The elusive 3.308:1 rear diff - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Suspension, Brakes, Drivetrain discuss the wondrous effects of boost and your miata...

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 01-31-2013, 12:16 PM   #1
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default The elusive 3.308:1 rear diff

Ok, so. First I realize that ALL of the 3.308:1 rear gears in America for a mazda are the 7.5" ring gear and NOT the 7" ring gear that we use. It is available in the manual tranny mazda b2000 pickup truck of the 82-84 vintage. I've found quite a few tiny tid bits of what I'm confident is good information. So, I know that the miata diff cover piece will bolt to the b2000 pumpkin, they have the same bolt pattern, grinding may be required to clear the bigger ring gear. I also know that the 2wd truck uses the same diff carrier as the 84-88 rx7 that we can swap into our diff, so in theory the carrier would be the same as the miata's. You need to swap the carriers because the splines for the axles in the carrier for the truck is bigger than the miata axles.

So my parts list of what I believe you need
2wd manual tranny 82-84 b2000 front diff section
miata diff cover/mount bit
any miata diff carrier (torsen, open, giken)
new bearings might be a good idea

So procedure wise
take stock truck diff and miata cover, line both up and keep grinding stuff off the miata cover until there is no more interference
pull the carrier and ring gear out of the diff housing
pull the ring gear off the b2000 carrier, bolt it to the miata carrier
put that into the b2000 housing, set preload and backlash
put miata cover on, put back in car, fill with fluid, use the axles already in the car

I'm not 100% on the diff cover bolt pattern being the same. But b2000 diff assemblies are so stupidly cheap around here that honestly money would not stop me from trying this. Time is. Time is the reason I dont already have one of these setup. I'll have time this summer once the rest of the car is together. Anyone else wants to try this before then, be my guest. IMO it makes the 6 speed a viable option, and I think the bigger ring gear with a giken would make this rear end bullet proof for the amount of power than pretty much anyone on here makes.

Last edited by Leafy; 01-31-2013 at 01:03 PM.
Leafy is offline   Reply With Quote
Old 01-31-2013, 12:54 PM   #2
Elite Member
iTrader: (10)
 
soviet's Avatar
 
Join Date: Jan 2010
Location: VA
Posts: 3,519
Total Cats: 260
Default

What year B2000? I think it has to be 82-84, no?
soviet is offline   Reply With Quote
Old 01-31-2013, 12:56 PM   #3
Elite Member
iTrader: (10)
 
soviet's Avatar
 
Join Date: Jan 2010
Location: VA
Posts: 3,519
Total Cats: 260
Default

79 80 81 82 83 84 Mazda B 2000 Carrier Assembly | eBay

Food for thought
"MAZDA B-2000 79-81 (3.31 ratio)"
"MAZDA B-2000 82-84 MT (3.31 ratio)"
soviet is offline   Reply With Quote
Old 01-31-2013, 01:02 PM   #4
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

Yes, I had to do some more searching on that one because some reports were stretching that all the way from 77 to like 88. And car-part thinks that as well, heck be careful with car part because if you put in the 84 b2000 axle assembly and choose the 3.31 ratio it will throw in the random 70's toyota land cruiser too.

1 more hitch that I have not seen mentioned is that I am not certain that the distance from the input shaft flange to the axle centerline is the same. And that would require a custom length axle if it was different which would suck a lot.
Leafy is offline   Reply With Quote
Old 01-31-2013, 03:45 PM   #5
Cpt. Slow
iTrader: (25)
 
curly's Avatar
 
Join Date: Oct 2005
Location: Oregon City, OR
Posts: 12,110
Total Cats: 518
Default

You're forgetting about the PPF me thinks.
curly is offline   Reply With Quote
Old 01-31-2013, 04:02 PM   #6
mkturbo.com
iTrader: (24)
 
shuiend's Avatar
 
Join Date: May 2006
Location: Charleston SC
Posts: 13,780
Total Cats: 1,106
Default

Quote:
Originally Posted by curly View Post
You're forgetting about the PPF me thinks.
Completely over rated, we have a driveshaft to keep everything aligned.
shuiend is offline   Reply With Quote
Old 01-31-2013, 04:04 PM   #7
Elite Member
iTrader: (3)
 
Join Date: Feb 2008
Location: Huntsville, AL
Posts: 1,882
Total Cats: 45
Default

Quote:
Originally Posted by shuiend View Post
Completely over rated, we have a driveshaft to keep everything aligned.
Aligned-ish is good enough.
vehicular is offline   Reply With Quote
Old 01-31-2013, 04:04 PM   #8
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

****. Yup, no PPF mounting. Well that ***** up that idea. Now it basically has no advantages over the putting in a ford irs.

