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.
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!
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.
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.
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.
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.
6. Lower the axle back to the starting position and support with jack stands.
7. Unmount the left shock from the axle. (13mm long & 10mm box end)
8. Unmount the left shock from the top mount. (14mm deep & 16mm open end, 17 ft-lbs.)
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.
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.
9. Temporarily re-mount the left tire on the axle with three lug nuts. (Tire iron, gently snug.)
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.
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.
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.
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.
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 ...
I couldn't turn the wheel to full right lock with the axle fully flexed because the sidewall was hitting the upper spring perch.
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.
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!
15. Unmount the tire. (Tire iron, gently snug.)
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.)
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.
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.