I want to switch to a hydraulic T/O bearing (McLeod PN 1400-22) to eliminate the need for a slave cylinder and clear the way for exhaust on the driver's side in my conversion.

There was a thread on the Impala SS forum which lists the flywheel (PN 460360-1A), clutch plate (PN 261871), and pressure plate (PN 360710) required to switch to a hydraulic T/O with the LT1 T56, however, I'm looking into running an "SBC" style Street Twin instead.

Two part numbers are listed for the '86-'92 305/350 w/1-piece rear seal and 1-1/8x26 spline, which is what the parts above were intended for. PN 64004-1A-07 (63004-1A-07 is the aluminum version) is listed as a "Diaphragm P/P" and PN 64004B-1A-07 (63004B-1A-07 = aluminum) is listed as "B&B/Long P/P". Does anyone know what the heck that means and which pressure plate combination is the correct one?

Thanks in advance.

 

Jimlab,

I'm thinking that there just isn't enough room in the stock LT1 T56 bell housing to convert over to a Hydraulic TOB and push style PP. I'm in the midst of converting my system over to a Mcleod Blowproof Bell housing , Revloc Long Finger clutch and Hyd TOB. The changes required are substantial. I'll need to buy a new Viper aftermarket GM T56 because the new BH moves everything back about 2". The Aftermarket GM T56 will put the shifter back to within 1/8" of the original position. Most of my desire for this expensive swap is driven from safety concerns about my tootsies, but I'm anxious to test out the adjustable PP and sintered iron disk as well. There's a group in the Northeast called ProStick and they all run iron disks. They dump the clutch at about 7500 , pull the front about 2 feet up, and barely chirp the slicks. If this mess actually works I'll be glad to share the "how to's". If it's a massive expensive failure, I'll just tuck my tail between my legs and make like the whole thing never happened.

D&D performance has some good dimensional info that may help you. Also check Forte's web site and Sallee Chevrolet as well.

 

Looks like it is referring to two types of pressure plates (P/P), diaphragm and Borg and Beck (B&B). A little bit about the differences here.

 

There's evidently enough room for a hydraulic T/O and the clutch/flywheel combination I listed above, because someone's done it and those are the parts that Thunder Racing recommended to them, apparently. I just want to know if the '86-'92 Street Twin has the same dimensions as the clutch package above and work as well.

It was my understanding from the magazine article on McLeod's SFI-approved modular bellhousing for the LT1 T56 that it included a pilot bearing extension to increase the effective length of the input shaft to LS1 specs, allowing the use of an LS1 push-style clutch and hydraulic throw-out bearing. Is the blowproof bellhousing you're talking about different? It was also my understanding that the modular bellhousing system wasn't available yet.

 

Thanks!

 

Jim,

You certainly could be right about the push type PP and TOB, I just know it's very crowded in the the LT1 bell housing.

Also,

Your correct, I'm not using the Mcleod new modular Bell Housing. I'm using a standard off the shelf Mcleod small block bellhousing. The package is about 2" longer than the LT1 T56 setup, but so far everything is bolting up and clearing things (like the headers) I was going to go the modular route but as you said it's still not available. Plus, I really wanted to go to a long finger style PP with adjustable static pressure.

Good Luck on your project!

Steve

 

Thanks Steve. I don't have room for the extra bellhousing length, since space is already at a premium in my car.

From talking to Doug Wood from the Impala SS forum, he's running the McLeod flywheel I listed above, but had problems with the balance of the McLeod clutch plate and cover and ended up with a SPEC Stage III disc and cover he bought from Thunder Racing.

According to him, there's plenty of room, and the hydraulic throw-out bearing has an adjustable collar which is adjusted out about 0.25" on his car to contact the pressure plate. The slave has a total throw of about 0.66", but only requires about 0.25" to disengage the clutch and release the disc.

He's run the bleed line vertically out of a hole at about 11 o'clock on the bellhousing to facilitate bleeding the slave from the top of the car. The hydraulic line has been run out of the stock slave cylinder/clutch fork opening in the bellhousing to a McLeod master cylinder.

Apparently it does work, and well, and he's taken the teething pains out of the process by tracking down the right parts.

 

Interesting. Does the Hyd TOB just slide over the input shaft and seat against the T56 front adaptor or are they using some kind of intermediate adaptor plate to bolt the TOB to? The front of the T56 doesn't look like was set up to accomodate this very well. It's always nice to have some pioneers out there to pave the way for us mortal men. They're the ones with the arrows in their butts.


Steve

 

It just slides on, apparently.

You're right, but apparently it isn't a problem. Of course, you could always machine a thrust washer or something to take the load.

You can say that again. I have way too many arrows in my butt as it is...

 

This is an old thread but hoping you had some luck with this Jim?
Any news on this process?
Let me know,
Mike

 

I'm curious also Jim. FWIW, my new iron disk setup w/ hydraulic TOB has worked flawlessly so far (knocking on wood). I have about 20 passes with the PP preload set pretty high. I had traction problems this Sunday so I'm tempted to softened up by lowering the preload a tad. The iron disk is "on or off" It can be slipped, but saying it's toutchy is generous. That being said, it does not chatter and is no different while going up through the gears. Not a great street clutch but passable if your only putting a couple of thousand miles a year on.

I'm a happy camper with my setup and I'm most relieved with the safety aspect of having a real bellhousing. Now I can go into the 11's and still be NHRA legal.

Steve

 

Haven't been around for awhile.

I ended up with a McLeod 1400-22 slide-on T/O bearing and '86-'92 1 1/8"x26 spline Street Twin (PN 63004-1A-07, aluminum flywheel) because McLeod said they'd fit in the LT1 bellhousing. A friend bought the same setup and has done some measuring and thinks we're about 0.25" too "long".

There is supposed to be about 0.10-0.15" clearance between the fingers of the clutch and the T/O bearing prior to bleeding, according to the instructions, and I haven't done the measurements myself yet to see if my friend is right or not.

The instructions do say that if there isn't sufficient room, that a bolt-on T/O bearing may be substituted because it has a shorter assembly, apparently.

 

It turns out that the '86-'92 McLeod Street Twin and hydraulic slip-on throw out bearing DO NOT fit in the stock LT1 bellhousing as McLeod claimed... but they will with a 1/2" spacer between the bellhousing and the body of the transmission.

Parts required:
1/2" down pins (2 required) - PN #8707-22 ($7.44 ea.)
1/2" spacer plate (1 required) - PN #8703-22 ($77.50)
1/2" pilot bushing (1 required) - PN #8617 ($26.35)