I’m having a hard time understanding how an HTOB spacer would prevent my HTOB from over expanding on my F23 (matted to a 3800SC). My understanding is the Fiero clutch master moves too much fluid for the F23 HTOB.. If I install an HTOB spacer, that should not change the amount of fluid displaced to the HTOB and therefore when I or someone else drives the car and depresses the clutch to the floor, the HTOB will still fail? No?

And if you do install a pedal stop, where and how do you install it? Or, would it be better to shim the Fiero’s clutch master?

Thanks guys… I know it’s been discussed to detach but I’m stuck on the whole fluid displacement and HTOB separation..

How about just using the proper master cylinder to start with? Larry

quote Originally posted by trotterlg: How about just using the proper master cylinder to start with? Larry

That's not the issue.

Hydraulic clutches self adjust by nature, then when the pedal is pushed they will extend a specific length based on many factorys (diameter and stroke of the clutch master being a couple of them)

The issue with all the F23 HTOB over extensions is that once they self adjust, the HTOB does not have sufficient range of motion to accomodate pressing the pedal to the floor w/o over extending the HTOB. This is an issue with a mismatch between clutch and transmission, mainly because most are using Fiero clutches for a transmission that was never used in Fieros.


Here is an example where I went through the process of poperly centring a F23 HTOB for a SBC swap. Now before you think these are the number for every F23 swap out there, the placement of the clutch fingers is clutch/pressure plate specific and this swap has the flywheel about .200" closer to the engine than 60 degree V6 or 3800. This flywheel differences, also allowed for more room for the pressure plate to clear the differential buldge... so this works for this swap, but you can follow the same process for your swap.

quote Originally posted by fieroguru: Once the new clutch/pressure plate were bolted to the flywheel and measured the height of the clutch fingers to the bellhousing surface: 2.112" Then I measured the range of motion of the HTOB w/o any spacer. 2.776" Retracted 1.899" Extended So if I just installed this like it is, there would only be .213" for release and .664" for wear... no chance this will work w/o a spacer. This car did come to me with a HTOB spacer installed that is .250" thick. So using it with this clutch the available room for release will be .463" and .414" for wear. Even with the spacer, there is a very good chance the HTOB will over extend. The HTOB spacer needed to be thicker, so I turned a very larger washer down for a tight press fit inside the HTOB spacer. With the washer inside, the HTOB spacer is now .437" thick. So now there is: .650" for release .227" for wear And this will work just fine...

Of the available range of motion for the HTOB, you would like 1/4 to 1/3 be for wear, and 2/3 to 3/4 be available for extension.

When measuring the range of motion for the HTOB, make sure to install the bleeder assy and open it before compressing the HTOB. There is a check valve in the HTOB, so w/o the bleeder assy installed, fluid will be trapped and your retracted measurements will be off.

The only time you want to add a pedal stop, run an adjustable banjo, or shim the clutch master is to avoid the pressure plate fingers from making contact with the clutch disk. This would be caused by the fiero clutch master being too large, but 90% of the clutch issues with the F23 are over extending the HTOB and blowing out the seal.

[This message has been edited by fieroguru (edited 05-13-2014).]

quote Originally posted by trotterlg: How about just using the proper master cylinder to start with? Larry

I'm not sure it is possible to use the 2002 Cavalier master on the Fiero. If anyone has successfully done it, I would like to hear about it.

Doesn't have to be that master, only one with the proper displacement

quote Originally posted by trotterlg: Doesn't have to be that master, only one with the proper displacement

Did you read what Fieroguru posted? It's not a problem with the master. It is a range of motion issue caused by using a combination of parts that were never used together in a production vehicle before. The master cylinder is not what restricts that motion it is the clutch components (Disk & Pressure Plate). The spacer is just something designed to take up the extra space to keep the HTOB from over extending when using the F23 transmission with some of the common engine/clutch combinations we like to use in Fieros. The 2.2OHV/F23 combination that came in the Caviler obviously had a smaller stack height for the flywheel/clutch components.

Thank you Fieroguru for the info! The spacer makes sense now !

Now I need to figure out what size spacer I need.

Called SPEC and spoke to Jerrimy. The spacer needed is the .250" and the part number is N1774-.250 Bearing Cap. They told me it is $49 plus shipping. Hope this info helps others as it was hard for me to find.

