HELP... rear suspension question
 

A buddy called today. He has a stock 56 Chevy frame - modified with triangulated 4 bar - Air bags.. This car is BEAUTIFUL... everything on it is PERFECT.

Everything except - he's asking me about a "wiggle" in the rear. When he steps on it a bit - or brakes - he says it sashays around "back there" -- is his description. So he's thinking it's the airbags -- and I'm saying "I don't think so" - they just go up and down = not back and forth...

There is no panhard bar - and for a street rod - and triangulated 4 bar - I wouldn't think a panhard would be required...

Anyone have any ideas what I should help him look for? Measurements I could take?

I was going to put it up on the lift == and put a laser pointer / level that I have on it - mark the point on the floor - raise and lower the rear and check for how much it moves side to side.... Look at all his bushings... and measure the degree of the arms etc. But from there - I'm not sure what else I'd do.
:_paranoid

was it always like this or something that just came up?

i'd be looking for something loose or something that came out of adjustment.

I doubt its anything airbag related. Is it an air bag and shock set up or airbag/coil over type?

vince

Vince -- I believe it's always been this way... They are air bags with separate QA1's --- NO COILOVERS -- just shocks and airbags...

I just called him and questioned this so I could respond. He says this "weird movement" all started with the addition of the triangulated 4 bar and bags... well -- DOH -- so in other words - it's been this way since the suspension was done. (I have to forgive him - he's 73 years old...). He then tells me he has a "bind" on the left side... This is new info to me... and that right away tells me he's got one or more of the bars out of whack somewhere.

Think I'll put the POS in the air - disconnect the bags and shocks - use my hydraulic tranny jack to raise and lower the rear a few times and find this binding. I also have a laser - which will let me mark a "point" - and see what "gives" when she's raised and lowered.

interesting, curious to see what type of system it is.

maybe a geometrical misalignment or a link convergance quandry. :willy:
yeah see what it does, look for back and forth movment
please post a few pictures, like to take a peek.
vince

Greg,

In most of the research I did on the triangulated 4-link the angled bars should be at an angle of at least 30 degrees to the frame rail. Less than that and you are significantly reducing the lateral locating ability of the system. Post up some pictures, I am intrigued with this one. :thumbsup:

Sounds like you've probably figured it out already. A bind in the rear suspension will throw everything off kilter. I'd check the simple stuff like tire pressure, bolt torque, and alignment first.

CHAD -- Thanks for that info - I would have done some research and probably found this info - but it's what I was looking for without trying to become a suspension master!

I will check all of the dimensions.

TODD -- I agree about the bind. He had failed to mention that little ditty when we first started talking about this. That was a big AH HA...

I'm going to have to check all of the linked convergence quandrys in this install! :rofl:

This is one of those "helping a buddy" things that I actually ENJOY - I always learn something from it - and I have a brain that is wired to solve (or try anyway). This is a really really beautiful car - that was home built - including the paint (over a 10 year period) = where the owner/builder was never truly satisfied with the end result and is now going back and upgrading and sorting out a list of "issues". He saw my 8 stack and went crazy... had to have it - which led to a new AutoRad radiator and core support (as long as he was there)... and then we started to work on his brakes (that didn't work at all)... he has 6 piston Wilwoods and the front rotors had never seen pressure from the pads! Serious! Ditched the vacuum pump (he hated the noise) and P/B booster - installed a 7/8 Wilwood manual - changed the pedal ratio - and bingo! Got that fixed. I don't think that BOTH sides of the caliper were ever bled... Now on to the "wiggle"...

The triangulated bar end links really take a beating. A panhard bar is a better set up in IMO for reliability.

It's supposed to be dry and somewhat sunny here (the Great Pacific NorthWET) by the end of the week -- so maybe I can get him to come over and we'll lift it up and give everything a look see..

Nobody drives their stuff in the wet up here... so we have the added disability of the weather to contend with. First up will be to discover the mysterious "binding". I'll get pics then and post em. :cheers:

Its dry and sunny right now Greg..... at least for the next 20 minutes.:_paranoid