Sky Render's Build Thread

sheizasosay

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J&M is trying to sell stuff. You cited an advertisement. Not that the information is bad, but it's still an ad.

No doubt and I get it. Your statement has a world of weight behind it in general. So I emailed Brian from J&M with a link and basic details and asked for him to address the questions. Lots of good questions and points and ones that I'm curious about myself. It will be next week when he gets back. He said to remind him. I will.

Whiskey makes a good point about the LCA being clamped by the ears and also the basic question of "how does this translate to wheel rate".

SoundGuyDave mirrors 99% of my thoughts. Almost all ....except the street extreme joint doesn't increase NVH in the LCA as much. And I've had heims (Chillin in a box).

The real question is how do you measure resistance of a bushing through travel?

The arc of the LCA should be consistent enough on all our cars to say that 1" of travel = "x" degrees of articulation.

So you should be able to measure from the top of the bumpstop to the chassis and define that number in inches of travel. At that point, you can assume wheel rate is going up regardless of bushing type once it's hitting a stop.

After that, it is the question of articulation in degrees and then what does that do to wheel rate.
 

Sky Render

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*Sticks head in, looks around*

Uh, hi, guys. Looks like you've all been having fun while I was gone. What'd I miss? :crazy:

ANYWAY. Tonight I got bored and finally installed that freaking diff cover. The entire point was to keep the stock TrackLock a little cooler. The TrackLock is a clutch-type differential, which means it uses friction to lock up the wheels when one starts to spin. Friction creates heat. And heat can eventually cause the diff fluid to break down and/or make said clutches melt.

Melty clutches are bad, mmkay?

The diff housing is thick metal. So it isn't exactly a good heat sink. And the stock diff cover is steel, which doesn't conduct heat very well. To that end, the GT500s are equipped with an aluminum diff cover that has a heat sink built into it. Aluminum conducts heat better than steel, and the heat sink increases the effective surface area of the diff cover, which aids in transferring the heat out to the ambient air.

Here's the Ford cover, which has been drilled and tapped for fill and drain plugs. Order the kit from Latemodel Restoration, and they'll include ARP fasteners. Because everyone loves ARP fasteners.

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Here you can see how much surface area the heat sinks add. The fins on the "flat" part of the differential stick up as far as the part that contains the ring gear:

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The fins also extend into the fluid reservoir, increasing the surface area in contact with the oil that is being cooled. Also note the "trench" around the perimeter of the cover for applying your black RTV!

16274253_large.jpg


I'm not going to bore you with pictures of the install, because nothing has changed in swapping 8.8" diff covers in the last 35 years. Here is its fully installed:

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I think it's a very nice-looking piece as well. It's starting to really heat up around here, so I'm glad I got it installed before my next autox. :thumb:
 

neema

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do you have any plans for a diff breather to mount to the top of the diff cover? Are you running both breathers right now or have you plugged one?
 

Sky Render

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do you have any plans for a diff breather to mount to the top of the diff cover? Are you running both breathers right now or have you plugged one?

I'm running both breathers right now; the one on the driver's side axle tube and the one on the top of the diff cover. I'm thinking of plugging the axle tube one, as it has a tendency to bang on my crappy Magnaflow over-axle pipe on bumps.

Thoughts?
 

Norm Peterson

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I'm kind of glad this thread got moved, else I'd probably never have found it. Lots of good information.

Why did you choose a non-articulating LCA for a handling-oriented setup?

What are you two talking about? Plenty of people run Whiteline LCAs for handling. And I don't want rod ends because I drive this car on the street daily.
I think if you look closely at the Whiteline bushings that you'll see some small differences between them and the "run of the mill" stuff that just about everybody else uses.

A plain poly cylinder with flat-faced flanges on both ends is about as unwilling of a shape to make articulate via compliance as you're likely to find. And it's about the easiest shape to make, so that's what most bushing suppliers do. Probably works better for the drag racers and the drag-race wanna-be's that way anyway.



The Boss 302R uses poly bushings too
I'd look at them for the same or similar detail differences. Haven't seen these myself.



Having used those types of joints, all of them added a LOT of NVH compared even to poly. But, they are free moving joints with no more friction than the sticky grease adds.

In my experience they are perfect for a competition car, but miserable to live with in a dual purpose or street car.
Odd - the Johnny-jointed LCAs I've had on my car for a while have been dead quiet and no more harsh than what you'd expect from firming up the bushings. However, they are J-jointed on only one end and poly-bushed on the other, and I did go to some effort to improve the poly ends' articulation and eliminate one of the causes of squeaks there.

Lube, or the lack of it, does make enough difference in friction/stiction to feel as additional ride harshness. Let it go too long past that point and even a 4.6L car may start chirping a tire exiting very tight corners where it wouldn't otherwise.


Vince - what offset are those 18 x 10 wheels?


Norm
 

Sky Render

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I'm kind of glad this thread got moved, else I'd probably never have found it. Lots of good information.

Vince - what offset are those 18 x 10 wheels?

Norm

Thanks!

The wheels are 18x10 AMRs from American Muscle:

http://www.americanmuscle.com/charcoal-amr-18x10-0512.html

According to their website, the offset is +48mm. They fit just fine up front, though at absolutely-full lock they rub on the struts a tiny bit. Not a big deal except in tight parking maneuvers. I recommend them if you can't afford nice forged wheels, but they are slightly heavy at 26.7 lbs each. (My street wheels, TSW Nurburgrings, are only 18.6 lbs each.)

