axle type / ratio
Apr 3, 2012 2:43:57 GMT -5
Post by sigmfsk on Apr 3, 2012 2:43:57 GMT -5
We had a good thread going on the BBC archives about axle types / ratios:
www.bluesbrotherscentral.com/forum/topic/9896-monaco-rear-end-gear-ratios/page__hl__axle__fromsearch__1
Here are the highlights:
--------------
[spanks79]
> Does anyone know what rear axle ratios came stock in 74-77 monacos?
> Civilian vs police?
[sigmfsk]
> The "brochures" thread on the board has all the info.
> Civilians: 2.71 or 3.23
> Police: 3.23
[bluzman]
> 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. There seems to be a lot more options for the 8.75 mopar
> rear..some of the earlier C-bodies came with them factory...
[sigmfsk]
> ...I recall that my 74 police package 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.
[spanks79]
> 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.
[bluzman]
> 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.
[cbodymoparfan]
> 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.
[sigmfsk]
> what leads you to believe that the 2.71 was not the original gearing (or
> axle)?
[cbodymoparfan]
> I had a friend of mine decode the build sheet. I was informed D53 is for
> a 3.21 axle.
[sigmfsk]
> Interesting!
> I see in my option code book that D53 for a 76 c-body is:
> 3.21: c body 9.25 axle.
> and the same is true for a 74.
> 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
> It seems that something is funny; I'm just not sure what it is.
> We know that:
> 1) the police brochures advertise 3.21, but every police car we've seen
> (Bluzman's, mine, yours) all had 2.71
> 2) your build sheet and 440RULEZs sheet show 3.21.
[sigmfsk]
> The 74 police brochure discusses a 9.25 (pic 1)
from brochure thread.
> The civilian brochure (pic 2)
discusses 2.71 and 3.23, but the list of axle
> ratios above (from the fender code book) shows a 3.21 (not a 3.23). It
> looks like a 3.23 was available in the 8.75 axle in a 73 c-body. I guess
> it's not that weird that the brochure lists a 3.23 instead of a 3.21. The
> 1975 advertising brochure was changed to list 3.21 instead of 3.23.
pic of 9 1/4, Marin County:
two pics of 8 1/4, 76 parts car:
I originally said that the parts car had a 9 1/4. Bluzman corrected me:
[bluzman]
> If your 74-77 Dodge Monaco/Royal Monaco came with a 318, 360, 0r
> 400 engine..you will have a 8.25 rear. If you have a cop car or factory
> 440 car you will have a 9.25 rear. But keep in mind you could special
> order stuff back then..so if you have an oddball...Ex: 360 car with a
> 9.25 rear, it could have came special orderd that way. Arthur...your
> parts car has a 8.25 rear, not a 9.25.
[sigmfsk]
> Ahhh, you're right; thanks for setting me straight!
>
> Pic 1: Below the axle centerline, a 9.25 has 6 bolts that attach the
> cover to the axle housing. A 8.25 has 5 bolts.
From
www.crankshaftcoalition.com/wiki/Mopar_Rear_Axle_Spotter%27s_Guide
> My 76 build sheet shows D51 axle code (pic 3)
> And, for 1976, a D51 for a c-body breaks down to a 2.71 (either 8.25
> axle or 9.25 axle).
and then talking about special ordering a 9.25 axle:
[sigmfsk]
> I don't know how one would order that. Take my 76 parts car for
> example. It has a 400, which, according to your axle mapping, means
> that it should have an 8.25, which it does. For a 2.71 ratio, the axle
> code for the 8.25 is the same as the axle code for a 9.25, so one
> couldn't upgrade to a 9.25 simply by selecting D51.
>
> Since "D51" alone would seem to be unable to upgrade the axle, I'd
> think that one would have to upgrade to some package that would
> include an axle upgrade, but I don't even know what the package would
> be (that could get you a 9.25 without getting you a 440). The trailer
> towing package included a 440.
>
> So maybe this
> > For a 74-77 c-body
> > 318,360,400 = 8.25
> > 440 = 9.25
> is entirely true, regardless of options. No matter what you special
> ordered, one needs only look at engine that was ultimately installed in
> the car as a result of all the options. 440 = 9.25. Any other engine
> means 8.25.
>
> I have to guess that it's not quite so simple, but it's certainly a good
> start, and any counterexample will help move along the theory.
