C3 Race Car Build

[teamzr1]

This sort of friction plate
View attachment 18219
Rather than these
View attachment 18220
PS Didn’t mean to discount your opinion on the clutch not being up to the task. I meant to write “I’m not sure” rather than “I’m sure it’s not”.

I have never used the disc type of the top one but being Ceramic lined clutch discs I would think it holds up under heat and looks stronger in design
I cannot see myself in using a single disc design for your HP/Tq, need at least dual with floater
I think though this is the cause of your shift issue and the top design you showed is to have soft clutch pedal feel

One customer even states for that RXT design

I had this clutch kit installed professionally by my mechanic in my 2007 Shelby Gt 500.
This clutch is by far the best mod investment I have made since buying this car almost seven years ago.
The pedal pressure is light, the shifting is smooth, and it falls right into gear. It has really enhanced the overall experience of driving my Shelby.

I trust George McLeod, I have used him for decades, and he has always come up with clutch designs that hold up in all kinds of race conditions
and suggest you talk to them as a matched setup with lighter flywheel, clutch and throw out bearing

 

[teamzr1]

If wanting pure designed race clutches, I have used Tilton
Was 3 5 inch discs with floater, with their race flywheel and adjustable clutch pedal system

They have been around since 1972 and are used with F1, IMSA, NASCAR, etc. but they are not cheap but good designs

As a compare, look at this and to the left select other clutch designs

Tilton Race parts

 

[Oneball]

Thanks @teamzr1

 

[teamzr1]

Hard to tell with pictures than in person but really looks
like the flywheel and clutch is fairly new and the surfaces themselves do not look really worn
but clearly the clutch disc has chatter & slipping, I think the engine is overpowering the clamping of pressure plate

I would not go further with tranny until better matched up clutch system, then testing and then secondary of the gate design of shifter, you're using
If still an issue

 

[Forrest Gump]

Obviously a major issue to sort with the clutch components, but I can’t see how this is related to the gear popping out on lifting off - the clutch is still fully engaged and no power being transmitted when lifting off. As I type this JR has posted again along same lines.

 

[Oneball]

Hard to tell with pictures than in person but really looks
like the flywheel and clutch is fairly new and the surfaces themselves do not look really worn
but clearly the clutch disc has chatter & slipping, I think the engine is overpowering the clamping of pressure plate

I would not go further with tranny until better matched up clutch system, then testing and then secondary of the gate design of shifter, you're using
If still an issue

View attachment 18221View attachment 18222

Yep there’s no wear on flywheel and pressure plate except for the cooked areas. The friction plate is completely shot though.

It also seems to have lunched the gearbox input bearing.

Can’t help but think this all has to be related. I’ll get a dial gauge on the bellhousing tomorrow

 

[teamzr1]

Obviously a major issue to sort with the clutch components, but I can’t see how this is related to the gear popping out on lifting off - the clutch is still fully engaged and no power being transmitted when lifting off. As I type this JR has posted again along same lines.

The clutch disc is bouncing, chattering,
it is on the end shaft of tranny so what would cause the main shaft to be bouncing back and forth
which could affect coming out of gear, so reason I say replace with proper matched clutch first
now Oneball says damage to input bearing, so clearly the shaft is bouncing back/forth
That also can affect what he feels with shifter's gate in fighting to get a gear engaged

 

[Oneball]

Do you think therefore that just lifting off the throttle rather than changing down would cause the clutch to chatter?

 

[Oneball]

The main issue I find with the Hurst shifter is the spring that holds it in the 3/4 gate isn’t much weaker than the one that “locks” out reverse so it’s very easy to go all the way past 1/2 and into the reverse slot.

 

[teamzr1]

Do you think therefore that just lifting off the throttle rather than changing down would cause the clutch to chatter?

Would be better to see a photos of the whole clutch disc and both sides of it

Clearly the center of disc has no dirt or wear signs, or even paint on springs showing heat
yet the disc material looks like it has been beat up and almost to the top of rivets, so lots of wear in short timeframe
Surely throttle on and off change torque output and when disc has odd load or unloading into the end shaft

 

[Oneball]

I’ll get some photos tomorrow, but the friction plate is worn out.

 

[Roscobbc]

When I 'pulled' the original 427 tp replace with my then new engine it had similar marks on the flywheel and driven plate surfaces and similar uneven down almost to the rivets wear. The cause of this was insufficiently tightened gearbox to bell housing bolts allowing the gearbox face to move around. This in my view allowed the friction plate to run eccentric and create the same wear patterns. In your case perhaps it was the insufficiently engaged nose of the gearbox shaft in to the pilot bearing causing a similar eccentric rotation.

 

[Forrest Gump]

The clutch disc is bouncing, chattering,
it is on the end shaft of tranny so what would cause the main shaft to be bouncing back and forth
which could affect coming out of gear, so reason I say replace with proper matched clutch first
now Oneball says damage to input bearing, so clearly the shaft is bouncing back/forth
That also can affect what he feels with shifter's gate in fighting to get a gear engaged

Yes and agree the input shaft bearing destruction is highly likely to mess up the gearbox function to say the least.
What is the condition of the pilot bearing?
Amazing all this has happened with no symptoms other than gears jumping out……such as burning clutch smell, vibration/ juddering or any apparent clutch slip.

 

[Oneball]

I wouldn’t say the input bearing is destroyed. There’s no in/out play but there’s a lot of radial play at the end of the shaft. And I think that’s a symptom not a cause.

