard.

rvlaintenance. Like such other vehicleparts as tires, engines, etc., the best madesprings may be greatly handicapped by lackof proper maintenance.

Page 23

T

~'FlfPSprings Cushion ~rake

and Torque Reactions.

Vehicle Driver. The driver is the last butvery important factor! To appreciate th.is,let's examine the action of the Hotchkissdrive, which is widely used because of its im­portant advantage in protecting other vehi­cle parts by providing resilient control ofbrake and torque applications.

In the Hotchkiss drive, the leaf springs dothree things: (a) resiliently support vehicle,to protect dnver and load from damage byroad shock, (b) resiliently control brake andtorque applications, (c) act as structu~al

members to position axle, both lengthwiseand crosswise, with regard to chassis frame.

When the brakes are suddenly applied,the entire momentum of the moving vehicletends to rotate the axle in a forward turningdirection. At high speeds, the power of thismomentum is terrific (As proven bycollisions!) and the effect of this momentumon the axle is limited only by the skidding ofthe rubber tires on the road. This causesbrake "wind-up of springs" which tends tobend springs in "S" form as shown insketch. Also, when starting a vehicle underadverse conditions of road, load or grade,the driver may race the engine and develop alot of momentum in the fly-wheel. Thistorque is greatly multiplied by the transmis­sion and this is again multiplied by the rearaxle gears. So it is better (for all parts of the

i,. ,I

Unfair to SpringsI Are Unequalized Brakes.

Busses travel over the same routes andwith the same variations in load for longperiods. and bus operators keep accu rate

I

iII,I

:1'III

'III

~

PROGFlESSIVE CONT ACT PADS

Like the inexpensive fuse which protects amore costly electric motor, the springs,which protect the more costly vehicle,should be regarded as "expendables"-to bereplaced, when the limit of their"economic" life has been reached.Batteries, tires, and springs could be design­ed to last the entire life of the vehicle. Butwell designed springs, even though they re­quire a minimum of care and occasionalreplacement, reduce vehicle costs permile-which is the final yardstick by whichsatisfactory spring service is measured.

records of costs per mile. Consequently.fleet operator's experiences are or value asto how low operating spring operating costsmay be achieved.

Page 25

Some bus operators hot stamp thenumeral "'" near the center bolt hole to in­dicate that the spring has been repaired onceby the installation of one or more leaves.After the second repair, the numeral "2" isstamped on. The next time repairs to thatspring are indicated (after the spring hasbeen repaired twice) a new spring is install­ed. Under continual flexing, all steel even­tually fatigues, although good steel lasts farlonger than poor steel. So it is necessary tofeed some new metal into a bus fleet oc­casionally, to secure reliability.

IL

u P ~." ••

I". I a·.I.C~""k' S! ...I., .---_ ,.__-"

.... ~1[1l N l .. S' ..

lb. P ..,~ .•••~.".d

1".,8·•••":0._.11...1•

.Iof

PfCC"{ .... N ....LyS' .....

T._ o'_'·".

<...

'.....". W)"J

11"

.·./XJ',

T.l '0 l~ <Cd} '0"~xrJ ..... ... ""'.1 ".~"oQ'l gJoo"/ 0 .'. lOCO

&700°/

.. ';.rdJ

l'XJo, :

1'~· ''XI"!

vehicle) nlll to race the engine and then letthe clutch in with a "Bang~"

Suppose the driver has b.een driving to?fast and doesn't see 3. bump m the road unt~;he is almost on to of It-what should he do.

Of course he should have had the vehicleunder better control. But in this predica­ment, he should apply the brake beforereaching the bump, and then .release bra~ein sufficient time to allow sprIngs to regamnormal position as the wheels (uncheckedby brakes) roll freely over the bump.

Otherwise it is possible for the brakereaction to have forced the spring into sucha position that one-half of the spring wascarrying the full weight of the vehlcl~, S?, theeffect of the bump would be "twice asgreat as when the wheels were allowed torun freely over it.

Page 26

PROGRESSIVE SPRING

Progressive Springs tend to equalizeriding comfort under both light and

heavy loads.

.;;.

~

Springs of the progressive type not onlygive almost equal riding comfort for thelightly loaded and fully loaded vehicle, butthey also have the additional advantage thatthere is less variation in spring deflectionfrom light load to full load. Consequentlythe chassis frame remains more nearly leveland better steering alignments and greatersafety are obtained.

~URE ALONG CURVEOF~

in ----- - ~

--- ~!Spring length is measured along curve

of main leaf.

Length of springs is measured along themain leaf, from center to center of the twoeyes. That's the same distance as center-to­center distance, between the two eyes, whenthe main leaf is nat under normal full load.