---------
I don't think we've had any counterexamples, so as far as I know, this is the rule:
> > For a 74-77 c-body
> > 318,360,400 = 8.25
> > 440 = 9.25
> is entirely true, regardless of options. No matter what you special
> ordered, one needs only look at engine that was ultimately installed in
> the car as a result of all the options. 440 = 9.25. Any other engine
> means 8.25.
www.bluesbrotherscentral.com/forum/topic/9896-monaco-rear-end-gear-ratios/page__hl__axle__fromsearch__1
Here are the highlights:
--------------
[spanks79]
> Does anyone know what rear axle ratios came stock in 74-77 monacos?
> Civilian vs police?
[sigmfsk]
> The "brochures" thread on the board has all the info.
> Civilians: 2.71 or 3.23
> Police: 3.23
[bluzman]
> 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. There seems to be a lot more options for the 8.75 mopar
> rear..some of the earlier C-bodies came with them factory...
[sigmfsk]
> ...I recall that my 74 police package 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.
[spanks79]
> 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.
[bluzman]
> 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.
[cbodymoparfan]
> 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.
[sigmfsk]
> what leads you to believe that the 2.71 was not the original gearing (or
> axle)?
[cbodymoparfan]
> I had a friend of mine decode the build sheet. I was informed D53 is for
> a 3.21 axle.
[sigmfsk]
> Interesting!
> I see in my option code book that D53 for a 76 c-body is:
> 3.21: c body 9.25 axle.
> and the same is true for a 74.
> 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
> It seems that something is funny; I'm just not sure what it is.
> We know that:
> 1) the police brochures advertise 3.21, but every police car we've seen
> (Bluzman's, mine, yours) all had 2.71
> 2) your build sheet and 440RULEZs sheet show 3.21.
[sigmfsk]
> The 74 police brochure discusses a 9.25 (pic 1)
from brochure thread.
> The civilian brochure (pic 2)
discusses 2.71 and 3.23, but the list of axle
> ratios above (from the fender code book) shows a 3.21 (not a 3.23). It
> looks like a 3.23 was available in the 8.75 axle in a 73 c-body. I guess
> it's not that weird that the brochure lists a 3.23 instead of a 3.21. The
> 1975 advertising brochure was changed to list 3.21 instead of 3.23.
pic of 9 1/4, Marin County:
two pics of 8 1/4, 76 parts car:
I originally said that the parts car had a 9 1/4. Bluzman corrected me:
[bluzman]
> If your 74-77 Dodge Monaco/Royal Monaco came with a 318, 360, 0r
> 400 engine..you will have a 8.25 rear. If you have a cop car or factory
> 440 car you will have a 9.25 rear. But keep in mind you could special
> order stuff back then..so if you have an oddball...Ex: 360 car with a
> 9.25 rear, it could have came special orderd that way. Arthur...your
> parts car has a 8.25 rear, not a 9.25.
[sigmfsk]
> Ahhh, you're right; thanks for setting me straight!
>
> Pic 1: Below the axle centerline, a 9.25 has 6 bolts that attach the
> cover to the axle housing. A 8.25 has 5 bolts.
From
www.crankshaftcoalition.com/wiki/Mopar_Rear_Axle_Spotter%27s_Guide
> My 76 build sheet shows D51 axle code (pic 3)
> And, for 1976, a D51 for a c-body breaks down to a 2.71 (either 8.25
> axle or 9.25 axle).
and then talking about special ordering a 9.25 axle:
[sigmfsk]
> I don't know how one would order that. Take my 76 parts car for
> example. It has a 400, which, according to your axle mapping, means
> that it should have an 8.25, which it does. For a 2.71 ratio, the axle
> code for the 8.25 is the same as the axle code for a 9.25, so one
> couldn't upgrade to a 9.25 simply by selecting D51.
>
> Since "D51" alone would seem to be unable to upgrade the axle, I'd
> think that one would have to upgrade to some package that would
> include an axle upgrade, but I don't even know what the package would
> be (that could get you a 9.25 without getting you a 440). The trailer
> towing package included a 440.
>
> So maybe this
> > For a 74-77 c-body
> > 318,360,400 = 8.25
> > 440 = 9.25
> is entirely true, regardless of options. No matter what you special
> ordered, one needs only look at engine that was ultimately installed in
> the car as a result of all the options. 440 = 9.25. Any other engine
> means 8.25.
>
> I have to guess that it's not quite so simple, but it's certainly a good
> start, and any counterexample will help move along the theory.
---------
I don't think we've had any counterexamples, so as far as I know, this is the rule:
> > For a 74-77 c-body
> > 318,360,400 = 8.25
> > 440 = 9.25
> is entirely true, regardless of options. No matter what you special
> ordered, one needs only look at engine that was ultimately installed in
> the car as a result of all the options. 440 = 9.25. Any other engine
> means 8.25.