When I 'pulled' the original 427 tp replace with my then new engine it had similar marks on the flywheel and driven plate surfaces and similar uneven down almost to the rivets wear. The cause of this was insufficiently tightened gearbox to bell housing bolts allowing the gearbox face to move around. This in my view allowed the friction plate to run eccentric and create the same wear patterns. In your case perhaps it was the insufficiently engaged nose of the gearbox shaft in to the pilot bearing causing a similar eccentric rotation.

This is my concern, that it’s not a clutch issue and that’s a symptom. So replacing the clutch assembly without determining for definite the problem I’ll end up back here with another destroyed clutch.

 

[Roscobbc]

I wouldn’t say the input bearing is destroyed. There’s no in/out play but there’s a lot of radial play at the end of the shaft. And I think that’s a symptom not a cause.



This is my concern, that it’s not a clutch issue and that’s a symptom. So replacing the clutch assembly without determining for definite the problem I’ll end up back here with another destroyed clutch.

The 'big' question is why the shaft doesn't fully engage in the pilot bearing........is it a gearbox issue? - is it a flywheel issue? - crankshaft too short. What is the benefit of a roller pilot bearing vs phospher bronze. You mentioned your doubts over the use of the Hurst shifter assembly vs stock shifter. Hurst has sturdy and adjustable shifter lever 'stops' - surely a 'must' when banging away at the gearchanges when racing............

 

[Oneball]

The 'big' question is why the shaft doesn't fully engage in the pilot bearing........is it a gearbox issue? - is it a flywheel issue? - crankshaft too short. What is the benefit of a roller pilot bearing vs phospher bronze. You mentioned your doubts over the use of the Hurst shifter assembly vs stock shifter. Hurst has sturdy and adjustable shifter lever 'stops' - surely a 'must' when banging away at the gearchanges when racing............

Less drag but I’ll put a bronze bush in. I’m not saying it is wrong as having measured the extended bearings that are 1/4” longer would be too long.

Very few boxes have stops, the Hurst to me is designed for drag racing. Stops may help but you should still set them so the synchro slider contacts the face of the gear. You shouldn’t bang away at gears that’s poor driving.

 

[Oneball]

Dial gauge out at lunch and the bellhousing centralisation is within 2 thou and perpendicular 4 thou. So it’s not that.

 

[Roscobbc]

Very few boxes have stops, the Hurst to me is designed for drag racing. Stops may help but you should still set them so the synchro slider contacts the face of the gear. You shouldn’t bang away at gears that’s poor driving.

The benefit of 'stops' is that (presuming they are adjusted correctly to allow correct gear engagement) irrespective of whether used for 'enthusiastic' street, drag racing, circuit, sprint.....whatever - its all too easy to get over enthusiastic in the car when shifting gear.......the 'stops' at least help protect the 'box and the linkage from abuse.
Wonder if the in-line sequencial shifter from Australian is still available - RENAGATE - is this race legal? I considered it when buying my Hurst shifter but it was super expensive........

 

[Oneball]

You definitely wouldn’t get away with that in historics.

 

[teamzr1]

This gives me heartburn and screaming spine pain just writing about all this

Starting with the C5 the normal design of tranny and location of it changed to a transaxle located in the back
Now a simple change of the release/throwout bearing means ripping out the whole ass end, transaxle and drivetube just to get
to it that then takes 5 minutes to swap out

Tearing the piss out of my 1999 C5 in 2000 as stock setup really sucked, miss shifts and clutch pedal not returning on high RPM shifts -(
Cannot have this, doing open road races moving at 160 to over 200 MPH over 100 miles of mountain hilly and over 120 turns up and down shifts are important, difference in losing or winning a race



GM designed how the clutch functioned so that some 90 pound person with no leg strength could shift 6 forward and 1 reverse gears
done by 1 shifting rod.
The stock shifter allowed an old lady to use but talk about bad and missed shifts that clunker did

I found a shop in the heart of the Kentucky mountains that for many years built racers and moonshine vehicles
They designed a shifter for C5 that was built well and had shift stops.



A lot of the issues is timing and travel
Solved in part with getting rid of stock shifter with one that allowed adjusting with shift stops.

At high RPMs like 6,500, like going from 4th to 5th gear the damn clutch pedal sticks to the floor and does not come back up on its own :-(

This is from ill design and wrong vendors used by GM

Release Bearing
The damn thing is made of metal and plastic, uses one large diameter spring
What I found is the bearing mounted to plastic would wear, and the spring caused it to cock at an angle and jam against the housing and cause of driving the bearing to pressure plate arms.



Timing of when putting the pedal to floor and the volume of clutch fluid at high RPMs caused a timing issue and overdriving the arms of pressure plate.
This in total then would do this in short timeframe




In part to solve the clutch pedal issue, I made up an adjustable pedal stop that I would adjust until it prevented overdriving pressure plate



And installed a larger clutch return spring
Lastly the design of the MN6 tranny I found a return spring inside for the shift rails, I found a way using a different bolt length to change the timing during high RPM shifts and helped greatly

Moral of story is the clutch design and adjustments is more involved than people think and ignore finding ways to better and assure correct shifting
Timing and travel, in the end the release bearing pushed the fingers of pressure plate too far inward causing then less clamping of disc
so slipping and hot spotting.
Timing, crappy shifter causes gears not fully engaging, screwing up syncros requiring tranny repairs.