Should I or shouldn't I, to bush or not Options

[IronHillRestorations]

I got the rear bushing kit from Elephant Racing. First one took about 45 minutes and the second one was about 10 minutes. Was easier with a heavy duty bar clamp than my press

[Superhawk996]

How should the rear trailing arm hang?

Without shocks or the axles hooked up my trailing arms fairly quickly fall till they point close to straight down.
My front A-arms stayed relativity fixed with the old rubber bushings, but now I have McMarks full motion (bearings) bushings they also will hang straight down like the rears.

I'm debating whether to rebuild the trailing arms or not, but I'm thinking seriously about bracing the console as I have 250+hp.
If I let her rip up to 7K rpm I can feel the ass end getting a little squirrelly, mostly from the right rear.

@Mark Henry

The bottom line it can hang whereever you want. (IMG:style_emoticons/default/shades.gif)

But here's the considerations why that is true in your case.

When you migrate to a low friction trailing arm mount like Bronze Poly, Delron, Rebel Racing etc, you esentially have no torsional rate from the bushing and it will hang free as you state. There is no torsional rate contribution to the suspension kinematics so it doesn't matter where you start from.

Why would you want a torsional rate from the trailing arm bushing?

The short answer is that it does two things:

1) As the angle of the torsion arm winds up or down you're effectively adding or subtracting spring rate in addition to what the coil spring provides. Removing this torsional rate means you need a larger spring. Well that doesn't seem like such a big deal. So you add a higher rate spring.

1a. Now that you have a higher rate spring you also need more damping from the damper to keep the wheel end under control. As an example 140 lb/in spring with a OEM damper is going to be underdamped and feel too floaty or bouncy.

2) The inherent nature of rubber is that it also adds some damping. It reduces the tendency of the training arm to oscillate after you hit a bump (i.e. it adds damping). It also adds NVH isolation and reduces transfered noise into the vehicle structure.

2a. Since most of us can't afford to tune our own dampers we take what the market offers and just settle for what we get. Some might use an adjustable damper which is fine but usually that is only adjusting rebound damping and only makes modest adjustements from one position to another. Sure there are better dampers out there (Ohlin, Penske, etc.) that are very adjustable both in compression, rebound, and even at high/medium/low damping rod speeds but that isn't what we're usually talking about for 914's for street use.

OK so now what? Where should my (Mark Henry's) trailing arm hang?

Since you don't have a torsional rate contribution to consider, the short answer is it doesn't matter to you due to the bushings you've chosen.

But what if others have have rubber OEM bushings?

The short answer is that the factory manual says that it shoud basically be horizontal to the outer control arm mount.



This is the "neutral postion" unloaded (no weigtht on it) position. It's been a while since I installed a set of trailing arms but I recall having to move the trailing arm slighlty with a jack to get the rear damper bottom bolt to line up. When you place the car on the ground the bushing is under some pre-load at curb height.

When you put the trailing arm into compression the bushing is adding torsional rate to the rate provided by the coil spring. As stated earlier the bushing also provides some damping in addtion to the actual damper.

So could it be positioned in other way? Yes.

It could be positioned higher or lower to change the wheel rate curve. Since I don't know anything about the actual rate curve of the OEM trailing arm bushing I can't say how much effect this would have as a percentage of the wheel rate. I know from other vehicles, the bushing contribution can have a sizeable effect depending whether the bushing is tightened in pre-loaded or not.

Many modern cars have a suspension that is tightened down or "neutralized" at curb ride height or even a moderately loaded ride height (say full tank of gas + driver). This is done by leaving the control arm fasteners loose, drawing the body of the car downward to a given ride height by ratchet straps or other means (it's automated in the plant via fixturing) and then tightening the fasteners. When this isn't done properly by the dealerships when a repair is made, the difference is very noticeable and results in a harsh, abrupt ride quality that even average customers will complain about. If the suspension was tightened in full rebuound, the "extra" wind up of various bushings can be excessive at curb height and even worse when fully loaded and leads to premature bushing degradation since the bushing is being cycled though an angular range of motion beyond what it was designed for.

[914_teener]

How should the rear trailing arm hang?

