grinding going into gear

[BadToTheBown]

I have a 2.4 six with a 901 trans. I bought assembled from a reputable guy I trust. Clutch worked for a little while (race car), 2 times out, now it grinds bad going into 1st and it started this on my last day at the track...trans is now out, clutch is off, this is all I see...
-Sachs aluminum 225mm pressure plate, Kennedy 6 puck disk, stock flywheel, 6 crank bolts, some bluing on pressure plate and flywheel, not burnt
-flywheel depth measures within 0.010" of spec (quarter of a mm)
-Disc measures 0.23 mm thicker (yes, thicker) than spec and obviously has life left in it
-disc spline center mounting rivets are rubbing against one bolt obviously, maybe a touch on a couple of other, the bolt that is rubbing is not backed out
-lube on pilot, not on splines
-throwout actuates freely

I do not know if the flywheel is too thin (haven't taken it off yet) but doubt it.

I'm wondering if this rub is slowing the input shaft enough to prevent synchronization, hence problem going into gear.

They ONLY idea I've come up with is the flywheel is iffy thin and the disc wore enough to matter but very open to suggestions...ideas?

[jess p]

My first thoughts are your clutch cable needs tightening. Since you have the trans out take a look at the adjustable steel ball that the shift fork pivots on as well as the Teflon cup inside the clutch fork. Do you have clutch slippage. If you are taking off in first a worn clutch disc, pressure plate and flywheel will not give you gear engagement problems. You will have slippage or even something called clutch chatter. If you do not notice anything out of the ordinary then the other thing to look for is removing the end cover of the trans. What kind of condition is 1,R shift sleeve, how does it engage with 1st gear dog teeth and how is the synchro, these three items in the trans will greatly affect 1 st gearengagement. BTW, that 1,R shift sleeve is about $400. As I recall I think you can flip it so that 1st gear will engage better. These things can be done with the trans in the car. Once you get it back together after inspection adjustproper pedal travel.

[BadToTheBown]

Hello Jess, thanx for answering.

-no clutch cable, hydraulic and it works (old lady depressed while I was under it)
-I'll pull the shift fork as suggested
-doesn't want to go into gear running, hence my suspicion of the clutch, just grinds
-I've never had these transaxles apart, watched Dr. Evil's vids and have 2 cores to practice on first, so I guess I need to get on with learning this and check that first gear

Thanx again.... :-)

[jess p]

You can buy the vids for $25. Btw that Hyperstrada is a nice bike. I have a 916 and couple 60’s 250 Diana’s

[BadToTheBown]

Bought them and watched them, working on making tools to take them apart and put them back together....Thanx on the Hyper, additive bike but I REALLY need to get rid of 1 of 2 bikes I have left.... :-(

[Dave at Pelican Parts]

It sounds like the clutch is not releasing all the way. I think you might need to verify that the throwout mechanism has enough throw to fully release the disk from the pressure plate and flywheel. A hydraulic clutch conversion means you are out of the realm of standard parts and into the realm of re-engineering, so you will need to take a good look at the full system. You have also introduced a fair bit of complexity to the system, so there are more things to check than with the stock system.

The system, BTW, includes the clutch pedal and its mountings. We already know that many 914s suffer from flex where the brake master cylinder bolts to the floorpan of the car, making for brakes that feel strange and don't work as well as they could. If your clutch master cylinder is having a similar problem, that could possibly result in the clutch not releasing all the way.

While replacing the 1st gear synchros should stop the grinding, it is likely a bandaid and would not fix the cause of the issue. BTW, You can do that without disassembling the trans; see the old Tech Article here: https://web.archive.org/web/20120107183621/https://www.pelicanparts.com/techarticles/914_tranny_repair/914_tranny_repair.htm . (Sadly that seems to be gone from our site now, not sure why!)

Bleeding a hydraulic clutch is also a very good idea, as air in the lines will keep it from fully actuating.

If you see there has been contact between the disk and any mounting bolts, that's a problem. On the four-cylinder cars, people will sometimes grind a little bit off the ends of the flywheel mounting bolts if the flywheel has been cut in order to avoid this sort of thing. I'm not sure about the Sixes, though.

