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# Brougham Standard axle ratio: 2.28:1
# Limo Standard axle ratio: 3.08:1
# Limousine Brakes: front disc, rear drum
# Brougham Brakes: four-wheel disc
Limited slip differential ($70)

So, in short, nope. I believe my 75 came with 2.73s but that's with the older differential (8 7/8 or something like that.) LSD was optional.
 

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Discussion Starter #3
davesdeville said:
# Brougham Standard axle ratio: 2.28:1
# Limo Standard axle ratio: 3.08:1
# Limousine Brakes: front disc, rear drum
# Brougham Brakes: four-wheel disc
Limited slip differential ($70)

So, in short, nope. I believe my 75 came with 2.73s but that's with the older differential (8 7/8 or something like that.) LSD was optional.
damnit....

from further reading, the Fleetwood came with 4 wheel disc brakes....

I thought they also had 2.73 and Posi, since I *may* have a chance to pick one up.

So what is the easiest way to tell if the car is a 2.28/2.73/3.08 and if it has Posi or not?
 

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What years did Broughams come with rear disc in the 70's and 80's?

I had always heard, but never saw one. I have the parts to build it from a 77 Eldo, but just haven't done it.

425 and 2.73's should be a nice combo.

Watch those old calipers, they are often jam up the ebrake cable adjuster and the rear caliper won't adjust. So you tend to get bad brakes often. That bolt is rather fragile, so don't manhandle it when you put on new brakes.

Oh, an use the EBrake everytime you park the car, it is the only way the rear brakes get adjusted at all.
 

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First of all there should be no 2.73s on a 79. Like I said that's the older (Pontiac sourced, 8 7/8" I think) differential used in the last of the truly big cars.

To check for a posi jack both rear wheels off the ground and turn one wheel. If both wheels turn in the same direction, then it is a posi. If they turn in opposite directions, then it is an open carrier or worn out posi. To check the gear ratio get under the car and spin the driveshaft lets say 10 times, then count how many times the wheel rotates. If it rotates 4.3x it's a 2.28, if it rotates 3.2x it's a 3.08.
 

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Ok, to ID the 8 7/8" rear end (NON Chevy 12 Bolt!) look for 10 bolts in the cover, dead center on the top and bottom, and 2 on each side with scallops and a drain plug on the back cover.

You are correct, this was the Pontiac sourced rear end.

Look for an axle code of:
open--ratio----posi
UN----2.41----(n/a)
UJ----2.56-----VJ (Note I have some conflicting codes I list 2.56 and 2.93 on this code)
UU----2.73-----YU
UW----2.93-----VW
UX----3.23-----VX
*YA---2.73-----ZA*
UA----2.73-----VA
YB----2.93-----ZB
YD----3.23-----ZD
UD----3.23-----UD
WF----2.56-----XF
UF----2.56-----UF
WA----2.73-----XA
WC----3.08-----XC
WK----2.56-----XK
WL----2.73-----XL
WM----2.93-----XM


* "Delta 88 350 W/ACRS or POLICE"

There were leaf sprung versions of this rear in the "bubble butt" Full Size wagons and Cutlass "Vista Cruiser" Wagons of yesteryear. Gears work fine in your rear.
Note these are 1976 axle codes from B/C bodies. The 2.18 ratio is a 77-up ratio. So you can now scour boneyards for GM B/D/C cars to get other used gears to put in your 77- car. Posi's are somewhat rare, I have honestly never seen one, and there was a time I was looking.

Codes are found on the RH tube, rear view of the rear end, next to the center section.
 

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Wonder what the highest gear ratio is that can be put in an original 1978 2.28 8-7/8 Cadillac posi 10 bolt. I have only seen one of these, they are so rare that I bought a whole car to get it.
 

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I have never seen higher than 3.23. And I have not ever seen one either. Wagons are the cars I would look for. Mainly, the equiv of the V4P in 74-76.

I say just get a HT4100 car rear end. 7.5" and 3.42's. The 425 doens't have enough power to hurt it unless you are drag racing with slicks or towing heavy.
 

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Discussion Starter #9
N0DIH said:
Ok, to ID the 8 7/8" rear end (NON Chevy 12 Bolt!) look for 10 bolts in the cover, dead center on the top and bottom, and 2 on each side with scallops and a drain plug on the back cover.

You are correct, this was the Pontiac sourced rear end.

Look for an axle code of:
open--ratio----posi
UN----2.41----(n/a)
UJ----2.56-----VJ (Note I have some conflicting codes I list 2.56 and 2.93 on this code)
UU----2.73-----YU
UW----2.93-----VW
UX----3.23-----VX
*YA---2.73-----ZA*
UA----2.73-----VA
YB----2.93-----ZB
YD----3.23-----ZD
UD----3.23-----UD
WF----2.56-----XF
UF----2.56-----UF
WA----2.73-----XA
WC----3.08-----XC
WK----2.56-----XK
WL----2.73-----XL
WM----2.93-----XM


* "Delta 88 350 W/ACRS or POLICE"

There were leaf sprung versions of this rear in the "bubble butt" Full Size wagons and Cutlass "Vista Cruiser" Wagons of yesteryear. Gears work fine in your rear.
Note these are 1976 axle codes from B/C bodies. The 2.18 ratio is a 77-up ratio. So you can now scour boneyards for GM B/D/C cars to get other used gears to put in your 77- car. Posi's are somewhat rare, I have honestly never seen one, and there was a time I was looking.

