Cadillac & LaSalle Club Discussion Forum

Cadillac & LaSalle Club Forums => Technical / Authenticity => Topic started by: Dan LeBlanc on May 09, 2019, 09:28:05 PM

Title: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 09, 2019, 09:28:05 PM
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?
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Scot Minesinger on May 09, 2019, 10:33:50 PM
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).
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 04:26:41 AM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 10, 2019, 08:16:01 AM
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.

Title: Re: 1977 Fleetwood Rear Suspension
Post by: TMoore - NTCLC on May 10, 2019, 09:09:06 AM
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 -

Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 09:13:38 AM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 10, 2019, 09:28:14 AM
Let us know how it works out.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 10:25:06 AM
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. 
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 05:49:15 PM
Good call, gentlemen. It is the shocks.

Now, keep air shocks or go gas charged? Disabling that level control is mighty tempting.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 10, 2019, 05:58:20 PM
Quote from: Dan LeBlanc on May 10, 2019, 05:49:15 PM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 06:13:02 PM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 10, 2019, 06:23:06 PM
I'd just leave everything in place for now and install the shocks you want.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 10, 2019, 06:32:09 PM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: maximln on May 17, 2019, 02:23:55 PM
Are you still using the original vacuum operated compressor?  I used to rebuild those things.  They always fascinated me! lol

Max
Title: Re: 1977 Fleetwood Rear Suspension
Post by: TJ Hopland on May 19, 2019, 08:53:24 AM
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?
Title: Re: 1977 Fleetwood Rear Suspension
Post by: cadillacmike68 on May 19, 2019, 11:20:08 PM
Quote from: TJ Hopland on May 19, 2019, 08:53:24 AM
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.

Title: Re: 1977 Fleetwood Rear Suspension
Post by: Scot Minesinger on May 20, 2019, 08:22:17 AM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: TJ Hopland on May 20, 2019, 11:00:08 AM
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?
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 21, 2019, 09:18:07 AM
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.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 21, 2019, 04:08:34 PM
Unless the car is sitting abnormally low in the back, or trim is uneven from one side to the other, leave the springs alone.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 21, 2019, 08:36:38 PM
After seeing other tri-7s over the weekend, it appears to be sitting normally. Should be fine.

Title: Re: 1977 Fleetwood Rear Suspension
Post by: Series75 on May 23, 2019, 09:17:49 PM
Air shocks are inexpensive, deliver a proper ride height and drive out right.  So why not go old school, bypass the leveling system, route the 2 Lines to a tee and install the fill valve behind the rear license plate.  These factory leveling systems blow.  Hate them.  I reworked the 66 and the 99 Fleetwoods with delco aftermarket systems.  The 66 is a vacuum system the 99 has an electric pump now in the trunk with a glove box remote control.  Think delco "jac pak".   Tom CLC 6866
Title: Re: 1977 Fleetwood Rear Suspension
Post by: The Tassie Devil(le) on May 23, 2019, 10:12:01 PM
The biggest problem with the single-fill air shocks, or any single-fill air suspension is that unless one installs a stop valve in the fill line, and activate it after filling, then as one goes around corners, the pressurised air from the outside shock will transfer to the inside shock, thus increasing the lean of the body.

Would be nice if there was a way of transferring the air to the outside shock to assist in leveling out the vehicle as it traverses the corner.

Bruce. >:D
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Glen on May 24, 2019, 02:44:22 AM
Quote from: The Tassie Devil(le) on May 23, 2019, 10:12:01 PM
The biggest problem with the single-fill air shocks, or any single-fill air suspension is that unless one installs a stop valve in the fill line, and activate it after filling, then as one goes around corners, the pressurised air from the outside shock will transfer to the inside shock, thus increasing the lean of the body.
Bruce. >:D

Is that really a problem?  The hose that feed the shocks is 1/8th  OD.  The ID is a lot smaller.  I would think that you would have to be in a hard turn for a long time for this to be a problem. 
Title: Re: 1977 Fleetwood Rear Suspension
Post by: The Tassie Devil(le) on May 24, 2019, 04:03:57 AM
It is a problem down here where I live, the place of mountainous winding roads, a bit like Hawaii.

But, you would be surprised just how much air would travel from side to side to create an imbalance.

Some people slow down when rounding corners, but not me.   I love to "drive" around corners.

Bruce. >:D
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 24, 2019, 08:21:23 AM
Quote from: The Tassie Devil(le) on May 23, 2019, 10:12:01 PM


Would be nice if there was a way of transferring the air to the outside shock to assist in leveling out the vehicle as it traverses the corner.



