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My selected tires (205/50-17) were 21.08 shipping wt. Not much packaging for tires other than wrapping. Several online sources show the Tethys style wheel to weigh in at 22 lb.
Pretty close to the estimates above.
I don't recall you addressing this issue so I will just point out that when you put in the shorter rear springs, the angle of the panhard rod changes forcing the centerline of the rear axle off of the centerline of the car. The solution is to modify the panhard rod so that you can reduce its length allowing you to return the CL of the rear axle to the CL of the car. The shorter the springs, the greater the required reduction in panhard length.
Originally Posted by jclars
Modification of the rod is relatively easy. Cut it and remove 1-2 " of the rod. Thread the internal of the rod to accept an externally threaded rod with two locknuts to allow for adjustment. I went overboard and got an aluminum rod with L and R threads on the opposite ends with matching heim joints to allow for adjustment without removal of one of the joints.
thanks, that's the info I was looking for
my steelies are 55lbs , I could drop 10lbs a wheel in un-sprung weight by going with alloy's. and just maybe, justify to myself the s60 brakes, which are significantly heavier
(big a$$ rotors+15lbs)
71' P1800E Turbo
68' 142 AKA Hanta Box
I had casually read about that mod, but recall someone stating that shortening by 40mm may not be enough to throw it too far off. Still, I want the geometry to work. Was the rod you used a replacement, or in addition to the cut original? Any pics?
Originally Posted by 142 Guy
The rod I used was a complete replacement. I purchased the material from Speedway Motors. Unfortunately, I don't have any pictures. I could give you the rod length; but, it would not be any use since my application is a 142, and even if the mount location on the axle is identical, the body mounting point is probably different.
These are the parts I used. The rods come in 1" length increments.
and a couple of these (in matching L and R threads). I can't remember whether I got the 5/8 or 3/4 hole.
I thought I had the correct heim joint for the axle mount; but, I was off by 1/32 or something silly like that. Turns out that there were no heim joint available with the correct hole size for the panhard mount on the Volvo axle (that I could find). The heim joints bushes are exceedingly hard steel, so drilling them out to fit the existing mount on the axle was a no go. I had to cut the axle mount off and weld on a new stud that matched the hole in the heim joint. That was a whole lot of hassle just to install a fancy aluminum panhard rod - I would not recommend that anybody do what I did unless they have a high self abuse quotient!
The amount you need to shorten the existing panhard rod will depend on how much you have dropped the ride height. I am a bit surprised that removing 40 mm would not be enough. Perhaps if the car was really lowered a lot and they installed really fat lock nuts, the 40 mm might have been minimal. However, I would start with removing less rather than more. If you find that the rod is still too long, it is always easier to shorten one end of the rod a bit. If you cut too much out of the rod, you can make up the gap with the threaded internal rod adjuster; however, my view is that you want to keep that exposed threaded rod section as short as possible because it will be weaker than the existing panhard rod. Modifying the panhard rod this way is a fairly low cost venture. The biggest expense will be purchasing the rather large tap required to thread the inside of the panhard rod to accept the threaded rod.
The most interesting part of this exercise is after installing the adjustable panhard rod, finding some datum points under the car that you can use to do measurements to determine that you have centered the back axle.
Last edited by 142 Guy; 03-29-2017 at 05:09 PM.
Also - take into consideration that if you radically alter your ride height, you may need to alter the length of your torque rods to keep the angle of the output flange on the transmission and input flange on the differential at the same (or within the allowable range) angle. If those angles get very far out, the driveshaft will go through angular acceleration with each rotation leading to vibration and unhappy U joints.
It looks like you have a lift, so at least you can get under the car to do the angle measurements on the flanges with some degree of ease.
I only had college level geometry. Do you have a link to a rough schematic that you might have studied enroute to your solution? I am a visual type guy...or just lazy and dont want to wrap my head around the verbals.
