Prothane Coil Insert Bump Stops (w/ Bonus Front Frame Stiffeners)
I was happy with my rear bump stops but the front bumps kind sucked. They were always harsh and one side kept trying to cut itself on the edge of my raised pad. I decided to try the Prothane coil bumps. There were quite a few positive reviews scattered over several threads. A few good references.
https://www.cherokeeforum.com/f67/prothane-coil-bumps-221747/
http://www.naxja.org/forum/showthread.php?t=985677
Key facts:
-Most folks start with the Prothane 10.5” coil inserts and cut down to whatever they decide is their happy length.
-A washer or pad can theoretically be bolted where the OEM bump cup was before. I’m not sure if it’s only certain XJ’s have this position threaded, but a few folks claimed it was an m10x1.5. Maybe the intent was to tap the hole to that since I’d think Jeep would be using imperial hardware rather than metric. I went a different way (more on this later).
-Some folks add hockey pucks or some form of strike pad that nest on top of the bump.
-A few folks who test claim they’ve been able to compress the coil bump by about 60% (40% residual height at max bump.
-2” air gap until the point of first strike seems to be the most common measurement. Some folks run all the way down at 1”.
4643 ran (runs?) a 3.5" airgap and 1.75" of prothane until it hits the hard bump.
-One of the downsides of the bump is that there’s not a hard bump so the hard bump alluded to above is a 1.5” UHMW rod that serves as an internal hardstop. Mcmaster 5243T15 is one option. I ended up using some 1 3/8” scrap I had lying around.
A couple sources of supply:
http://www.jegs.com/p/Prothane/Prothane-Coil-Spring-Inserts/762178/10002/-1
https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=prothane coil insert
I started this project about 2 weeks out from SoCal Fest and barely made it.
In order to get enough droop to pull the springs I had to remove: shocks, tie rod, and drag link.
When pulling that apart I found one of my shock bushings was trashed so rigged up another right quick from some spare parts.
Bump pads I mentioned were a pain to get off. Regular socket wouldn’t fit so I had to hammer in a 1/4" drive socket to get it apart.
Hadn’t really played with the stock bumps before so went looking for the m10 some folks had mentioned.
Nope, you just yank and it pops free.
I was going to make a bolt in setup. 1.375” tube was about right to keep it aligned.
But then I went digging. I could probably drill and tap one side. Other one? Not so much.
I decided to weld in a bump stop plate (after confirming my spring could slip over this). I tried hole sawing ¼” plate but it just chattered too much.
Almost broke out the plasma cutter but for two plates it hardly seemed worth it. Ended up getting creative with some extra hole saw support via some plywood and that did the trick. 3” hole saw, left me with about 2 3/4” pads. Shown cutting is a smaller 1.5” plate for the bottom end.
After that I just couldn’t weld to that lousy cup for the stock bumps. Took some measurements, and decided a longer insert would be good for me and proceeded to cut off the stock cups. Used an angle grinder to cut around the 75% of perimeter I ccould get to. Slicing right on the middle of the weld worked nicely. Beat it down with a hammer and finished it off with a sawzall. By the way, angle grinder cutting discs come in either 0.040” or 0.060”, if you have a lot of metal to move, spring for the thin discs (aka not what you get at harbor freight), they cut a great deal faster.
For the bottom end, made a short 1.5” riser from 1.5” 1/8” tube and plate to help keep the insert from flapping around everywhere in there. Note the ID of the insert is just under 1.5” so this makes for a minor stretch fit. Then decided to get elaborate and make a threaded stud for the plastic hardstop.
Note on the threaded stud bit. Yeah. DON’T DO THIS. In hindsight (and following the experience of some wheeling) I should have just let the plastic rod float. I’ll cut off the studs next time I’m in there.
But that’s given hindsight… What I actually did? Plenty of weld through primer like usual.
I had so much of the front opened up at this point that I couldn’t help it. I launched into the front frame stiffeners too. I’d had the front HD Engineering bits floating around the garage for a while.
Bend angles marked if you care, might be better to verify on your own rig.
