Better Bump Stops for all 2003-2008 FX35/FX45 Coilovers

Chedman13

Chedman13

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Location
Illinois
Car
2014 Mercedes-Benz GL63 4Matic
I'll help out Turbocad with this thread by posting some information he already did and hopefully await for him to add his full DIY on the coilover install of KIDO Racing on his most recent customer.

1) All coilover kits do not come with "high-end" polyurethane bump stops.

2) To have good ride quality while adjusting the height low, you will need aftermarket bump stops to not "jackhammer" down the road and hit your bump stops all the time.

Here is what you need to know:

Front Bump Stops
Brand Energy Suspension
Manufacturer's Part Number 7-6104R
Part Type Bump Stops
Product Line Energy Suspension Bump Stops
Summit Racing Part Number ENS-7-6104R
UPC 703639394945

Bushing Color Red
Bushing Material Polyurethane
Shape Conical
Height (in) 1.750 in.
Length (in) 1.750 in.
Width (in) 2.000 in.
Bump Stop Attachment 3/4 in. strut shaft
http://www.summitracing.com/parts/ENS-7-6104R/

Rear Bump Stops (for now)
Part Nr: 770052
Free Length(In): 2.56
MaxEffLoad (Lbs): 2293
Inside Dia (In): .709
Outside Dia (In): 1.890
Weight (Lbs): .093
Height@50%Load (In): 1.970

In mm: 65mm length, 18mm ID, 48mm OD.

Made From a Micro-Cellular Polyurethane Elastomer
Progressive Compression and Damping Characteristics

http://m.eibach.com/products/770052.shtml
http://eibach.com/cgi-bin/htmlos.cgi/003123.2.145913986887797588

Other details
Rear shock shaft ~12mm, front ~21mm

Since we have the dimensions of the rear bump stop, John, what do you suggest we get from Energy Suspension as a similar replacement, but longer?

As you mentioned, since the KIDO and other coilovers for the FX are fully adjustable, a longer bump stop would be more ideal, since technically you can "ride" the bump stop a little to avoid full on slams on bumps and being polyurethane, you most likely won't wear it out like "regular" rubber.

This should also help from bottoming out and rubbing on extreme fitments and lowering.

I really have no idea what bump stop to get, maybe this information can help you point us in the right direction? Sounds like Eibach would be a directly bolt-on, but I like the idea of a taller bump stop?
http://energysuspension.com/universal-products/bump-stops-shock-strut.html

Just so people know, the Eibach bump stop should be available soon at TireRack and Summit Racing. I had to call and get the part number added to their systems, it takes as long as it takes for Eibach to respond to them authorized dealers so they can get it added to their database. It's currently not there.

http://www.summitracing.com/search/?keyword=eibach bump stops&dds=1
 
sorry man been so busy haven't had much time to put together any instructions yet. the bump stops you'll want for the rear are these: http://www.summitracing.com/parts/ENS-16-9101R/

the rear shock is a 12mm shaft and these will give a HUGE improvement over the stock little rubber bushings included with the coilovers but they will only do what there supposed to do if the shock is adjusted properly.

the idea of bump stops are just like they sound, you want a cushioned end of travel for your suspension. think of these bump stops as almost springs for the end of the spring travel... without them it will hit the end of travel very hard, with these it is much more progressive... think of the difference as hitting the frame with a sledge hammer VS hitting it with a rubber mallot... properly installed and adjusted bump stops can also pretty much eliminate any tire rubbing at the end of travel because the idea is to set it up that it hits the bump stop before the tire hits the body.

