Front end bounce when braking

64 cj5, D27 front axel with the disk brake swap. tires are a set of donated 31's with 50% tread on steel rims, but are balanced.

driving down the road, jeep is straight and smooth - doesn't shimmy, pull, hop or bounce.

Speed 25 mph or less and when the brakes are applied, I usually get a pulsating in the front end, I suspect I need to replace the rotors. Over 30 mph and braking takes on an entiely different experiance, if I attempt to use just the brakes and not down shift, I end up having the front end bounce and I mean BoUnCe ReAly BaD! It literally feals like the front end is pulling off the jeep, which it is not, I have looked over everything looking for loose or broken stuff.

To stop, when it starts to bounce, I let off the brakes and reapply a couple times, the bounce settles down and I am able to stop, being aware of the situation has me driving very carefully, I owuld like it fixed.

I suspect the rotors are warped and need to be replaced. a budy who observed the bounce from a vehicale behind me, suspects a front end allignment - but I do not see anything to adjust in an alignment.

I have a complet set of stock tires mounted on rims, I was thinking of putting them on to see if it changed things as far as the bounce.

Next is to replace the rotors - need the cash on hand to do that. Any other suggestions?

 

i'm thinking time for new front shocks.

 

If the brakes aren't grabbing, then I'd think about the suspension, or whether you need a proportioning valve with the new disk brakes. Rear brakes in good condition? The bounce could be weight transfer due to too much braking on the front. When the front tires start to slide, weight transfers back to the rear, causing a bounce (just speculating). You're sure this is not from your braking force changing (ie your body movement) as the nose dives? What happens if you lock up the brakes? Do all 4 wheels lock up?

You should be able to look between the rotors and the pads as the rotor turns with the tire off to see if the rotor is warped.

You can adjust the suspension toe-in easily, and the caster pretty easily (with shims). Loss of control due to improper caster is a common problem after installation of lift springs, but that usually affects steering. The camber is welded into the housing, and can't be easily adjusted, though I think you can install special ball joints that let you adjust the camber.

 

Shocks are new

 

I think Tim nailed it with lack of proportioning valve, though rotors might also be warped. Your factory drums were "proportioned" by having larger bore brake cylinder on front vs back. On my 73 there is no valve of any sort between front and rear circuits (two-barrel master cylinder) Later CJ5 models (74+ I think) with drums had a brass block with a spring loaded plunger that shifted front or rear to help isolate a brake line rupture to either front or rear circuit. This valve also had a switch to energize a brake warning light in speedo. Later still there was a valve that delayed rear brake slightly after front brake to help prevent rear tire skid due to rapid weight tranfer (I think that's how it worked). That was the last version of drum brake valving, I think. I don't think these drum brake do-dads were "proportioning valves" per se, because the proportioning effect was still accomplished by different sized brake cylinders. However, I'm pretty sure there was never a disc/drum combo WITHOUT a proportioning valve because drums and discs require different pressures to do their thing.

 

new rotors - 110 clams

what a differance

 

If you lightly apply your breaks and can feel a pulsation through the peddle, then you have warped rotors.