Without shocks or the axles hooked up my trailing arms fairly quickly fall till they point close to straight down.
My front A-arms stayed relativity fixed with the old rubber bushings, but now I have McMarks full motion (bearings) bushings they also will hang straight down like the rears.

I'm debating whether to rebuild the trailing arms or not, but I'm thinking seriously about bracing the console as I have 250+hp.
If I let her rip up to 7K rpm I can feel the ass end getting a little squirrelly, mostly from the right rear.

@Mark Henry

The bottom line it can hang whereever you want. (IMG:style_emoticons/default/shades.gif)

But here's the considerations why that is true in your case.

When you migrate to a low friction trailing arm mount like Bronze Poly, Delron, Rebel Racing etc, you esentially have no torsional rate from the busing and it will hang free as you state. There is no torsional rate contribution to the suspension kinematics so it doesn't matter where you start from.

Why would you want a torsional rate from the trailing arm bushing?

The short answer is that it does two things:

1) As the angle of the torsion arm winds up or down you're effectively adding or subtracting spring rate in addition to what the coil spring provides. Removing this torsional rate means you need a larger spring. Well that doesn't seem like such a big deal. So you add a higher rate spring.

1a. Now that you have a higher rate spring you also need more damping from the damper to keep the wheel end under control.

2) The inherent nature of rubber is that it also adds some damping. It reduces the tendency of the training arm to oscillate after you hit a bump (i.e. it adds damping). It also adds NVH isolation and reduces transfered noise into the vehicle structure.

2a. Since most of us can't afford to tune our own dampers we take what the market offers and just settle for what we get. Some might use an adjustable damper which is fine but usually that is only adjusting rebound damping and only makes modest adjustements from one position to another. Sure there are better dampers out there (Ohlin, Penske, etc.) that are very adjustable both in compression, rebound, and even at high/medium/low damping rod speeds but that isn't what we're usually talking about for 914's for street use.

OK so now what? Where should my (Mark Henry's) trailing arm hang?

Since you don't have a torsional rate contribution to consider, the short answer is it doesn't matter to you due to the bushings you've chosen.

But what if others have have rubber OEM bushings?

The short answer is that the factory manual says that it shoud basically be horizontal to the outer control arm mount.



This is the "neutral postion" unloaded (no weigtht on it) position. It's been a while since I installed a set of trailing arms but I recall having to move the trailing arm slighlty with a jack to get the rear damper bottom bolt to line up. When you place the car on the ground the bushing is under some pre-load at curb height.

When you put the trailing arm into compression the bushing is adding torsional rate to the rate provided by the coil spring. As stated earlier the bushing also provides some damping in addtion to the actual damper.

So could it be positioned in other way? Yes.

It could be positioned higher or lower to change the wheel rate curve. Since I don't know anything about the actual rate curve of the OEM trailing arm bushing I can't say how much effect this would have as a percentage of the wheel rate. I know from other vehicles, the bushing contribution can have a sizeable effect depending whether the bushing is tightened in pre-loaded or not.

Many modern cars have a suspension that is tightened down or "neutralized" at curb ride height or even a moderately loaded ride height (say full tank of gas + driver). This is done by leaving the control arm fasteners loose, drawing the body of the car downward to a given ride height by ratchet straps or other means (it's automated in the plant via fixturing) and then tightening the fasteners. When this isn't done properly by the dealerships when a repair is made, the difference is very noticeable and results in a harsh, abrupt ride quality that even average customers will complain about. If the suspension was tightened in full rebuound, the "extra" wind up of various bushings can be excessive at curb height and even worse when fully loaded and leads to premature bushing degradation since the bushing is being cycled though an angular range of motion beyond what it was designed for.

This is a great thread and comments.

I did this replacement many years ago on my car and the bushing replacement is definately a compromise to the stock arm. I ended up customizing the Billy's with progressive valving and upping the spring rate slightly IIRC.

[Montreal914]

Superhawk; Thank you for this very complete detailed explanation. (IMG:style_emoticons/default/smile.gif)

So, unless I am mistaking, there is no rubber bushing option available today that is bonded to both the trailing arm and shaft that would recreate the factory setup, and there probably never will be. Which means that we are all stuck with this problem now or in the future, and will have to somehow compensate for this reduction of spring and dampening rate. (IMG:style_emoticons/default/sad.gif)

To my knowledge the current market offering for these replacement are (...and please add):

PolyBronze: Elephant Racing
Rubber: Elephant Racing
Rubber: 914Rubber
Polyeurethane / Polygraphite: Various
Exotic needle bearing and other mods: Custom

[Montreal914]

@914_teener What bushings did you end up using?

