Bump Stop Check Walk-Thru With Pics

fuse

TJ Enthusiast
Supporting Member
Joined
Jun 5, 2018
Messages
706
Location
San Diego, CA
While I was replacing my sagging stock springs, I figured I would do a full bump stop check, as described in How to set your bump stop on a Jeep Wrangler TJ. Once you have the springs out, doing a bump stop check seemed pretty simple.

I figured that since the PO had installed 31x10.5 tires on the stock "Ravine" 15x8 wheels with 5.5" backspacing, I might want to make sure everything fit. From the discussion in Sagging stock front springs?, there was some question about whether my RS9000XL shocks were hitting full compression first, and that actually turned out to be true.

According to the What size tires will fit a stock Wrangler TJ? thread, "You can put a 31x10.50 - 15 tire on your stock Wrangler TJ with stock wheels. It may rub a little at full lock ..." For my Jeep, I found that the 31x10.5 tires fit fine in the rear. In the front, though, I found that my tires were actually hitting the fender, and that they were rubbing substantially on the shock perch at anything close to full flex and full lock.

I took pictures and documented everything in the Stock Spring Swap Walk-Thru with Pics, so I figured I would do the same for the bump stop check.

If you want to follow the same process, you'll want to do the Front Spring Removal from the spring swap thread, do the Front Bump Stop Check here, then do the Front Spring Install from the other thread. It's the same sequence for the rear: Rear Spring Removal from the other thread, Rear Bump Stop Check here, then Rear Spring Install from the other thread.

As in the other thread, I've included the tools and torque spec for each fastener in parens, even for disassembly where it's nice to know how hard you should have to push on a bolt to get it loose. These specs are for my 05 Sport. I don't know if other models or years might have different fasteners or specs, so check yours before you start wrenching.
 
Front Bump Stop Check

If you haven't already done so, remove the front springs. If you follow the steps in my earlier Front Spring Removal post, the last step will leave you right where you want to be to start the bump stop check.

1. Temporarily reinstall the drag link to the right steering knuckle. (19mm, hand tight) — The bump stop check will be testing steering geometry. We want the drag link connected so we can check the wheel position at full lock in both directions.
IMAG0793.jpg

2. Temporarily reinstall the track bar to the axle bracket. (15mm, hand tight). — The How to set your bump stop on a Jeep Wrangler TJ page suggests that you could perform the bump stop check with the track bar disconnected. I tried that, and it didn't make sense to me. The track bar controls the axle's lateral movement (i.e. left and right) across the frame. When you're doing a bump stop check at full flex, axle position matters!
IMAG0794.jpg
This is the first problem that requires a creative solution. I've got the springs out, and the axle dropped nearly to its lowest position. So the track bar doesn't line up with the bracket, and I can't get the bolt in. If I had the Jeep sitting on the ground, I could use some dry steering to shift the frame position slightly, but I can't do that with the wheels off and the axle on jack stands.

So, I put a ratchet strap across the axle yoke and track bar frame bracket to draw the axle into position. I figure the track bar is already attached to the frame bracket, so that's strong enough, and the axle yoke looks stronger than the track bar bracket on the axle.
IMAG0798.jpg IMAG0797.jpg IMAG0799.jpg
Turns out, you don't need much tension to shift the frame into position relative to the axle. The suspension pivots flex nicely so that everything lines up.

3. Temporarily re-mount the left shock at the axle. (13mm long & 10mm box end, hand tight.) — I'm testing shock compression first.
IMAG0737.jpg

4. Lift the left side of the axle until either the bump stop cup contacts the axle pad or the shock reaches full compression. — In my case, the shock hit full compression first.
IMAG0800.jpg IMAG0801.jpg

5. Measure the remaining gap at the axle pad or shock shaft. — Ideally, there would be a gap at the top of the shock, but the gap is at the axle pad in my case. Looks like about 5mm.
IMAG0803.jpg

6. Lower the axle back to the starting position and support with jack stands.
IMAG0804.jpg

7. Unmount the left shock from the axle. (13mm long & 10mm box end)
IMAG0826.jpg

8. Unmount the left shock from the top mount. (14mm deep & 16mm open end, 17 ft-lbs.)
IMAG0829.jpg
You may need a thin open-end wrench to hold the nut at the top of the shock body while you turn the mounting nut. A 16mm bicycle cone wrench works well for my shocks — other shocks may be different.
IMAG0828.jpg
You also may find that fitting the 14mm socket on the top nut is difficult because there isn't enough clearance in the hole in the body. You can lean on the shock to bend the mounts a little to get things to line up.
IMAG0827.jpg

9. Temporarily re-mount the left tire on the axle with three lug nuts. (Tire iron, gently snug.)
IMAG0767.jpg
You want your tire inflated to its normal pressure at this point, since inflation affects tire size.

