1977 Fleetwood Rear Suspension

[Dan LeBlanc]

I've got a strange issue with the rear suspension in the 77.

I jacked up the rear, put Jack stands under the frame, jacked up the front, and took the tires and had them rebalanced today. Came home tonight, mounted the tires, and pulling out of the garage, I noticed no travel in the rear suspension. None. The only movement if I try to articulate the suspension with a knee on the bumper is the squish of the tires.

Crawled underneath, can't see anything obvious. Bushings look great. Shocks are new AC Delco. ALC is connected, ride height unit is a rebuilt unit from Ted Holcombe. Car is sitting level on the ground. The rear suspension just doesn't move.

With the frame supported, if I lower the Jack, the rear axle will drop.

What am I missing here?

[Scot Minesinger]

Dan,

Did I get your meaning that with the back of the car raised, and jack under rear axle raising and lower the jack, the suspension compresses and un-compresses, but when the tires bear the weight of the car the rear suspension is locked?

With tires on the ground if you slip the jack under the rear axle does the car raise as is suspension is locked?

I probably would be looking at a faulty set of new shocks that locked in place.  You can easily check this out by disconnecting bottom of one shock and see if the suspension travels.  With modern cars if you leave the suspension not compressed overnight as you did, this also happens (happened to my friend's Suburban).

[Dan LeBlanc]

Hi Scot

Yes, if I put a Jack under the rear differential,  I can raise the car up immediately. Support the frame, remove the Jack, the differential lowers.

Basically the suspension won't compress beyond normal ride height. If I sit on the bumper, and that's a lot of weight placed on the rear of the car, the tires squish and that's it.

Yes, the suspension was left hanging overnight. I didn't even know that shocks locking in an overextended position was a thing but seems plausible and easy enough to check.

[Eric DeVirgilis CLC# 8621]

Sounds like the shocks locked up. I once had a similar situation with a 2001 DeVille. I have no idea what causes this nor would it have even occurred to me such a thing was possible but that's what I was told by the shop.

Disconnecting the air lines from the rear shocks had no effect. All was well once the rear shocks were replaced.

 

[TMoore - NTCLC]

Agree - locked air shocks.  I have had it happen before.  Jacking instructions for the replacement shocks warn that shocks must be kept under pressure during jacking.  I once had the rear of one of my cars up to replace the coil springs, and once I got everything back together and took it for a test drive, I was dismayed by the ride - it was as if the the coils were solid and the car rode like a tractor.   Replaced the air shocks, and everything was back to normal.  These were the replacement Monroe air ride shocks, but I understand that it can happen with the Delco and Gabriel air shocks as well -

[Dan LeBlanc]

Wow.  Great to know that I'm not alone.  I'll do as suggested later when I get home from work - ie., disconnect the rear shocks at the rear axle and see if I get my travel back.

[Eric DeVirgilis CLC# 8621]

Let us know how it works out.

[Dan LeBlanc]

This must be an air shock thing as I've never had conventional shocks do this.  If that's the case, I may replace the air shocks with conventional. 

[Dan LeBlanc]

Good call, gentlemen. It is the shocks.

Now, keep air shocks or go gas charged? Disabling that level control is mighty tempting.

[Eric DeVirgilis CLC# 8621]

Good call, gentlemen. It is the shocks.

Now, keep air shocks or go gas charged? Disabling that level control is mighty tempting.

I guess it depends on how important load leveling ability is going to be, ie: how often the car will be driven with a lot of extra weight and how tolerable the sag will be. Personally I can live without level ride but I've noticed just a tankful of gas can make a difference.

[Dan LeBlanc]

That's the thing. In the last 15 years of antique vehicle ownership, I can count on my fingers the number of times I've had passengers in the back seat and I don't carry a full trunk of stuff.

Current thought process is to remove all of the components, box them up, and send them for reconditioning at a later date if I choose to restore functionality to the system.

