LSXus300

hey guys I recently got my lS swapped Lexus is300 running. It's a Gen IV aluminum 5.3 block with an fbody t56 and bell housing with a brand new GM slave , monster 6 puck clutch kit with there flywheel. I'm using a wilwood master from dedicated motorsports, I think it's a 3/4 bore but I'm not positive. The pedal is a universal wilwood pedal I have cut and welded into position, I've never adjusted a clutch before. I know how I have it welded at the moment it has a fairly long throw and the clutch disengages close to the floor. Seems to shift just fine. The first night I drove it the clutch went to the flood on the way home and was puking fluid out the bell housing. Pulled it out and had a giant hairline crack around the whole inner shaft hole. I thought it was a casting defect until a few hundred miles later the next one went out last night. Haven't gotten a chance to take it out yet though but once again fluid out the bell housing and it drained the whole thing overnight. I really need some advice on what could be causing this

Darth_V8r

iTrader: (4)

Here is what it sounds like based on your description.

Sounds like there is too much gap between your fully collapsed slave and pressure plate and it's been compensated for by making the master have a long stroke. The master can over stroke and blow the slave apart.

There is a sticky on measuring for a shim behind the slave. If you shim the slave, then you will need less stroke to disengage. Too much shim and it won't fully disengage.

Adding a shim will also move the engagement point higher off the floor.

LSXus300

That does sound like the best answer yet, would over extending the slave cause it to crack potentially? The first one had a crack around the hole the input shaft goes into. I'm just worried I'm gonna pull this second one out and it have a crack in the same spot and it be something not related to needing a shim

Darth_V8r

iTrader: (4)

Yes it can. The slave only has 13mm of total stroke. You need most of the stroke to push against the PP. You need some amount of free play so that you aren't holding the clutch partially disengaged all the time. So, let's say you have 1/4" (6.3mm) of slop in the slave for free play - that's half your available stroke! Leaves only 1/4" (6.3mm) to actually work the clutch. It's the long pedal throw in your OP that makes me think this is the issue.

Now, cut that to 1/8" (3mm) free play, and that leaves you 10mm to work the clutch. You use up 7-8mm on the clutch, 3mm for the free play, and still have 2-3mm unused.

The way I measured mine was to fully collapse the slave with a construction level while attached tot he transmission and measure from the end of the throw out bearing to the transmission case. Again, this was fully collapsed. I then installed the bell housing, an using a straight edge measured from the bell housing to the highest point on the pressure plate. The second measurement should be longer than the first measurement. I had 7/64" difference between them, or roughly 0.110", which is again, roughly 2.75mm. So I didn't need a shim. I've seen others measure close to 0.300" difference. I suspect you'll find yours is in that neighborhood.

You'll have to take it off anyway to replace it. Don't just throw a shim in on a hunch, but if you measure and you find that there is a huge difference, that is almost certainly the culprit, and the shim should fix it. There's a sticky that does a better job explaining it.

And just checking - I've seen people say they bought a GM slave, and it was the autozone / NAPA / etc stock version. I bought from Tick performance, and it was genuine GM.

Darth_V8r

iTrader: (4)

Oh, and you might want to un-weld the rod for the master cylinder and put a turnbuckle on it to control the rod length. give yourself enough pedal to disengage the clutch, but no more. You can still over stroke the slave if you don't shorten that rod.