1973 620, 2 inch drop, now bouncing

[XLT]

I have a 73 620  regular bed that I have been working on with my son.  We have rebuilt most of the  front suspension, added disc brakes, redone the interior, added kyb shocks etc.  We have titan 17 inch wheels for it with 225x45x17 tires at 36 lbs pressure.  i reindex the bars one notch,and added 2 inch blocks to the rear.  I put in energy suspension bump stops an, measured the front drop at 2 and 1/4 inches.  We have about 1 and 1/2 to 1 and 3/4 before the bump stop hits.  I cut the rear bump stops down 2 inches.  I drove the truck for a short period of time and found that it was really bouncy for lack of a better term.  I didn't think that would happened with just 2 inch drop.  The tires are new with 36 lbs in them and maybe that is too much for the light weight truck. The truck also needs to be aligned, but its not bad as far as toe and chamber right now. Any suggestions would be appreciated, I know I can raise the shock towers 2 inches but I didn't think I would have to with this little of a drop.  Or did I do something incorrectly.  thanks  I would post photos but my son needs to help with that.  I will do it later as I kept a photo record of the changes.    the forum has been a wealth of information and yes I did use the search engine and read all.  

[datzenmike]

Run the lowest pressure that the sidewall recommends. The problem is that very low pressure generates heat from flexing but as these are on a much lighter 620 and they are very large and can radiate any heat much easier, you can probably go lower with caution. Check the tires regularly with your hand to feel for warmth, specially on long drives. If they stay cool then you are probably ok.. 

 

Definitely get the toe corrected. That will really chew those new tires up and worse the handling is badly affected and 5x worse in the rain.

[ggzilla]

Yes. 36 psi is for 5000 pound or so load carrying. The sidewall will give the exact figure per tire.

 

Bouncing means going up and down repeatedly. It is controlled by the shocks.

 

If you are hitting the bump stops, that results in a violently harsh ride.

[MikeRL411]

If worse comes to worse a hint from the 1950s.  Filling with Nitrogen, not air, gives a much better heat transfer and the tires will run cooler !  Pure Nitrogen is not as good as the all time champion Helium, but you would not last a quarter mile with Helium.

[mhub91]

I ran into a similar problem, but it wasn't "bouncing" ... It was more of a violent jerking from left to right rapidly at around 45 mph or so and could easily be confused with bouncing. This was due to the alignment being severely altered. When you lower the front end the toe goes waayyyyyy out positively. This can cause the tires to fight each other. Do a quick adjustment of the toe at home using a crescent wrench, vice grips and a tape measure. Get back to us and tell if it worked.

 

PS - is the steering wheel at a different angle now that you lowered it? i.e.  ... was it fading to the right, but now left? or is a really squirly and wanting to grab every rut / pot hole? These are definite signs of a lot of positive toe (front of tires point outward).

[XLT]

I took the advice and lowered the tire pressure and that made all the difference, I plan on having it aligned as soon as I finish some other improvements, don't use it as a daily driver but I really appreciate the

suggestions, I will add photos when I can get my kid to show the old man how to.  This forum has been a great source of info and I do appreciate it