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Front Diving While Braking

S

Super mud

NAXJA Forum User
Location
Bel Air Maryland
So I got stock TJ coils with a 2" spacer and stock replacement Monroe LT shocks. The axle side lower brackets have been raised to the center of the axle and nothing else has been moved. So now that everything that was setup for 4" lift clears, the front end handles horribly bad. Instant bottoming with less than hard braking is the main problem. At 4" it never was apparent but I had 5/8" thick coils. So I'm wondering if the geometry change doesnt create enough "antidive" or if I just need to correctly bump stop with this soft of a setup.

I plan to redo the frame side bracket since it has pushed the axle out ~1" but would require pocketing the frame to move up. Just looking for any input to tell me im wrong before I start messing with the calculator. Feel free to bash away.
 
cnjcherokee said:
TJ coils? those with a spacer should be 1" above normal ride height IIRC
Click to expand...

Yea 1.5" according to dirty measurement method and .75" in the rear though the rocker measures .75" higher in the rear so who knows. Thats accounting for the 8.8 tubes too. Yea 8.8 on 31s and no lift, not sure how that happened.
 
you need to move your uppers up to match the lowers. low anti-dive is a symptom of not enough vertical separation. do some measuring but you want to be at 8" min.
 
Rockclimber has it right, but for the wrong reason. The amount of separation itself doesn't matter, but it gets you want you want. The upper arm angle needs to be less, so either the frame side mount needs to come down or the axle side mount needs to go up. I believe this would help your problem. Don't bother with the calculator, other than just for curiosity, it doesn't really tell you anything about a front application.
 
Goatman said:
Rockclimber has it right, but for the wrong reason. The amount of separation itself doesn't matter, but it gets you want you want. The upper arm angle needs to be less, so either the frame side mount needs to come down or the axle side mount needs to go up. I believe this would help your problem. Don't bother with the calculator, other than just for curiosity, it doesn't really tell you anything about a front application.
Click to expand...

So raising the frame side lower should also correct the angle against the uppers.
 
Super mud said:
So raising the frame side lower should also correct the angle against the uppers.
Click to expand...

Negative. Well, I guess it could help, but it's a lousy solution. It's not just the relative angle of the upper and lower arms, that's a part of it, but it's also the angle of both the lower and upper arms and where the instant center has moved. The instant center is where the two arms (upper and lower looking at the side) would intersect if you drew a line forwards from each arm. You started a good process by decreasing the angle of the lowers, finish the job by decreasing the angle of the uppers.....if possible.

If it were me, I'd cut off the stock pass side UCA axle mount and weld on an 8" pre-fabbed UCA axle mount from a place like Poly Performance or Blue Torch Fab and eliminate the drivers side arm. You'd need to make a new upper arm with a proper joint on the end, and reinforce or replace the stock frame side UCA mount. By eliminating the stock rubber bushing in the axle side UCA you'd also be eliminating some axle wrap and removing the necessity of periodic replacement of those rubber axle bushings.
 
RE adjustable arms came on the jeep so I can make up for the distance change. I like the idea of getting rid of the 4th link. Though it would be nice to keep the bushing for the DD purpose and I could raise the pass side mount but doing the frame side with a hard joint would be tolerable and I could get rid of the crappy RE bushing, which I also need to address on the lowers.

Also with the instant center business, how come raising the frame side lower the same amount as the axle side not correct it? Or does it have to do with the spacing/relation to the axle?
 
Super mud said:
RE adjustable arms came on the jeep so I can make up for the distance change. I like the idea of getting rid of the 4th link. Though it would be nice to keep the bushing for the DD purpose and I could raise the pass side mount but doing the frame side with a hard joint would be tolerable and I could get rid of the crappy RE bushing, which I also need to address on the lowers.

Also with the instant center business, how come raising the frame side lower the same amount as the axle side not correct it? Or does it have to do with the spacing/relation to the axle?
Click to expand...


I never get the comments about keeping a bushing for DD usage. Why? Who cares? Do you really think there is that much NVH difference between a crappy bushing and a good solid joint?

Like I said previously, it's not just the relative angle of the two arms, it's also the actual arm angle. You raised the axle mount of the LCA which made less arm angle, which is a good thing. Now you want to increase the angle of the LCA to fix a handling problem. All you've actually accomplished by doing all that is decreased the separation of you upper and lower arms. Decreasing the angle of the LCA is a good thing, as well as the extra ground clerance, now decrease the angle of the upper arm and you'll have an improvement.

