assembling track rod call for setting the length at 49.5cm, which would make a perfect rectangle with
the bolt centres of the Pitman arm and Idler Arm, see attached sketch.
my issue is that I cannot wind in the new draglink ends any further, and it is still 51cm long
the old ones are identical, and were also wound all in, this is the specific correct part for this car
(suit late MKX, 420G, Limo)
I have 2 choices;
accept as is, but I do not know whether this will affect steering geometry thru entire range?
after checking whether trackrod internal thread is long enough, carefully hacksaw off ~1cm from each end of trackbar, hopefully allowing draglinks to be screwed in equally to make total length 49.5cm
there is ~60mm of thread, so it is hard to understand why they are still to long even wound all the way in
The inconsistency in your information does confound, I see why you are perplexed. Before cutting, there are some questions and ideas which might help find your answer.
Verification that track rod is correct part. By what means is it known to be correct? How does it compare to other cars of similar build time (not in the abstract or the shop manual, but real tape measure on a car)? Did the track rod work fine previously?
How is it known this particular track rod should be at a particular length? Sometimes manufacturers change parts during production but do not modify either shop manual or parts listing at the level of detail one might encounter when doing repairs.
If the part is correct, what motivation caused the part change to occur and what benefit to the use happens? Sometimes some engineering sleuthing will help sort.
All of this is because I would be cautious about cutting the track rod without having a spare and knowing why I was changing a steering component. Good luck!
to clarify yours & my questions,.apologies for the poverty of my sketch
FSM specifies setting draglink ends to 49.5cm…this is the same distance I measured centre-to-centre of Pitman Arm, and Idler Arm, so therefore should make a perfect rectangle.
My main question relates to the steering geometry of whether the toe of each wheel will alter in respect to each other thru the arc of travel?,potentially causing various issues such as tyre scrubbing, improper handling, draglink end stress. (an effective alteration to Ackerman angle or similar effect)…if the geometry is not a perfect rectangle when the draglink is 51cm
Toe-in for the straight ahead is set via tie-rods, but they are connected to draglink ends
I do have access to 2 wrecks, and other spare parts, the draglink and ends are very specific and changed several times from 62-70, the incorrect ones are different and will not fit, my vehicle (was) very original, the (very) old and new parts are both wound fully in. I do believe the fitted parts are correct
Unfortunately wiithdrawing draglink from a MKX/420G is not easy, as regular joint sepaators will not fit
I will do NO cutting until I have a much better understanding of the issue
I did make a rudimentary effort to apply trigonometry, but alas my skills were insufficient
(the pitman and idler arm are fixed length and should travel thru a parallel arc)
following your good suggestions, I measured the draglink on a '66 MKX wreck
draglink rod length is 430mm, same as mine, ends wound all in, same as mine, total centre-to-centre length 510mm same as mine, which is a '69 420G. These 2 vehicles are meant to have the same parts
asked a specialist suspension mechanic his thoughts on my steering geometry…but he did not know!
I have figured out an easy way to check.
Using scrap dowel, I will simply make the dummy parts correct length, pin them together, and measure there movement with respect to centreline.
results to follow, (and a better diagram to explain exactly what I am talking of, if its not clear)
Hearing another car has the same part length and installed centre-to-centre length suggests your piece is correct even though the geometry results in a non-rectangular geometry. I don’t know enough about steering to explain whether this is desirable or not.
“Wound all in” may have multiple interpretations. Steering bits may have many centimeters of thread which engage the inside of the pipe deeply to several diameters interior to the pipe end. Near the pipe ends the pipe may be cut to allow a compression fitting which may act partially on non-threaded shaft region. If your setup is like this, what may look like “wound all in” actually has length adjustment still possible.
So far, one possibility is that your steering setup is correct even though it differs from part of the shop manual description.
I don’t quite understand the issue but will nevertheless, as usual, offer a couple of comments.
I have two cars with similar steering, but both have fixed (non-adjustable) track/relay rods. If yours is too long, I assume that the pitman and idler arms will be pointing slightly outboard when the wheels are straight ahead? That means that the steering gear, if typically fitted with some sort of extra resistance in the straight ahead position, would not work properly and allow the car to wander.
Another concern is that the tie rod length would necessarily be too short on each side. This means that the usual design whereby the tie rods pivot about the same arc radius as the wishbones would be off. With a bump, the car would self-steer.
Don’t know if either of these concerns are realistic for a minimal misalignment. I’m also pretty sure that there would be some scrubbing with sharp turns, but not sure exactly why. The Ackermann angles would be initially correct, but the track rod would move fore-aft a little more than design. That fore-aft movement is what is minimized with the ideal rectangular geometry. IMHO.
overly modest Robert, as you appear to understand exactly.
straight ahead toe is set and ok
If I verify with my test item (and/or by calculation) that there is measurable variation in respective wheel travel, then i will proceed to the next step, which will be to measure the INTERNAL thread depth of the draglink rod.
@Roger, the draglink external thread is wound all the way in. If there is enough internal thread, cutting 7mm of the hollow draglink at each end will allow the draglink ends to be correct centre-centre.
albeit still screwded in all the way
it doesnt make sense to me to have an adjustable item that is all the way, still not right, and does not allow adjustment.
