Will 3.308:1 gears from a 1982-1984 Mazda B2000 pickup truck fit into a RX-7 rear end?
 

 Latest update: 1/4/09
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Contrary to what some websites and a reply to a post I made on a Mazda truck website said, 1982-1984 Mazda B2000 stick shift, GAS engined pick up truck rear end gears WILL NOT fit into a RX-7 1st generation 7" ring gear carrier (pumpkin, chunk, pig, banjo, 3rd member or what ever you want to call it). Tru$t me on thi$.

I bought a 1984 B2000 gas engined p/u carrier biased on information stated on several websites and the gears are 7-1/2" in diameter and won't fit! Other people on the LocostUSA forum have found that they don't fit into a '94-'97 Miata either. The B2000, B2200 & Courier gas engined pick up trucks of that era seem to all use a 7-1/2" gear set.

Cat shooting     Here's how I felt after finding that the 1984 gas B2000 has a 7-1/2" diameter ring gear!



I've decided to once and for all try to find out if there are any 3.308:1 Mazda 7" ring gears that will fit into a RX-7 carrier and post the results here.

First off:
The following link was probably the main source that information on the web is based on. The information presented on the original site was fundamentally correct but just vague enough (IMHO) so that it caused confusion as to what trucks have the 7" gear set.

http://www.solomiata.com/Drivetrain.html   (New link address.)

1/1/09:  The site has been updated and now clearly states: "Mazda has discontinued the 3.308 (optional on 82-83 B2000 diesel) gears."

Further down on the original page there is a quote that the 1982-1984 Mazda Courier stick shift Diesel pickup gears are the ones the author was referring to.  Right away you have to wonder is it the '82-'83 or '82-'84 gears that are the ones to get.

Another quote from the site is:
"Mazda also made what I call the "hybrid" 7.5 inch rear. It was installed on most '84-93 trucks and was also later used on the rear of the Sportage. They basically took the 7" pinion housing and pinion and mated it with a larger ring gear. It also used larger diameter axles. The 7.5 pumpkin will bolt into the rear aluminum housing of a 7" rear (the hold down bolts positions are the same) but you will have to perform minor grinding surgery to clearance the larger ring gear and then machine the side seal pocket for the larger diameter axles. It's been done."

So far I've found that the 1984 B2000 GAS engined stick shift xmission trucks all have the "Hybrid" 7.5" gear set. And I can't in my wildest dreams imagine that you can stuff a 7-1/2" carrier into a 7"  axle housing.

Then there are posters on other forums that have their information flat out wrong and say that any '82-'84 B2000 3:308:1 gears will fit. They will NOT fit, no matter what they say.

See my chart below for measurements of the 7" RX-7 and 7-1/2" B2000 carriers. The bolt PCD of the 7-1/2" ring gear is larger than the max diameter of the  7" spool. And the final kicker is that the dimensions of the carrier bolt pattern that holds the 7-1/2 carrier housing on the axle housing is much larger than the 7" dimensions. Other than those problems.........



Facts found out so far from forum posts etc,

11/10/07
I've found out that the Courier Diesel wasn't even imported to the USA. They were sold in Canada, New Zealand, Australia and other countries though. The jury is out on where the Mazda Diesel B2000 trucks were sold.



11/19/07
I received a response from a poster on the "Mazda Diesel" forum that his stick shift 1981 gas Courier "K" measurement (see chart below) is ~9-5/8" which is close enough to the measurements I took on my B2K 7-1/2" ring gear carrier. His gear ratio is 3.54:1 though.

I received another forum response from a guy in Australia and he mentioned the usual MX-626 RWD gears (3.626:1) that should fit but no mention of pick up truck gears.



11/20/07
I got another response from the "Mazda Diesel" forum where the same Courier owner says that his 1984 Mazda Diesel B2200 "K" measurement is ~9-3/4". His "E" measurement is ~7-1/2".

These measurements are rather difficult to take since you can't measure them directly due to other parts being in the way. I use a large Caliper I made for measuring wheel widths to take the dimensions.

So it looks like we can rule out the '81 gas Courier and the '84 Diesel B2200 carriers (built from 1982-1985) as having suitable gears. I don't know what transmission his B2200 truck has.

Considering that the 1981 Mazda built gas "Ford" Courier had a 7-1/2" ring gear, the 1984 Mazda Diesel B2200 and the 1984 Mazda gas B2000 used the same 7-1/2" gear size, it would seem logical that the '82-'84 Mazda B2000 Diesel would also use the same sized gear that all the other 1981 through (at least) 1984 trucks used.

It seems strange that once 7-1/2" gears were used on the 1981 Courier that Mazda would have gone to a 7" gear on the '82 and '83 trucks. But apparently they did use some 7" gears if the information is correct.

After finding out that my 1983 donor RX-7 rear end has a 1984 gear set in it I guess anything is possible. Even Mazda going to a smaller carrier and gear set as a low volume option on the Diesel truck. The 7-1/2" rear axle housings are pretty substantial looking compared to the 7" RX-7 axle.

I like proof positive so I'll continue to look for information. I would be delighted if someone proves me wrong and the 7" gears do really exist.



11/21/07
A member of the LocostUSA forum posted this response in answer to my request for information on the 3.308:1 gear set.

