Rennline high density suspension bushings

[LJ851]

There is plenty of experience related to aftermarket stock replacement suspension bushings but i can't find any actual experience relating to the Rennline high density suspension bushings. Is anyone currently using them ?


I've been on the fence about going to a sliding bushing setup like polybronze or Rebel's product vs. rubber bushes. I have decided to not do poly bushes. It appears with a combination rennline and elephant rubber parts i could have a fully "sport" rubber setup.


I'm confident in the elephant products, would like to hear about the Rennline pieces. I think they are pretty new to the market.


Bushings-Rennline, Inc.

[chris_seven]

Material selection for suspension bushes is a subject I find quite interesting.

For many years bushes were made from either a Natural Rubber or an NBR. These materials have properties that make them a good choice.

They have reasonable to good tensile and tear strength, a good resistance to compression set, they are oil resistant and have good adhesion to steel.

NR and NBR is also available in a wide range of hardness and have very good damping properties.

Operating temperature is typically a maximum of 100 degC.

The Shore Hardness of rubber is an indirect measure of the material's Static Stiffness or modulus.

This value is always much lower then the Dynamic Modulus of stiffness when subjected to vibration which is not so strongly related to basic hardness.

The damping factor of a specific rubber is not strongly related to its hardness so NBR bushes with relatively high levels of hardness still damp relatively well.

There is some variation is density with NBR materials but specific gravities would normally be in the range of 1.0 to 1.2.

Over the years significant developments have been made in the field of Rubber and Polymer engineering and the improvements we have seen in NVH have been remarkable.

New materials and a much better understanding of road induced vibrations has revolutionised ride and handling but I am not sure simply substituting one material for another is always a great idea.

It is fair to say that using harder NBR bushes will generally improve and reduce changes in alignment with a minor impact on NHV but these bushes may deteriorate in a different way and have a shorter life than the original part and extensive and very costly testing would be needed to determine the real effects.

Having said that I would always opt for a 'Sport' Hardness bush.

The question of High Density Rubber is even more interesting and as a basic statement has no value whatsoever.

Without knowing what rubber has been used and how the density has been increased it is impossible to evaluate the impact on performance.

Viton A for example has a specific gravity of 1.85 and is very dense in rubber terms. It has good hardness, strength, oil resistance and temperature capacity.

Its damping behaviour is lousy and in absolute terms it would make a poor bush if NHV were important.

I would be very keen to know more about these HD bushes as I am not a fan of PU and prefer NBR type materials.

[gtc]

I bet these are just the Elephant bushings.
There's a lot of marketing mumbo jumbo in there... "machined out of a tougher rubber compound"? I think not...

[Ferrino]

I also wondered if these were just rebranded Elephant products.

[gregwils]

Originally Posted by Ferrino

I also wondered if these were just rebranded Elephant products.

I don't know the answer, but there is a difference in their descriptions. Also, Rennline is $5 less, so it seems unlikely that they would undersell Elephant's price.

Rennline: "Replacing your factory bushings with our 25% stiffer units"

Elephant Racing: "A true OEM spec bushing replacement for spring plates"

I need to replace mine, might give the Rennline's a try, even though I have Elephant Rubber everywhere else. I wish Elephant would offer a sport formulation like they do for the trailing arm bushings.

[JJ 911SC]

Originally Posted by gregwils

Rennline: "Replacing your factory bushings with our 25% stiffer units"

Elephant Racing: "A true OEM spec bushing replacement for spring plates"

...

Correct, short of having an independent lab test the rubber bushing of the OEM, E.R. and Rennline (using BS ISO 48 or other Standards) you have to take their word for it.

When I replace my engine & transmission mounts, I ordered the Sport version. Would I know the difference by looking at them or from the road feel, I doubt it.

I did get the Rennline version because of the 25% stiffier claim.

[Traveller]

Originally Posted by gregwils

Rennline: "Replacing your factory bushings with our 25% stiffer units"

If you are referring to the Spring Plate bushings for example, the part number RL lists them as is the same part number that the manufacturer who makes these for Porsche lists them as. And they are 85 shores.

[gtc]

Ok, i guess i was imagining harder spring plate bushings from elephant. I see now that they have harder strut and trailing arm bushings.

[JJ 911SC]

Originally Posted by Traveller

If you are referring to the Spring Plate bushings for example, the part number RL lists them as is the same part number that the manufacturer who makes these for Porsche lists them as. And they are 85 shores.

So the OEM and E.R. would be at 68 shores.

I'll bring the RL one at the office tomorrow and check it agains the samples we got.

[JJ 911SC]

While this would not pass any receiving inspection for the submarine spare parts that we supply, using some samples from our supplier, tacitly you can feel the difference between a 50, 60, 70 and an 80 duro.

The RL feel stiffer then our 80 samples, and of course, we don't have a 90 sample...

As mentioned below they have the same part number of the OEM supplier so they are not E.R or E.R rebranded. Prekom - Porsche parts, Ferrari parts

If someone has an E.R. bushing on hands, you should see the Prekom logo (or a variation) on them:

What did we do before Google

[chris_seven]

I bought a Durometer about a year ago when we started to look at making a few bushes and it has been very useful.

I would be interested to know how difficult it is to fit an 85 ShoreA Spring Plate Bush.

The standard bush Porsche supply is a bit of a fight and 85A could need significantly more force.

I have also been looking at the High Density Rubbers and HNBR has similar Damping and Resilience to NBR.

It has a greater tensile strength and higher temperature capacity at 150degC but they are inferior in terms of taking a 'compression set'.

I have been discussing this with a local AV Mount supplier and they are not sure if the changes would be significant.

I am sure the increased static stiffness is generally a good thing.

[JJ 911SC]

Originally Posted by chris_seven

... I would be interested to know how difficult it is to fit an 85 ShoreA Spring Plate Bush...

I'll let you know in a few months (waiting for the Winter to come by )

[LJ851]

Great info, thanks guys.

Does anyone have these bushings in a car yet?

[safe]

In my 69 I have installed bushings of slightly harder rubber, not sure by how much.
Haven't driven the car yet, but I am sceptical.
When I put my 200 lbs on the springplate, it barely moves and when you put some more force into it, it slides.

I think a rubber bushing needs to be relatively soft or it won't work at all.

[LJ851]

bump

[JJ 911SC]

RL Black Friday sale is on now...

[gyrotuner]

Originally Posted by JJ 911SC

RL Black Friday sale is on now...

Did you end up putting them in the car yet? Impressions? Debating between these and elephant as well.

[JJ 911SC]

Originally Posted by gyrotuner

Did you end up putting them in the car yet? Impressions? Debating between these and elephant as well.

Unfortunately it won't be this winter project as I'm still working converting the garage... http://forums.pelicanparts.com/porsche-911-technical-forum/728449-what-did-you-do-your-911-today-5.html#post8830893

[LJ851]

Has anyone had a chance to try these out yet?

[Dubbin']

Rennline makes solid products, not to worry. I would not undermine them when comparing with Elephant racing.

I just installed these bushings when replacing my shocks with Bilstein Sports. They feel good.

Poly-Graphite Front Upper Strut Mount Kit PELRSRSSUSM - PEL-RSRSSUSM | Pelican Parts

Thanks,
Mark