Rear end jacking on brakes

[ironbenderii]

Hi guys. I"ve got an early Bronco w/ a 4-link rear. I'm running 2.5" King coilovers that are attached to the lower links about a foot away from the axle. 350 over 500 lb springs. Factory valving in the coilovers.

The problem that I'm having is on braking the rear end lifts. On hard braking it really lifts. The front end is part of the problem, it's got a pair of crappy shocks and the front end dives on braking. I don't think that is all of the problem though. The *** end is sitting a little high, I'm planning on brining the 500 lb spring down to a 450. Also, running 150 lbs. of nitrogen, considering bringing that down to 100.

So here's my question. I've done a lot of reading on the valving of shocks (lots on this site). Do you think that not having enough rebound dampening (too fast) could be causing some of the problem? The rear pogo's a little on bumps (first bump and a series).

I'll be tearing the shocks down and playing with the valving over the next couple of days, any advice you can give to save me some time would be great.

Jack

[maxyedor]

Souds like you need a little more rebound damping to kill the pogo-ing in the rear. The brake dive comes from the front more than anything. Every car/truck does it, it's just more noticeable in some. When you brake most of the weight transfers forward, and on a soft desert suspension you get crazy amounts of dive. You can try a little more compression and or a stiffer spring up front, and possibly a prroportioning valve to shift a little brake bias to the rear. Other than that I would call Ricor, their shocks aren't cheap, but they use similar valving to the Curnutt "stable platform", they can make a HUGE impact on your trucks handling.

[Moss2]

Hey Jack

Seems like more of a linkage geometry issue than valving. You can make it more driveable by dialing in the shocks but it will still jack up as high if you stay on the brakes for a couple seconds. If the links are pretty steep angle at ride height it could be tough to get rid of. Of course I havent built any linked rigs so take that with a grain of salt. See ya in Baja.

Ken

[ironbenderii]

Hey Ken. Actually the links are nearly flat, top and bottom. I'm sitting at about 105% anti-squat.

[ACID_RAIN28]

The bronco is still I-Beam right?? Most of the I-beam trucks I have seen always have a tendency to dive the front and jack rear some less than others but those are set generally at a lower ride hight. How high does it sit off the ground, IE lowest chassis point??

[ironbenderii]

It's an early early bronco (first generation) so it has a solid axle. It's running about 5" of lift, rear has like 6 or a little more lift (need to change springs out). It's a top-heavy truck for sure, which doesn't help things.

[Triaged]

Your problems are for the most part (in order of worst to not noticeable)
1: Very high Center of Gravity
2: Very short Wheelbase
3: Everything else.

Chances are that you already have a good amount of anti-dive up front and anti-lift in the back. Any more and you would most likely compromise handling in other areas. You could stiffen up the springs on both ends but again it's a compromise. Same with rebound damping (which wouldn't change the amount of lift just take longer to get there).

[ironbenderii]

Yeah, here's where I'm at. I am lowering the rear down so that it sits lower than the trucks center of gravity. Hopefully this will help drive the weight down more than up (currently the way it's sitting it starts off over the center and gets worse when the front dives).

To lower it I got some shorter coilovers (had too much droop anyway). King is also stiffening up the valving quite a bit, which should help. I'm also going from a 350/500 spring to a 300/400 spring.

I should get that all in next week and get to test it. This is one of our chase trucks for the 1000 so I need to have it all dialed in before we get there. The owner/driver is going to be stationed @ Mike's so he'll need a good working suspension :).

Jack