hey all, i'm new to this forum and i'm looking for some help. i have a 99 standard cab shortbox with a 5.5 fabtech lift kit and 33 inch tires. i'm noticing a serious hop or bounce or just a bad vibration in 4 wheel drive. i have the stock axles and gear sets... 3.54 front and 3.55 rear. both diffs are open. any tips or suggestions would be a great help. thanks alot

 

Is the vibration during acceleration or constant? A little vibration might be expected if you have a lift kit, I stress a little vibration. Are you running lift blocks out back? There could be a number or reasons for your vibration.

 

i think i have blocks and springs. it kind of feels like its binding in 4x4</P>

 

Have you checked the driveline angles? I'm no expert but I have always heard that you cannot haveexcessive angles and that you should use shims to correct themfor lift kits.

 

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That could be a possiblity, althoughFabtech has not been known for extremedriveline angles. Then again, the trailing arms are pretty short in relation to theangle increasegained from the lift kit. Check your drivelines, front and rear driveshafts and yokes as well. There should not beexcessive play ineither one. Last time I heard this problem was from a Ram with over120K miles that needed a tranny rebuild. </P>

 

the driveline angles are good. the fabtech kit comes with new longer control arms for the axle that bolt on back at the crossmember in the middle of the truck. there is no looseness in the u joints and from what i can tell there are no stiff spots. i've been told that the 3.54 gears in the front will cause a binding effect with the 3.55 gears in the rear when in four wheel drive with the larger sized tires. any one have any experience with this?

 

anybody?

 

Silly me but have not heard of 3.54 gears in the front of the ram?? I do know that the gear ratio must be matched!! front and rear. <edited><editID>nuckingfuts</editID><editDate>38020.0295486111</editDate></edited>

 

I believe Chrysler uses a 39 tooth ring and a 11 tooth pinion in this axle. This would give a mathimatical gear ratio of 3.545454545454545454545...:1. Most will round this up to 3.55 while some may round down to a 3.54. I am sure that Chrysler has the same 39/11 gears in both ends of your truck. </P>


Depending on how many miles are on the tires I would look at the wear on both ends. If the rear tires are evenjust a little more worn than the front or viseversa then it will make a difference (diameter of tire will be different).I once read in a road test of a Porche Carrerra 4that was having a problem just like this. It was the rear tires being a slight bitmore worn than the fronts.As soon as they put new tires onit the problem was solved. This is a good example as to why to rotate those tires every 5K mikes. Also, check the tire pressures. If one end is lower than the other it will have a smaller diameter and create binding when in 4WD.</P>


Eric</P>

 

Hey eric, good job on the explaination. I thought it odd that he mentioned specifically 3.54 front/3.55 rear. I rationalized that perhaps he wasn't sure that both must match. Your comparison to the porche is a bit skewed due to the fact that it is awd. Wear patterns will always be different with awd versus part time 4Xespecially in that particular vehicle. It is difficult to envision exactly what the problem is here but I would guess the binding happens only when turning sharply if indeed the "binding" is caused by the diffs. As always there can be numerous explanations to the problem, wheel bearings, u-joints man o man this could go on for awhile.