Spherical rod ends (heims) for suspension use

Suspension, including wheel, tire and brake.
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S15DET
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Re: Spherical rod ends (heims) for suspension use

Post by S15DET »

Check this out! I looked into the design of the RX-7 toe link and was surprised to find that the large end contains a spherical bearing, housed within a thin layer of rubber. This gives total freedom of movement, and a degree of NVH isolation! This might be a great solution for a front T/C rod.

My only concern is the compliance. In hard braking this will be in tension, and the rubber flex will very slightly reduce castor. I might measure the deflection of my poly bushings and compare it to the deflection in this bearing/bushing to see which is greater. Any thoughts?

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S15DET
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Re: Spherical rod ends (heims) for suspension use

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As far as my Goolging has found, this RX-7 "pillow bushing" (right side above) is unique in the universe. I haven't found another shperical bearing built with a thin rubber over-mould. It appears that it didn't carry over to the RX-8. Does anyone know of another pillow bushing on any other cars because it may prove hard to find replacements for this older model (93-95 in the US)? On late-model Nissans, the T/C rod bushing is solid rubber, and the aftermarket "upgrades" are all spherical, none are a combination. I did find that Mazdaspeed offered a replacement version with 40% stiffer rubber, part number F128-28-42Y.

I'm considering this an ideal replacement for the LCA bushing and the T/C rod bushing. I'll keep searching for newer alternatives before I start making metal chips.
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510wizard
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Re: Spherical rod ends (heims) for suspension use

Post by 510wizard »

S15DET wrote:Check this out! I looked into the design of the RX-7 toe link and was surprised to find that the large end contains a spherical bearing, housed within a thin layer of rubber. This gives total freedom of movement, and a degree of NVH isolation! This might be a great solution for a front T/C rod.

My only concern is the compliance. In hard braking this will be in tension, and the rubber flex will very slightly reduce castor. I might measure the deflection of my poly bushings and compare it to the deflection in this bearing/bushing to see which is greater. Any thoughts?

Image
I wonder if it might be possible to use that "spherical bearing, housed within a thin layer of rubber" for the inner control arm bushing? It would allow for increase in caster without binding and limit NVH. Center hole might not be of the correct size.
HudsonMC
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Re: Spherical rod ends (heims) for suspension use

Post by HudsonMC »

Could you make a TC rod with an off the shelf spherical bearing and make yourself a "pillow" out of some material that is a little more workable than rubber? It would sleeve the OD of the spherical bearing. Maybe poly or delrin? Won't provide the same level of NVH reduction as rubber, of course, but would be something you could do yourself...assuming you have access to a lathe and a welder.
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okayfine
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Re: Spherical rod ends (heims) for suspension use

Post by okayfine »

What would the differences be between either what Hudson proposes, or what Brad wants to do, compared to this:

Image

Uses the stock T/C rod, so no shortening/increasing castor unless you either thread it or turn the washer stop (and the shaft is hardened, so...). Also uses a stock rubber bushing on the wheel side, with the UHMW pillow/alloy cup on the bumper side. This is mainly used as an alternative to poly T/C bushings with all the control but none of the NVH and T/C-rod-breakage potential.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson
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S15DET
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Re: Spherical rod ends (heims) for suspension use

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An important aspect of this E.E. kit is that the pivot point remains in the same point as stock. I did a test of this point once; I removed both sides of the T/C bushing, leaving just the rod sticking through the hole, then I moved the suspension through the full range of motion. Because I'm using a poly LCA bushing, the LCA was located positively and couldn't twist. I was impressed that the T/C rod remained centered in the mounting hole throughout the whole range of travel. I also realized that any method of locating this rod that alters this point, was going to put a twist in the LCA. A lot of guys use a heim joint bolted into a clevis that stands off of this hole, and others use essentially a ball-and-socket tie rod end, both move the pivot point rearward of the stock pivot point, which isn't ideal, and slightly alters geometry. I like the E.E. kit, because in tension (braking), there will be no deflection, no loss of caster under braking.

If I pursue the pillow bushing above, I'll have to re-build the stock body attachment feature. I may consider raising or lowering the point to alter anti-dive properties as discussed in this important thread...

http://www.the510realm.com/viewtopic.ph ... t=lca+bolt

...but I need to consider all of the ramifications first, I have much to learn.

Hudson, the rubber is quite thin, and is bonded permanetly to teh metal during vulcanization. I doubt this could be recreated. Machining a delrin/nylon sleeve is doable, but this is a high quality off-the-shelf OEM part, which is a big plus to me.
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Re: Spherical rod ends (heims) for suspension use

Post by okayfine »

For historical purposes, here's how BRE did it:
Front Suspension - Side View - No Rotor.jpg
Front Suspension - Side View - No Rotor.jpg (130.8 KiB) Viewed 2937 times
Link to embiggened:
https://docs.google.com/file/d/0ByCvxnH ... E9TZw/edit

From the BRE Technical Description document:

Modifying the tension rod mounting box

The lower trailing arms, or tension rods, as they are called in the service manual, that locate the lower transverse link in braking and acceleration are mounted in sheet metal box forms at the from end of the unit construction just under the radiator. Tension rod mounting boxes take a tremendous amount of stress and strain in competition, especially if the standard rubber doughnuts are removed and replaced with a BRE type competition tension rod, which is nothing more than a metal-to-metal ball joint, which does not allow for any rubber compliance or distortion. It is definitely recommended that BRE type ball joint metal-to-metal compression rods be used in this area, as the stock rubber mounted ones tend to distort under heavy braking creating deflections in the desired steering path. As the normal stock rods are mounted in rubber and they do absorb some shock load it is necessary that the bracket be boxed in for maximum strength use with the metal-to-metal BRE competition tension rod. While these modifications are being carried about, the stock hole can be filled in and moved upward if the whole BRE Trans-Am competition suspension is planned it will not be necessary to relocate the mounting hole for the tension rod, (see photo).

(There are other photos of the T/C box area, but none appear to modify the box other than to seam-weld it)
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson
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