[914_teener]

Superhawk; Thank you for this very complete detailed explanation. (IMG:style_emoticons/default/smile.gif)

So, unless I am mistaking, there is no rubber bushing option available today that is bonded to both the trailing arm and shaft that would recreate the factory setup, and there probably never will be. Which means that we are all stuck with this problem now or in the future, and will have to somehow compensate for this reduction of spring and dampening rate. (IMG:style_emoticons/default/sad.gif)

To my knowledge the current market offering for these replacement are (...and please add):

PolyBronze: Elephant Racing
Rubber: Elephant Racing
Rubber: 914Rubber
Polyeurethane / Polygraphite: Various
Exotic needle bearing and other mods: Custom

Yes to all the above....for most people they'll not notice the difference. Not many people are using the stock tires and stock struts ect. anymore.

I used what was available then and the choices were more limited then. Elephant had only a hard polyurethane and PMB had sourced a hard rubber bushing and I talked with Eric several times about setups in changing these. In the end I decided on the harder rubber compound, adjusted the rear spring rate with adjustable perches and helper springs when unloading the rears would occur. I think when I went with progressive valved shocks it made huge difference and now I think you can get progressive springs which in my opinion would be another level of adjustability. Back then you'd cooiuldn't find anyone (at least at a reasonable price) to get progressive springs for a 914. I think Eibach who is here locally in So Cal is doing them.

Anyway...I did a thread on them a while back. I didn't do the progressive shock valving until afterwards. I'll say this: after I did the suspension on the car....front and back it was like night and day and for those who are restoring these cars I'd do suspension first before any engine mods or work. I'd put my money there instead.

Oh...and I talked to several people about powder coating......and mind you....this is not my experience but I do have experience in metalurgy, stress relieving and powdercoating.

The angle(s) on the rear a arm is compound. If you look at their suspension geometry and the degress of freedom you will see why. I never experienced this problem but these are weldments and old ones at that. Check the geometry of the arm and you will need a good surface plate to do this. If these are bent you will never align the rear end of your car if it is bent.

Power coating is dependent on heat to cure the powder and it is baked on with heat. If it were I.......(emphasis on vernacular) I'd paint the surface of the arms with a good quality paint after a through inspection. I'd also check the suspension console ear throughly as well. These two things are probably more important than the type of bushing used in my opinion.

Good Luck and Happy Thanksgiving everyone.

[Mark Henry]

Thanks, but my real question was is it normal for the bare arms to just hang straight down ?
I was expecting it to not fall very far due to the stock (original) rubber bushings.

FYI I'm running, 160lb progressive springs, brand new billys, 205's and a stock rear bar. I realize I'm pushing the limit of the otherwise stock suspention when I let'er rip and I think my rear bushings are OK...but then again I was wrong about the condition of my front bushings.

[iankarr]

The left control arm on my car swung down to vertical without much resistance. The right side actually needed to be helped down and never went vertical on its own.

This is a great thread with tons of excellent info. I thought I had resigned myself to replacing the pivot and bushings and doing a video on it to help the community. But destroying a good (albeit old) and irreplaceable factory setup seems like I might be doing this car a disservice. I already have the new pivot and bushings from 914rubber. How about this...if someone is willing to send me a trailing arm (or two) I’ll do the install / video and send back.

[mepstein]

The left control arm on my car swung down to vertical without much resistance. The right side actually needed to be helped down and never went vertical on its own.

This is a great thread with tons of excellent info. I thought I had resigned myself to replacing the pivot and bushings and doing a video on it to help the community. But destroying a good (albeit old) and irreplaceable factory setup seems like I might be doing this car a disservice. I already have the new pivot and bushings from 914rubber. How about this...if someone is willing to send me a trailing arm (or two) I’ll do the install / video and send back.