now as far as adjusting the shocks/struts, I really need to put together some diagrams and a good visual explanation. seems there is a lot of confusion s to spring pre load and most don't really know what to do with this adjustment. what it really amounts to is that the shock/strut itself is actually adjustable for it's total length. you have a minimum shock length and a maximum shock length and what's in between is the shock stroke. the very simple explanation of adjustment is to simply remove the spring and raise the wheel in question until it hits/bottoms out to the body.... now adjust the length of the shock so that it touches the bump stop like 3/4" before the tire touches the body... now at full compression these bump stops will compress almost 3/4", meaning that with the largest hit the tire will just about make it to almost touching, but can never really slam into the body because the bump stop is preventing it. once the proper bump stop height is adjusted into the shock/strut you will no longer be changing this adjustment when you adjust the suspension height up or down in the future because this stop position remains the same, only time this would be changed is if you change wheel/tire combo or something. you are simply adjusting the shock/strut to be long enough that at full compression the shock is bottoming(on the bump stop) before the car is bottoming

one really good way to picture what is going on is to picture a door stop. if you swing the door open the door knob will hit the wall causing damage, so instead you use a door stop, a cushioned stop that impacts the door before the knob can hit the wall... this is very similar but you are adjusting the shock long enough that it pinches the bump stop before the tire actually bottoms out. I'll put some diagrams and better explanation as soon as I can.
 
Just blew my mind, will have to re-read it a few times.

thanks for the link, a few of us in chicago are ordering, seems like back-ordered.
 
bump stop = door stop :smile (2): Slam (jack up) the body = slam the door. Got it! :wink (2):
 
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John, please let me know if my interpretation of your explanation is far out : smile (2):

I would take the spring off the strut. Insert the bigger bump stop onto the strut shaft without the bellow for better view of the gap. Mount up the strut without the spring. Mount the tire back on. Crank the bottom ring all the way up high to get it out of the way for now.

Ok, here is where I got lost; "adjust the length of the shock so that it touches the bump stop like 3/4" before the tire touches the body". You mean the gap from the top spring cup to the strut body is equal to the height of the bump stop plus another 3/4"?
 
Cruiser said:
I have a dumb question guys, can this be applied to the BC coilover set up?
Click to expand...

Definitely, same concept. Just need to check what the shaft size of the shock is so the bump stop fits properly.

---------- Post added at 07:14 PM ---------- Previous post was at 12:27 PM ----------

John -- just thinking of this now. Why did we go to a taller bump stop? Wouldn't that make it more susceptible to hitting the bump stop and also more chance of "riding" the bump stop?

This would all create a harsher ride quality.
 
guys I'm really sorry been so tied up with work and projects and 100 other things I never had a chance to clarify much here.

think of the bump stop as a progressive spring, that is what it is really. how it works is, lets say your spring rate is 400, what this means is that it takes 400lb's of force to compress that spring 1". lets say you had 400lb springs all around to illustrate this concept. when you lower he vehicle to the ground each spring will have ~1,000lbs of weight on it asuming equal weight distribution and each spring will compress ~2.5" with the vehicle weight in this situation...

now evey additional 400lbs of downforce will compress each spring an additional 1", so lets say you have an extra 2" of travel at a lowered ride height, this means that an aditional 800 lbs of force at one wheel and it bottoms, goes from a 400lb spring rate to a spring rate of infinity as it can not compress anymore at the end of travel... this is the harsh bump you feel, the spring bottoming and going from 400lb spring rate to a dead stop/hit... what the bump stop does is it increases the rate towards the end of travel, so the first inch of travel is ~400lb spring rate, then the bump stop starts to contact... from that point on the bump stop will take more and more pressure to compress it, 1.2" will be ~450lb spring rate, 1.4" will be ~500 effective rate, 1.6" will be ~600lb effective spring rate, at the full 2" travel the spring rate has increased to maybe 900lb rate or more before it to eventually runs out of travel, but here you can see that it will take much more pressure to fully bottom and this is what takes that harsh edge off, so much so that you can barely even percieve it actually bottoming in most cases... if the bushing was NOT compressable then yes, it would make the ride harsher because it would be limiting stroke even more, but the fact that it does compress and add a linear ramp up towards the end of travel and it actually does the opposite and smooths out an otherwise harsh ride.

