axles / ratios
Oct 10, 2011 16:55:05 GMT -5
Post by sigmfsk on Oct 10, 2011 16:55:05 GMT -5
On BBC, we had a long good thread about axles and ratios:
www.bluesbrotherscentral.com/forum/topic/9896-monaco-rear-end-gear-ratios/page__hl__axle__fromsearch__1
I attempt to summarize here.
The line of thinking is that:
- a 74-77 c-body Monaco came with either a 8.25 axle, or a 9.25 axle.
- if the car had a 440, the axle was a 9.25
- if the car had any other motor, the axle was an 8.25
Please let me know if there's reason to believe otherwise; that's just my understanding at the moment.
This is a 9.25 (74 Marin County, 440)
This is an 8.25 (76 parts car, 400)
And a handy spotters guide:
from
www.crankshaftcoalition.com/wiki/Mopar_Rear_Axle_Spotter%27s_Guide
My option code book provides the following for 74 c-bodies:
D51 - 2.71 - 8.25
D51 - 2.71 - 9.25
D52 - 2.94 - 8.25
D53 - 3.21 - 9.25
The brochures indicate that cop cars came with the 3.21, but Bluzman writes:
I have had 8, 2 were police Monacos..all have been 2.71 open rears. I have read that police models came with 3.23 gears, but the two I had were both 2.71s..these were the 9.25 rears. I have bought a couple of factory posi's from ebay over the years and one of them came with 3.23 gears. I have also read that you can use gears from a Dodge Dakota if you have the 8.25, but not the carrier because the axle spline count is different.
-----------
my 74 Marin County was an open rear, and I spun the wheels and looked at the driveshaft and, if I remember correctly, my quick calculations pointed to it being a 2.71 instead of the 3.23.
What we have:
1) the police brochures advertise 3.21, but every police car we've seen (Bluzman's, mine, cbodymoparfan) all had 2.71
2) cbodymoparfan's build sheet and 440RULEZ's sheet show 3.21.
So something funny is going on (brochures and build sheets show 3.21, but actual ratio is 2.71)
------------
A monaco didn't come with an 8.75, but its a nice axle to install in a one.
Bluzman writes:
There seems to be a lot more options for the 8.75 mopar rear..some of the earlier C-bodies came with them factory....keep your eyes open for your local craigslist, you could probaly buy a whole car for 3-400$ and get the rear from it.
then Country Bunker responds:
Thats exactly what I did... I got a 67 fury 3, for $250. Grabbed the rear, and off she went.
Im not sure about ALL pre 74 c bodys, but Im pretty sure any 8.75 axle out of a common c body will fit. Ill check the width of the one under my newport... The one Ive got from the 67 is the same width as the 8.25 in the car. So it should bolt right up in place of the 8.25 without any problems.
If your going from a 8.25 to a 8.75 you will need to shorten your driveshaft.
You will want to grab the shock plates as you will need them for the new 8 3/4. A good thing about the older shock plates is you will get rid of the isoclamp (mushy rubber) leaf spring mounts. I know my 75 has the rubber isolated springs, but do the 74s have them?
[
arthur: answer - yes, see here:
bluesmobiles.proboards.com/index.cgi?board=police&action=display&thread=300
]
Also your gonna want the brakes, and backing plates from the 8 3/4. but if your going to upgrade to disks, then you prolly wont need them...
Theres 3 common 3rd members,
741 case - Weakest of the cases, non performance cars
742 case - Most common case in the performance built cars in the late 60s
489 case - Strongest case for performance, but harder to rebuild, and find parts for
All this should bolt right in without any mods, except ofcoarse new brake lines and what not..
I dont have a clue about the 9.25s, or dana 60s... never messed with them.
-------------------
Cbodymoparfan wrote:
I had the 2.7's in my 76 when I bought it. I am pretty sure it was not the original rear. Swapped it out for the 3.21. Decent difference out of the hole but not tire smoking. I was told that the torque converter in the C bodies after 75 really prevented the ability to do a hole-shot. Every time I fill up I wish I still had the highway gears. 15 mpg VS 10 mpg (with a lightbar on top of the car) I still have the 2.7 rear too. Car is 440 ucoded police pkg.
