Rack and Pinion Rebuild
Rack and Pinion Rebuild
From: Wray E. Schelin
To: xk-lovers@honcho.columbiasc.ncr.com
Subject: Resolving Robs Rack Problems
Date: Thursday, November 07, 1996 12:43AM
Windward Connection wrote:
>
Rob it has been over twenty years since I rebuilt a 140 rack but I think
I can explain how the rack works and where it fails. The rack and pinion
consists of a housing which hold two shafts perpendicular to each other
The small shaft is the pinion it converts rotary motion (steering wheel
input) into linear motion when it meshes with the large shaft, called
the rack.
The pinion shaft is supported by Torrington caged needle bearings on
either side of the pinions gear teeth. The pinion is adjustable by the
method that you quoted in the manual.This adjustment moves the pinion
gears closer in mesh to the rack gears; too tight and they will bind and
gall; too loose and they will have backlash or slop, possibly stripping.
The wear points on the pinion are; ONE- the wear on the gear teeth;
TWO- wear on the pinion shafts bearing surfaces THREE- Wear on the
needle bearings;
The rack shaft is supported in the housing by bushings at each end of
the housing.
Wear points are; FOUR- the bushings; FIVE- the rack shaft bearing
surface where it comes into contact with the bushings; SIX-the gear
teeth on the rack, which wear more in the region that comes into play
when you move the steering wheel from the ten o'clock to the two o'clock
position.
The tierod shafts are connected to the the ends of the rack shaft by
special nuts which have ball seats ground inside the outer ends of them.
These nuts thread onto the ends of the rack shaft securing them. These
nuts are locked in place so they won't turn off. I forget which method
that Jaguar uses to secure these nuts , but its usually a thin locknut
with lock tabs bent over the flats of the nuts.
The tie rod shafts have threads on one end and a ground ball on the
other end. The ball
resides inside the special nuts , the rest of the shaft passes through
the nut out to the tie rod ends which screw onto the threads . A ball
socket rides against the the other side of the ground ball. A heavy
spring which resides in the end of the rack provides constant tension.
This relationship between the tie rod shaft, the special nut and the
spring tensioner is a adjustment that should be not too tight not too
loose.
Wear points are Seven- the specialnuts inside ground surface; Eight- The
ball on the end of the tie rod shaft NINE- the ball socket.TEN- the
springs condition.
Now the bad news.
Add up all the wear on those ten points plus throw in some loose tie rod
ends, sloppy ball joints, jello rubber rack mounts,loose
wheelbearings,underinflated tires, a stiff crosswind, and a bumpy twisty
road- you have no steering from the ten o'clock to the two o'clock
position. Argghh! Don't despair everybody else's rack is worn too. Some
more than others.
Part two tomorrow night. Titled Rob Tightens His Rack But
Loosens His Wallet
Peace,
Wray E Schelin
From: Wray E. Schelin
To: xk-lovers@honcho.columbiasc.ncr.com
Subject: PT. TWO ROB'S RACK
Date: Friday, November 08, 1996 1:39AM
Rob's RACK PART TWO
Rob lets assume that you tried adjusting the pinion closer to the rack
and in the process you've, skun all your knuckles, bumped your head
twice and soiled every shirt you own. You decide to wait a couple of
days for all your wounds to heal,then you summon your courage and take
the test drive. In the driveway the steering feels good but now your
stomach begins to knot because you know the real test is on the twisty
and bumpy road. Panic!!! Its worse not only does it wander now it sticks
too!
Time for plan B
Plan B requires you face facts.
ONE- the rack is forty years old.
TWO-it probably has had lots of use.
THREE- it probably has never been lubricated other than its original
allotment.
Lets assume that you've removed the rack from the car, cleaned and
dismantled all its parts. You arrange the parts neatly on a large and
clean bench. You should have a six inch dail caliper to measure the
parts.
The housing in most cases will be allright unless it is bent ,cracked,
or severely rusted. The bushings that the rack shaft rides on will need
replacement. They can be knocked out with a long punch or steel shaft.
These bushings are pressed in originally with a one thousand
interference fit and they can be stubborn about surrendering their
positions. Do not get carried away with your hammering or you might
damage the housing. The bushings are dimpled on the inside surface.
The dimples are little pockets where the lubricant can well. I don't
think any of the replacement bushings will have this feature. You can
get bushings with spirals grooves cut into them , providing the same
function as the dimples.
