924Board.org

[endwrench]

OK, I finally got around to putting my car back together. Just as a refresher it is a 1979 924 NA with a supercharger and EFI. It had the original snail shell tranny with obligitory bad syncros in 1st and 2nd gear. I found a deal on a 944 tranny so I jumped on it. Got it and the torquetube with shifter. Ofcoarse this is the larger 25mm shaft so I needed to change the clutch disc to the Mustang unit atleast.

Because my clutch was already beginning to slip a little on 3rd gear shifts I decided now was the time to upgrade as I plan to up the power output in the future. After pricing a couple aftermarket kits I decided to try something a little different (and much cheaper!). This will not be for everyone. I know this. I am mearly posting this so as to show what a cheap bastard with a lathe can do. Hopefully this will also spawn some other ideas as I am sure this is not the best way of going about this, it is just the way I did it.

I researched several clutches and decided on a new set for a 1989 Ford Ranger 2.9L. It is built by Precision and sold by CarQuest. These are the reasons why:

8 13\16" disc with a 23 spline 25mm hole
Cover is rated at 1500lbs versus 1150lbs stock NA
Good for 235lbs torque versus 173lbs stock NA
Pilot bearing is same as porsche unit
Alignment tool works
Release bearing can be used on modded stock unit
It's $125 versus $5-600 for a custom unit
A plethera of Hi-Po clutches available for application if this isn't enough holding power for you!

The bad part is it does not just bolt on. The flywheel will need to be redrilled for the new bolt pattern. You can make this as easy or as hard as you want. This is the way I did it.

I obtained a stock 2.9L ford flywheel and an old burnt up clutch to use as patterns. I removed the ring gear then pulled the dowles on the flywheel. the dowles are 1\4" on top and 5\16" were they enter the flywheel. I drilled these holes all the way thru the flywheel with a 5\16" bit. I then built a simple 5\16" bushing with a 1\4" hole to place in these holes to pilot a 1\4" bit.

The ford flywheel is actually slightly smaller diameter than the porsche unit. I imagined all sorts of different ways of centering the 2 flywheels face to face. I ended up with building a simple stepped "gauge" I could place at the edge of the stacked flywheels and check with a feeler gauge untill it was essentially the same distance at any point on the flywheel. I then clamped them together and drilled the three 1\4" holes thru the before mentioned bushing. This worked very well as it ended up in perfect balance after all was said and done.

After placing 1\4" dowles in the newly drilled porsche flywheel I then built a set of bushings I could press into the old ford pressure plate with an appropriate sized hole for drill bit to be used with what ever size bolt you plan to use. I used the stock 8mm bolts that held the stock clutch. If you look close you can see the centering bushings in the plate. Be careful as the holes will come out right at the edge of the step for the ring gear and will break the drill bit if you go too deep. Be sure to remove the ring gear before drilling.



Next problem is bellhousing clearance. This pressure plate has three "wings" that need to be trimmed back. This is pretty straight forward but you need to be careful not to fill the plate with grinding or cutting dust. Tape everything shut or stuff with rags. As you can imagine this has the potential to throw things out of balance so be careful to trim evenly as you can.

Before:



After:



You can see here how close this runs to the bellhousing. During my first trial assembly it just touched. You see here where it hits.



Last big problem is the throwout bearing. It needs to be changed because the face is too small to make proper contact with the fingers. Luckily, the bearing for the ford setup pops right off the plastic carrier and the stock unit can be seperated so an adapter can be built to join the two. If you look here you can see where the "pinches" need to be ground out to remove the stock bearing from the carrier. Only grind out the three from one side and then pry the bearing out leaving the other side un molested. This will serve as a depth guide for the adapter and the grinding of the "ears".



This picture shows the stock throwout and the seprated ford unit.



This one shows the 3 pieces ready to go together. The adapter will be self explanitary to any machinest. Just bring them the parts and let them measure them after you explain what you want to do. Show them this picture too if you want. Be sure to explain you want this unit as "short" as possible. You do not want any extra "thickness" in the overall height of this piece. You want the bearing to just clear the top od the unmolested side of the carrier. You will then need to grind the "ears" down to clear the bearing as it hangs over. Do not grind this any further than is absolutly needed as this is a rather high stress area and needs to remain strong.




So far I think this is going to work out well. I just got it back on the road and it works very well. I was a little afraid the pedal effort would be too much but it is not at all. It is definetly firmer than before but not in an aggrivating way. It would be fine in traffic and such. I do have one reservation that may pan out in the future. As the clutch wears the fingers will come out and the clutch will need adjusted. There is a limited amount of room between the back of the throwout bearing and the bolts that hold on the throwout guide tube. At this point I feel the clutch will be nearly worn out by the time these things touch but it will limit the amount clutch adjustment to be had.

