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This might get a it lengthy, but if you have ever rebuilt a first gen LSD diff, please read through and give an opinion.
I have a 79 Rx7. Bought it new in may of '78 and in '81 I believe, I installed a Mazdaspeed competition LSD from Racing Beat. The car still has the original drum brakes and so should have the 24 spline axles. I have a donor rear end assembly with disc brakes with 26 spline axles.
After reading the archives I know you cannot just swap my LSD into the Disc equipped assembly because of the splines. I also know that I would likely need another driveshaft if I used the donor diff in it's entirety.
After searching through the fiches for both early and later LSDs, both GSL's and GSL-SE's it appears, although not 100% certain, that the only parts that I believe would cause a problem between the diffs are the two gears that are actually splined and connect with the axles. The parts and gears that mate to them all carry the same part numbers in both fiches.
To me that indicates that you could swap those gears on either stock LSD and retain whichever axle you want. So, has anyone done that?
Of course a positive answer to that question still won't guarantee that the competition LSD I have will have swappable guts. So, does anyone have any experience with the rebuild of the competition diff or performed the operation I am hoping for? I really would hate to lose that diff!
The car is in excellent shape, 78,000km, 4,000 km on the 13b street port with Dellortos, never winter driven. It was an awesome Solo car winning 8 Ontario Autocross and 4 Time Attack Championships between 1979 and 1985.
Okay got my fingers crossed!
thanks
Tom
Last edited by Tom Cinnamon; Nov 10, 2015 at 11:35 AM.
the STOCK 81-85 limited slips have different side gears depending on the axle size (big vs small). other than that and the GSL-SE having less lockup, via a flipped disc, they are all the same.
we also know that the Mazdaspeed diff, 0820-79-960B, worked from the Rx3 to the early Rx7's, so it must be small axle.
i was able to find a parts breakdown of the Mazdaspeed diff, but it doesn't include the side gears, the friction discs are different, although the unit fits in the same axle, so it can't be radically different.
what we don't know, is the interchangeability of the side gears between the comp diff and the street car diff
What needs to be replaced? Is your ring+pinion worn out or the LSD unit?
j_tso, nothing is worn out, I want to change the small axle 24 spline side gears inside my Late 70's early 80's competition LSD to the later 26 spline side gears in order to use the bigger axle disc brake differential housing. Currently the rear end is a drum brake housing.
Last edited by Tom Cinnamon; Nov 10, 2015 at 07:53 PM.
the STOCK 81-85 limited slips have different side gears depending on the axle size (big vs small). other than that and the GSL-SE having less lockup, via a flipped disc, they are all the same.
we also know that the Mazdaspeed diff, 0820-79-960B, worked from the Rx3 to the early Rx7's, so it must be small axle.
i was able to find a parts breakdown of the Mazdaspeed diff, but it doesn't include the side gears, the friction discs are different, although the unit fits in the same axle, so it can't be radically different.
what we don't know, is the interchangeability of the side gears between the comp diff and the street car diff
Exactly, I was certainly hoping someone in the past might have had reason to try this.
LOL, I am more than 30 years behind the curve. I can't be the first to have thought of it. I didn't really want to strip both LSD's down completely only to find it wouldn't work or worse. Getting the part numbers of the competition diff's guts would either shut me down or encourage me to pursue it further.
You might also want to check how the retaining collar on each axle attaches to the housing. If the diff works out you might also need to swap those which would mean new axle bearings.
Exactly, I was certainly hoping someone in the past might have had reason to try this.
LOL, I am more than 30 years behind the curve. I can't be the first to have thought of it. I didn't really want to strip both LSD's down completely only to find it wouldn't work or worse. Getting the part numbers of the competition diff's guts would either shut me down or encourage me to pursue it further.
i've seen a few drum to disc brake brackets, maybe that is the easy way to go? its fairly simple, its a square with a hole in it that bolts to the axle, and then a set of ears that hold the caliper.
Guys, he has a large-axle rearend that he wants to put his Competition diff into. Talk of bearing swapping is immaterial - there's no swapping of anything between a large axle and small axle rear besides bolt-on stuff.
The only drum to disc brake conversion brackets that I have seen made available commercially that would use First gen rear calipers were by RE Speed who have been extremely hard to get product from even when paying in advance. They were banned from this forum.
The only drum to disc brake conversion brackets that I have seen made available commercially that would use First gen rear calipers were by RE Speed who have been extremely hard to get product from even when paying in advance. They were banned from this forum.
true, my friend had a set in the 90's though, so its not complex, and ReSpeed isn't the only one to have done it
The images in the thread are gone, but I have included a shot of the ramps in the Mazda competition LSD.
So the side gear compatibility is still a guess.
