Hey guys. I know...another ls7 clutch thread. Sorry in advance. You will be glad to know that I've read nearly every thread posted on this topic more than once over the past year that I'd like to think I'm pretty up to snuff on most of the details of the job, so this shouldn't be too much of a repeat thread.

I'm just wondering if anyone can explain to me how exactly the TQ setting of the pressure plate bolts affects the actuation of the clutch, IE over 50 ft lbs of tq is said to put pressure on the fingers of the clutch, thus "pre-loading" it and giving us issues with very low pedals and even issues with improper (dis)engagement.

Now I'm no mechanic, so I'm not looking for anything super in-depth and complicated. My mechanic though, who is also a mechanical engineer, pointed out that it appeared that the way the PP attaches to the rest of the assembly, it looks like it would "bottom out" (metal against metal), regardless of how much tq you put on it. Looking at the ls7 in the box, I saw where the bolt hole's mating surfaces would come together, and I don't see what/where anything could move even if it was tq'd to death either.

Now, my mechanic wasn't arguing anything at all and the clutch was installed today with the PP bolts at 48 ft lbs and a dab of blue loc-tite for good measure. It'll be buttoned up, bled, and hopefully driven away without any hitches tomorrow afternoon. But he and I are both curious about the mechanics behind this ever-important torque setting. Anyone care to indulge us?

EDIT: He did tell me today that he tried to over-tq the stock pressure plate bolts just to see if it would put any pressure on the forks. He brought it up to 90 lbs and did not see any movement though. Maybe the LS7 is different in that respect, but he wasn't about to go experimenting with that... thankfully.

 

i wondered the exact same thing but didnt want to tempt fate as others have seemed to have issues when going over 50lbs.. so I did mine at 48lbs I belive and called it good.

 

I did mine to 47ft/lbs. Love the way the clutch feels. At first it engaged right at the floor but within a few days of driving it came up more and more and now it's about Stock.

 

The c6 zo6 clutch is supposed to be torqued to like 70ft pounds on the vette!! Were as our cars are only supposed to be torqued at 48 I believe. I'm no mechanic either but I know my bolts were torqued to V1 specs and the clutch engages in a very stock possession.

 

Yes, I'm well aware of this. I'm just trying to find out WHY this is the case...

 

For the single discs my guess is the tq rating is more for not stripping the threads out. On the twin discs you have the floater plates so the more torque you put on it the more compressed the straps get and it will change the position of the fingers. At least thats what I could tell when installing the two Mcleod RXTs.

 

There are a number of people who've installed the ls7 oem clutch and found that over 50 ft lb of tq on the pp bolts will actually put tension on the forks/fingers of the clutch... this is what I'm trying to understand. Because it looks to me like there's nowhere for anyting to move, regardless of how tight these bolts are... it would either be tight, or not... or the bolts would strip, as you stated... But I don't see how anything would change in terms of pressure on the forks and engagement of the clutch...

 

Mine are torqued to 52 ftlbs in the correct sequence per the directions that came with my Monster clutch. I've had zero issues.

 

I just follow the directions on all TQ specs.....I know, weird huh? lol

My buddy is a mechanical engineer as well, and questions everything. It's in their nature. Just tell him to shut it, and follow the directions.

 

Classic lolly. LOL

 

LOL He had no bones about following my request to tq to 48#, but he did (and still does) question why. That actually reassured me that not only he knows what he's doing, but he's also THINKING about it and interested in the job, which I like. His interest peaked mine too though... someone's gotta have an answer!

 

Well, I picked the car up today. A couple minor issues that we have to iron out, but the car felt great on my 5 minute drive to work after picking it up. No more shitty vibrations from the POS dual mass flywheel...YAY!! If anyone wants to offer up any opinions/suggestions on the issues I'm having though, have at 'er...

1) I don't have a speedo. I'm assuming they just forgot to hook up a sensor somewhere...could anyone point out where this connector would be so I can have a quick look?

2) Pedal is very low. I know this is quite common, so I'm not freaking out about it, but the clutch engages right at the floor right now. I know it comes back up a bit as you drive it more, but I suspect it may require some more bleeding (see next)...

3) I can't get it into reverse with the engine running. I'm hoping/thinking that this may be a sign that it just needs more bleeding. It'll go into R when the engine's off, but I haven't been able to get it in with the engine running. My mechanic test drove the car earlier today and when I arrived to pick it up it had been backed into it's parking spot...so he got it into R, but I haven't been able to yet.

I will add that the mechanic told me that he didn't use a speed bleeder to bleed the system, but rather just the pedal pump/lift method. I had him install the Tick remote line while they were in there, so the pedal bleeding would have been an ok way to do things, but I'm wondering if a bunch more bleeding with my Motive bleeder will bring things around...

Thoughts?

 

On the back of the transmission, there are two connector that are exactly the same and can be switched. Speed sensor and transmission temp sensor. I can almost guarantee you that they are switch around and it will cause the symptoms you are describing, ask me how I know.... Just switch them back and I bet all will be well.

 

Oh, and when I first installed my ls7 clutch, it engaged directly have the floor, but within 300-500 miles, it engaged just like before. So give it a few hundred miles and it should be ok.

 

hope this helps

Tremec 6-Speed

Vehicle Speed Sensor (VSS) Replacement
Removal Procedure

picture should be here


Raise and suitably support the vehicle. Refer to Vehicle Lifting.
Disconnect the vehicle speed sensor electrical connector.
Remove the attaching bolt and the vehicle speed sensor.
Remove the vehicle speed sensor (1).
Installation Procedure

Picture should be here


Install the vehicle speed sensor (1).
Notice: Refer to Fastener Notice in Service Precautions.
Install the vehicle speed sensor bolt.
Tighten the vehicle speed sensor bolt to 10 Nm (89 inch lbs.) .
Connect the vehicle speed sensor electrical connector.
Lower the vehicle.

 

silver1r - Are you saying the reverse problem could be caused by this too? I'll definitely have a look at that! My trans temp gauge was operational, but I didn't look at how accurate it may have been. Thanks a lot for the info.

demang - thanks

 

The reverse problem while running would probably be caused due to the clutch needing to be bled again. Sorry, I didn't read it close enough, but the speedo not working explains it. But when my two connectors where switch, the reverse lockout wouldn't engage at speed and when I tried to go from 4th-5th I would grind reverse. Just switch those 2 connectors and the speedo should work.

 

I'll have a look at it tomorrow. Thanks for the tip!

 

I just had my LS7 oem clutch installed a few weeks ago. The pedal started coming back up within 300-500 miles like others have said. It's not back to stock yet within 600 miles now but its much better. Plus the clutch pedal is way lighter vs stock which I like.

 

Good to know, thanks for the input.
I noticed on my way home from work this morning that my trans temp display/readout was jumping all over the place, so even more evidence that the 2 plugs got switched around. I was also able to find R a couple times (but also got blocked out of it a few times too). Once I get up this afternoon I plan on bleeding the system again (with my Motive bleeder and utilizing my new remote line) and getting under the car to swap those connectors around. Thanks for the help!!