Rear Axle Refresher

randomguy

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Just curious does anyone know if most of the 89 Chrysler Fifth Avenues have came with a 8 1/4 rear end and I'm just curious up to what point J-Bodies came with an 8 1/4 axle. I was thinking that platform switched to the 7 1/4 in 83 I think for V8 cars? Thank you in advance.
 

BudW

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Most F, M & J bodies came with a 7-1/4" differential (maybe 85% did, and that might be a low number)
All Station Wagons came with 8-1/4" differential as well as cars ordered with factory towing package.
Many Police and Taxis came with 8-1/4" differential as well as many with manual transmissions (but not all).

All FMJ 7-1/4" differentials are the same and will interchange with other FMJ 7-1/4" (except for a few early ones).
All FMJ 8-1/4" differentials are the same and will interchange with other FMJ 8-1/4".
The exception is some came with 11" drum brakes and some parking brake cables are different (not hard to change).
You can put an 8-1/4" in place of a 7-1/4" but driveshaft length is different.
Some of the earlier 7-1/4" has a smaller outer tube size which may require different spring hold-downs - but those older ones are really hard to find.

Other Chrysler corp. differentials can fit, but all will require some modifications first.

Some, but not many, J-bodies came with 8-1/4", but I would guess at maybe 5% (which might be on the high side).

Why are you asking - or what is on your mind?
BudW
 

F body Deconstructor Jim

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The exception is some came with 11" drum brakes and some parking brake cables are different (not hard to change).

Some of the earlier 7-1/4" has a smaller outer tube size which may require different spring hold-downs - but those older ones are really hard to find.

BudW

Wagons had finned HD 10" drum brakes and 5 leaf spring packs to go with the 8.25.

I believe the 3" axle tube 7.25 came along in 1980.

7.25 (smaller axle tube) and 8.25 both use the same axle mounting U brackets but different plates and U-bolts.
Also the 5 leaf spring packs used a different U bracket, about 1/4" deeper to accomodate the extra leaf.

Backing plates (10") are all the same no matter which rear end so the existing E brake cables will work.
 

80mirada

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Actual police package cars should have 8.25" no matter the engine. Gran Fury, Caravelle and Diplomat are more likely to have an 8.25" than a Fifth Ave. Earlier production years are also more likely to have the 8.25". Miradas are more likely than Cordoba to have the 8.25" also. I have also noticed that certain regions are more likely to have the heavier differential.
 

BudW

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ctual police package cars should have 8.25" no matter the engine.
In theory I would agree – but will have to disagree, though.

Tulsa (Oklahoma) Police dept. and Wagner county (Oklahoma) Sheriff’s dept. F/M body police cars - most did not come with 8¼”, back in the day.
I know because I replaced/repaired a large number of them. It could be they didn’t get the AHB package, maybe most were 318 2 bbl cars – I have no idea – but both departments purchased their cars in mass. At the time, I mostly worked suspension, brakes, differentials and some transmission work on them (not much under hood).
I do remember seeing the cars did have 11” brakes and blue hoses on them.

Wagons had finned HD 10" drum brakes and 5 leaf spring packs to go with the 8.25.
I’m not in a position to agree or disagree with 10” HD brake drums (finned).
My 37k mile ’77 Volare wagon has non-finned drums and an 8¼” differential I removed from a ’80 Aspen wagon yesterday has 10” non-finned drums.
I wonder if it was a year of manufacture thing or an option (trailer towing), maybe?
It might also be that both above mentioned wagons has had their drums replaced.
It might be what the factory had (or didn’t have) on the shelf at time of manufacture. Me shrugs.
Correction: the '77 Wagon does have 10" fined drums.

I believe the 3" axle tube 7.25 came along in 1980.
I couldn’t remember the year the small tube 7¼”. I was thinking ’78 – but couldn’t remember.
I just know finding a “good” small tube 7¼” is harder than finding a large tube one.

It might also be that Tulsa Police dept. and Wagner county sheriffs dept. ruined most of them (again, me shrugs).

BudW
 
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F body Deconstructor Jim

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All 5 of the wagons I've had (76-79, including my current 76 slant six Aspen DD) had finned 10" drums...360, 318 or 225.
The only other non-wagon I remember seeing the finned drums on was a 78 Volare kit.
 

80mirada

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AHB package calls out for the 8.25. Many departments though ordered cars to their own specifications without the AHB package, or A38 on earlier cars. If someone from account was involved in the order, eliminating the cost of the upgraded axel would look like a huge savings.
 

BudW

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eliminating the cost of the upgraded axle would look like a huge savings.
Well, it didn't work. At one time, there was a pile of 7¼”s you couldn't see over.

The Tulsa Police Dept. has never had anything faster than a souped up bicycle.
I only wrenched on ‘em, not anything else.
Wagoner County Sheriff’s Dept didn’t need much - population then was 35k people and most of them were ones that wanted out of Tulsa city limits.


Jim, I went looked. I made a mistake, my ‘77 Volare wagon does have 10" fined drums, as well as my ‘86 5th Ave.
20160725_205544.jpg
'77 wagon (with 14" wheels)
20160725_200505.jpg

'86 5th Ave (with 15" wheels)
20160725_205709.jpg

'80 Aspen Wagen (with 15" wheels added to move it)
Now it could have been the drums were changed on the ‘80 Aspen wagon, maybe.
20160725_205719.jpg

Still in bed of my pickup.
 

randomguy

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Thank you for the information. I was just curious as I would rather not deal with an axle swap if I have to. I'm sure the 7.25 would be alright as I don't hot rod but, the 8.25 would be better and IIRC I read somewhere that more of the 1989 M-Bodies came with 8.25 rears to get rid of them but, wasn't sure.
 

80mirada

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Cedar Falls, IA had a 87 Fifth Ave that was equipped as an unmarked . It had all three external coolers, heavy sway bars, 5 leaf springs and a 318\4v. They special ordered it from Des Moines since the local dealers wouldn't. My dad almost bought it when it was retired, but didn't want a three year old car with over 100,000 miles on it.
 
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