craig1410
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| posted on 21/4/03 at 09:40 PM |
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Rod ends - Suitable for trailing links??
Hi,
For those of you who have read my increasingly large thread about Nylaspa nylon bushes from Lolocost this is a related post to ask if you think that
Rod-Ends/Spherical bearings are suitable for use on one end of each of the 4 trailing links to avoid the problems associated with pure nylon bushes in
this application.
I would intend to use a rod end with a 1/2 inch bore and probably a 5/8 inch shank which according to the Rally Design catalogue will give me USRL
ranging from 7000lbs to 31000lbs and a respective price from £8 to £24 each. I would also use rubber boots and side spacers to allow greasing and
hopefully get decent life from them.
My question is really whether they are suitable for this application or not and what sort of load rating is really required. I'm expecting
200BHP or so from my Rover V8 ultimately and intend to use the car for fast road and track days at approximately 3000 miles per year. My "finger
in the air" estimate on loading is, assuming 1G maximum acceleration and deceleration for ease of calculation and based on a 650Kg estimated
maximum car weight comes to a lowly 360 lbs per link. This should be distributed evenly as well because my suspension is de-dion with a Sierra diff
and thus no torque reaction in the links.
So what should I use?
What USRL gives enough overhead?
Do I use PTFE lined or steel on steel
Is 1/2 bore and 5/8 shank overkill?
etc. etc.
I'll probably need to use a rod end on my panhard rod too and given that it's a single link I guess it'll need to be beefier but
again assuming 1G lateral acceleration equally spread front and back this is only 715lbs (650Kg*2.2lbs per Kg / 2 (front rear split of forces)
Am I missing something here?
Any advice would be welcomed.
Cheers,
Craig.
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Rorty
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| posted on 22/4/03 at 02:35 AM |
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craig1410, rod ends are very suitable for the trailing links, as they offer superb articulation, though I'd recommend you use them in pairs.
There are a few things to consider first before shelling out for them.
There are so many manufacturers, grades and prices of rod ends around, that you need to really do your homework on them. Sounds like the ones you
mention are the "high strength" type (thread size one size up from bore diameter), as made by the likes of Aurora, National etc.
Aim for a rod end at least 2.5 times the strength you estimate is required.
Don't use the "precision" 3 piece metal-on-metal rod ends, as they require lubrication, and even with boots on them, they'll
gather grit and chop out in no time. Go for the PTFE lined ones, as the PTFE liner acts like a wiper seal, and they don't require any
lubrication. In fact, some lubricants will ultimately damage the liner.
You also should be aware that the rod ends will transmit a fair bit of road noise and vibration through the car, though if you were considering using
Nylon bushes initally, there won't be that much difference due to the rigidity of Nylon (I still can't find anything on
"Nylaspa", though it's probably either silicone or moly impregnated, which actually reduces its tensile strength and flexural
modulus even further).
To make the job easier, fit a LH rod end to one end of the link, and a RH to the other end. It will make adjustment a doddle.
To get the links the same length initally, I made up a long aluminium plate with a pin (the same ID as the rod ends) screwed into one end, and a
second, adjustable pin that can be moved along a milled slot in the plate. There is a scale lasered into the AL alongside the slot.
I select the length I want, tighten the moveable pin at the appropriate position on the scale, and then fit the link (with the two rodends attached)
over the pins. The jam nuts can then be tightened, and all four links done this way will obviously be the exact same length.
But then you've got to ask yourself how accurate is your chassis/axle brackets to start with!
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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craig1410
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| posted on 22/4/03 at 11:14 AM |
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Rorty,
Thanks for the advice, it is indeed a complicated area for a beginner such as myself.
The rod-ends are available in all sorts of sizes and I just thought that a 1/2 inch bore sounded about right. I went for the larger shank because I
understand that it makes a lot of difference to the strength for very little increase in cost.