I suggest that you try to figure out exactly what flywheel/clutch/pressure plate combo you have, and then contact Kennedy to make sure that it is known to work. It is possible that you have a combination that almost works--it wouldn't be the first time that something like that has happened.

Good luck!

--DD

[BadToTheBown]

Originally Posted by Dave at Pelican Parts

It sounds like the clutch is not releasing all the way. I think you might need to verify that the throwout mechanism has enough throw to fully release the disk from the pressure plate and flywheel. A hydraulic clutch conversion means you are out of the realm of standard parts and into the realm of re-engineering, so you will need to take a good look at the full system. You have also introduced a fair bit of complexity to the system, so there are more things to check than with the stock system.

My present speculation is just that. I think the disk is hanging up on the crank bolts and preventing the shafts from synchronizing. How the disc is that far forward is obviously a concern. Was the flywheel machined one too many times below spec and the disc worn enough to move forward enough to hit them? Is the crank trust allowing the crank to move back some? Doubt it. Is there something in the trans that could move the main shaft forward? Doubt but really don't know. It's an old HSR Vintage race car someone built (I don't have the pedigree), appears they knew what they were doing. It has a Tilton pull hydraulic cylinder, it's freshly bled, appears to be pulling the fork back to disengage the pressure plate. It originally had a problem with the aft cylinder mount but I welded up a new one that works better, so that part is now solid. I also adjusted the pull rod to the cylinder to keep the fork just off the pressure plate fingers, so it's close but not riding on them.

Originally Posted by Dave at Pelican Parts

The system, BTW, includes the clutch pedal and its mountings. We already know that many 914s suffer from flex where the brake master cylinder bolts to the floorpan of the car, making for brakes that feel strange and don't work as well as they could. If your clutch master cylinder is having a similar problem, that could possibly result in the clutch not releasing all the way.

The pedals are Tilton hanging ones, welded in and mounted solid. No leaks. Maybe I need to rebuild the Tilton cylinder. Anyone know what the fork travel is supposed to be?

Originally Posted by Dave at Pelican Parts

While replacing the 1st gear synchros should stop the grinding, it is likely a bandaid and would not fix the cause of the issue. BTW, You can do that without disassembling the trans; see the old Tech Article here: https://web.archive.org/web/20120107183621/https://www.pelicanparts.com/techarticles/914_tranny_repair/914_tranny_repair.htm . (Sadly that seems to be gone from our site now, not sure why!)

Where I'm going next. I have 2 core transaxles to learn on first and draw on for parts.

Originally Posted by Dave at Pelican Parts

Bleeding a hydraulic clutch is also a very good idea, as air in the lines will keep it from fully actuating.

Bled and topped off. Went there early.

Originally Posted by Dave at Pelican Parts

If you see there has been contact between the disk and any mounting bolts, that's a problem. On the four-cylinder cars, people will sometimes grind a little bit off the ends of the flywheel mounting bolts if the flywheel has been cut in order to avoid this sort of thing. I'm not sure about the Sixes, though.

Hmmm...didn't expect to hear this, I think I have ARP bolts (heads a tad taller?) and a 911 flywheel (waiting on triple square bit to get it off to check). Hurry up Snap-On....

Originally Posted by Dave at Pelican Parts

I suggest that you try to figure out exactly what flywheel/clutch/pressure plate combo you have, and then contact Kennedy to make sure that it is known to work. It is possible that you have a combination that almost works--it wouldn't be the first time that something like that has happened.

I can do that. I can say, it did work. Guy I bought it from has done this combo before and it worked. I keep coming back to it worked but worked just enough and now that it has a bit more wear on it, took it out of spec enough to not work but I haven't dug into the trans yet or verified the flywheel, so I guess we'll see....

Grateful for the help, thanx for making the time....

