(DRIVETRAIN) GSL Vs. GSL-SE differentials
 

hey guys, i just purchased a used 85 SE DIFF (supposedly) and i wanted to make sure that it really was an SE and not a GSL or i might have even been suckered into an 83 LSD DIFF. i just wanted to know if anyone knew any tips on how i can confirm whether its really an SE DIFF. i counted the teeth on the ring and i counted 43. i didn't count the teeth on pinion. by looking at the driveshaft flange i can tell its an 84-85 and that it does have an LSD unit. can anyone help me or confirm whether 43 teeth on the ring is an 85 SE DIFF?

If it is the full diff, that a gsl wheel won't fit. Different bolt patterns for the wheels.

just the DIFF buddy... im not changing axles... i just want to make sure i purchased only a GSLSE DIFFERENTIAL

Count the teeth, divide the pinion gear teeth into the ring gear teeth. SE=4.09 GSL=3.90

yeah, apparently i did the math and it was 43 on the ring and 11 on the pinion and it looks like i got suckered for a GSL DIFF and not the SE DIFF like i wanted. that sucks

I have an SE and a late non-SE ring gear in my hands,both are fine pitch gears so they have a lot more teeth than yours....53 and 59.
With only 43 teeth on yours,Id say you have an older gearset from an earlier car with the coarse gears.If the diff is LSD,then you have an 81-82ish GSL third member.The SE diff isnt really a big deal,the 4.07 gearset is only a slight difference from the 3.90 ratio of the other 1st gens.Plus,the SE LSD is actually inferior to the GSL units.I recently switched back to the 3.909 gearset to gain more MPH per gearshift....didnt really make much difference.If you really want an SE ratio,Ill sell you my old SE gearset for cheap and you can use my rebuild threads to put it all together.
See my two archieved rearend rebuild threads to see the difference between the GSL and SE diffs......

Yea,11 teeth on the pinion would be a coarse set.My fine pitch units have 14 teeth. I re-read your first and last posts about the diff flange and LSD......sounds like you have an 83 GSL unit.

The main problem is going to be the side gears.The older diffs had smaller size sidegears to fit the skinnier axles.Your coarse gears tell me you probably have an older,small axle unit.If you have a small axle rearend,then this is fine.You can still add the 4.07 SE gears,and you have the better LSD unit already with the GSL rearend.

how do you know whether i have a 83 LSD DIFF or an 84-85 LSD DIFF??? the flange fits the 84-85 driveshaft??? so i'm assuming that i have an 84-85 GSL DIFF not an SE. but i'm hoping ur not right about it being an 83 DIFF.

ok i attached my extra driveshaft to the diff and i have confirmed that i have an 84-85 GSL DIFF. its just the only downfall is that i don't have the 4.11 gear ratio like the SE but i have LSD now. thanks for the help steve i appreciate it man

hey steve how far are you from LA? would u be interested in rebuilding a DIFF??? the diff i really want is something with 4.44??? how much would u charge?

The large driveshaft flanges started in 83 and went to 85.

The only way to tell if you have an 83 GSL diff or an 84-85 GSL diff,is to check the axle splines.The 84-85 cars had bigger axles,thus more splines.The axle spline count is really the only difference between the 83 and 84-85 GSL units.

4.44 gears can be had for the 1st gen and they will fit into any pumpkin.Im about 50 miles north of SanFrancisco and I wouldnt mind doing a full rebuild,but its gonna have to wait a while.Im in the middle of moving AND remodeling,plus I have to pave and landscape my new backyard so I can move the cars/projects in safely.Naturally,this is all very slow going thanks to this stinkin' weather were having.When Im done, it will be awesome since Ill have my own private loft shop to do all my dirtywork in.
BTW,the SE has a 4.07 diff ratio,not 4.11.......

85 FSM, section 9, page 2 lists the tooth counts.

ring/pinion
43/11 > 3.909 ratio
53/13 > 4.076 "

From your #s you have the GSL gear set. It's my understanding that in mid-83 when Mazda went with the larger diff flange, they also went with the larger axles. I cannot confirm that this is 100% true as I've read conflicting information such as what Steve just posted. Easiest way to tell the difference between early and late 83 diffs is the pinion flange bolts. Later 83's have bolts and nuts for the driveshft to pinion flange, early 83's have bolts only.

To determine which diff you have, the large axles have 26 splines and an O.D. of ~1-1/16"

Explain. I've been looking for confirmation on this.

