Trailing arm bushing removal Options

[mwizard1]

Making good progress on my upgrade to 5 bolt 911 parts, but... I also want to change the OEM rubber bushings on the rear trailing arms to delron. Any tips for getting the old rubber bushings out?

[brant]

Original bushings are vulcanized in

Aftermarket creates a surface that needs to rotate where as original just flexes

So any aftermarket bushing has to rotate in the housing at the ID of the torsion tube and since it wasn’t created to be a bearing surface you will have to fight and make sure the torsion tube can rotate in there


Lots of them get sticky and stop rotating
So you get stiction or a bit corner that doesn’t rotate back to baseline
Often causing one corner not to return down and weight jack the car

For that reason fit is critical

One of my cars has poly or aftermarket from a long time ago

We created grease channels inside the bushing and drilled the arm and bushing to allow the grease path with zerk installed

Cut the ID spiral grease path with a dremel


My other car has roller bearings that are not prone to stickiion because of the installed bearing race

You can never go back to stock without replacing the suspension

Removal of stock involves a press and fire

Most folks melt the stock bushing loose with a torch
But there is a ton of cleanup required to get the melted rubber out and create a clean surface

[mwizard1]

Original bushings are vulcanized in

Aftermarket creates a surface that needs to rotate where as original just flexes

So any aftermarket bushing has to rotate in the housing at the ID of the torsion tube and since it wasn’t created to be a bearing surface you will have to fight and make sure the torsion tube can rotate in there


Lots of them get sticky and stop rotating
So you get stiction or a bit corner that doesn’t rotate back to baseline
Often causing one corner not to return down and weight jack the car

For that reason fit is critical

One of my cars has poly or aftermarket from a long time ago

We created grease channels inside the bushing and drilled the arm and bushing to allow the grease path

Cut the ID spiral grease path with a dremel


My other car has roller bearings that are not prone to stickiion because of the installed bearing race

You can never go back to stock without replacing the suspension

Removal of stock involves a press and fire

Most folks melt the stock bushing loose with a torch
But there is a ton of cleanup required to get the melted rubber out and create a clean surface

Thank you for the info. Where did you find roller bearings?

[brant]

Mine are Mueller bearings from long ago

But check smart and elephant for current offerings

[brant]

Just reread that your question is for rear bushings

Same thing applies

My rears are not rollers but actually a product called mono-ball
But believe smart or elephant sell a rear kit also

Miono-ball.is a race shop product produced and installed on site so not for everyone

[technicalninja]

I'm surprised no-one has chimed in about the use of rubber over others.

First question is street or race car?

The aftermarket bushings (other than rubber) all allow rotation of the trailing arm shaft in the bushings.

Elephant has what I believe are the best ones.

https://www.elephantracing.com/porsche/914/...914/polybronze/

Elephant ALSO has rubber bushings.

https://www.elephantracing.com/porsche/914/...ng-arm-bushings

And the old school rubber bushings are more expensive than their poly-bronze stuff.

Why would the Alpha suspension company offer both AND the rubber version be more expensive?

Comfort alone is the answer.

Aftermarket (non-rubber) have limited NVH abilities. On a racetrack for short periods of time this is optimal.

Driving cross country for hours and the hard bushings will kick your ass...

The hard bushings commonly make noise. Doing as Brant has suggested is the best way to reduce this. You also get to grease them pretty regular.

The rubber versions require zero maintenance.

Properly sized rubber bushings bond to both the trailing arm and the shaft and "flex" instead of slip.
Because of this the shafts have to be "pre-loaded" before they are tightened up.
Two people and 100lbs in the rear trunk is how I'd preload a 914.

This procedure requires access with the rear wheels fully loaded. So, you're either working in a pit or the car is on what I call a storage lift that you drive onto.

Just saw Brant's last post...

Mono-ball is the ultimate "no-striction" bushings. They are more "bearing" than "bushing". These have ZERO NVH abilities.

This is what you end up with when performance is the ONLY goal.
They usually suck bigtime for street use and do not have long service lives.