If you decrease the angle of your upper arm then your instant center will move up. If you increase the angle of your lower arm your instant center will go down. I assume you have drop brackets? Otherwise, why would you want to raise your LCA frame mounts?

BTW, what is your goal in what you are doing? Why did you raise the LCA mount to even with the axle tube?
 
Goatman said:
If it were me, I'd cut off the stock pass side UCA axle mount and weld on an 8" pre-fabbed UCA axle mount from a place like Poly Performance or Blue Torch Fab and eliminate the drivers side arm. You'd need to make a new upper arm with a proper joint on the end, and reinforce or replace the stock frame side UCA mount. By eliminating the stock rubber bushing in the axle side UCA you'd also be eliminating some axle wrap and removing the necessity of periodic replacement of those rubber axle bushings.
Click to expand...

richard, do you have a write-up or some pictures of a reinforced passenger frame side UCA mount in the stock location?

I'd like to eliminate the drivers side upper, and run 2.5" joints on the upper, but I haven't figured out how do that with the stock location.
 
I'd cut off the stock mount, plate the frame, and weld on a pre-fabbed mount of choice with the bolt in the vertical position. Simple, just do a good job of attaching the plate to the existing crappy frame. The UCA mount on my buggy's front 3 link is done this way. You can move the mount downward and rearward while you're at it to get a little longer arm and a flatter arm angle.

If you're going to do long arms, just get the Synergy mount from Poly Performance.
 
I raised my axle side lowers when I built the front axle, along with OTK steering and the track bar mounts to match. That was at 4" of lift. My goal currently is to get the jeep working well for everyday use at a lower height for the 31s. It would be nice to start from a stock one but there is alot into this one and I still wheel it. I do not have drop brackets but thought of pocketing the frame to raise/correct my lower angle. The frame is plated up front currently so I could reinforce it the rest of the way. So at this point the arms should be at stock angles compared to each other and I should further angle them away from each other with either raising the axle side upper or lowering the frame side?

Also I was under the assumption hard joints make a difference in harshness and I find the oem bushings quite nice being that their molded and don't develop slop. I understand for offroad they give but the leaf springs in the rear are gonna see alot more movement.
 
Last edited:
Goatman said:
I never get the comments about keeping a bushing for DD usage. Why? Who cares? Do you really think there is that much NVH difference between a crappy bushing and a good solid joint?
Click to expand...

Besides NVH (and I agree, so what?), the other common web-wheeler complaint is that 2 hard joints in a link increase stress and will wear much more quickly. So the issue with a DD is that the mileage piles on quickly: 15k mile lifespan may be 1 year in a DD, but 5 in a trail rig.

I have no experience so can't speak on this. What's your take?
 
Super mud said:
I raised my axle side lowers when I built the front axle, along with OTK steering and the track bar mounts to match. That was at 4" of lift. My goal currently is to get the jeep working well for everyday use at a lower height for the 31s. It would be nice to start from a stock one but there is alot into this one and I still wheel it. I do not have drop brackets but thought of pocketing the frame to raise/correct my lower angle. The frame is plated up front currently so I could reinforce it the rest of the way. So at this point the arms should be at stock angles compared to each other and I should further angle them away from each other with either raising the axle side upper or lowering the frame side?

Also I was under the assumption hard joints make a difference in harshness and I find the oem bushings quite nice being that their molded and don't develop slop. I understand for offroad they give but the leaf springs in the rear are gonna see alot more movement.
Click to expand...


If you think increasing the arm angle is a solution, go for it. You asked, I'm taking the time to answer, but it sounds like you had it figured out to your satisfaction before you even asked.

With the LCA's even with the axle tube, all the UCA's do is control axle torque, so you can't get any harshness out of any joint you run in the uppers. Joints don't cause enough harshness on their own to be an issue anyway, unless you're posting on the internet. Steeper control arm angles cause harshness, but you're already deciding that fabbing up a lower mount that is recessed into the frame is the best solution, so I guess harshness isn't really an issue for you.

BTW, do you know if your shocks are OK?
 
Love Richard's bluntness :D

Shocks control the speed of compression, i would have guessed that, but i'm a n00b so what do i know.
 