The pinion shaft must be checked for pitting on its bearing surfaces and
any obvious wear. The gear teeth on the pinion shaft engage in a narrow
region , on either side of the engagement region virgin teeth remain
allowing an easy visual check of the wear. That holds true for the rack
shafts teeth too.
The rack shaft must be checked for wear on the teeth as I just
mentioned, straigtness, and wear on its surfaces which contact the
bushings. I forget what the true diameter of the rack shaft is but lets
assume that its 1.125" or one an eighth inches.
A general machinist rule is. A shaft of 1.125" dia. to have a good fit
with a bushing must have a clearance of .001". That means that the shaft
OD is 1.125" and the bushings ID will be 1.126". Anything less is too
tight anything more too loose.
Now measure your shaft OD. If its seven thousands less,for example, in
the most traveled region, junk it. I would say two thousands under would
be the limit of acceptible wear. It must also pass the teeth inspection
test and the straightness test. Sraightness can be checked by using a
machinist staight edge or a surface plate.
Next the tie-rods should be checked. The ground balls on the inboard
side egg shape and score. The tentioner sockets, spring,and the
special nuts must all be checked for scoring and galling caused by
grease starvation.
The bushings ,the Torrington caged needle bearings, the pinion shaft
seal,and also as Tom Veale mentioned,the small U-joints on the steering
shaft, are all avaiable as generic items at most industrial bearing
suppliers.
If your rack shaft,pinion shaft, and tie rod assemblies proved to be
within acceptible tolerences The rebuild should be accomplished
inexpensively, other than labor.
If you have bad luck and everthing is heavly worn. Go to plan C
Plan C is;
ONE scour the world for NOS parts(if they exist),look for new
manufactured parts, or acceptible used parts.
TWO- exchange the rack for a rebuilt unit( I would want to see a spec.
sheet and list of the parts that were replaced to make sure the work has
been done properly)
THREE purchase a good used one ( this can put you back to Plan B quickly
if the sellers definition of "good" varies from acceptible usage.
I have one more thing to add concerning how to fit the bushings, but it
will have to wait till my next posting.
Good Luck,
Wray E. Schelin
From: Wray E. Schelin
To: xk-lovers@honcho.columbiasc.ncr.com
Subject: Rob's RACK PT. 3
Date: Tuesday, November 12, 1996 1:42AM
Rob,
Don't panic you didn't miss anything. As I said at the end of part two
theres more to be said about the rack shaft bushings. By far the most
unforgiving part of the rack and pinion rebuild job( on a XK140 or
XK150) is replacing these bushings. Removing the old ones can be
difficult and as I said before don't get carried away with your hammer
and punch. If they don't move you can erode a slot in them with a die
grinder or a Dremel tool. Be carefull that you don't cut completely
through the bushings wall and into the housing. The slot allows the
circumference of the bushing to collapse easing removal. Installation of
the new bushings is the most critical part of the rebuild. If its done
right its like brand new if its done poorly....why bother. If you first
attempt isn't perfect, don't tolerate it remove them and have another go
at it. The new bushings should be pressed in, but lacking a large press
a hammer could be used with a properly sized bushing driver.I,m assuming
at this point you have a new rack shaft or a in spec. one. To acheive
that nice one thousands fit, You will need a reamer. But the problem is
not just opening up the new bushing ID the infitesimal amount to acheive
that beautiful fit. The problem is twofold because theres two bushings.
We assume that the housing is relatively staight and we checked the
straigtness of the rack shaft. But the problem now is how do we know
that the centerline of the bushings are in alignment. We don't and they
probably are off a minute amount. This is corrected by an allign
reaming. A special tool was probably avaiable for this procedure but
don't expect to find one. What can be used is a adjustible reamer of the
right size with a pilot-shaft on it. The pilot-shaft will hold the
reamer in allignment with the other bushing while your reaming to size
and alligning them in one pass. This procedure that I just descibed can
be done by most machine shops anywhere. You will know if they did the
job right by the feel. With a little oil on the rack shaft you should be
able to slide it effortlessly through the housing in its normal travel
path. If it sticks or you can wiggle the shaft where it emerges from the
bushing- NO GOOD-bring it back have them do it again.
As I said before the the bushings, bearings,and seal are attainable at
any industrial bearing supplier, they're generic off the shelf parts.
The question is the rack shaft, pinion shaft and the inner tie rods.
Does anybody know of a source with stock on the shelf? Has anybody
bought these parts recently and were you satisfied with the quality? Is
any body offering a rebuilt rack and pinion with new shafts in them?
