I picked up an '88 Formula on the weekend, my first '88.
I knew it had clutch issues. It had, as it turned out, an exploded clutch disc.
I just had its neutrally balanced flywheel resurfaced. About .010" was removed. I have no idea if the flywheel had been resurfaced previously.
First question - How thick of a flywheel shim can I use without causing a problem? Is there any danger of using a .050" shim (which I happen to have here), or would it be more prudent to use a .025" thick shim?
Second question - There are six pressure plate mounting holes around ther perimeter of the flywheel. On either side of all six mounting holes are two other holes. On my flywheel, all of these extra holes are empty, except for the two holes on either side of one of the pressure plate mounting holes. What is the purpose of these extra holes, and why are two filled in?
Here's a picture that Bloozberry had previously posted. I've indicated where the pressure plate mounting holes are located with a red dot. The other holes I'm referring to are indicated with blue dots. It's interesting that on this particular '88 neutrally balanced flywheel, different holes than on my '88 flywheel are filled in. Does anyone know what these holes (indicated with the blue dots) are for? Is it simply to assist in balancing the flywheel?
[This message has been edited by Patrick (edited 07-30-2013).]
I suspect that's what they're for, but it seems odd that they're all drilled out, and then a couple are filled in with a plug of some sort.
I haven't seen this on other Fiero flywheels, but perhaps the '88 neutrally balanced flywheels are balanced in a different manner than the earlier years.
Originally posted by trotterlg:
Why would you put a shim under the flywheel?
This is something that has been discussed and debated here for years.
Here's the argument - Even when new from the factory, the Fiero clutch system barely gives enough throw to completely disengage the clutch. When metal is removed from the flywheel during resurfacing, the flywheel becomes thinner. The clutch pressure plate mounts to the face of this thinner flywheel, and is now positioned further away from the clutch fork. This then changes the whole geometry of the clutch fork in relation to the throwout bearing, pressure plate, slave, etc. Whatever it changes, it appears the ("self-adjusting") hydraulic clutch can't effectively make up for this difference. The end result is that the clutch now becomes difficult or impossible to disengage properly.
Because of this situation, some experienced Fiero owners/mechanics insist on simply replacing the flywheel with a new unit anytime that the clutch is replaced. Other experienced Fiero owners/mechanics use a shim behind a resurfaced flywheel instead of replacing the flywheel. The shim behind the flywheel pushes the face of the thinner resurfaced flywheel back to where it originally sat in relation to the rest of the clutch system components.
I know it seems that .025" or so wouldn't make a bit of difference, but there are too many Fiero owners/mechanics who know a heck of l lot more than I do who absolutely swear by this. And for $10, I'll splurge on a shim to prevent potential shifting problems.
When I had my 87 flywheel resurfaces 0.02", Marc made a 0.02" shim for spacing..
I agree with that practice. I guess my concern is if there's potentially any problem if the shim used is a little thicker than what was taken off.
Let's face it, most of us have no idea if our flywheels might've been resurfaced previously. Therefore, I'd like to use a shim that is a little thicker than the amount taken off of the flywheel if there are no negative consequences.
The plugs add weight and taking them out removes weight. If .010 or .020 makes a difference in your clutch releasing or not then you have bigger problems going on some place esle. The mount of clutch travel has to do with the stroke of the slave, and if you hit the limit then a longer rod will solve the problem. Guess it woun't hurt to shim it, but I think the less stuff between the FW and crank the better, less stuff to slip, more, get stuff under and all that.
If .010 or .020 makes a difference in your clutch releasing or not then you have bigger problems going on some place else.
Oh, we've heard this all before.
I'm just the messenger. This has been discussed a hundred times here over the years. The shim does make a difference, especially if the flywheel has been resurfaced numerous times and/or if excessive wear results in more than the usual minimal amount to be ground off the flywheel.
Originally posted by trotterlg:
The mount of clutch travel has to do with the stroke of the slave, and if you hit the limit then a longer rod will solve the problem.
Larry, it's also been discussed a hundred (maybe even a thousand) times that unless an incorrect shorter rod had been earlier substituted, installing a longer slave rod in a hydraulic clutch system accomplishes absolutely nothing. So I guess we're even.
[This message has been edited by Patrick (edited 07-31-2013).]
Thanks for this info since I'm going to have my clutch replaced, with hope that the flylwheel only needs resurfacing. I'll advise the mechanic about the shim. Incidentally, I was checking up on the Sachs flywheel that RockAuto has listed for pre-88 Fieros. Its for externally balanced engines, which, according to what I've read, won't work for the pre-88s. I passed this along to the customer service department, since I had purchased an Beck Arnley flywheel that was also advertised as a replacement for the 86 2.8. It isn't, but it only cost $28 dollars. I was able to give it to another Forum member who is doing a 3.4 modification.
Thanks for this info since I'm going to have my clutch replaced, with hope that the flylwheel only needs resurfacing. I'll advise the mechanic about the shim.
Hey, you're welcome. There's nothing more depressing about owning a Fiero than to do a clutch job (which is a big undertaking for most of us), and then to discover that the clutch won't properly disengage because a $10 shim wasn't used.
Originally posted by Bruce:
Incidentally, I was checking up on the Sachs flywheel that RockAuto has listed for pre-88 Fieros. Its for externally balanced engines, which, according to what I've read, won't work for the pre-88s.
I don't quite follow you, but don't get confused with the externally balanced 2.8 flywheels used on '85-'87 Fieros and the neutrally balanced 2.8 flywheels used on the '88 Fieros.
