RCsGX

I finally got around to installing the rear 5100s. I have over 100K miles so it was time for new shocks. There's a main road by my house that has a deep dip in the road and every time I would cross the intersection I would bottom out bad. If I was able to catch the light and raise the rear I was fine.

I went w/ the 5100s because I've used them before on my Tundra so I knew what to expect and I didn't care about loosing the comfort / sport settings on the stock shocks. Removing the stock shocks was easy. I didn't have to cut the top bolt, I was able to grab the shock body by hand and remove the top nut w/ a flex head wrench and I didn't need to use any penetrating oil either. You gotta love a Texas GX. Because the 5100s are taller than the stock shocks I had to lower the axle a bit which made it easier than trying to compress them by hand and lining them up.

Done....






After installing them I went down that street w/ the bad dip and I still hit the bump stops but once I hit it, it didn't bounce 1-2 more times like the stock shocks did, the 5100s soaked the initial bump right up. Just driving around I could tell a huge difference compared to stock, they soak up the small bumps so much better. Even my wife can a difference and she's not into cars at all. They're more firm that the stock shocks on the highest sport setting but they are in no way harsh.

I'm planning on doing 5100s up front w/ OME 2-3" lift coils soon so when I install those I'll trick the rear to get some lift so that will take care of the bottoming out once and for all!



EDIT: Added washers to the ride height sensor bracket to lift the rear 1/2". Ride is SO much better!! Details are in post # 13 below....

sprocket

I'm impressed with the DIY work you do. What's your billing rate? I'll bring mine over! And I'm serious. Anywhere in Winter Springs is less than 15 minutes from me.

RCsGX

I wish it got cold here, If it wasn't so damn hot I wouldn't mind working on cars. Even though it's been nice here the past few days (no humidity) it was still hot as hell yesterday in the garage. When I finished I had to take a dip in the pool for about an hour just to cool off. A fan can only do so
much. Last night after the kids went to bed I changed the rear diff oil...it was probably 10pm and it was still hot but at least changing the diff oil only involves removing 2 bolts so it wasn't bad.

I honestly don't know how people can work on cars for a living here. I was born in Orlando but I grew up in Northern Virginia and for a few years I worked in a alignment / spring shop that did suspension work on large work trucks. We had an account for all of D.C. and Arlington's police cars, fire trucks and ambulances. Summers were horrible, it got just as hot and humid up there as it does down here but when spring and especially fall & winter rolled around I loved it.

Maybe around Jan / Feb when it's in the 70s hopefully high 60s give me a holler.

stiles_s

Glad to see someone trying the 5100s! I think i'll be going to them w/stock springs after my 2nd set of OE shocks wear out.

Quick note: I'd adjust your height sensors to give yourself a little more travel before you hit the bump stops. It's an easy adjustment. Just loosen the nut holding the arm to the "adjustment slot" and move up slightly. Rinse & repeat.

the rear shocks are a piece of cake, aren't they? The fronts are a bit of a PITA though. There are some good DIYs on the T4r forum.

PS. Consider using the adjustment rings on the front 5100s to get the extra height. That's what I plan on doing. They come pre slotted for 2 (or 3) different heights. IIRC the first slot gives you about an extra inch of height. That feels about right IMO. Keep us posted.

RCsGX

I was thinking about it but it'd give me a pretty big rake...yes my GX is vain, what can I say. But seriously I would adjust them if it bottomed out over every little bump but it only bottoms out when I go over a speed bump fast OR hit large dips in the road and there's only one large dip by my house. Driving around town and on the beltway it's fine.


Yeah they're easy. If you can take your tire off you can replace your rear shocks.

Fronts are another story. I tried doing them on my Tundra and no matter what I did (disconnected the sway bar ends, removed the lower ball joint bolts) I couldn't get the bottom shock bolt to line up. I was less than 1/4" off. I ended up taking it to a shop and had them do it because I didn't have the tools to pop the upper ball joint apart and I didn't want to damage the boot either.


If I were to get 2.5" of lift through the Bilsteins I'd be maxing them out and putting a lot of preload on our stock springs so I want to achieve lift though springs rather than a strut. Just for comparison, the stock 4th gen 4Runner V8 front spring rate is 580lb., the OME 884/885 (not sure which one I'm going with yet) is 590lbs., not much of a difference compared to stock other than them being taller for lift.







The 5100s got rid of the rebounding bounces after bottoming out but I'm still bottoming out, why? My ride height sensors appear to work fine, my airbags don't leak air, I replaced both rear shocks, what else could make me bottom out? Several members on here replaced their ride height sensors and they said it didn't help. I'd hate to spend that kind of money and it still bottom out. If I recall one member even had all of the rear suspension parts replaced I believe under warrant and it still bottomed out!

Time to get technical...


MY MEASUREMENTS

• 22.125" High (+ 1.375") | Per Lexus it should be 1.57"
• 20.75" Normal Ride Height (I wish Lexus gave us the "normal" measurement)
• 19.875" Low (- 0.875") | Per Lexus it should be 0.79"

I was only able to find one guy with a stock GX that measured his normal ride height (center hub to the bottom of the fender flare) and he got 20.6". Mines taller, not by much at all, but he said he didn't have any bottoming out so why is my GX bottoming out?









