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Ride Leveling systems 77 vs 78 Eldorado differences?

Started by dennisspeaks, January 31, 2021, 07:14:16 PM

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dennisspeaks

What is the difference for the ride leveling system for a 77 Eldorado vs 78 Eldorado?  My friend Bruce was telling me that earlier models had a vacuum system and later had electric.

Is one better than other especially when it comes to repairing?

Thanks,

Dennis 

CURRENT CLASSIC CARS
1939 Cadillac
1976 Eldorado convertible
1978 Toronado XS
1994 Deville
1989 Fleetwood
1989 Town Car
1982 Mark VI

PAST CARS
1978 Biarritz
1978 Eldorado
1978 Biarritz
1978 Biarritz
1974 Eldorado - RIP
1976 Eldorado Vert
1975 Sedan d'Elegance
1990 Sedan Deville -gave to son
1988 Fleetwood Brougham - gave to daughter
1968 GTO
1965 Olds 442
1975 Caprice Classic Sold

79 Eldorado

Hi Dennis,
I don't know much about the systems earlier than 1979 but the system used in 1979 was close to systems at least as new as ~1997. The Pontiac Transport is the 1997 vehicle I'm thinking of specifically. They dual purposed the level ride compressor as a sports ball pump and even used it in TV advertising.

So I suspect one of the systems you are referring to is likely similar/the same as the 1979 system. The car has an air compressor under the hood with a nylon line running to the left rear shock and a second line crossing over to the right rear shock. Crazy they didn't simply use a "T" as that set-up made the left and right shock PNs different. The leftt side shock actually had 2 fittings and the right side had one. When I changed my shocks I just used a "T" with push connectors common for 1/8" nylaflow lines which allowed me to use any aftermarket replacement air shock.

That compressor was controlled by a module/box and an arm which detected the level of the car based on the rear suspension. The most common failures seemed to be a leak in an air line and second a bad module/box/arm as they were in a position susceptible to moisture which was followed by corrosion.

The lines are super easy to fix. The compressors seemed to be pretty robust but they seemed to create a new box/arm assembly for every application (exaggerating but there seem to be many of them with little obvious interchange). It could even simply be a difference in arm geometry; not certain. So that system is easy to fix but good luck finding specific module/box/arm assembly.

That system adds pressure when the rear suspension sits low and it exhausts pressure when it's too high. The system doesn't need vacuum but the module/box controls the compressor with an electronic signal.

When my module/arm went bad on one of my cars I simply ran a "T" using 1/8" nylaflow tubing to a location near the rear license plate. It rarely ever really needed adjustment but it was nice if you were carrying a heavy load. I thought about adding a switch under the dash which would use the original compressor but I never bothered.

Scott

TJ Hopland

I don't remember if it was a mid year thing or if it mattered Eldo vs C car vs Seville but 77-78 was the change time from the vacuum powered compressor to the electric one.   

Like Scott said the electric ones the compressor was mounted under the hood and had a control module sensor back near the rear axle.   Other than the shocks themselves aging which is the same for either system the weak point of the electric seemed to be the height sensor module thing. 

As far as I know aftermarket never make replacements and no on ever repaired them on any sort of scale.   What the module did was the timing buffering so the system didn't try to react every time you went over a bump.   IF the sensor sensed it was high and enough time had passed that it wasn't just a bump it would send a signal to the compressor to open a vent solenoid that would bleed off some air.   If it was low after the timer it would send the signal to a relay under the dash that would then operate the compressor.   I'm not sure what fails in them but I can only think of maybe one I ever saw working out of dozens.

The electric compressors seemed to be fairly reliable and didn't seem to change much over the years or for different models.   Only the mounting brackets seemed to change.   Even in the 90's when they thought it was a good idea to move it under the car near the axle it was a very similar pump.   You saw them on models other than Cadillac and over a 20 some year span so they used to be easy to find used and in junkyards.   You sometimes saw them on lower models like a Chev as part of a towing package.


The vacuum compressors were a little different in that they worked more like the compressor in your garage did.   When ever it had power (from vacuum rather than electric in this case) they just tried to maintain their tank pressure.  If the pressure was low they would operate till it got back to its set pressure.  This in theory constant pressure was sent to the rear where there was what was basically a valve attached to the axle.  If the car was low the valve would let some compressor air to the shocks and if it was low would open a bleed port.   The valve did have some sort of mechanical damping mechanism so it didn't instantly respond like going over bumps and such.   I think the other part of the damping was the orifices were pretty tiny so it took some time to either add or bleed air so if it was just a quick bump there just wasn't time for it to really move far.

Vacuum compressors appear to be similar to the electronic modules were aftermarket never got into the game and no one appeared to do large scale repairs.   Parts have not been available for a long time and NOS doesn't help if you can find any because they are soft parts that age on the shelf almost as fast as they do in use.   Some people more recently have had some luck fabricating or improvising their own rebuild kits but it sounds like the results are mixed.