10. Raise the left side of the axle until either the bump stop cup contacts the axle pad or the tire contacts the fender. — Note that the jack is near the left end of the axle (actually right under the lower control arm). You want to flex the suspension at this point, since that's a likely position while driving over an obstacle. If the tire is going to rub, you can spin it while gently raising it up the last few fractions of an inch, so you can hear when it starts to contact the fender.
IMAG0830.jpg
I didn't bother taking the flares off, and it didn't seem to matter at this point. If you're doing the check with wider tires or less backspace, you might want to take the flares off to get them out of the way.

11. Measure the remaining gap at the axle pad or fender. — In my case, the tire was rubbing before the axle pad contacted the bump stop cup.
IMAG0812.jpg
It's a little dark, but you can just see the tire hitting the fender. This would have been a better pic if I had taken the flares off, but that wouldn't have changed the results.
IMAG0832.jpg
Looks like I have about 5mm of gap before the axle pad hits the bump stop, but the tire is already hitting the fender. So much for the common wisdom that 31x10.5 tires fit stock Jeeps! (To be fair, tires marked the same nominal size actually have slightly different dimensions, so other tires might fit.)

12. If there is a gap at the fender, rotate the steering wheel to lock in both directions, stopping if the tire contacts the fender or other components.If the tire rubs the fender, lower the axle until you can rotate the wheel to lock without tire contact.
IMAG0841.jpg
Without lowering the axle (same position as step 11), I don't have any other body clearance issues at full left lock. The tire is gently pressing on the flare, but not enough to be significant. I can still spin the tire without damaging the flare. Right lock is a different story ...
IMAG0838.jpg
I couldn't turn the wheel to full right lock with the axle fully flexed because the sidewall was hitting the upper spring perch.
IMAG0808.jpg
So I dropped the axle until I could get to full right lock. What I should have done first (but didn't) was to measure the gap at the steering stop. That would have told me if I could add a couple of washers to keep the wheels out of positions where they would contact the spring perch.

13. Measure the remaining gap at the fender or axle pad with the tire rotated in either direction.
IMAG0839.jpg
That's about 2.5" of gap between the axle pad and bump stop cup, which is a lot. So, as expected, 31x10.5 tires on stock wheels with 5.5" of backspace rub when you get close to full lock.

14. Lower the axle to the starting position and support with jack stands. — Make sure the right jack stand is still in place at this point!
IMAG0778.jpg

15. Unmount the tire. (Tire iron, gently snug.)
IMAG0845.jpg

I happen to have a stock 30x9.5 tire on the same wheel, since the PO only put the 31s on four wheels and left the original stock tire on the spare. For kicks, I swapped in the spare at this point, and ran the whole bump stop check again with the stock tire. It cleared everything just fine — we'd all be surprised if it didn't. That's useful information though, because it means I could solve the clearance issues at steering lock with 5.0" backspace wheels, or maybe 4.75" backspace so there's a little margin of error.

16. Remount the left shock at the top mount. You may need a thin open-end wrench to hold the nut at the top of the shock body while you turn the mounting nut. A 16mm bicycle cone wrench works well. (14mm open end & 16mm open end, 17 ft-lbs.)
IMAG0848.jpg

17. Disconnect the track bar from the axle bracket. Use a ratchet strap across the axle yoke and track bar frame bracket to release the tension on the track bar bolt. (15mm, hand tight) — Take your time with this step. It shouldn't take much tension on the ratchet strap to release the tension on the bolt, and it's easy to get too much tension and bind the bolt from the other direction. It's worth going slowly at this point so you can get the bolt out without damaging the threads.
IMAG0796.jpg

18. Disconnect the drag link from the right steering knuckle. (19mm, hand tight)

At this point, everything is back where it started at the beginning of the bump stop check. You can continue with the Front Spring Install walk-thru to reinstall the front springs and put everything back together.
 
Last edited:
Rear Bump Stop Check

If you haven't already done so, remove the rear springs. If you follow the steps in my earlier Rear Spring Removal post, the last step will leave you right where you want to be to start the bump stop check.

1. Temporarily re-mount the left shock at the axle (hand tight). (15mm/18mm, hand tight.)
IMAG0968.jpg

2. At this point, I should have also temporarily reattached the rear track bar to the frame bracket. I didn't, but I suspect it wouldn't have made much difference in my case. With a lift kit installed, I think you'd want to reattach the track bar to make sure the axle moves the same way during the check as it would when you're driving.

