T56 mods for LS7 Clutch kit

[Aussie Mike]

Warning: Boring Tech Post


Hi All,

Haven't posting much lately as I've had not much Cobra time lately. Family and work has been pretty busy. However one thing that may interest you is a T56 gearbox rebuild I've been doing for a bloke in NSW.

Apart from wanting it beefing it up and fixing the shift he bought an LS7 clutch kit from the US and it looks like there might be some compatibility issues with some gearboxes and this clutch kit. I've recommended the LS7 clutch kit myself as it seems to be a very good piece of OEM equipment at a good price. However it looks like you probably need to check a few measurements before buying one.

John bolted up his LS7 flywheel and clutch and measured the distance between the back of the block (Where the bell housing bolts to) and the tips of the fingers on the pressure plate. He got 108mm with a straight edge across it. I measured the distance from face of his bell housing to the face of the thrust bearing and got 90mm. This means that just bolting the thing together has already compressed the clutch diaphragm 18mm before you've even pressed the pedal. Probably not a good recipe for a healthy clutch operation. I believe there is some adjustment in the diaphram to compensate for clutch wear but not enough to deal with that 18mm.

I was looking at machining up a new housing for hydraulic throwout or a new thrust bearing carriage but there just didn't seem to be any easy way to do it. In the end since I had the gearbox apart for the rebuild I figured re-machine the boss where the slave bolts to would be the neatest option.

Here's the front plate of the box on the mill and I've started rough cutting to remove material from the hydraulic throw out mounting boss.



I've removed about 16mm of material and machined the boss square and flat. I can't really go any further down as I need to leave enough metal for the input shaft seal to seat against.



I've all but machined off the original bolt holes that hold the hydraulic throw out in place so have to drill and tap new ones. There's still plenty of material in the front plate to accommodate these.



There was a register ring machined into the outside of the boss that located the hydraulic throwout central to the input shaft. This had to be machined into the new location and required a bit of thought. I looked at mounting it on a face plate in the lathe but just didn't have enough clearance to turn it. In the end I used the rotary table on the mill and located it off the front bearing race. This will keep the register ring perfectly centered in relation to the input shaft.



The new register ring. I love machining aluminum.



The end result turned out pretty good and fits like a glove.



Give it all a good clean and it's time to reassemble.

We now have 106mm from the thrust bearing to the bell housing face. I think this should be OK once we mess with the clutch wear adjusters.



I will keep you posted how it runs once it goes back into the car.

Cheers

[muzzza]

Mike, I have A "Ram" aluminium flywheel with standard GM LS7 clutch in front of my T56 gearbox. It all seemed to go together fine. Information I had at the time indicated there was a problem only if you used the standard LS7 flywheel. Having said that......I might just re-visit things ( again ! ).........just to be on the safe side. I can remember cooking more than one clutch years ago....when I thought things were near enough.

Muz - Beerwah

[Aussie Mike]

i figured you would be OK muzza with an after market clutch. I just thought id point this issue out to anyone trying an LS7 clutch and flywheel kit.

Im running a yella terra light weight steel flywheel that only tips the scales at 7kg which is not much more than an aluminum one. The clutch is a Spec stage 3 unit which is a copper ceramic puck syle friction with a sprung center.

Cheers

[alffie]

Hi Mike
Go and buy a LS7 bellhousing they are 18mm longer!! I had the same problem when I bought my T56, Mal Wood stregthened my T56 for the LS7 but used a LS1 bellhousing and imput shaft. So when I rang him he was shocked!! So he sent me up a LS7 bellhousing and all bolted up fine, You may need to look at your spiggot bearing as the LS7 has a larger one installed in the first recess in the crank which is where most of the 18mm comes from so I had to remove it and fit a Holden V8 bronze spiggot to keep the imput shaft.

[Mando]

I wish I had room for a lathe and mill, that looks like great fun!

Regards.

[Modena]

great info thanks fellas. I have an LS7 clutch and flywheel for my build, along with a T56 from VZ, so I guess I'll need to do something like one of these suggestions!

[Gav]

Boring...

Real men have at least 40 clutches in their cars

[Aussie Mike]

Hi Alfie.

This bloke has a completed registered car. Changing the bell housing would be a tricky prospect. He has a square tube CR chassis and clearance is tight at the rear mount already. An 18mm longer bell housing would mean cutting the rear x member and a shorter drive shaft. Alternatively mod or move the front engine mounts forward but that would put the headers out of place.

The spiggot is not an issue as its an LS1 with a regular crank.

Cheers

[boxhead]

Gav, you like lots of clutches as you allways have your hand on it.



The clutch I mean

[Aussie Mike]

Originally Posted by Gav

Boring...

Real men have at least 40 clutches in their cars

Weren't most of your 40 clutches sitting in the bottom of your trans pan a while back?

[Gav]

No, only half of them

[PeterAllen]

I'm not sure if this is as much an issue with Cobras as it is with my GTO

I noticed you have retained the original t56 clutch bleed nipple. In my experience they are a nightmare to operate and I have fitted the extended hose, available from Mal Wood, eBay, etc. Much easier to use in my case.

[Philm]

Awesome work as usual Mike.

Just for some reference, this the a mal wood bellhousing and an after market throw out on the tko600 to bolt onlto the LS3 with an LS7 clutch and flywheel set.







Phil

[Aussie Mike]

That's a very nice setup Phil.

Mal Wood does some nice stuff. I think that's the McLeod or Tilton hydraulic throw out. The nice thing about it is the body of the assembly is threaded so you can dial out the position of the throwout to get exactly the right amount of free play.

Cheers

[Aussie Mike]

Originally Posted by PeterAllen

I'm not sure if this is as much an issue with Cobras as it is with my GTO

I noticed you have retained the original t56 clutch bleed nipple. In my experience they are a nightmare to operate and I have fitted the extended hose, available from Mal Wood, eBay, etc. Much easier to use in my case.

Hi Peter,

This one is getting a remote bleeder too, I just haven't fitted it yet.

I've made the hose style bleeders before but I have my own design simple remote bleeder that seems to work very well. The hose ones are good for tight engine bays where you can't easily get in to the bell housing but I'm not keen on extra hoses. Plus they are often seem to get installed with the bleeder lower than the slave cylinder which I reckon could give trouble with air locks when bleeding. The bubbles always go to the highest point in the system so that's where the bleeder should be.

Here's the setup I make. It's an extension that brings the bleed fitting out to a regular bleed nipple that you can clip a hose to and bleed just like your brakes.



Here's the view on the outside of the bell housing. It's pretty easy to get to. I can get a spanner on it just reaching into the engine bay on my CR.



The bleed nipple is at the highest point on the slave so air bubbles will head there on their own.

Cheers

[Philm]

Thats a great solution, very tidy.

[Mrs flatchat]

I think Phils TOB is a Quartermaster
Note to Aussie Mike --your TOB has plastic piston components that apparently melt and distort with heat etc. Mal Wood has an Al. piston replacement for this--(whileya dare like)

[Mrs flatchat]

Heres something else we've been working on that would give a competitive edge in the power down department --all the drifter boys have been using 'em

[Aussie Mike]

Thats a very nice bit of kit. Any details?
How many plates? Will it work on the street? Are you making an LS1 version?

Cheers

[Mrs flatchat]

Jim Berry at Race Clutch Australia -- if you don't mind a chat 07 38479999