But it does use the samish length pinion shaft as the miata. I say samish because it keeps getting refereed to as "the short one like the miata so it wont work in you FC"

Last edited by Leafy; 01-31-2013 at 06:01 PM.
Leafy is offline   Reply With Quote
Old 01-31-2013, 05:55 PM   #9
Elite Member
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 2,904
Total Cats: 109
Default

That will give you an opportunity to hone your fabrication skills. Don't give up now.
miata2fast is offline   Reply With Quote
Old 01-31-2013, 05:59 PM   #10
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

Quote:
Originally Posted by miata2fast View Post
That will give you an opportunity to hone your fabrication skills. Don't give up now.
What, welding PPF mounts onto the b2000 diff housing? F that, I dont want to risk warping it.
Leafy is offline   Reply With Quote
Old 01-31-2013, 06:09 PM   #11
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Front diff.
hustler is offline   Reply With Quote
Old 01-31-2013, 06:09 PM   #12
Elite Member
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 2,904
Total Cats: 109
Default

Quote:
Originally Posted by Leafy View Post
What, welding PPF mounts onto the b2000 diff housing? F that, I dont want to risk warping it.
There are a million ways to skin a cat. The same could be said for mounting a diff. Motivation to me would be a stronger, lower ratio than the miata 7", but not the power robbing overkill of the Ford 8.8".
miata2fast is offline   Reply With Quote
Old 01-31-2013, 06:17 PM   #13
Destroyer of Inconel
iTrader: (37)
 
EO2K's Avatar
 
Join Date: Apr 2010
Location: In ur driveway, abusin' ur WPA
Posts: 9,642
Total Cats: 954
Default

Quote:
Originally Posted by Leafy View Post
But b2000 diff assemblies are so stupidly cheap around here that honestly money would not stop me from trying this.
Quote:
Originally Posted by Leafy View Post
What, welding PPF mounts onto the b2000 diff housing? F that, I dont want to risk warping it.
I'm failing to see why you are worried about warping it

Interesting academic thought experiment though, assuming you don't try it of course.
EO2K is offline   Reply With Quote
Old 01-31-2013, 07:07 PM   #14
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,206
Total Cats: 2,587
Default

Yeah, I'll +1 and "cool story bro", and wait for someone to actually do it rather than hypothesize
18psi is offline   Reply With Quote
Old 01-31-2013, 07:12 PM   #15
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

Quote:
Originally Posted by hustler View Post
Front diff.
There is only 1, its 117 miles away from me, and I dont know if it has the correct ratio. Though I had seen mention in a couple spots that they are in fact the 7" ring and not the 7.5".

And... there is a 1982 manual diesel b2200 20 miles from my house...

Last edited by Leafy; 01-31-2013 at 11:15 PM.
Leafy is offline   Reply With Quote
Old 02-01-2013, 12:05 PM   #16
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Have em measure the diameter and count the teeth.
JasonC SBB is offline   Reply With Quote
Old 02-01-2013, 12:12 PM   #17
Elite Member
Thread Starter
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

I have. Called the close place, they scrapped theirs, the place in NY is snowed in but will check when they get the chance. I also called mazdaspeed, and here is where it gets interesting. The part number for the 82-83 diesel manual 3.31 R&P is the same as the 82-84 B2000 auto trans 3.31 R&P. BUT his documentation shows that both of them are the big gear, it does show though that the 82-83 diesel R&P is a different part number than the 84 diesel R&P. He said though that they have 3.63 sets for the 7" ring coming out their ears, that I already knew.
Leafy is offline   Reply With Quote
Old 02-06-2013, 01:31 AM   #18
Newb
 
Join Date: Jan 2012
Posts: 27
Total Cats: -2
Default

I always considered getting a six speed and getting the shortest final drive available to make third the ideal gear for autocross. 4.778 or the 4.625 from a Sportage. This makes the sixth gear highway cruising pretty awful considering the 6th gear ratio is already shorter than the 5th gear in the 5 speed. I did some part number research though and the main and counter 6th for the Miata 6 speed matches that of the early RX8. The later RX8 got a taller ratio for sixth gear so that could be an option to alleviate the very high cruise rpm with a 4.778 or 4.625. That's what I would do to make the six speed work for autocross and the street.
ED9man is offline   Reply With Quote
Old 02-06-2013, 01:54 AM   #19
Newb
 
Join Date: Jan 2012
Posts: 27
Total Cats: -2
Default

I made this little table that demonstrates what I'm talking about. You see that if you swap in the newer RX8 6th and run a 4.625 you have a third gear that is virtually identical to the 2nd in a stock NA and your highway cruise is less than 200 rpm more than it is usually in a stock NB. Plus you have shorter gears all around which makes the car more fun anyways vs turning the car into a total dog with an ultra tall final to get the 2nd gear to work.

Max speed autox

5 speed 2nd 4.1 64 mph
5 speed 2nd 4.3 61 mph
6 speed 3rd 4.778 63 mph
6 speed 3rd 4.625 65 mph

80mph top gear

5 speed 5th 4.1 3890 rpm
5 speed 5th 4.3 4080 rpm
6 speed .843 6th 4.625 4550 rpm
6 speed .843 6th 4.778 4700 rpm
6 speed .787 6th 4.625 4550 rpm
6 speed .787 6th 4.778 4250 rpm
ED9man is offline   Reply With Quote
Old 02-06-2013, 01:59 AM   #20
Newb
 
Join Date: Jan 2012
Posts: 27
Total Cats: -2
Default

You can see here how the 6th interchanges. I would be pretty surprised if the revised 09+ .787 6th didn't also interchange, maybe someone has tried it?

GEAR, 6TH. 2004 Mazda # Y61117631
GEAR, COUNTER (6TH). 2000 Mazda Miata # Y60117309
ED9man is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Raleigh: Fiberglass headlight scope, 1.6L ECU, AFM, Hardtop latches, more bigmackloud Miata parts for sale/trade 13 09-22-2017 01:34 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Another Alternator thread ihiryu General Miata Chat 9 09-28-2015 11:22 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 05:11 AM.