Blackbird wrote:
A discussion I found on the Miata forum, the user Dynra Rockets is Randy from Solomiata.com .

        http://forum.miata.net/vb/showthread.php?t=150935&page=1&pp=25&highlight=3.308

__________________________________

I've compiled the following question/answer from the the 2nd post (page 1) on the above link. It has the most definitive description of which Mazda built trucks have the elusive 7" gear set. This is the information we should have all seen -before- we bought the wrong Mazda carriers. To bad the information isn't on Randy's website. (Hint-hint.)
__________________________________

17th September 2005, 06:30
Dynra Rockets
Overdrive

bmeup wrote:
Surely this topic has been covered before, but I'm not finding exactly what I'm looking for in the posts and other links. I'm trying to confirm precisely what vehicles had the 3.308 final drive. The bits & pieces I've pulled together so far are:

* '82-'84 B2000/Ford Courier pickup
* diesel engine
* manual transmission
* may have been optional?

Are all of these true?
--------------------------------
Ans: yes
--------------------------------
bmeup wrote:
Were there possibly any other vehicles which had them?
--------------------------------
Ans: no
--------------------------------
bmeup wrote:
Are there any other important details a person should know before trying to locate one?
--------------------------------
Ans: good luck. I've seen one in 15 years.
--------------------------------
bmeup wrote:
I've also seen references to how rare these are. Are they really that rare, or are we just asking the wrong questions, looking in the wrong places? Is it worth even trying to find one?
--------------------------------
Ans:
made for 2 years on a limited production diesel and as an option. There are probably less than 100 that existed and most of those have likely been crushed (they are 23 years old now!)

I called MazdaMart a few years ago and they hadn't seen one in a decade.

Probably easier to buy a whole truck and then swap out the rear to a more common 3.909 and then sell the truck again.
[snip]

Randy


I think that Randy didn't notice that bmeup said "'82-'84" since Randy answered that the gears were used for TWO years (presumably 1982 and 1983). So that is probably just a oversight on his part. But it might have fueled the belief by others that  the 1982-1984 gears were the ones to get.

Basically the 3.308:1 7" gear set is made out of unobtainium.  But we now hopefully, have the real answer even if the parts are going to be extremely rare.

Considering that the Courier Diesel pickup was not imported to the USA it will be even harder to find one.



The following information will help you identify a 7" carrier from a 7-1/2" one.

The '84 gas B2000 carrier I have looks like a RX-7 carrier that's been on steroids. Even if the rear end is still assembled, it is easy to see the difference just by looking at the diameter of the carrier mounting flange (symbol "K" on the drawing).

Several sites say the 1994-1997 Miata uses the same 7" gears that the early RX-7 uses. (I'm just repeating what they said.) Unfortunately most of the Miata gears are a higher numerical ratio than the stock RX-7. So the Miata gears won't help RX-7 axle owners if you need to go to a numerically lower ratio.

If you call a "used" (junk) car parts place they may say they have a '82-'83 ('84 also) Mazda or Courier Diesel carrier with the 3.308:1 gear ratio.

*** Find out exactly what diameter the ring gear is BEFORE you buy it! ***

The correct place to measure the diameter of the ring gear is at the root of the gear teeth (at the "bottom" of the teeth). See the chart below for details. You can probably get the same results by getting any measurement from "A" to "K" (except "G") and compare them to my chart.

So far all the carriers that I've heard of have the wrong, 7-1/2" diameter, gears.

The chart below gives the measurements I took from my RX-7 carrier (ring gear p/n M050) and the B2000 (ring gear p/n 8789). I've been asked if it might be possible to put the 7-1/2" gears in my carrier. The biggest problem (discounting whether the pinion would even line up correctly) is that the bolt circle that holds the 7-1/2" gear to the spool is 1/16" greater in diameter than the maximum RX-7 spool diameter. Other than that.

You've been warned.




Carrier chart



Next minor problem:
Luckily I also wanted to reset the backlash on my ring & pinion (r/p), so it wasn't a completely wasted effort to take my rear end apart. I also found out that my wheel bearings needed replacement. That's another story altogether.

I'll tell it here so others can profit from my mistake.
Once I got the RX-7 carrier out of the car I found the part number (p/n) on the ring gear to be "M050". This gear set was only used "through April of 1984" and is a 3.933:1 ratio. The 1979-1983 RX-7 cars normally used a 3.909:1 rear end gear set with a different p/n.

Based on all the above, it would be natural for a person to assume that my rear end was a 1984 axle. The first three letters of assume is what you can sometimes become if you make assumptions.

I ordered the wheel bearings etc for a 1984 axle and when they arrived they were too large. After doing more research on the web, measuring my present bearings, looking at my RX-7 fiches and finding bearing dimensions on this Timken bearing page on the web that gives the actual bearing sizes for many cars, I realized that I have a 1983 GSL axle -housing- (which does take the smaller bearings) with "1984" gears installed in it!

And to make the story even more strange, my axle came out of a 1983 RX-7 GSL! Can it be that Mazda has a time machine? Or the parts fiche doesn't quite give all the info one might desire.

Moral of story, trust but verify.

P.S. After adjusting the backlash and replacing the wheel bearings, my car shifts much quieter, the "grunching" noises from the wheel bearings are gone, and the crashing noises when lifting and giving the car gas have quieted WAY down. The remaining crashing noise is due to the clearances in the LSD and seems to be normal for these units.