Codes are found on the RH tube, rear view of the rear end, next to the center section.
These are for the pre '76, or '77+?

if pre '76, how to tell what gears a '79 has?
 

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Discussion Starter #10
N0DIH said:
I have never seen higher than 3.23. And I have not ever seen one either. Wagons are the cars I would look for. Mainly, the equiv of the V4P in 74-76.

I say just get a HT4100 car rear end. 7.5" and 3.42's. The 425 doens't have enough power to hurt it unless you are drag racing with slicks or towing heavy.
3.42's would to be too low of a gear, even for the 425 though.
 

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Agreed, it likely would be out of powerband too fast and probably slow the car down some, mainly for higher rpm use. But maybe with a larger cam, or better breathing, it might be worth it.

And for not hard use, it would be rather enjoyable. What is redline on the 425? How is the useful power? I haven't driven one in years, it was a fuelie 78 TTop Eldo. Ran good, but the car was very heavy, the 500 would have been more welcome!
 

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alright, so i was reading the "Standard Catalog of Cadillac 1903-2000" and it says that the standard axle ratio in the '79 Deville/ Brougham is a 2.28:1. Thats from the original Cadillac service manuals i believe.
 

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Discussion Starter #13
N0DIH said:
Agreed, it likely would be out of powerband too fast and probably slow the car down some, mainly for higher rpm use. But maybe with a larger cam, or better breathing, it might be worth it.

And for not hard use, it would be rather enjoyable. What is redline on the 425? How is the useful power? I haven't driven one in years, it was a fuelie 78 TTop Eldo. Ran good, but the car was very heavy, the 500 would have been more welcome!
Well, the reason why I REALLY want 2.73/Posi is because it would be PERFECT for a nicely built 500.

I heard that the 2.73/Posi/rear disc came with '77-'79 commercial chassis and factory towing package... is that much true?

the redline on the 425 is about 4,200RPM, but in drive it shifts into 2nd at 3,900RPM and 3rd at 3,400RPM... so I consider 4,000RPM the useful redline, beyond that it is losing power anyway.

the useful power, I would say between 1,000-2,500RPM

simply because if you drive around all day, never really hitting the gas to open the secondaires, it'll never go above 2,000RPM, it only goes from 2,200-4,000RPM when you are running wide open, it pretty much dosn't like those high RPM.

although at 80mph, it'll pull better in 2nd (about 3,600RPM... manually held back) then it will in 3rd (about 3,000RPM) or maybe that is just what it seems... it'll also top out at 110mph in 2nd, at about 4,100RPM.

I really don't want to get too involved with the 425, but I badly want 2.73/Posi, so I just need to know what really has them, so far I found out that the Fleetwood Brougham dosn't, but they have rear disc brakes.... so from what I know, the '77-'79 commercial chassis (limo/hearse etc...) and DeVille w/ towing pacakge DO have the 2.73/Posi/rear disc rear end... is that much true? is that what I have to look for?

the car has an open 2.28 now, and it sucks
 

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I~LUV~Caddys8792 said:
alright, so i was reading the "Standard Catalog of Cadillac 1903-2000" and it says that the standard axle ratio in the '79 Deville/ Brougham is a 2.28:1. Thats from the original Cadillac service manuals i believe.
You are way ahead of the pack by quoting the source for the information that you found.
 

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I did a few 500 and 425 swaps into HT4100 cars where I left the original rear axle in there for a short time and ran the car that way. The original 3.41 or 3.42 (dunno) gear wakes the car up. It really flys compared to the 2.28 or 2.41. Almost totally useless from a standing start though as the power goes up in tire smoke. There is a lot more to picking a rear axle ratio than keeping your cruise RPM somewhere near the torque peak of the engine.
A change from 2.28 to 2.73 will make a good difference. Good choice for mostly stock Cadillac engines. I have no experience otherwise. You probably will not find a set of 273's in a Cadillac. Start looking under station wagons in the junkyard. You may land up with a different axle bolt pattern so rims will be different on the front and back. Some space saver spare tires have dual bolt patterns. Most station wagon drum to drum axles can fit into a Cadillac with a little work. Biggest problem is the pinion flange. Cadillac and some Oldsmobile used the round one while others used the saddle type. These can be swapped over (or maybe you can just use the saddle and remove the round flange from the U-joint) but you have to be sure that the flange is not overtorqued when installed.
Sometimes, the driveshaft lands up being about 1 inch too long. It will not go into place unless the car is on the ground with weight on the rear wheels. Done this several times with no problems of the yoke binding into the back of the trans.
 
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