Shock Absorber Comparison Test

[Sparweb]

I'm slowly sorting out what's wrong with the new suspension on my own car, which was replaced recently, with detrimental effect.
The shop is insisting that they have used the specified parts, and I insist that my Acura handles like a Buick now.

I've convinced the shop to keep the old suspension parts (removed at >300,000 km still working fine but leaking oil), and replace the (probably defective) replacements with another set. Now in the back of my mind is the idea of testing and measuring the load-stroke curve of the original parts and comparing with the supposedly-equivalent replacement parts. If these were aircraft Oleos, I would know what to do. Aircraft shock absorbers have an air chamber that resists displacements, and returns the shock to its original position. A force-displacement test is not hard to set up: a 5-ton press with a pressure gauge on the ram would give the force, a ruler would give the stroke. However, I don't believe this would be fruitful with an automobile shock. I doubt that I could do a "force-velocity" test as simply as a force-displacement test. Maybe I can... Is there a simple, practical test that I could do in my garage that would demonstrate that shock 1 is/is not equivalent to shock 2?

Are there aftermarket suspension makers that publish data for their shocks (I know Monroe doesn't)?

Is there any other way to deal with this, other than buy-it-try-it-too-bad?

STF

 

[Sparweb]

Interesting data Greg. Especially that change in slope at +1m/sec.

I realize now that my previous comparison of the TSX to the BMW 325 was inappropriate. Roughly the same size, engine, and market segment, but they don't have similar suspensions. The Beemer has MacPherson, the TSX has a Double wishbone suspension. This is my fourth Honda with this suspension:

Norm's plots comparing stock struts to the alternatives are the kind of plot that I was looking for. Getting that data for a specific car model and any specific strut turns out to be a lot to ask. Thanks for looking!

Before starting this change, I though that auto shocks came in just 2 varieties: replacement parts with spec's equivalent to OEM parts, and performance parts for racing or autocross. Wrong on both counts.

STF

 

[SwinnyGG]

Before starting this change, I though that auto shocks came in just 2 varieties: replacement parts with spec's equivalent to OEM parts, and performance parts for racing or autocross. Wrong on both counts.

There's definitely a wide range beyond that.

Based on what you've said in this thread, I suspect that you'd be happy with the KYB setup.

This is anecdotal, but my personal opinion is another vote in favor of Koni Yellows.

Koni Yellows are on my current car, and were installed well before it was necessary, and they took a car that handled pretty well ('13 VW Golf R) and only made it better.

Pretty much every car I've owned over the last 10 or so years has had Koni shocks fitted when either the suspension needed to be replaced, or I decided I was unhappy with the way it was working.

The nice thing about them is that while you don't get the super fine levels of adjustment you would from something like a fully adjustable Ohlins damper (which is a level of adjustment unnecessary for a street car, in my opinion) , you get a relatively wide range of adjustment so that the character of the car can be tailored to what you like, with steps that are discrete enough to be meaningful.

If you're willing to spend the money,

 

[Sparweb]

Well,
I thought a bad one was likely, but what do you know: two defective Monroe shocks!
One offered no damping at all; sitting on the bench, you could draw the piston to any position with no effort.
Another had negligible resistance.

The shop didn't charge me anything for the KYB's (maybe not much price diff).

If you see a silver Acura being flung madly around the streets and highways around Calgary for the next few days, it's me. Testing. Thoroughly.


STF

 

[GregLocock]

two? That does surprise me. What a waste of their time and money, and yours.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Tmoose]

What part number monroe ?
If they are not gas shox then they have to be cycled a bunch of times full stroke while in operating position to purge air.
If they are real gas shox they ought to try to extend fully, requiring serious effort to move from fully extended.

The online catalog suggest the only parts offered for front or rear are "Low Gas Charged Units" which might take a few minutes to extend on their own.

http://www.monroe.com/downloads/servicegrams/monroe-ride-control-servicegram-vol1-no1-english.pdf

 

[cibachrome]

Joined the party late here, but a few details:

You mentioned leaking shock, both left and right or just one? If both, then perhaps the car likes the reduced chamber oil volume and blows off early. If only one, then it should be possible to compare not only the old vs. new, but old left vs. old right. Correct? If the new shocks are very 'stiff', then the car/tires are not happy because they over constrain the suspension motion.

Get and old trailer and weld brackets on the frame and axle. Offset the hitch so that the test tire and shock don't run in the path of the tow vehicle. Yes I know the trailer tires could be /are different than the Acuras, if that bothers you, bolt a TSX wheel on the trailer. (You are testing the trailer, not the tow vehicle). Ballast the trailer for the TSX axle load(s) you are investigating,

Then run the trailer over a board. Pick several thicknesses and widths. Run the trailer with the test shock and wheel over the board(s) as a sequence and video the events. When you compare the impact dynamics, you are looking for similarity OR NOT. That means amplitude and cyclic response at specific road speeds.

Sounds to me like you are investigating equality of parts, not what the actual force velocity characteristics are. If the results are identical, you have an answer. If not, then you know which parts are more or less 'stiff'.

A few more 'cute' ways to investigate shocks, but you would need access to signals from your smart phone to get vehicle yaw velocity and speed. Run the car in a circle, run over a board, measure the abrupt change in yaw velocity during board encounters. Plot vs. lateral acceleration for constant speed runs (Steady state Ay is yaw velocity times speed). There are some apps around to do this for you, but you need some computational abilities (Matlab or Excel) to do the job right.

 

[Sparweb]

Just for fun:

https://youtu.be/hbthI35rfi4

Pictured in the vid is the rear shock, Monroe "OESpectrum" p/n 72324. Also removed are the similar p/n 72322. Both rear shocks have packed it in. The fronts had some leakage though they were still acting normally.

If you look carefully, you can see the KYB boxes in the background.

Tonight's drive home on KYB's was excellent. Handling on pavement returned to normal. Interestingly, control actually improved on the gravel roads.


STF