Oh, almost forgot, what about balance? Well, I used a tire balancer. Yep. I used a friends low speed Snap-On spin balancer. It is quite amazing how sensitive it is. My setup is balaned under 4 grams. Mine actually came out perfect with no need to add weight. I had to machine a centering bushing as the balancing cones will not work with the pressure plate bolted on. If you do this, be sure to set the balancer to static only. You don't want dynamic balance.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Min]

now what do you do if you get a performance clutch with a different shaped pressure plate? ... I was looking at some of the availiable aftermarket stuff for this particular clutch setup, and the plates look like they are a different shape than the stock one.

Btw, very good info. I'm surprised noone else has commented yet.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[morghen]

I would not re-drill the pressure plate mount holes on the flywheel. Reason? I'm not sure that even using a CNC would get the pressure plate and disk corectly centred and balanced, then you may ruin the balance of the flywheel itself.....6000 RPM and a few grams can develop some force you know...
_________________
https://www.the924.com

[Min]

[morghen]

i'm not saying that it is not possible or it would not work. I'm sure he did a good job...but i would not trust myself on doing this or any machinist.
_________________
https://www.the924.com

[endwrench]

Min,

Not sure what you mean by "different shaped pressure plate". Are you talking about the same Ford application or a different application? The overall diameter and bolt pattern would need to be the same for this application it is modified for. So would the height and balance. What have you seen? The pictures I have seen f the Centerforce Unit look exactly the same as the stock unit I used.

Not sure how well this will hold yet as I haven't had a chance to abuse it yet . I'm trying to build a new 2 1\2" mandrel bent exhaust system for it so I am running an open header at the moment and am trying not to draw too much attention to myself. Redline shifting is not very conducive to this end .

Morghen, I understand your concern as I had the same but after talking to some knowledgeable clutch guys I found most stock pressure plates are only balanced within 7 grams (1\4 ounce) and if you look at the size of the weights they weld on you'll concur. My entire setup is under 5 grams. I admit this is luck and I already planned to weld weight onto the PP. Others may not be so lucky. If I should ever need to change out my pressure plate in the future, it would need to be modified like this one then re-balance checked. Just a draw back to custom crap .

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Min]

[endwrench]

Ya, I found a lot of 'stock' pictures while researching this on the net.

Just thinkin', the flywheel mods for this would be cake for anyone with a Bridgport and a turntable. You would still need a stock ford flywheel for setup though.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Min]

Ok, now here's some more questions, heh, would this modification work with a regular 924 na clutch(you know, the one with the smaller shaft)

And how much would you charge to perform this modification if someone dropped a flywheel on your doorstep.(the drilling/tapping of the flywheel)

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[endwrench]

Well, after a quick search I can only find 2 possible solutions. You could use the stock disc. It is only 8 1\2" versus 8 13\16" but I can see no reason it would not work. The face of the PP does not really wear to any significance over the life of the clutch. It would have slightly less holding power (228lbs versus 235lbs). I wouldn't run a fullsize disc against the PP after running this one for any extended amount of time.

Only other close one would be a Type 2 Vanagon disc. They are 228mm versus 225mm for stock ford. It would need to be shaved down to fit properly. I think this could be done easily on a lathe with a mounted tool grinder. There is nothing on the outer edge of the disc to interfere with this. There may be other options with more research.

As for cost I guess I could drill your flywheel for dowles, build and install the dowles, then drill, tap and bottem tap the PP holes for about $40. Remember you will need to then modify your PP, mount it to the flywheel and have the assembly checked for balance. Theoretically, it should not need balanced if I get the dowles perfectly centered on the flywheel. I am not guranteeing that . If I had a bridgeport and a turn table I might I feel I just got lucky on mine. Also keep in mind you will probably need to build some sort of cetering bushing for the flywheel to fit the tire balancer as the cones wont work with the PP mounted.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Min]

ok, definately giving me some things to think about, we will be needing to do something with our clutch for sure, and I don't want to swap the tranny out until I break it

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[endwrench]

Ya, should onteresting to see what actually breaks first seeing as the clutch seemed to be the "fuse" in the system and your about to wrap tinfoil around it

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Min]

[endwrench]

Quick report on the clutch performance. I finally found the time to finish the exaust system and get it bolted up so I could do a little spirited driving. The sucker hooks up hard now. As I reported before I was starting to get some slippage during hard shifts to 3rd, now I just get screaming tire bark! 4th gear in this new tranny is so much shorter than the snail unit I may get tire bark out of it too but I haven't tried yet.

I was a little concerned about the pedal pressure but I didn't even notice it while driving. Seemingly no balance problems either. Overall, I'm pretty happy with the whole deal.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....