You exactly hit on what Cadillac addressed many years ago. On OEM air shocks (when equipped with Level Ride), the air line feeds only one shock; from there, another line runs from that shock to the other thus maintaining equal pressure between the two rear shocks at all times.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: The Tassie Devil(le) on May 24, 2019, 08:39:57 AM
I agree, but when the centrifugal force of a vehicle going around a corner causes the outside of the vehicle to "drop" down, and the opposite side of the car rises, raising the length of the Shocker, this creates a lesser pressure within, and the air from the compressed shocker equalises to the other side, encouraging the increase of the roll of the vehicle as it traverses the corner.

In the case of a Roundabout, where the vehicle is cornering for an extended period of time, the air transfer is greater.

Bruce. >:D

PS.  Yes, we have roundabouts in Australia.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Series75 on May 24, 2019, 11:21:23 AM
Really important points when Dan is headed thru the S curves at Limerock park at 82mph, getting around town, maybe not.   Tom CLC 6866
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 24, 2019, 03:27:24 PM
anybody who's seen me drive an old Cadillac knows I'm not giving it all she's got in the turns (and on the straightaways too).
Title: Re: 1977 Fleetwood Rear Suspension
Post by: maximln on May 24, 2019, 05:32:40 PM
Quote from: Dan LeBlanc on May 21, 2019, 09:18:07 AM
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.

The compressor is very easy to rebuild.  There are usually only 2 parts that fail.  The piston & the rubber diaphragm.  The piston gets worn out & the diaphragm will get a tear in the rubber & leak.  I'm sure the biggest problem is being able to find those parts somewhere.

Max
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 27, 2019, 07:36:44 AM
I had the car out on Saturday, finally.  Put more miles on it in one day than it got in the last 5 years.  Rode just fine with conventional shocks.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Scot Minesinger on May 27, 2019, 08:20:25 AM
Dan,

That is how I would do it.  Many rave about their 1977, 78 and 79 large RWD Cadillacs (and they should) most of which are equipped without ALC.  Back in the 1960 and 70's it was not uncommon to see the family sedan driving down the highway with too much stuff in the trunk and the rear end sagging, hence ALC cured that.  Collector cars are not driven that way today, so in the RWD cars ALC is not essential.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 27, 2019, 10:14:49 AM
To this day I've never seen in person a 1977 DeVille equipped with Level Ride (standard on Brougham, Eldorado, Seville & Limousine) which was also the last year for the vacuum system. Seen a few DeVilles so equipped from 1978 & up but I would guess the number was far less than 50%.

Level Ride became standard on DeVilles in 1984.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: TJ Hopland on May 27, 2019, 12:08:27 PM
When I was shopping for and messing around with 77-79's I would say more than half of them I saw had ALC.  Out of maybe 30 cars that had it none of them worked.  If it was the vac system it appeared to be the compressor that wasn't working.  If it was the electric it seemed to be the control module that wasn't working.   I was not looking for higher end cars, if I had been maybe I would have found some that worked.

So how did this magic factory valve thing worked that kept the air from moving side to side?   They had to be passive, no electrical modules or sensors were involved.  They could not have been check valves because there was only single lines involved and the air had to be able to move both directions depending on what the main level control valve was wanting them to do. 

I once worked on a car where the guy had it set up with solenoids and switches to isolate things or combine things as needed which I thought was cool and was planning on doing it to my cars but I could not tell any difference with the sides connected or not connected so I didn't bother. 
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Eric DeVirgilis CLC# 8621 on May 27, 2019, 12:20:05 PM
Quote from: TJ Hopland on May 27, 2019, 12:08:27 PM
When I was shopping for and messing around with 77-79's I would say more than half of them I saw had ALC. 

Level Ride was standard on all models except DeVille (and Cimarron) 77-83.

On 77-79 DeVille I have never found Level Ride to be a common option.

Title: Re: 1977 Fleetwood Rear Suspension
Post by: Dan LeBlanc on May 27, 2019, 12:27:48 PM
I can see the ALC as potentially more trouble than it's worth.  The only part of the equation on my car that had not been touched was the compressor.  Of course, that's what failed.

As I mentioned, the springs that were on the car when I got it (could be factory) with conventional gas charged shocks gave an acceptable Cadillac ride and upon filling the fuel tank, there wasn't much of an appreciable drop in the rear end.

Boy the car ran great though.  I understand why there was a Super Snooper K-band radar detector installed on this car when new - they do creep away on you.  Our local highway speed limit is 70 and looked down a couple times and saw that I crossed the 80 mark.  People were definitely looking - must be the triple black!

One more thing to do before summer - that's isolate a wind leak around the rear door.  I think it's the seal between the operable and fixed window.  The plastic trim seems loose and sounds like it's acting like a wind scoop and admitting air between the window frame and glass.
Title: Re: 1977 Fleetwood Rear Suspension
Post by: Scot Minesinger on May 27, 2019, 01:24:09 PM
More trouble than it is worth is exactly right IMO.

Glad you are enjoying your Cadillac now!