The range marketed by Rally Design include: Carborace and National (Clubman, Super Clubman, Light Race Car, Heavy Duty Race Car and Ultimate Duty Race
Car series). Sizes range from 3/16 to 3/4 inch in left and right hand threads. I can also buy tubes and inserts for each size with appropriate
threading already cut.
Okay, here is what I think I need. Please correct me if I'm wrong on any of this:
USRL must be 10x expected maximum load (ie 3600lbs and 7150lbs for trailing links and panhard rod resp.)
PTFE Lined
1/2 inch bore or larger
Chrome plated ball
Corrosion resistant coating
Rubber boots and side spacers
Looking at what Raldes have available, the "Clubman Series" National rod end seems suitable since it has the following spec:
Ball Material - 52100 Steel, RC56 Min, Hard Chrome Plated
Body Material - Low carbon steel, Zinc Plated,Clear Chromate Finish
PTFE Lined or Steel on Steel
Says that it is suitable for "lightly loaded" rear suspension systems.
For the 1/2 inch bore, 5/8 inch shank rod end it has USRL=8204lbs, Misalign angle=17deg, Price=£9.50ea
The above rod end should be suitable for both trailing links and panhard rod. Do you agree? Any concerns with this choice?
Sorry to ask so many questions...
Cheers,
Craig.
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Simon
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| posted on 22/4/03 at 02:02 PM |
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Craig,
If it's any use (I know we're going for different rear set ups) but when I needed rose joints for my lower rear wishbones I phoned Tiger
Racing and said I was building their chassis (not quite true, but my IRS is loosely based on thiers) and saind I needed the rosejoints for the lower
inner pivots (and inserts to be welded into wishbone).
She said ok, and quoted me (wild guess £16 each) - she said "... because they're the good ones).
1/2" bore / bolt
ATB
Simon
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craig1410
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| posted on 22/4/03 at 04:07 PM |
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Simon,
Thanks, that at least confirms that a 1/2 inch bore is at least strong enough for the job. I'd like a bit more of a quantitative specification
than "the good ones" mind you... 
Are there any markings on the rod ends which might give a clue as to who makes them and what part number they are?
Cheers,
Craig.
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Simon
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| posted on 22/4/03 at 04:15 PM |
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Craig,
I don't think they're marked. I'll have a look tonight and let you know tomorrow.
I agree that "they're the good ones" isn't terribly technical. But, for my purposes I reckon they must be ok.
Tiger would/will be in the do do if not!!
ATB
Simon
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craig1410
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| posted on 22/4/03 at 04:35 PM |
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Simon,
Yes sorry I didn't mean to suggest that they aren't suitable for your purposes when most likely they are ideal. I'm just trying to
understand the "best practice" for the usage of these joints so that I can confidently select a suitable rod end for my application.
If there are no markings on your rod ends, can you tell if they are 2 or 3 piece. If they are three piece then the ball will be surrounded by a ring
of steel which in turn will be surrounded by the body of the joint. If they are 2 piece then it is only ball and body with no middle sleeve. Also, is
it black oxide coated or clear chromate (yellowish) or nickel plated? Do they have rubber boots or are they just bare joints?
Cheers,
Craig.
ps. Rorty should be due to get out of his bed soon so I'm sure we'll here from him in due course.
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Rorty
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| posted on 23/4/03 at 02:44 AM |
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I'm awake now! I obviously don't have the same National catalogue as Raldes (unless all that nomenclature is their own), but if they
supply National bearings, then this is what's available in ferous male rodends, using PTFE lined, RH, 1/2" as an example:
MSM8T - 1/2" x 1/2" - 7,106 lbs. (2 piece)
MTSM8T - 1/2" x 1/2" - 6,660 lbs (3 piece)
TSMX8T - 1/2" x 1/2" - 16,238 lbs (CroMo 3 piece)
RM8T - 1/2" x 5/8" - 12,807 lbs (3 piece)
UMAX8T - 1/2" x 5/8" - 23,632 lbs (CroMo 3 piece)
I'll leave it up to you to do the math, but as a guide, the maximum radial load shouldn't exceed 10% of the stated URSL. With axial loads,
the maximum for 2 piece bearings shouldn't exceed 15%, and for 3 piece bearings shouldn't exceed 10% of the stated URSL.