[This message has been edited by Purple86GT (edited 05-14-2014).]

quote Originally posted by Purple86GT: Called SPEC and spoke to Jerrimy. The spacer needed is the .250" and the part number is N1774-.250 Bearing Cap. They told me it is $49 plus shipping. Hope this info helps others as it was hard gor me to find.

Just a word of caution, but don't go by what Spec tells you need - they have never mocked up a F23 with a Fiero clutch to determine the needed spacer... all they know is people are buying these spacers for the F23 for some reason (and having mixed results) and so they keep recommending them.

Measure your clutch, measure the range of motion for the HTOB and then determine if you need a spacer (some don't - it depends entirely on clutch disk and style of pressure plate) and then you decide if the 1/4" thick one will work or should it really be 3/16", 5/16" or some other thickness.

It not fun to put everything together and install it back in a Fiero just to have to pull the whole thing back out because it didn't work.

quote Originally posted by fieroguru: Just a word of caution, but don't go by what Spec tells you need - they have never mocked up a F23 with a Fiero clutch to determine the needed spacer... all they know is people are buying these spacers for the F23 for some reason (and having mixed results) and so they keep recommending them. Measure your clutch, measure the range of motion for the HTOB and then determine if you need a spacer (some don't - it depends entirely on clutch disk and style of pressure plate) and then you decide if the 1/4" thick one will work or should it really be 3/16", 5/16" or some other thickness. It not fun to put everything together and install it back in a Fiero just to have to pull the whole thing back out because it didn't work.

I guess what I'm not understanding is the range of motion of the HTOB.. How is that measured? Will it act differently once hydraulic fluid is in it?

Is there a magic number on the transmission side I can deduct from my clutch, pressure plate and flywheel assembly?

After reading several posts (often one post cancels the other *sigh* ) the norm seems to be the .250" spacer but some are reporting using the 0.260" spacer.

Since everything on the F23 side should remain standard.. It would be nice to have a formula that all you need is the distance from the engine / trans mounting surface to the fingers on the pressure plate and deduct it from this magic number to get your spacer.

In your post, you said these were the values for the F23?
2.776" Retracted
1.899" Extended

So I would measure from the mating surface of the engine (in my case a 3800SC L32) and deduct the value of the extended HTOB?


Any thoughts?

Thanks!

[This message has been edited by Purple86GT (edited 05-14-2014).]

Most F23's should measure +/- .020" of so of the measurements I took (the bearing wobbles some, so there will be some variation in the measurement). The dimensions below were from a brand new F23 HTOB with the bleeder assy installed and open, so there was no air or trapped fluid to alter the measurements.

2.776" Retracted
1.899" Extended

With these measurements, the HTOB has a range of travel of about 0.877". If you go with the assumption that room for extension (releasing the clutch) should be 2/3rd (0.585")to 3/4ths (0.658") of the available travel,

Then you want the clutch figners of the pressure plate to be between (1.899 + .585 =) 2.484" and (1.899 + .658" =) 2.557"

So measure your clutch fingers and see what the dimension is. If it falls between 2.484" to 2.557 then you don't need a HTOB spacer. If not, then a spacer is needed. For example if your pressure plate fingers are 2.200" from the bellhousing surface, then you will need a spacer 0.284 to 0.357" thick.

quote Originally posted by fieroguru: Most F23's should measure +/- .020" of so of the measurements I took (the bearing wobbles some, so there will be some variation in the measurement). The dimensions below were from a brand new F23 HTOB with the bleeder assy installed and open, so there was no air or trapped fluid to alter the measurements. 2.776" Retracted 1.899" Extended With these measurements, the HTOB has a range of travel of about 0.877". If you go with the assumption that room for extension (releasing the clutch) should be 2/3rd (0.585")to 3/4ths (0.658") of the available travel, Then you want the clutch figners of the pressure plate to be between (1.899 + .585 =) 2.484" and (1.899 + .658" =) 2.557" So measure your clutch fingers and see what the dimension is. If it falls between 2.484" to 2.557 then you don't need a HTOB spacer. If not, then a spacer is needed. For example if your pressure plate fingers are 2.200" from the bellhousing surface, then you will need a spacer 0.284 to 0.357" thick.

Thank you!

I hope to be able to measure it this weekend and know for sure! +1 from me bro! (unless I already have? haha)