I'll try to put up an illustraition soon to show how to adjust these properly, basically you want the bump stop to just start to contact with ~3/4"-1" or so of travel left so it can do it's job on the last remaining inch of travel, the last inch is where it all happens and makes so much of a difference
 
ok, I finally got around to getting the new bump stops for the rear and there is a problem.

because the springs on these coil overs are so stiff they do not compress much under vehicle weight, what this means is that the springs are pretty short, combined with a lowered ride height this causes a problem. the new bump stop is 2" where the original is not even 3/4", what this means is that I have to legthen the shock a bit to compensate but here is where the problem comes in... when I lengthen the shock enough that the bump stop is adjusted correctly then the shock is too long because it will cause a situation that the spring is too short and when you raise the car up fully the spring will be s loose that it can fall out of it's seat.

I tried using them and keping the shock just short enough that the spring is still in place when the car is fiully raised and figured the bump stop may be able to just absorb this discrepancy but it did not really work, after driving the fx in that way for just one night I winded up breaking both bump stops, they actually split right down the middle and ejected from the shock. this is not a problem in the front because the front spring can not fall out no matter what. only real solution now is to find a smaller than 2" bumpstop but a little more than the less than 3/4" of the stock, I'm thinking ~1" polyurethane may do the trick but so far I've redone everything with another 3/4" bushing and it's been ok as is for now, may try to find something a little better suited to this and let you know.... this is why I didn't want to start a thread for this and really recommend something that I haven't fully confirmed yet. for any who bought these 2" bump stops for the rear I'm sorry to have steered you wrong but I too winded up getting a set of these just to realize after that there just not going to work for me.... if your not severly lowered then this might still work for you but at this point I'm going to recommend rear bump stops that are ~1" or so, not the 2" ones I originally thought would work... sorry :(

another alternaive is to fabricate a bump stop to a control arm rather than the shock itself. many cars use bump stops in the suspension at a point other than the shock itself which in my opinion is much better anyway as it creates less load on the shock itself... if/when I come up with something on that front I'll let you know too...
 
I guess I'll be the #2 test subject for 2" bump stops with 3/4" gap=)

So far no issues...

---------- Post added at 04:34 PM ---------- Previous post was at 04:14 PM ----------

BTW, what if the bump stop comes out, it is safe to drive?
 
3/4" gap then it might be ok with the 2" stops, I have like 0" gap and am pretty low so the spring is too short when the car is lifted all the way, an extra 3/4" would probably make all the difference, I split my bump stops in half within the first hour of driving, if yours is ok still then the 2" is probably ok at your hieght

---------- Post added at 05:44 PM ---------- Previous post was at 05:40 PM ----------

yeah, if it comes out you just won't have any bump stop... I mean keep an eye on it... if it splits and ejects you'll notice a huge bulge on one side of the dust boot cause it'll still be in there, kinda looks like a snake that just swallowed a whole rat or something :) if your really adjusted it the right way then even with the bump stop missing you'll still wind up rubbing the tire before ever bottoming the shock...
 
Yeah Andy test drove it aggressively for me and if it didn't break after flying over the railroad tracks, I should be good.

Makes sense, I'm 3/4" higher so instead of 1" bump stop I'm at 2" bump stop, 1/4" taller.

No rub on full turns both ways, alignment all good (slight camber, at -2 but good for cornering and shouldn't be noticeable tire wear, I think -3 and more I would worry and rotate frequently).

What a journey.

Hey John, if I change my coilovers to all the way soft, will that impact my tires rubbing?

It just controls the rebound? Since springs do the compression? So thinking I would be fine regardless of the settings?
 
Ed, I saw your alignment printout just now. I can't believe that you're still a -2 degree in the rear. Just by eyeballing it, yours were way better than mine on the rear camber. I gotta slot my sub frame and get an alignment to compare with yours. Mine rear camber is -1.8 oem. Yeah, I test drive the heck out of Ed's ride after setting it to 3/4" gap without any rub.
 
I slotted and also used 2 camber bolt kits and I got desilvias down to -1.5 both sides in the rear which is perfect for a daily driver I think, wouldn't want any less than that really, I have the part #'s for the 2 bolt kits I used at work if you need it.

spring rate is high, it's gonna ride a bit choppy on the big stuff no matter what, the dampening adjustment can be backed off until you start to feel a pogo stick type effect or you start to scrape or bottom more on big hits but it's only going to make it slightly softer, harder has more control, can't hurt to try different settings and feel how it reacts and feels to you
 
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