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Front End Shimmey

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Hi all;
I've searched the threads but can't find an answer to this hypothesis I have. I'm working on the 68. Car tracks fine, is smooth, no problems UNTIL I hit a bump or rough spot in the road. When this happens, the whole front end shakes BAD! Have brand new tires and are balanced fine. Again, on a smooth road everything feels tight. The wheel bearings are fine. Now, the control valve leaks so I have the system dry right now. However, I don't think it being dry is making this happen as the 81 had a leaky system and I drove it awhile with no ps fluid and didn't have this phenomena.

So, my hypothesis is that the cylinder is no longer functioning... in other words the seals inside are broke and allowing extra movement in the system when there is a perturbance. DO YOU GUYS CONCUR? The rest of the front end isn't perfect but isn't bad. There isn't anything obvious or loose as far as balljoints, tie rods,etc. Front end feels pretty tight otherwise.

Thanks!
 
W

WhiteKnight

Guest
Does the shimmy transfer to the steering wheel?

I think you are on the right track.. as some dampening is provided from the control valve and cylinder.

I saw an article somewhere on not running without ps fluid.. let me find it.. here it is.

http://www.docrebuild.com/dr-r-web/tip20.html
 
P

purpleRac3r

Guest
It's possible the control valve may be worn, contributing some slop to the system, made more no noticeable by the lack of damping from the cylinder. My '74 has this condition, though I've kept the fluid level up. Next week I'll be installing a Steeroids power conversion kit, so hopefully my shimmy will go away.
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
Impact-induced shimmy as you describe is usually a result of worn ball joints and/or tie rod ends; in your case it's probably aggravated by running a P/S unit with no fluid, which causes slop in the ball stud connection at the control valve - the ball stud is normally held tight by hydraulic pressure.

Flabby shocks can also cause vertical impact shimmy; does it feel like it's lateral (kicks the steering wheel back and forth) or the front wheels bouncing up and down?

:beer
 

bossvette

Gone but not forgotten
Joined
May 19, 2003
Messages
3,233
Location
West Unity Ohio
Corvette
1968 1997
I had a 59 Impala that did that until I replaced the shocks.
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Impact-induced shimmy as you describe is usually a result of worn ball joints and/or tie rod ends; in your case it's probably aggravated by running a P/S unit with no fluid, which causes slop in the ball stud connection at the control valve - the ball stud is normally held tight by hydraulic pressure.

Flabby shocks can also cause vertical impact shimmy; does it feel like it's lateral (kicks the steering wheel back and forth) or the front wheels bouncing up and down?

:beer

Definitely a kick back and forth...... almost takes the steering wheel out of my hand actually. Didn't think about the shocks but I'm sure they are old. I'll have to check that out - seems like an easy fix. AND, I'll quite driving it fluid empty and fix it... I just want to determine what is leaking for sure! I'll do that this week!
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,457
Location
CenCoast CA
Corvette
71 04 12 19
A "dry" power steering system isn't going to cause front-end "shmmy" unless there's a problem in the control valve or the relay rod.

You need to inspect all four ball joints, the control arm bushings, tire rod ends, relay rod, idler arm and shock absorbers. Also, check the frame and the front cross member for cracks. Replace any worn parts and repair any cracks, align the front end then road test.
 

chevyaddict

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Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
I take it the hood latches worked out OK then?

I don't know!!!! Can't seem to get past other issues to find out! They will certainly bolt up so I suspect yes... I'm actually afraid that if I put them on and close the hood it'll not open again.... I need to better understand how the cable works since its very different than the 81... its not intuitive to me just yet but haven't really examined it closely to figure it out!!!
 

chevyaddict

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Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Don't forget the idler arm, it will give some shimmy affects also.

Yeah, this was the first thing I looked at aside from the bearings and it *appears* to be in good shape but it is hard to know by tuggin' and pullin'..... thanks though!
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
A "dry" power steering system isn't going to cause front-end "shmmy" unless there's a problem in the control valve or the relay rod.

You need to inspect all four ball joints, the control arm bushings, tire rod ends, relay rod, idler arm and shock absorbers. Also, check the frame and the front cross member for cracks. Replace any worn parts and repair any cracks, align the front end then road test.

Yeah, I knew that... and I have inspected all these parts except the shocks... I haven't looked for cracks so that is certainly something to inspect for. But I guess all these posts then are dominately discounting my hypothesis about the cylinder being the main contributor..... Unfortunately I don't have the money to rebuild the front end at this time...spent too much money on bodywork, tires, and other misc parts recently (and I'm also redoing my 81 and 71 Camaro).... DARN IT!!!!!!!!!!!!! Thanks for the reply though!
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Impact-induced shimmy as you describe is usually a result of worn ball joints and/or tie rod ends; in your case it's probably aggravated by running a P/S unit with no fluid, which causes slop in the ball stud connection at the control valve - the ball stud is normally held tight by hydraulic pressure.

Flabby shocks can also cause vertical impact shimmy; does it feel like it's lateral (kicks the steering wheel back and forth) or the front wheels bouncing up and down?

:beer

Ok, just went for a test drive with the ps fluid full. First, comment is how nice to be able to easily steer! ;) I also determined that the return PS hose is leaking, not the control valve or cylinder.... its leaking high so it made it look like these parts were leaking. Easy fix - already ordered the four hose kit because I can't stand doing things in pieces - might as well replace them all.

So, I drove it full of fluid though and the shimmey and shake still happens, again, only when hitting a bump. I'm leading to trying the shock hypothesis as this isn't an expensive troubleshooting item so that is what I'm gonna try first. Lets hope. *If* that doesn't work then it will have to wait as I plan on buying that suspension conversion package and will rebuild the entire front end then! I just got done rebuilding an entire front end on my 71 Camaro last month and its EXPENSIVE!
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Still think its an idler arm

In my experience in the past when these go you can jack up the car and make the passenger side move while the driver's side doesn't and then you see the slop in the idler arm. Its solid as a rock so I doubt that is it... unless you've had a different experience?????
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
get it fixed yet??/ need results. what fixed the problem

Nope... its gonna be awhile before I can stick any more money into this car... with major body work, new tires, and a multitude of other fixes I've poored around $6000 in it in two months and I'm broke! :) But when I do I'll certainly post!
 

6880 Mike

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Jun 30, 2006
Messages
2,723
Location
The Bluegrass State
Corvette
1968 convertible; 1980 L-82
Bump Steer. '68s without power steering had what amounted to a shock absorber to eliminate a little of this. On PS cars, the fluid in the ram absorbs most bump steer shock.
:)
 

LVMYVT76

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Joined
Apr 21, 2006
Messages
664
Location
springfield, mo
Corvette
1976 medium blue
I just took one of our company vehicles to Ar. It shimmied when the brakes were applied. Have you checked the rotors??
 

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