Aligning the rear track bar to its bracket would have been difficult at this point, though. You can't use dry steering to shift the frame while it's on jack stands. And unlike the front track bar, using a ratchet strap around the rear track bar bracket is awkward. I'd love to hear suggestions of how to make this work.

3. Lift the left side of the axle until either the bump stop cup contacts the axle pad or the shock reaches full compression, support with jack stands. — In my case, the axle pad contacts the bump stop cup first, which is what we want.
IMAG0970.jpg IMAG0974.jpg

4. Measure the remaining gap at the axle pad or shock shaft.
IMAG0978.jpg
That's about 1" of remaining shock stroke.

5. Lower the axle back to the starting position and support with jack stands.
IMAG0980.jpg

6. Unmount the left shock from the axle and position it so that it doesn’t interfere with axle movement.
IMAG0981.jpg

7. Temporarily re-mount the left tire on the axle with three lug nuts. (Tire iron, gently snug.)
IMAG0983.jpg
I disengaged the parking brake and shifted the transfer case into neutral at this point so I could spin the rear wheel.

8. Raise the left side of the axle until either the bump stop cup contacts the axle pad or the tire contacts the fender, support with jack stands.
IMAG0984.jpg IMAG0988.jpg
The axle pad is on the bump stop, and the tire still spins without hitting anything but the flare. I should have removed the flare, but my tire was only gently pushing it out at this point.

9. Measure the remaining gap at the axle pad or fender. — If I had removed the flare, I would have been able to measure the gap between tire and fender. I was just satisfied that the tire wasn't hitting any metal, though.

10. Lower the axle to the starting position and support with jack stands. — I put the transfer case back into 2H and re-engaged the parking brake at this point. It's nice to keep the wheels from turning when you're working on lug nuts.
IMAG0993.jpg

11. Unmount the tire. (Tire iron, gently snug.)
IMAG0995.jpg

12. If I had temporarily reattached the track bar to the frame bracket, I would remove it at this point. I left the track bar disconnected the whole time, though. I think if you had a lift kit, you would want the track bar attached for the bump stop check so the axle would move the same way during the check as it would when you're driving.

At this point, everything is back where it started at the beginning of the bump stop check. You can continue with the Rear Spring Install walk-thru to reinstall the rear springs and put everything back together.
 
Last edited:
Bravo sir, well done!

This is something that everyone needs to do after installing a lift, increasing tire size, adding new shocks, etc. Anytime you mess with your tires, suspension, or even add new steering for that matter, you should be checking and adjusting bump stop. Thank you for taking the time to detail how you did it. This is tremendously helpful!
 
Bravo, Sir! So, the answer to "Do 31x10.50's fit on a stock TJ?" is the same as everything else. Maybe...Maybe not. You gotta check.

Like the write-up.

Thanks. I think that for a DD or light off-roading, you really wouldn't see any issues with 31x10.50s. I only had issues at extreme suspension angles, and you'd only get there if you were pushing your Jeep to the limit.

So, yeah, it depends!
 
This is great!

Once you go through the process, it really changes how you view the suspension, doesn't it? Now you can visualize what a larger tire or a different length shock will do to the system.

I've always kept the track bars attached, just loosened, btw. Same with the control arms. Disconnecting the sway bar also helps you move things around.

It is also a good idea to fully raise the axle to full bump both sides. This is important up especially front in order to make sure that an aftermarket track bar doesn't hit an aftermarket diff cover.
 
2. Temporarily reinstall the track bar to the axle bracket. (15mm, hand tight). — The How to set your bump stop on a Jeep Wrangler TJ page suggests that you could perform the bump stop check with the track bar disconnected. I tried that, and it didn't make sense to me. The track bar controls the axle's lateral movement (i.e. left and right) across the frame. When you're doing a bump stop check at full flex, axle position matters!

You are correct.

4. Lift the left side of the axle until either the bump stop cup contacts the axle pad or the shock reaches full compression. — In my case, the shock hit full compression first.

It sounds like you are first checking for BS at flex (articulation)? I would check at full bump first. It's okay if they don't line up perfectly at flex. It however is very important that everything else clears at flex until the shock bottoms out. When checking flex, make sure you have the opposite side hanging off the end of the shock when checking — no jackstand. If you can't lift the Jeep frame high enough for that, take the tire off the drooped side.

So I dropped the axle until I could get to full right lock. What I should have done first (but didn't) was to measure the gap at the steering stop. That would have told me if I could add a couple of washers to keep the wheels out of positions where they would contact the spring perch.

I would probably favor more uptravel and add a few washer to the steering stop. Also remember the conditions when you'll be at full flex and full lock — very slowly and low tire pressure — you may be fine with some light rubbing.