Ian - I have a set of trailing arms if you want to do the install video. Mark
Mark@MarkEpstein.net

Powder coating heats the metal to 400 for 20-30 minutes. Enough to melt the plastic powder. It won't warp the suspension pieces on our cars.

[Superhawk996]

Thanks, but my real question was is it normal for the bare arms to just hang straight down ?
I was expecting it to not fall very far due to the stock (original) rubber bushings.

FYI I'm running, 160lb progressive springs, brand new billys, 205's and a stock rear bar. I realize I'm pushing the limit of the otherwise stock suspention when I let'er rip and I think my rear bushings are OK...but then again I was wrong about the condition of my front bushings.

@Mark Henry

My mistake in reading your post. I thought you had changed bushings on both front and rear already not just the front.

They should not swing to vertical freely. Probably have lost clamp load between the trailing arm pivot shaft and the body/suspension console ears and it's rotating there.

With the horsepower you're running, I'd agree that console braces are probably in order. You're pushing a lot of force though suspension mounts that were never intended to handle 250HP and modern tires. I'm sure the consoles are flexing with that type of thrust. If the inner console flexes more than the outer, you end up with toe out and that will feel squirely for sure.

In your case, where you're already running high HP, that is the sort of condition where I'd persoanally lean toward the Poly Bronze type bushing solutions that have less compliance when you get hard on the throttle. You will be trading ride and NVH quiteness for handling but when you start going high HP, it has cascading implications to suspension, brakes, chassis. A vehicle is a system of systems. Changes to one system affect others.

My position laid out above is largely for street cars with sub 160 HP. Rember even at 165 HP that is a 50% increase in power vs. OEM /6 that started at 110 HP. And at levels around 200 HP, we already know the the factory 914/6 GT was struggling with handling stability on its race cars thus the chassis stiffening, trailing arm boxing, etc. Modern tire rubber and even more HP would only be worse.

[914_teener]

The left control arm on my car swung down to vertical without much resistance. The right side actually needed to be helped down and never went vertical on its own.

This is a great thread with tons of excellent info. I thought I had resigned myself to replacing the pivot and bushings and doing a video on it to help the community. But destroying a good (albeit old) and irreplaceable factory setup seems like I might be doing this car a disservice. I already have the new pivot and bushings from 914rubber. How about this...if someone is willing to send me a trailing arm (or two) I’ll do the install / video and send back.

Ian - I have a set of trailing arms if you want to do the install video. Mark
Mark@MarkEpstein.net

Powder coating heats the metal to 400 for 20-30 minutes. Enough to melt the plastic powder. It won't warp the suspension pieces on our cars.

Stress relieving happens at about 500 to 600 degrees. I'm sure the guy running the bake oven uses a templestick to check the temperature. Not. Warping is something different and happens when the steel gets to the transformation phase....so called red hot. So if were I and I was heating up the arm to take out the old bushing and pivot shaft and then heating up again to powder coat it, I'd check it after all that.

It's a lot of work to assemble the bushing, hub and new bearing and CV rehab to find out you can't align the rear end to spec.

I'm not saying it will happen, I'm saying check it, as it is a possibility and I've seen it happen with weldments.

[mepstein]

The left control arm on my car swung down to vertical without much resistance. The right side actually needed to be helped down and never went vertical on its own.

This is a great thread with tons of excellent info. I thought I had resigned myself to replacing the pivot and bushings and doing a video on it to help the community. But destroying a good (albeit old) and irreplaceable factory setup seems like I might be doing this car a disservice. I already have the new pivot and bushings from 914rubber. How about this...if someone is willing to send me a trailing arm (or two) I’ll do the install / video and send back.

Ian - I have a set of trailing arms if you want to do the install video. Mark
Mark@MarkEpstein.net

Powder coating heats the metal to 400 for 20-30 minutes. Enough to melt the plastic powder. It won't warp the suspension pieces on our cars.

Stress relieving happens at about 500 to 600 degrees. I'm sure the guy running the bake oven uses a templestick to check the temperature. Not. Warping is something different and happens when the steel gets to the transformation phase....so called red hot. So if were I and I was heating up the arm to take out the old bushing and pivot shaft and then heating up again to powder coat it, I'd check it after all that.

