Norm Peterson

If it's abrupt in a direct bump, it probably is the bump stops you're hitting.

If the abruptness is in rebound with the car moving up, it's the springs getting into their softer range as the closely spaced coils start to open up a gap. Then on the way back down when they close up again you'll get a little sudden firmness shortly before getting a lot more (when you catch the stops).

If you do cut, and there is a choice of how/where to cut, you want to cut from the solid end. That will leave any progressive part at the other end intact, and will leave the bump stop contact that you will get softer than it would be if the stops were cut to leave them with no "give" at all.


Norm

scottybaccus

I have the Eibach Sportline springs. I picked them up on ebay from someone that couldn't stomach them and pulled them back off after only one day. The kit came with shorter stops for the rear, but required no change in the front. The seller failed to include the stops when sending the kit to me, probably because he didn't save his originals. The Eibach instructions happened to include the dimensions of the shorter stop, so I just cut mine to that height. It was 5/8", cut in the first narrow groove. They have worked out well with only myself and maybe one other in the car. I do carry my kids often. They are both nearly grown, so when we have four in the car, it has been bottoming out too frequently. The car appeared to be level, or maybe even a tad lower in the rear. I decided to shim the rear springs back up and had some 1/4" spacers made to put at each end of the spring. When I went to install these, I didn't think the lower spring seat on the axle was tall enough to be comfortable with raising the spring 1/4", so I put both on top of the spring. The upper seat has a long plastic isolator that hangs a couple of inches into the center of the coil. There is no question that both spacers will stay in place on top. We went on a 600 mile road trip this last week, mostly on wavy and bumpy two-lane highways. We had the four of us, a loaded cooler, a couple of lawn chairs, skateboards, and all our clothes for a 4 day trip in the back. The trunk was full, wall to wall. The added half inch did the trick. I only felt it getting on the shortened stops on the worst of dips at highway speeds. It sits with a little rake, with a kinda muscle car stance. I like it a lot and have no further changes planned for the suspension.
I guess, in short, cutting the stops down by 5/8" was necessary. The Sportline Springs are very low, like 1.4" in front & 1.7" in the rear, so don't go there if you use your car routinely for passenger transport. The rear may be too low if you do. The front is fine.

MOTRHD

Hey Norm,
Thanks for your answer, it does indeed feel like more of a spring issue rather than hitting the bumpstops abrutly, but I don't think the progressive coils are ever opening up which limits travel and spring movement to the lower
2/3's or the spring. This has been the issue with all the lowering springs I have ever used!!
By definition the progressive coils should compress when the force on the lower coils(or the widely spaced section)is great enough to cause that, not to have them always be compressed. As it stands right now you would get the same result ie. lower height and firmer spring rate if you "tied" the top two coils of a factory spring together.
Is there a progressive lowering spring that acts/reacts like a stock spring?
Does anyone make a linear rate lowering spring?
I really would like to start a poll to see how many people that have ever lowered there car were completely satisfied with the result!
Now for bumpstops. Again by definition, on a stock suspension the bumpstop is exactly that, a limit to maximum suspension travel. On a lowered setup it seems to become an active part of the suspension. For instance on a stock setup the bumpstop is about 2" from the frame. That distance being juuust.. beyound the maximum limit of travel. So following that theory on the lowered setup the bumpstop should again be just beyound the maximum range of travel. There isn't really any compression to the bumpstop making it act like an "absorber". On the Mustang the bumpstop is placed on the angled part of the frame so it doesn't really hit with direct vertical force.
Sorry so long but just wanted to put that out there.

scottybaccus

The stops on a mustang are actually called a secondary spring by Ford. They are made of a urethane foam, like memory foam, not hard rubber or the urethane bushing material. They do play an active roll in managing suspension travel at the extreme. Changing the height and/or density of the stop is part of tuning. They are far away in stock trim for comfort and up close in Shelby or race trim for performance. I think Ford even offers various density with several alternate part numbers. I've seen them listed, but unsure all yhe specs.

MOTRHD

OK so I took pictures but I couldn't figure out how to post them, but anyhow I didn't just cut the bumpstops leaving a flat surface and a hole to collect water in essence I sectioned them.
I cut off the rounded top (with a cutoff disc) then I cut the next section off (down to the second rib with the dots around the circumfrence).
I smoothed and shaped the cut surfaces with a bench grinder, then I epoxyed the rounded cap back on. This leaves the same round top to contact the frame and covers the hole in the bumpstop.
The pictures would have showed that the FRPP bumpstop was actually a smidge higher than the stock (on a lowered suspension??), as well as the comparision after cutting. Pictures also showed that I went from just under a finger gap (<1") to just over 2 fingers (>2") which is just about the space on the stock setup.
Prior to my modification I could see a big rub spot on the frame so I know the bumpstop was hitting frequently, and that is with a week of normal driving, driver only, and empty trunk.
I'm sticking to my theory that the bumpstop should be just beyond the limit of travel and only contact on severe load or a huge pothole. I don't think my stock ones really ever hit with factory parts. So that should should be the same for a lowered, tighter suspension, with really less travel.
Haven't driven it yet (epoxy still drying) but I will let you know.

Hamhole

A bump stop is a progressive rate "spring" so you shouldn't cut it. Some lowering kits come with shorter bump stop replacements or you can order a set.

Here is an example of the stock Mustang bump stop on the left and the Eibach replacement on the right:

Norm Peterson

Unless there's some detail we can't see, it looks like when you hit the Eibach piece, you're gonna hit it hard. No visible progression to speak of. Ugh.


Norm

scottybaccus

I would think that you're right in the sense that it's a more noticeable start, but it looks to me like the compressed mass would be about equal, so they likely have a similar compressed state. It starts more abrubtly but ends about the same.

MOTRHD

After my mod of the FRRP bumpstop which was easy and didn't take long at all it looks rather like the Eibach in terms of height, but with a rounded top which would seem to soften the contact to the frame.
But did that bumpstop come in a kit or did you order intseparately, because on their website I couldn't find any listing for bumpstops.

Norm Peterson

The final positions might be about the same, but the chassis/body decelerations experienced in getting there (and the forces developed) are going to be quite a bit different. It's sort of like the "crush zone" thinking vs more rigid structure that reduces crash decelerations, except it's in a different direction and can be encountered on a more frequent basis.

Unless a little more bump travel could ruin the shocks by bottomming them out internally or let some other damage occur, I think the Eibach stops could be made a little more progressive.


Norm