-------------------
Spanks79 asked:
Bluzman, from your experience, is there any benefit to the 9.25 over the 8.75? Sounds like it is likely whatever car I buy is likely to have a 2.71 in it.
and Bluzman responded:
The choice is really yours. I would not personally waste any money building the 8.25, I am using the 9.25 because I have a plethora of parts for it. My donor 9.25 came from a 74 Chrylser Imperial, 3.23 posi with the super rare rear disc brakes....supposedly only a few hundred built that way. My car is going to make some power too, but I also want it to stop, and every car thus far..that I built to keep has 4 wheel disc brakes. Do your own research, check prices and availability for parts and such. The benefit of the 8.75 rear is..you can have several third members built with the gear ratios/Posi/open of your choice....and you can swap them out in about an hour or so, depending on what you want to do, example: Drag strip=4.10, Around town /normal cruising/short trip=3.55, or that Hot Rod power tour=2.71 The potentials are unlimited and I have seen complete 8.75 Posi third members for as little as $75.00. If I have learned anything in my 37 years of life is this...don't settle...get what you want..you will thank yourself later.
-------------------
Axl Rosenberg wrote:
The main benefit aside from the slightly larger size to running a 9.25 rear is that it's correct for a '74. The 8.75 is a much more easily serviceable rear and fairly plentiful to find in a C-body width. I'm running a 2.76 open 8.75 / stock 727 / with a very streetable 440 because I wanted something as versatile as a real pursuit package police car, that I can drive without excessive maintenance, fuel additives, horrendous mileage, etc. If money were no object, I'd probably step up to a 3.55 gear with a Gear Vendors overdrive unit. I'm happy with the way mine performs. It's built as a highway car. It's impressive off the line, but in no way is it going to win anything at a dragstrip.
--------------
TI4438 provided a link on axle dimensions:
www.dippy.org/forum2/index.php/topic,189.0.html
--------------
www.bluesbrotherscentral.com/forum/topic/9896-monaco-rear-end-gear-ratios/page__hl__axle__fromsearch__1
I attempt to summarize here.
The line of thinking is that:
- a 74-77 c-body Monaco came with either a 8.25 axle, or a 9.25 axle.
- if the car had a 440, the axle was a 9.25
- if the car had any other motor, the axle was an 8.25
Please let me know if there's reason to believe otherwise; that's just my understanding at the moment.
This is a 9.25 (74 Marin County, 440)
This is an 8.25 (76 parts car, 400)
And a handy spotters guide:
from
www.crankshaftcoalition.com/wiki/Mopar_Rear_Axle_Spotter%27s_Guide
My option code book provides the following for 74 c-bodies:
D51 - 2.71 - 8.25
D51 - 2.71 - 9.25
D52 - 2.94 - 8.25
D53 - 3.21 - 9.25
The brochures indicate that cop cars came with the 3.21, but Bluzman writes:
I have had 8, 2 were police Monacos..all have been 2.71 open rears. I have read that police models came with 3.23 gears, but the two I had were both 2.71s..these were the 9.25 rears. I have bought a couple of factory posi's from ebay over the years and one of them came with 3.23 gears. I have also read that you can use gears from a Dodge Dakota if you have the 8.25, but not the carrier because the axle spline count is different.
-----------
my 74 Marin County was an open rear, and I spun the wheels and looked at the driveshaft and, if I remember correctly, my quick calculations pointed to it being a 2.71 instead of the 3.23.
What we have:
1) the police brochures advertise 3.21, but every police car we've seen (Bluzman's, mine, cbodymoparfan) all had 2.71
2) cbodymoparfan's build sheet and 440RULEZ's sheet show 3.21.
So something funny is going on (brochures and build sheets show 3.21, but actual ratio is 2.71)
------------
A monaco didn't come with an 8.75, but its a nice axle to install in a one.
