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1976 Fleetwood Rear differential and Front Suspension Questions

Started by narnone, January 30, 2014, 09:22:08 AM

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narnone

I have a 1976 Fleetwood. I noticed the rear differential is different than other Cadillac and other GM full size cars. Can anyone enlighten me on this rear differential? Is it a good differential? Are parts available, mainly gears? I am putting a 4 speed auto in and need to change the gears to match the transmission. The differential seems heavy duty. Is it a better differential then the standard Cadillac differential? Is the standard Cadillac differential, used in Deville’s, the same as other GM full size cars or are they Cadillac only?
Front suspension. I noticed the Cadillac front suspension is totally different the other full size GM cars. What is the advantages and disadvantages of the front suspension?
Nick Arnone
Shavertown, PA 18651
570-760-7956
Email: narnone@hlsm.com
1959 21' Century Coronado
1956 26' Chris Craft Continental
1967 Cadillac Eldorado - Normandy Blue
1977 Cadillac Seville San Remo - White
1973 Cadillac Eldorado Convertible Pace Car (Mark Donahue's VIP car)
1978 Lincoln Town Coupe Convertible (Custom) - Blue

mgbeda

That differential should be the same as a DeVille or Calais of the same year.  Unless it's a limosine (or 9-passenger sedan) which had a higher rear axle ratio (3.15 vs. 2.73).  But that shouldn't look any different.  I believe the 3.15 was also an option on other models, but I'm not sure.  I don't really know if the rear axle is interchangeable with other GM's.  I know the driveshaft is different.

I was shocked when I found out that the front suspension is totally different from even other C-bodies from the same year.  Makes parts a lot harder to find, but not impossible.  One advantage I can think of is you don't need shims to adjust camber.

All the mechanicals in these cars are very rugged, though after 40 years anything can wear out.  I think the one weak spot would be the transmission, though a TH400 isn't exactly weak; just weak compared to the rest.

-mB
-Mike Beda
CLC #24610
1976 Sedan DeVille (Bessie)

narnone

I have a 1976 Fleetwood, I am using the frame on a restomod. A friend said I should replace the differential because the differential is physically different than the ones used in the Deville. This differential is part front loader and part rear loader. I do not know what differential is under a Deville. Is it the same as full size GM’s or is it Cadillac only?
The frame is going under is a Cadillac and I want to keep the car all Cadillac. The ride of a Cadillac is important to me.  Is this differential better or worse or the same as a Deville’s? It looks heavy duty. I will have to change the gears as this is going to have an overdrive transmission. I have not determined the gear ratio yet. But it appears to be somewhere between 3.73 and 3.53. If this is a good differential, I’d just as soon use it. The frame is being cut down by at least 6.5 inches to get it under the body and get the correct wheel base.
As far as gearing:
If I use a 700R4, first gear is 3.06 and a final of 0.70. This car will be a rocket with a 500 EFI attached to it. I believe I need a RPM of about 2200 2400 at cruising which should be 70 â€" 75 mph for my best economy and performance. I have a MTS #5 cam with higher compression pistons with 73 heads. More along the lines of a 70 Eldorado’s engine.
The 4L80E has a first gear 2.48 and a final of 0.75. I like the range of the 700R4 better range, Lower first gear and higher final gear.
Nick Arnone
Shavertown, PA 18651
570-760-7956
Email: narnone@hlsm.com
1959 21' Century Coronado
1956 26' Chris Craft Continental
1967 Cadillac Eldorado - Normandy Blue
1977 Cadillac Seville San Remo - White
1973 Cadillac Eldorado Convertible Pace Car (Mark Donahue's VIP car)
1978 Lincoln Town Coupe Convertible (Custom) - Blue

narnone

I did some research. Found this differential is the same they used in the Deville. It appears top be the same from 1970 through 1976.  I read where it is a Saginaw differential.
Does anyone know if parts are available for this?
Is there rear covers available?
Are gear sets available?
I have seen gaskets and bearings for the rear at Rockauto, which is fine, but I did not see gear sets or a rear cover.
Has anyone ever swapped out for a different GM rear that you can get parts for?
Nick Arnone
Shavertown, PA 18651
570-760-7956
Email: narnone@hlsm.com
1959 21' Century Coronado
1956 26' Chris Craft Continental
1967 Cadillac Eldorado - Normandy Blue
1977 Cadillac Seville San Remo - White
1973 Cadillac Eldorado Convertible Pace Car (Mark Donahue's VIP car)
1978 Lincoln Town Coupe Convertible (Custom) - Blue

Scot Minesinger

The rear differential case is same as 1970 through 1976, but in 1975 and 1976 the rear ratio is taller (2.76, in lieu of 2.93 for 1970-1974).  The 3.15 ratio was used in the 1970 thru 1974 Fleetwoods and it may have been used in 75 and 76 too, not sure.  Retain the original ratio if you can to keep your speedo accurate.  The ring gear is fastened with left handed (counter clockwise to tighten) bolts.  I have restored three 1970 differentials.  You cannot replace the ring and pinion gears except with good used.  They are rugged and good used remain plentiful.  Same with rear cover, good used is about your only option.  The bearings and seals are available as new, and they may need replacement - be careful - many crappy bearing producers out there - don't shop price, shop quality form a trusted source.  The labor to replace bearings and seals far outweighs the cost differential between bad and god bearings.

The front suspension is fine, just replace worn parts.  The rubber bushings on control arms do not hold up even for low mileage Caddys and they probably should be replaced if original.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

speach

Scott do you know about interchangeability of the 69 vs 70 rear ends? I know the 70 has a rear cover? Can you only swap out other Cadillac ratios on the 70 up ones? Or are there other GM alternatives that you know of. I now you know a lot about the 69 / 70 Cars.
Current cars:
1986 Military Chevrolet Diesel G30 Box Van
1968 Conv DeVille
1989 Toyota SpaceCruiser


You cant take your car with you in the end so drive the dang thing.

WilliamTrausch

Scot Minesinger

The 1969 and 1970 differential are different.  They may swap out if drive shaft mounting and length of drive shaft is same.  The control arm bushings and mounts should be same on a 1969 and 1970 rear axel.  The 1970 was a much more service friendly unit, and was the exact same from gearing and mechanicals 1970 thru 1974, however the control arm bushings and arms for a 71thru 74 may not work for a 1970 axle housing.  The 1969 had a 3.23 and the 1970 had a 2.93.  If you have a 1969, I would stay with the 1969 axle/diff. and same for a 1970. 
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Coupe Deville

Nick,

Your RPM range when in O.D. is in the right ball park. Make the rear end to numerically low, and you will start lugging the engine. Those numbers should be alright. They have great engine R.P.M. calculators online, for trying to figure out gearing. This one even has tire diameter selection. ( http://www.crawlpedia.com/rpm_gear_calculator.htm ) A transmission I would consider and use would be the 2004r. Its a 4 speed O.D transmission and I don't think you need an adapter plate because the 2004r shares the BOPC (Buick, olds, Pontiac, Cadillac) bell-housing. And the 200r4 has an even lower overdrive ratio at 0.60. Be very cautious with eather transmission though. When built with proper parts they can handle the torque of the Cadillac, but In stock form I have been told that neither transmission will last very long. This is something you really need to do your homework on and check it again. I always told myself if I had the money I would probably do this swap on my 72', but all I can do for now is watch people do the swap.

-Gavin 
-Gavin Myers CLC Member #27431
"The 59' Cadillac says more about America than a whole trunk full of history books, It was the American Dream"