A good rubber bushing is a 50-100K mile solution. Mono-ball will have 1/10 the lifespan.

Mono-ball is a "trailered race car" solution. It is the BEST solution for what it is intended for.

Do some research before you jump here.
What do you really want?

Some members who tried the aftermarket moved back to the rubber ones due to the "un-friendly" aspects of hard bushings.

[technicalninja]

Stolen from the Elephant racing web site. Pretty good explanation.

Those "heim joints" the article mentioned are "mono-ball" joints.



Polyurethane Bushing Friction
Rubber vs. Plastic Compound Bushings
Polyurethane, delrin and other plastic compound bushings are a common replacement for rubber suspension bushings. They reduce suspension deformation under load, providing more precise cornering. They also transmit road vibration and create ride harshness.

Ride harshness is often blamed on the hard-compound of polyurethane bushings. Though partly true, that is not the primary cause of harshness.

In fact, there is another process in play – friction. Friction is the primary cause of ride harshness with polyurethane bushings.
ronze bearings maintain full contact with the race and deliver even wear for small and large angular rotations. Friction is consistently low over the bearing life.



Rubber Bushings – How They Work
Rubber bushing rotation
Rubber Bushing
Rotates via Deformation

For all their faults, rubber bushings allow suspension movement with very little friction. Rubber bushings do not slide in their mounts, they accommodate movement by deforming in a twisting motion. There is no friction surface hence the friction is very, very low. Rubber bushings resist movement due to the spring rate of the rubber, not friction. Their behavior is similar to a torsion spring though the spring rate is small.



Friction And Damping
Polyurethene bushing rotation
Polyurethane Bushing Rotates on friction surface

Early automobiles actually used friction-type dampers. Their performance is horrible and use was quickly eliminated in favor of hydraulic dampers.

The key problem with friction dampers is static friction and the resulting large force to start the suspension moving. Once moving, the dampers begin absorbing energy with relatively low kinetic friction. Essentially the suspension is locked in position until a large bump creates enough force to overcome the static friction of the suspension. The result is a very harsh ride that is insensitive to small bumps.

Contrast this with a modern hydraulic damper that begins motion with very low force. The damping action increases with the speed of the damper. The suspension responds well to both small and large bumps yielding improved ride quality, superior tire-to-road contact, and road-holding.

Though friction-type dampers are an extreme case, any friction in the suspension causes similar ride harshness.

Stiction
Static friction in suspensions is often called “stiction”. The word invokes an appropriate image of a sticking, jerky, binding suspension that does not operate smoothly and only responds to large inputs (bumps).

Unfortunately, some level of stiction is present in all automotive suspensions. Ball joints, shock seals, and bushings all introduce some stiction.

Stiction is the enemy of road-holding performance and ride quality. Though it can’t be eliminated, all good handling cars take pains to minimize stiction. True race cars use metal heim joints and suspension bearings to minimize friction.

The high-stiction characteristics of polyurethane bushings have created their reputation for harshness.



Stiction And Performance
The purpose of a performance suspension is to keep the tire contact patch optimal at all times to maximize grip. For a suspension to work it must move in response to bumps, road contours and driver input. Stiction interferes with movement attempting to lock the suspension in place.

Unfortunately, stiction is greatest under high corner and braking loads – just when grip is most critical.

Stiction also makes accurate corner balancing of the vehicle nearly impossible. Stiction creates corner weights that lack repeatability.



Measuring Stiction
With the car parked on a level surface, lift one bumper corner by hand extending the suspension as high as possible. Don’t simply release, but SLOWLY let the car return to normal height under it’s own weight. Do not push down. Measure and record the bumper height.

Next press down on same corner compressing the suspension. SLOWLY allow the car to return to normal height. Measure and record the bumper height.

The difference between the two heights is a measure of the cumulative stiction.

Several factors influence the acceptable range of good values including spring rate and vehicle type. But in general a difference of 1/4 inch would indicate low stiction, a difference of 1 inch or greater would indicate high stiction.