Bluzman writes:
There seems to be a lot more options for the 8.75 mopar rear..some of the earlier C-bodies came with them factory....keep your eyes open for your local craigslist, you could probaly buy a whole car for 3-400$ and get the rear from it.
then Country Bunker responds:
Thats exactly what I did... I got a 67 fury 3, for $250. Grabbed the rear, and off she went.
Im not sure about ALL pre 74 c bodys, but Im pretty sure any 8.75 axle out of a common c body will fit. Ill check the width of the one under my newport... The one Ive got from the 67 is the same width as the 8.25 in the car. So it should bolt right up in place of the 8.25 without any problems.
If your going from a 8.25 to a 8.75 you will need to shorten your driveshaft.
You will want to grab the shock plates as you will need them for the new 8 3/4. A good thing about the older shock plates is you will get rid of the isoclamp (mushy rubber) leaf spring mounts. I know my 75 has the rubber isolated springs, but do the 74s have them?
[
arthur: answer - yes, see here:
bluesmobiles.proboards.com/index.cgi?board=police&action=display&thread=300
]
Also your gonna want the brakes, and backing plates from the 8 3/4. but if your going to upgrade to disks, then you prolly wont need them...
Theres 3 common 3rd members,
741 case - Weakest of the cases, non performance cars
742 case - Most common case in the performance built cars in the late 60s
489 case - Strongest case for performance, but harder to rebuild, and find parts for
All this should bolt right in without any mods, except ofcoarse new brake lines and what not..
I dont have a clue about the 9.25s, or dana 60s... never messed with them.
-------------------
Cbodymoparfan wrote:
I had the 2.7's in my 76 when I bought it. I am pretty sure it was not the original rear. Swapped it out for the 3.21. Decent difference out of the hole but not tire smoking. I was told that the torque converter in the C bodies after 75 really prevented the ability to do a hole-shot. Every time I fill up I wish I still had the highway gears. 15 mpg VS 10 mpg (with a lightbar on top of the car) I still have the 2.7 rear too. Car is 440 ucoded police pkg.
-------------------
Spanks79 asked:
Bluzman, from your experience, is there any benefit to the 9.25 over the 8.75? Sounds like it is likely whatever car I buy is likely to have a 2.71 in it.
and Bluzman responded:
The choice is really yours. I would not personally waste any money building the 8.25, I am using the 9.25 because I have a plethora of parts for it. My donor 9.25 came from a 74 Chrylser Imperial, 3.23 posi with the super rare rear disc brakes....supposedly only a few hundred built that way. My car is going to make some power too, but I also want it to stop, and every car thus far..that I built to keep has 4 wheel disc brakes. Do your own research, check prices and availability for parts and such. The benefit of the 8.75 rear is..you can have several third members built with the gear ratios/Posi/open of your choice....and you can swap them out in about an hour or so, depending on what you want to do, example: Drag strip=4.10, Around town /normal cruising/short trip=3.55, or that Hot Rod power tour=2.71 The potentials are unlimited and I have seen complete 8.75 Posi third members for as little as $75.00. If I have learned anything in my 37 years of life is this...don't settle...get what you want..you will thank yourself later.
-------------------
Axl Rosenberg wrote:
The main benefit aside from the slightly larger size to running a 9.25 rear is that it's correct for a '74. The 8.75 is a much more easily serviceable rear and fairly plentiful to find in a C-body width. I'm running a 2.76 open 8.75 / stock 727 / with a very streetable 440 because I wanted something as versatile as a real pursuit package police car, that I can drive without excessive maintenance, fuel additives, horrendous mileage, etc. If money were no object, I'd probably step up to a 3.55 gear with a Gear Vendors overdrive unit. I'm happy with the way mine performs. It's built as a highway car. It's impressive off the line, but in no way is it going to win anything at a dragstrip.
--------------
TI4438 provided a link on axle dimensions:
www.dippy.org/forum2/index.php/topic,189.0.html
--------------