If you have the vacuum system and only the compressor is bad in theory you could buy any sort of mini 12v compressor with a small tank and pressure switch and the rest of the system won't know or care as long as it can get air when it wants it.    With the electric without that module you are kinda stuck unless you can build your own.  About the best you can do with a failed module is rig up manual switches to operate the solenoid or motor from inside or maybe the trunk?   Or just skip it all and get a manual fill setup that has a tire valve you mount near the gas filler.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

dennisspeaks

Thanks for your input TJ and 79 Eldorado.  I have the electric on my 78.  I looked at a 77 and it had the vacuum.  My motor is bad, what years can I replace it with?  Not sure if I will just go with air shocks if I can't get the original system to work.
CURRENT CLASSIC CARS
1939 Cadillac
1976 Eldorado convertible
1978 Toronado XS
1994 Deville
1989 Fleetwood
1989 Town Car
1982 Mark VI

PAST CARS
1978 Biarritz
1978 Eldorado
1978 Biarritz
1978 Biarritz
1974 Eldorado - RIP
1976 Eldorado Vert
1975 Sedan d'Elegance
1990 Sedan Deville -gave to son
1988 Fleetwood Brougham - gave to daughter
1968 GTO
1965 Olds 442
1975 Caprice Classic Sold

TJ Hopland

Which is bad?    If its the electric I think anything GM into the late 80's was the same,  90's maybe have even used the same motor just the layout changed a bit because they mounted it under the car.   Only differences I saw were in how and where it mounted to the car but as long as you had the original bracket for your car you could just swap em.

IF its the vacuum system I think the difference was just in the tanks.   I think 71+ was all the same but earlier there were shorter tanks.  Problem will be finding one that works.   Tanks often rusted out and the 'soft' parts in the compressor just get hard and brittle.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

The Tassie Devil(le)

Definitely rust out when positioned inside the right fender on the '71 Eldo.

And yes, the car was just as bad.   Notice the line halfway up the cylinder?   This was the level of leaves and dirt.

BUT, the funny thing was that the pump still worked, even though it was disconnected.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

dennisspeaks

TJ that is great news because they have some in the local wrecking yard, mine is electric, I did find one at someone who restores them but what he's asking is too rich for my wallet. 
CURRENT CLASSIC CARS
1939 Cadillac
1976 Eldorado convertible
1978 Toronado XS
1994 Deville
1989 Fleetwood
1989 Town Car
1982 Mark VI

PAST CARS
1978 Biarritz
1978 Eldorado
1978 Biarritz
1978 Biarritz
1974 Eldorado - RIP
1976 Eldorado Vert
1975 Sedan d'Elegance
1990 Sedan Deville -gave to son
1988 Fleetwood Brougham - gave to daughter
1968 GTO
1965 Olds 442
1975 Caprice Classic Sold

dennisspeaks

Bruce that thing looks like a old timex watch, took a beating and keeps on ticking.
CURRENT CLASSIC CARS
1939 Cadillac
1976 Eldorado convertible
1978 Toronado XS
1994 Deville
1989 Fleetwood
1989 Town Car
1982 Mark VI

PAST CARS
1978 Biarritz
1978 Eldorado
1978 Biarritz
1978 Biarritz
1974 Eldorado - RIP
1976 Eldorado Vert
1975 Sedan d'Elegance
1990 Sedan Deville -gave to son
1988 Fleetwood Brougham - gave to daughter
1968 GTO
1965 Olds 442
1975 Caprice Classic Sold

TJ Hopland

Round body RWD cars and wagons it was just in front of the rear axle drivers side.   I'm not sure that one will interchange with the under hood ones and those are often dead from corrosion so not likely worth looking too close at those unless you can't find any under hood ones.

Cars like the Deville and Park Ave around 90 it was still under the hood.   On my 90 deville it was kinda tucked under the brake booster.    If there are any square body cars those would almost for sure be the identical pump and on those there was room under the hood so should be easy to see.  If they have any square body wagons that was a common place to find them.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

dennisspeaks

TJ, yes I kinda remember the 90 Deville's had them.  I gave my 90 to our son, I will have to go over and check out the differences.
CURRENT CLASSIC CARS
1939 Cadillac
1976 Eldorado convertible
1978 Toronado XS
1994 Deville
1989 Fleetwood
1989 Town Car
1982 Mark VI

PAST CARS
1978 Biarritz
1978 Eldorado
1978 Biarritz
1978 Biarritz
1974 Eldorado - RIP
1976 Eldorado Vert
1975 Sedan d'Elegance
1990 Sedan Deville -gave to son
1988 Fleetwood Brougham - gave to daughter
1968 GTO
1965 Olds 442
1975 Caprice Classic Sold