Another question is the rack mounts . Has anybody made a polyurethene
substitute for the original metalastic ones?
Regards,
Wray E. Schelin
From: Oates, Robert[SMTP:Robert.Oates@fhwa.dot.gov]
Sent: Wednesday, May 07, 1997 10:55 AM
To: xk-lovers@honcho.columbiasc.ncr.com
Subject: steering and rack problems XK-140 -Reply
Rob - Wow! It appears as though you have opened a Pandora's box.
I just finished working with a good mechanic friend to rebuild my 150
rack and pinion. It of course is similar to your 140. This is not a task for
the uninitiated. I am fair at mechanical work but there are a lot of subtlies
to properly reworking this assembly.
I am sure you have noticed by now that everything you rework on these
cars ends up being a major undertaking in money and time. Don't get me
wrong. I have enjoyed or endured these cars since 1965. I have 5 XK
series cars: 3 drivable and 2 under restoration at various stages. I
sometimes get discouraged at my progress and say I've had enough.
Maybe I'm stupid, foolish or whatever, but I continue to throw time and
money into my collection.
So, what I'm saying is that I attack each job as a major project.
Rebuilding the rack and pinion assembly is a major project if you want to
return it to factory specifications. If you don't, then expect sloppy
handling to continue to get worse.
Let me try to help. After complete reassembly, check the condition of the
rack and pinion parts. Like anything mechancial, if much wear is visible
on the teeth or the mesh is bad, you may not have a foundation and
should start with these as new parts. They are expensive. XKs
Unlimited at $399 sometime ago. If the rack and pinion looks good, you
are in luck.
Buy a bushing kit. You will need a machine shop for this work. The old
bushings must be removed and the new ones installed and reamed to fit
the rack with the appropriate lubrication clearance.
Disassemble the inner tie rods. Check the condition of the parts. Same
applies as for the rack and pinion. If you are knowledgeable, "read" the
wear of the ball and socket. Make a judgment.
You will have to have adjusting shims and locking tabs. Assuming that
the ball and sockets are good, you will have to "set-up" the ball properly
with the correct shimming. Set them up dry. If you don't know what I'm
talking about, find a good mechanic to help you with this.
Check the condition of your outer tie-rods. If you can read "wear", make
a judgment. Use or replace. I find that if they have been properly
greased, they usually survive. As I said above, if you don't know what
I'm talking about, find a good mechanic to help you read the condition of
the outer tie-rods.
My friend adjusted the "load" on the pinion. He knew the feel and used
the proper amount of shimming to get this feel.
Buy new rack boots.
After you have assessed the condition of the parts and your machine
work is finished, you should be ready for reassembly.
There is a left- and right-handed, inner tie-rod which threads into the
rack. With the outer tie-rod removed, install a rack boot. Slide it out of
the way and screw the inner tie-rod into the rack. Tighten securely.
Make certain the tab of the tie- rod lock washer is located properly at the
tab notch. Bend, with a hammer, at least two edges of the tie-rod lock
washer to the flats of the large nut. Smear the joint with a light
application of wheel bearing grease.
Position the boot over the joint. Don't install the boot clamps yet.
Install the outer tie-rod. These should both be left-hand threads. Make
certain the threads are clean so it can be easily turned for toe-in
adjustment.
Now install the large or inner boot clamps.
Doing the above completes one side, except the small or outer boot
clamp. Clamping will be discussed below. Do the other side.
I always use new rubber (Metalisk) mounts. Also, I use new nuts, bolts,
and washers, preferably made of stainless steel.
Slide the completed assembly through the wheel opening. (I assume you
have the car on jack stands with the front wheels removed. It might be
tight you still have the radiator in place. Who said this job was easy?)
Fit the outer tie-rods in each steering arm, install the nuts, adjust the
toe-in, fasten the assembly to the mounting brackets, make sure you turn
the front wheel straight ahead, etc.
Lubricate the fitted assembly. Fit a grease gun with a needle fitting
under the small boot and fill until you can feel the boot full of grease. The
rack should be turned so the boot is extended and not contracted. Fill
just before the boot is completely full. Remember when the wheels are
turned to compress the boot the grease will also be compressed. Leave
some room in the boot for this action. Do both sides.
After lubricating both sides, fit the clamps.
Next, lubricate the pinion at the grease fitting. Use about 6 to 8 pumps of
the gun.
Good luck
Bob Oates
|
View the latest posts from our Forums via an RSS Feed!