[BadToTheBown]

Update....I've learned a little more, largely thanx to PCA posting and namely:
-Triple square crank bolts are NOT M10 as I had read in another post, shame on me, they are M12 (verified)
-Clutch disc thickness should be 8.5mm (7.5mm for '69S lightweight pressure plate), NOT 6.5mm as I had previously read in yet another post, shame on me again
-Should typically have 1-2mm clearance from disc to bolts, wish I had some shop manuals
-I have an early Kennedy clutch (pressure plate painted blue, they paint them gray now I think) and disc (this I knew) and the pressure plate is not the lightweight one, it's the stock heavy cast iron one

This quickly leads to my 1st theory on what was wrong. Anyone know where/how to measure stock flywheel for clutch surface depth or over machining? Then I'll know what I have to order....

[jess p]

Look at your flywheel with respect to the second ledge from the top edge. You can see this ledge better when you look at the bolt holes where the pressure plate bolts to the flywheel. Just above the bolt holes you will see the ledge. From this ledge to the clutch face will be 22.5 mm when new. I don’t know what the wear limit is, maybe Dave can chime in on the wear limit value.

[Dave at Pelican Parts]

There is no limit published for the four-cylinder cars. I know that there is a limit for the 914-6, but I don't know it offhand and don't have most of my references available at present. That spec is in the 914 "Little Spec Book"; presumably the equivalent 911 info is in the 911's version of the book.

--DD

[BadToTheBown]

Whoever reground the flywheel did also ground the pressure plate mounting land and it's within 0.010" of spec. I'm looking for the dimension from the flywheel friction surface to where the flywheel mounts to the crank.

Compared flywheel with a known good one and it appears to be almost 1mm down, so between this and the thin disc and the 0.010" high on the 22.5mm clutch depth, and the Kennedy solid disc with rivets close to the base circle of the crank bolts, looks like it all just added up. Ordered new Patrick Motorsport super light race flywheel/clutch, I'm doubling down now.

Thanx for all the help...

[jess p]

From the flywheel friction surface to the face where the flywheel mounts to the crankshaft must be a minimum distance of 11.0 mm. That face is from the front, that is looking at the side of the friction surface. Do you want the distance from the friction surface to where the flywheel mounts on the crank on the backside?

[BadToTheBown]

Originally Posted by jess p

Do you want the distance from the friction surface to where the flywheel mounts on the crank on the backside?

Yes, this is what I'm looking for...all I have now is it relative to another known good flywheel but it's been reground at least once...since this flywheel needs to be reground too and is measuring lower than the borrowed good flywheel, is now scrap but I yet another flywheel I want to measure to see if it is good, so I still need the dimension, thanx....

[jess p]

Ok first to make sure we are talking about the same flywheel. From the picture it appears you have the cup style flywheel used on 911s from 1965-1969 and not the flat type flywheel used on all 911s since 1970. I doubt your flywheel is for the 1980 911 sc.
The reason I ask is I own several early 911s also. I can pull out my flywheels and measure them. I own many manuals on 911s and I’ll look through some of the manuals today to double check on what the new measurements are.

[jess p]

Additionally, there should be a Porsche number stamped on the back of your flywheel

[jess p]

I measured one of my flat style flywheels from my 911 and I found from the friction surface to the backside was 21 mm. I would think that would be the standard distance considering 901 applications of the era and should cross over to the cup style flywheels which would be standard to accommodate manufacturing tolerances for the discs and pressure plates.

[jess p]

In 901 applications.

[BadToTheBown]

Hello Jess, you're correct, cup style, '65 to '69, 215mm disc, 22.5mm depth from pressure plate mounting down to disc friction surface for a 901 transaxle, push style clutch....later ones are pull and are 225mm for 915 transaxle...Not sure I understood all this when i started this journey but I do now...I take what I can get on dimensions and specs, empirical from one of your flywheels is better than nothing, would be great to understand what the shop manual say it should be, thanx for offering to help... :-)

[Dave at Pelican Parts]

I found the reference I was looking for. It's not in the "Little Spec Book", it's in the 914-6 Engine section of the factory manual.


This is what the manual has to say about the 914-6 flywheel:





I hope this helps.

--DD

[BadToTheBown]

Hello Dave, yes it does help (confirm what Jess said) and also tells me "bowl" thickness/depth overall...though it doesn't give me the dim I asked Jess for, I can work with what provides (11mm dim)...I'll check them both today and thanx again... :-)