Goatman said:
Rockclimber has it right, but for the wrong reason. The amount of separation itself doesn't matter, but it gets you want you want. The upper arm angle needs to be less, so either the frame side mount needs to come down or the axle side mount needs to go up. I believe this would help your problem. Don't bother with the calculator, other than just for curiosity, it doesn't really tell you anything about a front application.
Click to expand...

I missed this.

I wasn't very clear, separation does matter, in the context of this suspension. if the
axle side mounts are closer together, and the frame side mounts are still stock distance apart the IC has gone down, if you keep the same amount of separation at both ends, your IC will go up.


Goatman said:
I'd cut off the stock mount, plate the frame, and weld on a pre-fabbed mount of choice with the bolt in the vertical position. Simple, just do a good job of attaching the plate to the existing crappy frame. The UCA mount on my buggy's front 3 link is done this way. You can move the mount downward and rearward while you're at it to get a little longer arm and a flatter arm angle.
Click to expand...
I like that idea, do you run into travel issues running the bolt vertical?

Super mud said:
I raised my axle side lowers when I built the front axle, along with OTK steering and the track bar mounts to match. That was at 4" of lift. My goal currently is to get the jeep working well for everyday use at a lower height for the 31s. It would be nice to start from a stock one but there is alot into this one and I still wheel it.
Click to expand...
if you are going to lower the ride height you don't need to raise the UCA mount at the axle, lowering the body will make the arm flatter.

I do not have drop brackets but thought of pocketing the frame to raise/correct my lower angle. The frame is plated up front currently so I could reinforce it the rest of the way. So at this point the arms should be at stock angles compared to each other and I should further angle them away from each other with either raising the axle side upper or lowering the frame side?
Click to expand...

its not just the angle to each other. its also the angle of the arm itself at ride-height.

also, how hard are you braking. inertia will cause some diving of the front end during hard braking. if you have crappy shocks and springs, that will be increased.

srimes said:
Besides NVH (and I agree, so what?), the other common web-wheeler complaint is that 2 hard joints in a link increase stress and will wear much more quickly. So the issue with a DD is that the mileage piles on quickly: 15k mile lifespan may be 1 year in a DD, but 5 in a trail rig.

I have no experience so can't speak on this. What's your take?
Click to expand...
I have had Currie Johnny joints on all 4 CA mounts of my XJ for the last 2 years. daily driven, 15-16k per year. all 8 joints are still perfectly tight.

the 7/8" rod end on my frame side TB mount has worn out in about 6 months. not sure why, the 3/4" lasted a year in that spot and is now in the axle side mount and still not worn out...
 
I'm not trying to ignore your solutions nor ask you to hold my hand but just make sure I understand the concept your explaining and make it work for my situation. Maybe i'll try 2 hard joints and see how it works. Maybe I'll raise the axle side upper and see if it clears on no lift. But it's all more involved steps and if I could accomplish the same correction to work easier in my case, which is different than most here, then I'm all for it.

I was trying to confirm that having the arms at stock angles compared to each other would correct the geometry or if I still need to make changes to the upper because of some different variables. I don't understand the concept as well so maybe theres something I'm not getting and didn't catch in your explanation. And maybe theres something you didn't know in my case like not having drop brackets.

Yea shocks are brand new and thanks for taking the time to share your ideas.
 
also, how hard are you braking. inertia will cause some diving of the front end during hard braking. if you have crappy shocks and springs, that will be increased.
Click to expand...

Just enough to stop safely but that involves the front end quickly bottoming out after a certain amount of braking. It dosn't compress much until a certain point it just gives. Also coming to a stop the front end will remained somewhat compressed until braking or power is removed (putting it in neutral) but I have noticed that in some other cars too.
 
I understand. Like I said before, you will get SOME improvement if you raise the LCA's at the frame, but it's not a very good overall solution. For less effort, you could change the angle of the uppers and get a better result. For less effort than building frame pockets for the LCA's, in my opinion, you could lower the UCA's at the frame, or change the frame and axle mount on one side and make a 3 link (weld the tube to the pumpkin on that side). Since you have the ability to make changes, to me, those are better changes.

BTW, I have experienced what you are describing, and I had moved my LCA's even with the axle. In my case, I had a 3 link already so I raised the UCA axle mount 2" and the excessive diving went away.
 
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