Impulse buy. Much nicer scraper than the old school extender sheet metal version everyone has from the 60s. Made short work of a 1.5 year old shipping sticker.
Trying to keep 1/4" steel floating was a little tricky. Only so many hands while working solo.
Opposite side for the weld shot since my passenger picture turned out crappy.
Process was much like the rear stiffeners I did a while back. 1) Mark stitch weld positions, 2) grind paint, 3) weld through primer, 4) Lotsa clamps.
5) Burn it in
Once the side was on I decided to plate the bottom at least on the driver rail since it sees more axle loads from both steering and track bar. Designed patches in cardboard and I was pretty happy with the fit of the results.
6) Grind for a while.
Quick plug here. My last angle grinder died so I decided to try a good one. Picked up a Makita 9564CV which was about the top rated thing on Amazon (
https://smile.amazon.com/gp/product/B00005Q7BE/). It’s unreal how much better this is. Doesn’t blow out your eardrums, starts with a ramp up in speed so it never tried to tear itself out of your hands and somehow manages to be much smoother running. It doesn’t vibrate anything likely my old $30 Ryobi used to. For the longest time I thought angle grinders were a great tool to cheap on. Just spins around right? No precision needed. If you’re in that school of thought, don’t use a nice one. There’s no going back.
Other side is the same.
There was one slight problem. Somewhere around here I decided to add a bit more weld to the bottom riser. Jumped right back down and started to weld. I was about 2 seconds on when there was a bit sizzle and pop, arc stopped. What the hell? Uh oh, I didn’t move the ground back down to the axle when I move from top to bottom.
Turns out control arm bushings are a decent isolator. You’re not getting any current through those. You know what does conduct electricity? Braided stainless steel brake lines.
Crispy critter, my bad.
Amazon prime to the rescue.
My wife did the POR15 (step 7) for me while I was at work (Thanks Babe!)
Came home and seam sealed the top edges only (step 8) based on the theory I should let the bottoms weep if needed. Then sprayed underbody coating over all that (step 9), finally (10) reassembly.
The coil insert themselves I cut down to 9” (7 rings instead of 8). This is a little longer than usual since I removed the cups up top so you could probably order the 6 ring version to begin with if you’re not significantly lifted. I was targeting a 2.5” air gap and ended up closer to 2”. The inserts cut fine on a band saw. I cleaned up the edges with a belt sander.
I then chamfered the ID on one end so it wouldn’t have a corner rest on the fillet welds around my riser. Required? Probably not, but I’ve been designing stuff too long to let it slide.
I made sure the springs would slip over the flat plat I welded. However, I forgot that I was running coil spacers. They don’t slip over the protrusion.
Screw it, sliced one side, flexed them around and added a hose clamp to be sure it stays put. Maybe I’ll find longer springs at some point in the future, for now it’s good enough.
Here’s the hardstop insert threaded on my “shouldn’t have done it, stud thingy”.
I cut this to a length such that it would bottom out about ¾” before the shock does and that should also keep the oil pan maybe 1.5” away from my truss. It would be more reliable to cycle the suspension with track bar and no springs, but I didn’t have time to re-assemble things twice so I based mine on measurements and went for it.
Anyone have hot tips for keeping the brake lines out of the coils? Mine seem convinced they want to rub which I’d like to adjust.
Everything else went back together pretty smoothly.
So how’s it ride? You can feel the bumps engage but it’s never harsh and didn’t seem to hold me back from flexing. To be fair, I haven’t hammered on anything yet. 1) I don’t really drive that way so a “big accidental jump” isn’t typical for me 2) had little girls in the back seat and 3) my ball joints were creaking and knocking all weekend (noticed it during reassembly but didn’t have time to do anything about it). I could feel the coils knocking against the insert on occasion with I assume is partly due to the mounted hardstops. As noted I plan to let those float. On net, I’m happy though. They’re cheap and work well what more do you want?
So that was my saga and hopefully it helps someone else out. Event was worth it though.
Climbing a waterfall on Doran.
-Joel
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