The rear springs were replaced at the same time as the shocks, so they should hold up ok.

[Eric DeVirgilis CLC# 8621]

I'd just leave everything in place for now and install the shocks you want.

[Dan LeBlanc]

Decision made. I just did the compressor output test in the FSM and it's not working. Made that one real easy.

Perhaps that's what got me in this mess. AC Delco recommends a minimum pressure of 25psi for the shocks. There is almost no air in the system.

[maximln]

Are you still using the original vacuum operated compressor?  I used to rebuild those things.  They always fascinated me! lol

Max

[TJ Hopland]

Interesting.   I have had a lot of cars with air shocks and I assume at some point I must have let them sit fully extended.  Apparently I have always had air in em.

So the air shocks must have some sort of internal check valve sort of thing in them that gets stuck so when they start with no pressure then suck air in when they get fully extended the air becomes trapped?  No more air in or out?

Or is is something like the air bag gets folded over and jammed mechanically? 

Or is there something different about the shock part and it has nothing to do with the air section other than something about the air section changes the design of the shock section?

[cadillacmike68]

Interesting.   I have had a lot of cars with air shocks and I assume at some point I must have let them sit fully extended.  Apparently I have always had air in em.

So the air shocks must have some sort of internal check valve sort of thing in them that gets stuck so when they start with no pressure then suck air in when they get fully extended the air becomes trapped?  No more air in or out?

Or is is something like the air bag gets folded over and jammed mechanically? 

Or is there something different about the shock part and it has nothing to do with the air section other than something about the air section changes the design of the shock section?

TJ,

This does not apply to the Eldorado Broughams or the mid-late 50s air suspension (although it might partially apply).

Cadillac's Auto / Electronic Level control used three main components connected by high pressure lines. Up front was a pump, initially a vacuum driven pump, later electric, that pumped air into the lines as needed. In the back was a control valve that linked the axle to the body. When the body got too close (bigger load in car - lower ride height), the control valve opened one way and compressed air from the pump went to the shocks until the car reached the proper height, then that valve closed. If the link got too far apart, (empty trunk, no passengers, etc.) a different valve opened to bleed off air from the shocks until equilibrium was once again reached. The shocks did not have open and close valves, only a single air line to them.

[Scot Minesinger]

Dan,

Nice to see you Sunday in Maryland.  Yes, I would replace the rear springs and shocks with DeVille standard issue and be done with it, leaving in place the standard ALC (air lines and all, but plug vacuum lines in case it ever leaks) in the event anyone is ever interested in restoring it.

[TJ Hopland]

What I was asking is how does the shock fail the way they did in this case?    They way I read it having them fully extended with no air pressure somehow caused them to have limited travel.   What is causing this limited travel?   Is there air trapped in there somewhere?  Or is it mechanical in the air bladder the way it folds and stacks?   Or is it something in the shock part?

[Dan LeBlanc]

Just to shed a little more light on the situation - sorry, I haven't been around much lately.

When the car was gone through before I got it, a rebuild level control valve was installed in the rear with a new set of AC Delco air shocks.  Upon removing the air shocks, I found them to be completely deflated.  Since AC Delco recommends a minimum 25psi for the shock to operate, that could have been an issue.  I noticed the car sits slightly higher than before.  I haven't driven it yet because I was busy preparing for the trip we just got back from.  Road test will be later this week to see how it rides with the current springs.  I rarely have back seat passengers, never jam pack the trunk, nor do I tow a trailer, so it may be fine for the interim.

One odd thing is, I can completely extend and retract the shocks out of the car.  That leads me to believe that the shock may have been too long.  The system must have been pressurized at one point if the suspension worked properly.

I may send out the vacuum compressor and get it rebuilt if I can find someone knowledgeable.  Jury is still out on that.

[Eric DeVirgilis CLC# 8621]

Unless the car is sitting abnormally low in the back, or trim is uneven from one side to the other, leave the springs alone.