Here's the argument - Even when new from the factory, the Fiero clutch system barely gives enough throw to completely disengage the clutch. )
I would disagree with this. Some complain that they have problems. The vast majority do not complain because their system works just fine. So it appears most have problems while the opposite is generally true. Mine grabs about 2/3rd's of the way up. If I'm not careful I give it gas too soon and it revs slightly as I am letting the clutch out when up shifting. If your system is not giving the ideal amount of fluid displacement or if you have air in the system is one variable. The other variables are the clutch and pressure plate. Many different types and manufacturers of clutch discs and pressure plates etc. Age etc. Many variables here.
------------------ Rodney Dickman
Fiero Parts And Acc's Web Page: All new web page!:www.rodneydickman.com Rodney Dickman's Fiero accessories 7604 Treeview Drive Caledonia, WI 53108 Phone/Fax (262) 835-9575
The other variables are the clutch and pressure plate. Many different types and manufacturers of clutch discs and pressure plates etc. Age etc. Many variables here.
Rodney, you disagree with what I've reported, but then you immediately turn around and mention the "many variables" that can contribute to a clutch not properly disengaging. A flywheel shim simply (and cheaply) reduces or eliminates one of those variables.
Seems to me there's even a very well known Fiero vendor who sells adjustable banjos which are used to help remedy this infamous Fiero clutch disengagement problem.
Rodney, I love your stuff... but don't diss the shim.
Unfortunately no one would be able to answer your first question with certainty unless they knew the original flywheel thickness and your current flywheel thickness, along with a few other details like the amount of T/O bearing travel necessary to fully release your clutch... which varies from manufacturer to manufacturer. Adding a shim behind the flywheel of the same thickness that was machined off the face is the right thing to do though to get best use of your clutch disk. If you don't, then you risk being unable to get enough throw-out bearing travel to disengage the clutch fully.
That doesn't stop us from speculating though! I believe that using a 0.050" spacer may be a better option than using none in your circumstance. The net result after accounting for the 0.010" removed from the flywheel is actually as though you were using a 0.040" spacer (or less if the flywheel's been machined once before). That translates into the pressure plate fingers sitting closer to the transmission by that amount, so the throw out bearing will sit further back, causing your slave cylinder pushrod to sit deeper into the slave. The amount by which it sits deeper into the slave is a function of the 0.040" amplified by the ratio of the throw out shaft fork fingers to the clutch arm length, which might result in the pushrod sitting a maximum of 1/8" deeper into the slave. As long as the pushrod piston doesn't bottom out in the cylinder, you should be fine (although it would be a different problem if the pushrod sat 1/8" further out rather than further in.)
For question #2, I have a hard time imagining the purpose of the extra holes being drilled other than for adding weight during balancing, especially given that some but not all are plugged. One tell tale would be if the untapped hole between the obvious areas where they removed material for balancing, were left empty on all such flywheels, like the one in your first post. Obviously they wouldn't plug that hole (adding weight) in an area where they were trying to reduce it. In any case, I highly doubt that the extra holes were intended for different clutch applications since they seem to be at the same diameter as the tapped ones for the Fiero pressure plate. You would think they would have been at different diameters if they were to be used for other clutches.
For comparison's sake, I took a picture of an externally balanced '86 flywheel and also looked at one from an '85 earlier today and found that they too had the extra holes, but none of them were plugged on either of those two. Here's the '86:
A few days back there was a post where the pressure plate fingers hit the clutch plate springs, that is an excellent reason not to shim the flywheel out. The shims are a solution to a problem that really doesn't exist. Just like mentioned above, variations on all these compontnts are far larger than a little bit of metal being removed to face off a flywheel. Larry
Given the poor quality record of some aftermarket clutch companies (one in particular) making clutch components for Fieros in the past couple years (hub spring failures, backwards mounted clutch hubs, oversized pressure plates, finger failures, etc etc) it would be risky to install the engine/trans back into the car before first determining if there were clearance issues, whether you use a flywheel shim or not. The bottom line is that if you take a known quantity of metal off the thickness of your flywheel without replacing it by using a shim, you increase the likelihood of problems, not decrease them.
[This message has been edited by Bloozberry (edited 08-01-2013).]
Assuming the flywheel was resurfaced once, and probably needs to be resurfaced with the next clutch installation, what is a safe shim size. Better yet, what is the stock height of the Fiero flywheel so that the shim can place the flywheel as close to stock dimensions as possible? Thanks! bb
Adding a shim behind the flywheel of the same thickness that was machined off the face is the right thing to do though to get best use of your clutch disk. If you don't, then you risk being unable to get enough throw-out bearing travel to disengage the clutch fully.
Yes, that's basically the argument that I've read many times here over the years.
Dave, thanks for the rest of your observations as well. Certainly food for thought.
How thick of a flywheel shim can I use without causing a problem? Is there any danger of using a .050" shim (which I happen to have here), or would it be more prudent to use a .025" thick shim?
I ordered a .025" shim from RockAuto very late on Wednesday evening, it was shipped via USPS on Thursday afternoon (from Texas), and it was delivered to a friend's place in Bellingham WA about noontime on Saturday. I thought that was pretty quick service!
So now I can debate (mostly in my own head ), whether to use a .050", .025", or no shim when we start putting things back together on Monday.
For even .050 inch you are way way over worring the "problem". You will have many times that amount of variation in the finger height of the pressure plate caused by your clutch plate thickness and variations in how the pressure plate is made. Adding more parts and complexity is nearly always a bad plan. If .025 causes your clutch to not work you have far bigger problems some place else. Larry