A buddy of mine says they look a lot like Forgestars but are cast. So we've taken to calling them "Castars."
 
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Norm Peterson

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Not only that, but, why were those angles chosen?
I doubt it was for any reason other than to determine points on a curve to show a trend.

The only test fixture that makes sense is something similar to setting the UCA in a vice and running a long bolt through the bushing's inner sleeve and pulling on it in a way that skews the inner sleeve with respect to 90° from the UCA axis. If you measure the force and angle, and know what the moment arm is, you can arrive at a moment value at whatever angle.

If you're looking at the effect that bushing stiffness has on lateral load transfer, it's not the bushing stiffness in lbs/in that you care about. It's the moment stiffness. At the very least, that represents an additional contribution to roll stiffness at every control arm. This can be resolved into lbs/in at the rear wheels, and in bad cases can add as much LLT as a softish rear sta-bar.


More than just roll is involved - once the car starts trying to roll, the chassis end of the UCA starts moving laterally with respect to the axle end (think plan view skew here). You end up with a vector sum of roll + plan view skew being the total angularity that the bushing is being forced to accommodate. That's a simplified picture, as it isn't necessary to fully consider the compliance effects with the geometry here.

I would expect some of the MM LCA bushing tests on the Fox/SN95 arrangement to be generally indicative of what to expect here, though the numbers themselves won't be the same. Obviously any cases where they tested with the uppers bound up would not be useful. One caveat is that the MM test isn't modeling pure roll (it's roll + bump/rebound).


Norm
 
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Norm Peterson

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...and in the case of a LCA both the front and rear bushings would absorb the twist. It may not be an even split front the rear but it would be divided up.
This is exactly why a spherical of some sort in one end has such good potential. The spherical absorbs virtually all of the twist and half of what I'll call "lateral bending" where the control arm plan view orientation varies with roll.


Theoretically for articulation purposes, you want sphericals in both ends of all control arms. Anything a else represents over-constraint (too many forces + moments locating the axle . . . aka "bind").

As soon as you go to cylindricals, you're introducing end moments on the links (control arms) that as "over-constraint" ultimately become harshness and roll stiffness.

OE bushings get around those downsides by being soft (and kind of let the matters of wheel hop and accuracy of axle location fall wherever they may - though undoubtedly these effects are known numerically by the OE engineering team).


Norm
 
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Norm Peterson

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The wheels are 18x10 AMRs from American Muscle:

According to their website, the offset is +48mm.
Thanks. I ran those numbers against what I'm running, and the inboard edges of those 18x10's with 285/40's are about half an inch further inboard than mine. I'm not sure that on my car I have that much clearance with the wheels steered straight, so your light rubbing out toward full lock does not surprise me at all.


Norm
 

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neema

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I'm running both breathers right now; the one on the driver's side axle tube and the one on the top of the diff cover. I'm thinking of plugging the axle tube one, as it has a tendency to bang on my crappy Magnaflow over-axle pipe on bumps.

Thoughts?

I use the same diff cover as you and I've been too lazy to plug the axle tube breather, so I'm still running breathers at both points. I finally pulled one out to see if I can buy a plug and some fittings to eventually make a catch can. I feel like if the axle tube is plugged, the top breather won't have a problem assuming the role of resident-spewer. Hopefully I can use the top breather for a catch can (more exhaust clearance)
 
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Rehagen Racing

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I use the same diff cover as you and I've been too lazy to plug the axle tube breather, so I'm still running breathers at both points. I finally pulled one out to see if I can buy a plug and some fittings to eventually make a catch can. I feel like if the axle tube is plugged, the top breather won't have a problem assuming the role of resident-spewer. Hopefully I can use the top breather for a catch can (more exhaust clearance)

We cap the the axle tube and run only from the top breather on our cars.
 

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There are two types of axle tubes. Some are AN -04 and you can cap those with a AN cap. Others are NPT thread and you can just screw in a plug.

We use aeroquip fittings, but a brass plug will do the trick.
 

Sky Render

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There are two types of axle tubes. Some are AN -04 and you can cap those with a AN cap. Others are NPT thread and you can just screw in a plug.

We use aeroquip fittings, but a brass plug will do the trick.

Gotcha. Next time I'm under there, I'll unscrew the axle breather, take it to the hardware store, and get a plug for it. :thumb:
 

neema

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Gotcha. Next time I'm under there, I'll unscrew the axle breather, take it to the hardware store, and get a plug for it. :thumb:

Mine took an AN -04 plug like rehagen said.

ImageUploadedByTapatalk1374489063.119124.jpg

While you're getting the plug, get a 90 degree fitting for the top breather and some pcv tubing and make yourself a diff catch can (use a Gatorade bottle if you need a temporary can). Spewing gear oil problem solved.
 

Sky Render

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Several people have asked me how those 18x10 AMRs fit up front. I just bolted on my "race" wheels/tires for an autox tomorrow and snapped a few pictures.

You can see they poke out a teeny bit up front, although running -2* camber up front (or more) makes it less noticeable.



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Sky Render

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When you get a chance, can you take a couple of pictures from directly ahead and directly behind?

Thanks in advance, no big hurry.


Norm

Yeah, I'll take them tomorrow if I can.

Note that my rear axle is centered with the "street" wheels on. The "race" tires are a slightly different diameter, so the axle isn't quite centered with them on.

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