Check out post #8 in this thread
Its probably a good description. I can't find any convenient drawings showing the issue. The problem relates to the fact that the trailing arms and the rear axle actually follow an arc (with the center of the arc at the front pivot of the trailing arms). Since the axle is more or less solidly connected to the trailing arm, the driveshaft flange angle changes as the axle traces that arc. This angle change is unavoidable and tolerable over a small range. If you significantly shorten the springs, the back axle sits higher relative to the rest of the car compared to where it was before, so the top of the driveshaft flange is probably tipped a bit to the front of the car compared to where it was before.
There is an excellent Spicer .pdf document that talks about driveshaft phasing and the importance of the flange angles. However, if you take that document to heart, you would never fiddle with your ride height because it sets very tight tolerances for matching angles on the driveshaft flanges. I will see if I can find the link to that document.
The adjustable torque rods are used to move the driveshaft housing angle back to the same angle that existed before you put in short springs. As an observation, I don't know that you will have a problem; but, the shorter the springs the greater the potential for a problem.
Yoshifab sells fancy (expensive ) adjustable torque arms for the 140 and 240.
I have an adjustable panhard rod which is set up about 1/4" - 1/2" shorter than the stock panhard rod to get my back axle centered. I don't have altered torque rods. I haven't experienced any driveline vibration and I haven't gone looking for problems by trying to check my driveshaft flange angles; but, I also have a rather modest reduction in ride height (about 25 mm) so I have not made huge changes. You may not have a problem either, just be aware of the potential.
So then, we can express this as follows:
I guess I need to get the rear end to bottom out to see the full effect and whether I have negative pinion angle as a minimum. Maybe if I use the rear axle as a monkey bar and get some buddies over to dangle from it, I can see what I need.
Thanks 142Guy for bringing this to my attention. Interesting details that I overlooked and will endeavor to bring into line.
You have been saving those definitions of derivatives for just the right occasion?
My advice, if you don't get vibration problems, don't go looking. Just be aware if mysterious vibrations do appear, or you start chewing up U joints..
Ha! All I remember about differential calculus is that it measured the rate of change and min/max points. Thought it was appropriate. I was about as lost in some of your explanation as I was in my classes of 30 years ago! Nostalgia I guess.
However, no vibrations so far, but it does make me curious enough to get under the car and bounce it a bit to see if the angles change significantly. Interesting discussion (to me).
Since you are a visual guy, I think if you go to Wikipedia and search u joints, there is a little simulation that shows the operation of a u joint as it rotates. The interesting feature of u joints is that they are not constant velocity joints. If there is a displacement angle across the u joint, (i.e. any time the joint is not straight on) the output side of the joint accelerates and de accelerates with each rotation. The greater the angle - the more accelerating and de accelerating. This all sounds bad, except if on the output end of the shaft there is another u joint with an equal and opposite displacement angle. That second u joint creates accelerations that are of the same magnitude but opposite phase (back end de accelerating when front end is accelerating) so you get a nice steady speed on the output end of the driveshaft.
If you would like to take another 30 year after the fact crack at some equations, I seem to recall that the Wikipedia page also provided or linked the equations of motion for the u joint (bet you didn't even know that there were equations of motion for u joints). You could do some calculations of what kind of velocity errors you would create if the input and output flange angles don't match up. I love Wikipedia - with the active links you can waste a whole afternoon going some place you never intended or needed to go!
I used a plumb bob, on the fender to wheel distance, to measure potential shift in the rear end and found it to favor the LH side by 12mm. I got the car up on the lift and sure enough, you could visually see that the drive shaft was reflecting that slant. Perhaps that is what is helping to prevent the u-joints from fighting themselves, as the angle L-R makes up for the shallower angle Up-Down.
Anyway, no shimmy or vibration, but I will start to track down a new panhard with adjustable ends. After looking at the actual geometry of the rod, the math is more like the Pythagorean Theorem than differential calculus...
fun rims or looks for vovlo p 1800
Any fun ideas for rims to fit a p 1800 that provide more width? I realize spacers seem possible but do they put pressure on bearings, etc.?
I saw these rims but don't know what they are. I like the classic wheels/chrome hub caps but don't like the narrow width. I have 195/65/15s now I think
Wonder what rims are on link?
Originally Posted by sweediron970