My off-road cars see huge shock loads landing off the higher jumps at 100+ kmh, and I use the equivalent of the MSM8T. Also, they're on
wishbones, not trailing links.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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craig1410
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| posted on 1/5/03 at 11:17 PM |
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Hi again,
Just an update to let you all know that I opted for the National MSM8T rod-end which is marketed by Rally Design as the "Clubman" series.
Having spoken to one of the technical guys from Rally Design he stated that they use the "Carborace" series (proper name Alinabal
Pro-Line) for their own panhard rod design. This is actually weaker than the MSM8T with a USRL of 5800lbs. The MSM8T has a USRL of 7106lbs which I
calculate to be more than adequate for trailing links and the panhard rod.
My calculations found that the maximum tension force in each trailing link will be 412lbs and 825lbs for the panhard rod. By using the 7106 lb rod
ends that gives me a 1700% and 860% safety factor respectively. I'm happy with the trailing links at this safety factor but I want stronger
rod-ends for the panhard rod, especially since there is only one panhard rod...
I actually tried to get the MAX8T rod-ends from Rally Design which have a 16000lb+ capacity but they have been discontinued. I'll go ahead with
the build just now and replace the rod-ends with uprated ones later.
So, does anyone have any good reason why a 1700% load rating for trailing links and, when I get the uprated ones, a 2000% load rating for the panhard
rod is insufficient? I know there will be shock loadings but my calculations above represent PEAK loadings under 1G lateral, 2G braking and 1.5G
acceleration for a 750Kg car with a 50:50 weight and brake balance. I am assuming that shock loadings will be handled by the large safety margins but
I don't know how severe shock loadings are likely to be tbh.
If anyone is concerned about my logic here then please speak up. I'm trying to apply some logic to a subject which seems a bit too "black
magic" for my liking. I could pay £56 a joint for a 3/4 inch UMAX12T which can cope with 48000 lbs of force and that would do the job but would
cost me nearly £600 in the process. My chosen joints cost £7.30 each and I can see no real reason why not to use them.
Anyone disagree?
Cheers,
Craig.
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dozracing
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| posted on 2/5/03 at 12:41 PM |
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As you can see from your calculations rod ends of this size are way stronger than you requirements. The bigger they are the more expensive they are,
the heavier and more ugly. You would have no concerns if you used 5/16" bore ends.
All these rod ends where out quickly with use. On an F1 car they are replaced after every race, and they are totally shagged. Drivers claim they can
tell the difference after about 10 laps.
Imagine how long they would last on a road car doing thousands of miles over pot holes etc.. This is why rubber bushes etc are favoured because they
lst a long time and they don't transmit noise.
Darren
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craig1410
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| posted on 2/5/03 at 02:12 PM |
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Darren,
Thanks for that, it puts my mind at rest in terms of the strength aspect at least.
As for wear and tear, I'm basically going to give it a try and see how it goes. I'm only intending to do about 3000 miles per year anyway
and if I need to replace the joints each year then that's okay. F1 cars are DESIGNED to last one race only and that includes the engine as well.
If the joints were capable of lasting for several races then heads would roll in the engineering department I think for over-engineering them...
I know you can get rubber boots for the joints to allow grease to be contained and to promote longer life but someone (Rorty?) said that this just
keeps the dirt in and forms grinding paste. The hope is that the PTFE joints will tend to clean themselves as long as they are perhaps cleaned down
after use. A mate of mine used to use Rose joints on his rally car and they would last a full season (maybe 12 rallies) so I am hopeful that mine will
last a year at least if they are kept clean and dry most of the time. I'll be sure to let you guys know how they perform in due course.
Noise is something else which may cause me to revert to rubber/polyu sooner than the wear aspect but time will tell...
Thanks again for confirming my strength calc's!
Craig.
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