The purpose of this post if to serve more as a FYI than a how to or info on a successful swap.
I was thinking of picking up an inexpensive S1 B16 transmission (small spline cable with the 4.4fd, 66 teeth etc) and swapping the LSD differential from a spare Y1 final drive I had laying around.
Reason is the Y1 has the same teeth count (64) as an LS transmission, thus also has a 4.26fd, that along with the less than tight gearing leaves something to be desired for my n/a setup.
If you’re also thinking of doing this - I regret to inform you it will not work.
The Y1 turns out to be a real oddball of a transmission. The OEM LSD unit bolts up to a 15-bolt ring gear, which seems to be exclusive to this transmission as all other ring gears for S1/J1/A1 etc all have 10 bolts regardless of the teeth count.
Here is an open small spline LS trans with a 10 bolt ring gear - my hunch is most open diff transmissions will have the 10 bolt as even the aftermarket LSDs and MFactory final drives for small spline transmissions have 10 bolt configurations.
So you are probably better off getting an aftermarket LSD unit. It seems the Y1 LSD is unique to the Y1 ring gear…I really thought I was onto something but I guess the hunt continues.
UPDATE: I’ve ultimately decided to go full bore on this transmission as luck would have it, my car started making a death rattle/knock. Noise only appears in neutral with the clutch out…making it likely the input shaft bearing. Initially thought the flywheel bolts got loose but upon pulling the transmission, there was no issue with those bolts. I’ve split the transmission up and started rebuilding the gearsets with synchrotech carbon lined replacements. Also on order is a 4.9 final drive and mfactory lsd so I will provide another update when that comes in…I will end up with a bunch of leftover 4.26 oem lsd units so if anyone wants one I might be able to ship it to you. The bearings took some researching to coordinate the part numbers but I think I’ve got it tabulated right below. This is for small spline b series only as described in the diagram. When removing the input shaft bearing I can hear noise and feel the wear when spinning it by hand so I hope that was the problem pin pointed.
My question now would be for anyone who has re-assembled gearsets, should their be any axial (up/down) movement between the gears and the hubs? I forgot to check when disassembling. I’ve tapped the synchro hubs back on the input shaft with all the gears and synchros in order but not sure if I need to press them in a little more to stop them from wiggling a bit. The service manual only shows the clearance between each gear and the respective synchro or the other gears it is stacked on…nothing about the hub.
Well it might’ve taken me 3 months, but I got it back together, in the car and to a few track days
To recap,
-Installed a master bearing kit and carbon synchros from synchrotech
-Verified input shaft thrust
-Installed new carrier bearings onto mFactory helical LSD
-Installed mFactory 4.9 final drive kit
-Verified preload on diff
-New throwout bearing
Some photos of the process are below. Really regret not tracking down an LS 5th, but I was in a hurry as the season was coming to a close.
It really isn’t too bad a job if you take your time. I got shafted a few times trying to purchase an ITR 4.7 trans, so I just got fed up and decided to work with what I have. The costs are not much different than converting to hydro and purchasing a Type R core.
There’s a video on youtube about the break in procedures for these differentials that involves driving in circles and figure 8s for 10-15 minutes at a time with/without the clutch engaged. I tried for maybe 5 minutes and pretty much got car sick lol. Here’s to hoping I installed everything to a degree that will hold up for a long time. I’ve driven it quite hard already and everything seems fine. The differential whines more than stock, which the manufacturer claims is normal as the teeth are cut in a semi helical fashion (slightly straighter than stock, but not straight cut). According to them, mechanical losses are less but there will be more noise straighter the gears are cut.
Cool thread and nice info! I would love to see a video of you rowing through the gears.
I’ve finally just started the rebuild on my y1. I’m doing more or less the same work, except I’m replacing my lsd (probably blown) with an open diff and a 4.4 FD from a GSR along with the synchrotec master kit.
Do you have any tips for getting the carrier bearings on without a press? Also I’d love to know how to check the diff preload and input shaft thrust on assembly
Thanks! To get the carrier bearings off I torched it and used some wedge shaped scrap metal i had laying around to hammer off. In hind sight it would have been easier to grab a bearing puller off amazon. I would take extra care removing the speedometer ring gear as the teeth are very soft. I damaged mine and it nolonger meshes properly with the plastic speedo sensor so I nolonger have a working speedometer with this transmission.
As for checking thrust, I don’t 100% think it is necessary unless you are changing the bearings or input shaft itself, the slight variances in manufacturing length of the shaft or the bearing width might cause thrust changes where you need to add or take away shims but if you are only doing synchros I think you can skip it. You need to get a magnetic dial gauge and 1320 performance sells a tool to pull up on the input shaft. I bought both and regret it, will probably only use it once and the thrust tool totally sucks for the price, probably could make something out of an old throw out bearing that works better.
Checking preload is easy, the diff should not spin easily when the case is closed. Put the diff in the case, fasten the case every other bolt about 20ftlbs each. Then get a preload checking tool and you might need to make a bit that fits in your diff (there is an X engraved in the diff you might be able to weld something that keyes into this) or I grabbed a socket and wrapped it tightly in hockey tape until it fights tightly in the diff and tapped it in gently with a hammer. Then you can move the tool and take a reading of how much torque it takes to rotate the diff. I think there’s an acceptable range I just cannot remember at the moment.