+1. I'd like to understand this as well.

If you're looking at a complete diff, the easiest way is to check the pinion - driveshaft bolt holes. If they're threaded, it's small-bearing. If they're thru-holes, big bearing. Either way's fine, but that's the easiest, and it's highly junkyard-compatible.

I bet I can explain. The SE diff is inferior because Mazda, according to Steve, reasoned that the extra torque could cause problems so they detuned the LSD to make the car less tail happy. There are four discs and on SE units, there are three on one side and one on the other while on GSL units there are two on each side. Or something like that.

I think I have a GSL rear end in my S model. It has the large flange so I don't know whether it's '83 or '84-'85. I don't have any other cars here to make a direct visual comparison. Man it would suck if I had a GSL-SE rear end.

An added update:

Small axle
Splines are ~ 31/32 in dia.
24 splines
2-7/8" outside housing dia., measured at the bearing.
Axle shaft is straight from the bearing to the beginning the splines where it narrows down. Overall dia. is 1-1/16"


Large axle
Splines are ~1-1/8" in dia.
26 splines.
3-3/4" housing diameter at the bearing.
Measuring from the spline end towards the bearing end, the shaft is 1-1/16" in dia. for the first 16-1/2", it then steps up to 1-7/32" dia. from that point to the bearing.

These measurements were taken from an early 83 LSD/disc unit and an 85 drum unit.

Crit, are you positive the through-bolts on the flange are the way to tell? Percent's '83 has through bolts, as does whatever year is in mine. I'd say through-bolts designates both as '83 units.

Through bolts designate the difference between large and small flanges. Mazda made the change mid year 83. The following measurements are from the early 83 listed above and the 85 LSD in the widebody.

Small axle/flange
Flange dia. 3-9/16"
Diagonal bolt centers 2-29/32"
Bolts only, no nuts.

Large axle/flange
Flange dia. 4-5/32"
Diagonal bolt centers 3-7/16"
Through bolts with nuts.

Didn't measure the bolts, but the later ones are a larger diameter.

Jeff, do you happen to know if either unit has the large axles and are you sure they are 83 units? I'm sure of the mid-year flange change, not sure if the axles changed then also or if they waited until the 84 model year.

I honestly don't know. I have seen an '83 with the small flange and these two with the large flange. My friend has an SE that I will be taking a look at in a few months when it goes to the shop for its ghetto engine. If I can compare it to a GSL I'll probably recognise the differences and get back to this thread if I remember.

84-85 GSL 3rd member > GSLSE LSD

^ If the car is stock it doesn't really matter.

Thru bolts mean late 83 - 85, so they're big bearing. Old schoolers (70s) and RX-7s through early 83 were threaded small bearing.

Thats basically the jist of it.
The LSD unit itself, is the same for all 1st gens.There are always four friction plates on each side of the unit.But the GSL-SE has the friction plates arranged so that there is less grab and less tendancy for the unit to stay locked.

Heres a basic explanation........The GSL's have drive(1) and driven(0) discs arranged in an alternating fashion.....1-0-1-0....the zeros are the driven discs and both sides of the zeros rub against the driven discs or driven carrier housing.That gives you four friction surfaces for each axle.
The SE has the EXACT same LSD unit but the friction discs are arranged like this......1-1-0-1......there is only one driven disc on each side of the LSD,so there are only 2 friction surfaces per axle vs 4 firction surfaces on the GSL.The two 1's are both driven by the carrier,so they do nothing by being adjacent to each other.And by ending the stack with a 1,you have another friction surface that rides against the driven portion of the LSD (the thrust blocks),this also accomplishes nothing.The only place you have LSD friction built up is on each side of the single 0.
Yes you can rebuild the SE limited slip with a GSL disc pattern,thats what I did.But youll need some extra,good condition discs to pull it off.
Youd have to talk to a Mazda engineer for the exact reason why this is the way it is,but like Jeff said I assumed it was due to the SE having a greater amount of torque and the 1st gens known tendancy to wag its tail.A torquier engine can bear down harder on the LSD unit and keep it locked up,even with less friction discs rubbing against each other.Check my LSD thread and youll see what happened to my SE limited slip unit's driven discs........

https://www.rx7club.com/1st-gen-archive-71/drivetrain-gsl-se-lsd-teardown-pics-drivetrain-tutorials-coming-soon-717591/

Also can do the redneck test. Burn out and see if there is a little mark for the drivers side.. then it's lsd. Solid on right.. stock.