It looks like you also missed checking full bump (both sides up)? That's where I would have started and made compromises based on conditions (such as tires rubbing at full flex while at full lock) if needed to maintain other benefits.
 
Last edited:
2. At this point, I should have also temporarily reattached the rear track bar to the frame bracket. I didn't, but I suspect it wouldn't have made much difference in my case. With a lift kit installed, I think you'd want to reattach the track bar to make sure the axle moves the same way during the check as it would when you're driving.

This can make a difference and you need to make sure the track bar clears. I bend a stock track bar unknowingly on a stock Jeep and this would have revealed that.

Aligning the rear track bar to its bracket would have been difficult at this point, though. You can't use dry steering to shift the frame while it's on jack stands. And unlike the front track bar, using a ratchet strap around the rear track bar bracket is awkward. I'd love to hear suggestions of how to make this work.

It can be tough with the stock control arm bushings. Currie's JJs allow for this alignment a bit easier. You should still be able to ratchet around the frame to diff or cycle the axle until it lines up.

Also see my comments about the front, they apply here too.
 
  • Like
Reactions: fuse
It looks like you also missed checking full bump (both sides up)?

Thanks for the other comments — all very helpful!

I actually did check full bump (i.e. both sides of the axle up), but only with the shocks, and not with the tire. I figured that wouldn't be a likely condition, since you'd have to drop both sides of the axle off a ledge at once, or hit something big at speed to get there. I'll launch my bike off a 5-foot drop to flat, but I didn't think people did that with their Jeeps!

As you and @jjvw say, checking full bump seems like a good way to look for clearance issues or other problems. It would be definitely be good to add to the procedure, since moving the axle around is the easy part.
 
...
I actually did check full bump (i.e. both sides of the axle up), but only with the shocks, and not with the tire. I figured that wouldn't be a likely condition, since you'd have to drop both sides of the axle off a ledge at once, or hit something big at speed to get there. I'll launch my bike off a 5-foot drop to flat, but I didn't think people did that with their Jeeps!
...

It doesn't take much to bottom out the suspension. Speed bumps, dips in the road....
 
Thanks for the other comments — all very helpful!

I actually did check full bump (i.e. both sides of the axle up), but only with the shocks, and not with the tire. I figured that wouldn't be a likely condition, since you'd have to drop both sides of the axle off a ledge at once, or hit something big at speed to get there. I'll launch my bike off a 5-foot drop to flat, but I didn't think people did that with their Jeeps!

As you and @jjvw say, checking full bump seems like a good way to look for clearance issues or other problems. It would be definitely be good to add to the procedure, since moving the axle around is the easy part.

You're probably fine leaving the tire off for checking full bump unless you're messing with geometry and tire size different than stock. It places the tire at a different location than flex.

I don't know about a 5ft drop, but some of us do cycle our suspension offroad quite a bit. You can place a ziptie around your shock shafts to see how much they travel (if your shocks came with a rubber bumper, move that instead of a ziptie.). If you're not getting more than a few inches of available travel you might need differently tuned shocks.
 
  • Like
Reactions: fuse
One of the largest benefits to this procedure is to be able to mimic the dynamic loads the suspension experiences on the road and on the trail. The Jeep hitting a bump/dip at speed or rolling of a ledge will compress the suspension in ways that a ramp or forklift can never replicate.
 
Nice write-up @fuse. Very helpful step by step procedure. Thank you
 
I would probably favor more uptravel and add a few washer to the steering stop. Also remember the conditions when you'll be at full flex and full lock — very slowly and low tire pressure — you may be fine with some light rubbing.

I've been thinking I could get some more clearance for the tire sidewalls by replacing my 5.5" backspace wheels with 4.75" backspace wheels. In theory, an extra half-inch of offset should be enough, but some extra space can't hurt. Moving the wheels out by 0.75" seems like a relatively minor change.

That way I'd be able to keep both the uptravel and the turning radius. You guys have more experience with this stuff than I do, though. Is that something that might work? Should I expect any other clearance issues if I move from 5.5" to 4.75" backspace?
 
  • Like
Reactions: Shane Mckinley
I've been thinking I could get some more clearance for the tire sidewalls by replacing my 5.5" backspace wheels with 4.75" backspace wheels. In theory, an extra half-inch of offset should be enough, but some extra space can't hurt. Moving the wheels out by 0.75" seems like a relatively minor change.

That way I'd be able to keep both the uptravel and the turning radius. You guys have more experience with this stuff than I do, though. Is that something that might work? Should I expect any other clearance issues if I move from 5.5" to 4.75" backspace?
Yes.
 
  • Like
Reactions: Shane Mckinley