MY MEASUREMENTS

• C (14.875") - D (11.3125") = 3.56" | Per Lexus is should be 3.04"
• ** I'm running 1" larger diameter tires so if you deduct .50" I'm at 3.06" which is almost exactly what it should be

stiles_s

You ask "why am I bottoming out"?

All things being equal, you've got these variables to deal with:
- Distance from resting position to the point where your bump stop hits the axle. The closer you are to the bump stop, the more likely it is that you'll bottom
- Amount of compression damping your shocks are doing (how much resistance your shocks give when being compressed): The more compression damping, the less likely it is that you'll bottom.
- Stiffness of the spring (in this case, stiffness of the air bag): The stiffer the spring, the less likely it is that you'll bottom.

Since you've picked shocks, the remaining variables are:
- height (distance to bump stop) and
- spring stiffness. Turns out airbags get stiffer the more you inflate them

In other words, a slight increase in rear height will both give you more distance to bump-stop, AND increase your spring rate slightly. Both work in your favor.

I'd be curious to know (but probably never will) whether the adaptive damping logic in the GX is able to detect when you've gone over something like a speed bump and temporarily increase the rear shock damping to compensate & prevent bottoming on compression. Again, in your case this is moot because you're using aftermarket shocks.

I'm not going after the same lift you are. I just want to achieve a more level ride height front-to-rear. I think I'll try the 5100s (when the time comes) at the first adjustment slot (.85" lf lift, I think) and then fine tune the rear as needed.

RCsGX

I get that. That's why when I raise the rear before hitting the dip I don't bottom out. What I don't get is why mine is bottoming out but theirs isn't. Mine is slightly higher (4mm) so my bump stops are 4mm further away than the other GX yet mine bottoms out and theirs doesn't?


I wish there was away to increase the PSI in the bags without increasing the height put they go hand in hand.

I'm not an expert when it comes to our air suspension but with our ride height sensors adjusted to stock specs wouldn't our air bag compressors have to have a pre-determined PSI for the "normal", "low" and "high" positions? If that's true and both of our "normal" measurements are almost identical then our airbags should have the same PSI, so I don't get why mine is bottoming out but theirs isn't.

I don't know what our stock shock valving is but I'd assume that the Bilsteins are more aggressive on both compression and rebound.

stiles_s

I have 3 guesses:
1) do they have fresh OEM shocks or very low miles? Something about the OEM shocks does a great job at preventing bottoming when fresh.
2) Do you have a bunch of extra weight in the trunk? 3rd row seats?
3) Maybe that adaptive damping is going its thing by tightening the rear damping when it senses a big rebound and an impending compression.
(one more): have *you* driven his GX over the same bumps and not experienced bottoming? Have you done a quick crawl under the rear visual of his truck to check for the clean marks on the axle? Maybe he doesn't know what you're talking about, or he drive like a granny

Bilstiens tend to have a fairly stiff initial damping "knee" (if you look at the curve) compared to other shocks. I believe this is referred to as "low speed damping (speed of the shaft) and a more relaxed high speed rate. It makes them feel a little harsh on initial impact but relatively forgiving overall. Could be that the OEM shocks actually have higher "high speed" damping for cases like the speed bump you're talking about.

I can't figure out another factor that would be contributing. I think you're right, PSI and height+stiffness of the rear bags go hand in hand.

PS. I'm at 21" on both sides when measuring from the center of the wheel to the arch.

RCsGX

That makes sense.


So I'm a 1/4" lower than your measurement which still isn't enough to stop the bottoming out. I tested that dip in the road late one night when nobody was on the streets by doing multiple passes raising the rear and then counting the seconds to see if I can find a sweet spot to lift it but the only sweet spot was when it was fully raised. <--- I guess that's my answer then. Hurry and lift the front so I can raise the rear.

Whenever you have time and if you wouldn't mind, could you also measure your front too like you did the rear. Thanks for all of your help, I really appreciate it!

sprocket

If you need to check out a stock configuration let me know.

stiles_s

My front measurement from the center of the center cap to the wheel arch is ~19 1/2 - 19 5/8"

RCsGX

Thanks!

RCsGX

For anyone bottoming out try adding washers to the bracket, it'll make a world of difference! I had some free time today and picked up some .20¢ 8mm washers from Ace. The ride now is like a night and day difference. I no longer bottom out over speed bumps. I can take them as fast or as slow as I want and the airbags and Bilsteins soak the bumps right up. I still slightly bottom out on that one dip but it's not a normal dip and pretty much every other car bottoms out too but the difference now is it's not jolting as before, it's tolerable, even my wife was amazed and she said it's perfect.

When my front Icon coilovers get here in the next week or two I'll raise the back even more and then we should be literally riding on air. It's amazing how just lifting the rear 1/2" makes such a huge difference.

Parts needed:

• Washers: 8mm: 1 washer = 1/16" thick / 2 washers = 1/8" thick
• Bolts: M8 (8mm) coarse thread / 1.5" in length; you can use 1" but I went w/ the longer since I'm going to lift it more once I get my coilovers on. Even 1.5" in length will screw all the way into the frame without any washers so you're fine using longer bolts.

I added 2 washers to each of the 2 bolts and I got 1/2" of lift.

ALAN553

I see you replaced the bolts too, what size were they? So I can have them on hand.
Thanks

RCsGX

M8 (8mm) / coarse threads, 1.5" long.