It's a lot of work to assemble the bushing, hub and new bearing and CV rehab to find out you can't align the rear end to spec.

I'm not saying it will happen, I'm saying check it, as it is a possibility and I've seen it happen with weldments.

Both our shop and the powder coat shop that I used to go to used an infrared thermometer to check temp on the metal part. They only cost $25 ish so even a diy guy could afford one. Since a piece like a trailing arm takes a while to heat up, I would pre heat the part, blow the powder and then bake the part for 20 minutes when it got up to ~380-400 degrees. The powder coat oven has a max temp of 420 so it's hard to damage even lightweight pieces. I have a feeling that while the surface of the trailing arms were 380-400, the piece never really gets close to that. Sort of like taking a blow torch to creme brulee.
When you heat up the arm to take out the bushing, you heat with a torch until the rubber starts to smoke. Then it's ready to come out. Still not very hot for the metal

[Mikey914]

Yes do it for a few reasons -
1- you are there and it's almost done- you will hate yourself for not doing it
2- the tube used for the pivot has the ends welded on. You really need to blast it to make sure there are no pinholes that let water in, and yes these will corrode from the inside out.
3- bearing can be pressed out fairly easily, to reinstall put it in the freezer overnight. I have heard youcan put it on dry ice for 30 min, but have yet to do it.

4- we really could use your video and I'm sure more folks will tune it (IMG:style_emoticons/default/biggrin.gif)

[914forme]

I thought jb weld was for polybronze bushings, not rubber?

Yes it is for the metal sleeve that the poly bronze bushing rides on, and Rebel Racings Bushings also benefit form this.

[iankarr]

Well...I went ahead and replaced the pivots and bushings. Pleasantly surprised at how easy it went after all I'd heard about discovering new expletives. I used the kit from 914 Rubber (which I believe is poly-graphite?) and a HF shop press. The new bushings seemed to have the same "gription" as the old, when fitting them in the arms. And the pivots seem to be held with about as much force...but of course I have no way of measuring that. Will report back once I've taken a ride.

Here's the video in case anyone wants to see the process.


https://www.youtube.com/watch?v=n37Yx7Nxil8

[ValcoOscar]

Well...I went ahead and replaced the pivots and bushings. Pleasantly surprised at how easy it went after all I'd heard about discovering new expletives. I used the kit from 914 Rubber (which I believe is poly-graphite?) and a HF shop press. The new bushings seemed to have the same "gription" as the old, when fitting them in the arms. And the pivots seem to be held with about as much force...but of course I have no way of measuring that. Will report back once I've taken a ride.

Here's the video in case anyone wants to see the process.


https://www.youtube.com/watch?v=n37Yx7Nxil8

Ian-

Gave your video (IMG:style_emoticons/default/14.gif)

Oscar

[StarBear]

Well...I went ahead and replaced the pivots and bushings. Pleasantly surprised at how easy it went after all I'd heard about discovering new expletives. I used the kit from 914 Rubber (which I believe is poly-graphite?) and a HF shop press. The new bushings seemed to have the same "gription" as the old, when fitting them in the arms. And the pivots seem to be held with about as much force...but of course I have no way of measuring that. Will report back once I've taken a ride.

Here's the video in case anyone wants to see the process.


https://www.youtube.com/watch?v=n37Yx7Nxil8

WOW! So impressive. Yet another great job, Ian.

[bbrock]

Another great video Ian. I'm pretty sure what you installed was 914Rubber's new(ish) rubber bushings. They did sell poly graphite bushings at one time (maybe still do?), but I installed a set of those without any tools at all. Just pushed them in by hand. Now I'm getting ready to replace with the rubber bushings and your video is very timely. Thank you! My only problem is that I don't have room in my overstuffed and cramped garage for a shop press. Will have to improvise.

[pete000]

I am going with the Elephant Racing rubber kit on my reinforced GT trailing arms. They will sell you just the bushes and will use the light weight stock pivot shafts. I posted the weight differences somewhere on here. The stock pivots are way lighter than the solid SS replacements. If this job is too big for you Elephant Racing offers an installation service. I agree with Bruce on the poly bushings. Fit, ride quality and noise are not so great.

[preach]

Love the vids!

My wife even watches them with me sometimes so she is learning about our little cars.