The FSM is somewhat deficient on MKX front end imo.
example in separate thread re starter motor removal
I made a simple jig to test (pictured), and the outcome is confusing
unfortunately it is unclear on my photo, but the arc of travel is different plane for each draglink end
my test jig had nails representing the draglink end centres…2 sets of holes for 510 and 495mm
The long piece is draglink & ends
short ones Pitman arm and Idler arm (175mm),
other one is pitman arm to idler centre = 495mm
essentially, the draglink does not remain perpendicular to vehicle centreline at 510mm, as it does at 495mm, so not only are the ends ~8mm off-centre, they are each displaced fore & aft
As the draglink ends are connected to the tie-rods, in turn to steering arms, which poke out from wheels, only a computer simulation, or good mathematics could predict the final outcome at each wheel centre, but I doubt it is good.
unfortunately, I have a few other issues to address, so might just have to get toe-in set dead ahead for the time being, and get back to this issue later
altering draglink length DOES directly change toe-in at dead ahead, FSM specifically mentions not to use draglinks to set toe-in
I will get the shop to set to 0 degrees on a laser machine using tie-rods, so i can drive about,
when I get a chance to try and rectify the matter, get it done again
I would be most obliged if any 420G/ 4.2 MKX owners could measure the draglink end centres
(should be 495mm) or draglink rod length, my 2 measured items are 430mm
The geometry and dimensions of your test rig lay out triangles which have a common point 5775 mm behind the Pitman/idler center points. This is a little more than double the wheelbase of 2728 mm and may well be in the design range. Without knowing the rest of the steering layout, classic Ackerman could be lining up these triangles to overlap the rear differential, an even larger length difference than you presently pose. I am not an expert in steering geometry but don’t think many cars are set up for classic Ackerman geometry. A book with an introduction to steering geometry is Race Car Vehicle Dynamics by William F. Milliken and Douglas L, Milliken, published by Society of Automotive Engineers, 1995, ISBN 1-56091-526-9. I used this book as one reference in my racing days.
It is troubling to hear the linkage is screwed all the way in to obtain that geometry, that suggests something is not correct.
Toe-in typically for street cars should be in the range of 1/16 - 3/16 inch. One eighth is pretty typical. Many people find a car set up with zero toe-in to be a little too lively on the steering response.
The Ackermann effect is designed into all automotive steering systems. In your situation it has to do with the arc of the Pittman arm (and idler arm) and the arc the steering arm (I think that is what it is called) that is attached to the wheel. Essentially when turning a corner the outside wheel has to scribe a larger circle than the inner wheel to prevent the tires from scrubbing. So what happens is the car changes from its standard straight ahead toe in setting (whatever that spec is) to an ever increasing tow out. Those that have converted Mark II, S Types, etc to a rack and pinion system loose the Ackermann effect and tires will scrub on these cars. As I have a 3.8S with a rack I have spent many hours and measurements attempting to find a solution to this but have not had any success. Having said that, the car drives so precisely with the rack versus the old steering box, I just live with it. And as a bonus, there are no leaks.
later on, i will take up a couple of pics with my jig at “full lock” position, and it is readily
apparent to the eye how each draglink end is displaced inappropriately.
so i need to await any info from owners of these cars, wont be holding my breath though, have a wrecked '67 420G that I am yet to check, as it is not located locally, pretty sure what I’m going to find
Landrover Defenders (and others) still used an identical setup still on post 2000 vehicles,
altho i do not know what they use now.
I did find a computer simulator online, but it is for rack & pinion
These pictures help clarify what is the geometric effect when turning the car. Here are a few more thoughts.
I am under the impression that few automobiles use classic Ackerman geometry. I don’t have a good in-depth steering engineering text and can’t name one, the Milliken book is just an introduction albeit published by a correct industry publisher. Use care to understand the engineering well instead of accepting a plausible line of thought you can’t verify. At this point, I’m skeptical that a correct assembly will result in parallel motion, I suspect a trapezoid and skew is correct. Your existing geometry seems plausible to me, but “plausible” is not assuring to me.
Knowing whether your parts or your book are correct and interpreted correctly still is unclear to me. If the parts worked well and the tires wore well previously, that suggests the setup was correct in actuality.
There is a Mark X track rod assembly for sale on eBay now, see item eBay item number:311730890636 “Jaguar MKX LHD Steering Idler Assembly, Arm, Drop Arm, Centre Tie Rod& Ends”. The seller has written to me that the pin-to-pin distance of his slightly bent assembly is 18 5/8" and the track rod length is 16 5/16". This information may be of use to you.
Sorry not to have more definitive, provable advice.
thanks for your guidance throughout, problem hopefully solved in 2.5hrs
took down the assembly and lo & behold, the draglink ends, which where screwed “all the way in”
where able to be screwed in enough to meet spec.
when I installed the new ones, they were tight with threaded section flush with tube end, and used pipe wrench, but did not use enough force evidently…as now they actually can screw past flush, into the tube.
its confusing looking at the old pics i took, and measuring another example, i did not measure my old one before taking it apart, which was a mistake, but did not realise the situation until assembly
can now get it aligned, which would have been a waste of money, and my steering geometry would have been severely compromised, could have been a real mongrel to get sorted
This is a problem when dismantling. When I first started taking the S apart I laid a folding ruler beside every hose, strip of Bailey channel, and similar bits, and taking hand written notes, but that gets old pretty quickly, and my eagerness to get on with it took over.
Eventually I used a bit of back and white chequered vinyl flooring, the squares were exactly 10x10cm. That frame of reference saved my bacon a couple of times.