Reducing Stiction
Identify and understand the operation of all friction points in your suspension. This includes “A” arm bushings, ball joints, steering tie rods, shock seals, shock mounts, sway bars, linkages and anything that moves with the suspension.

Ensure that all these friction components are in top shape, replace anything that is worn. Ensure that all items requiring lubrication are properly lubricated.

Replace high-friction elements like polyurethane bushings with low friction alternatives. Low friction alternatives include PolyBronze Bearings for 911, 914 and 944, monoballs for 911, 914, and 944 as appropriate.

Ensure that all bushing mounts are properly aligned. Misaligned mounts result in pinching, binding and excessive stiction.

[mwizard1]

Mine are Mueller bearings from long ago

But check smart and elephant for current offerings

Got the rubber bushings out. They were "glued" to the shaft. I drilled them and a couple other things to facilitate removal. Problem w/ the delron bushings is that they are designed to be very tight and require some mods to keep them from pinching the shaft.

[rjames]

Another option and one I’ll likely go with:
https://www.rsrproducts.com/product-page/re...ear-bushing-set

[technicalninja]

Looking back through your posts gave me "autocross".

What are your uses for the car?

Is it going to be competition only and trailered to each event?

Suspension set up is different for "combat" use.

The ID of the bushing bores in the original trailing arms might not be concentric.

Those RSR setups are cool but require JB welding into the trailing arms.

Properly centering those will be critical and there is NO going back with that style.

I bought a set of 911 front control arms with the Elephant Poly-Bronze kit already installed.

Those require JB welding a sleeve on the control arms and there is no going back with that kit either.

If I was trying to install Delron bushings in a stock trailing arm I'd WANT them undersize to allow final sizing after installation.
That might be a PIA...

Autocrossing usually creates more side loading and faster transient movements (change g-force directions more often) than any other type of competition.

Hardening suspension compliance always induces higher forces into the suspension mount points.

Autocrossing induces MUCH higher forces as well.

By the time I was going to Delron all of my suspension mount points would be significantly strengthened.

Your 914 had ALL of its suspension points spot welded a half a century ago...

What do your suspension mounts look like?

How do your "hell hole" and longs look.

What's the rust "quotient" on the car?

[mwizard1]

Mine are Mueller bearings from long ago

But check smart and elephant for current offerings

Got the rubber bushings out. They were "glued" to the shaft. I drilled them and a couple other things to facilitate removal. Problem w/ the delron bushings is that they are designed to be very tight and require some mods to keep them from pinching the shaft.

2nd shaft was able to be pressed out, easy.

[mepstein]

To remove, I heat the outside with a torch until I see a little smoke and then pull them out with pliers. Do it outside.

[mwizard1]

Looking back through your posts gave me "autocross".

What are your uses for the car?

Is it going to be competition only and trailered to each event?

Suspension set up is different for "combat" use.

The ID of the bushing bores in the original trailing arms might not be concentric.

Those RSR setups are cool but require JB welding into the trailing arms.

Properly centering those will be critical and there is NO going back with that style.

I bought a set of 911 front control arms with the Elephant Poly-Bronze kit already installed.

Those require JB welding a sleeve on the control arms and there is no going back with that kit either.

If I was trying to install Delron bushings in a stock trailing arm I'd WANT them undersize to allow final sizing after installation.
That might be a PIA...

Autocrossing usually creates more side loading and faster transient movements (change g-force directions more often) than any other type of competition.

Hardening suspension compliance always induces higher forces into the suspension mount points.

Autocrossing induces MUCH higher forces as well.

By the time I was going to Delron all of my suspension mount points would be significantly strengthened.

Your 914 had ALL of its suspension points spot welded a half a century ago...

What do your suspension mounts look like?

How do your "hell hole" and longs look.

What's the rust "quotient" on the car?

Yes, 914s are a tin can. I have added 12 reinforcing "plates" to the rear around the suspension. Also added about 2 sqft of material to repair rust .