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Measuring HTOB to determine need for spacer? by FieroGT42
Started on: 02-23-2013 12:57 PM
Replies: 28 (766 views)
Last post by: mcguiver3 on 10-13-2014 07:58 PM
FieroGT42
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Report this Post02-23-2013 12:57 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
Getting ready to install my flywheel, clutch and F23 on a stock 2.8. I haven't done a swap before so I'm not sure how everyone's measuring this, what's okay and what isn't. Thanks in advance for any help.

Jason
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Report this Post05-27-2013 03:41 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
Anybody? I know I found a thread on some forum at one point that gave very clear descriptions on how to measure what and the formulas used, but I can't seem to find it now.
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Report this Post05-27-2013 04:19 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
First measurement: Distance from the bellhousing face to the tips of the pressure plate fingers. With the clutch/pressure plate bolted/torque to the flywheel, place a straight edge across the center of the pressure plate and measure the distance from the edge of the straight edge to the bellhousing face. If the fingers are recessed below the surface of the pressure place, measure that distance and subtract it from the previous measurement.

Second Measurement: Distance from the bellhousing face to the fully extended end of the HTOB. Install the hard line (or plastic bleeder fitting) to the HTOB to disengage the check valve (this is a critical step and where many people mess up). Let the spring in the HTOB fully extend it while you place the straight edge across the center of the bellhousing. Measure the distance from the bellhousing face to the fully extended HTOB.

Third Measurement: Distance from the bellhousing face to the fully compressed HTOB. It helps if you clamp your straight edge in place, as you will need 1 hand to compress the bearing and the other hand to take the measurement. Measure the distance from the bellhousing face to the fully compressed HTOB.

The difference between the 3rd and 2nd measurement is the normal range of motion of the HTOB. The first measurement must be between the 2nd and 3rd and ideally it would be 2/3rds of the distance from the second one and 1/3rd the distance from the 3rd one. As the clutch wears, the fingers will go closer to the HTOB, so you need to keep 1/3 of the range of motion for clutch wear and 2/3's for clutch release.

For example (not real numbers, just keeping the math easy to follow): say your clutch fingers are at 2.0" and the extended HTOB is 1.5" and the compressed HTOB is 2.25. The range of motion is 2.25-1.5 = 3/4". There is 2.0-1.5 = .5" of available travel to release the clutch. 2.25-2.0 = .25" of available travel for clutch disk wear, and 2/3 of the available travel is for release and 1/3 of the available travel is for wear.
Some may argue that you should have a 50/50 split to maximize the wear life of the clutch and that could work, but I think 66/33 is a safer place to avoid the chance of over extending the HTOB.

I walked through this process in my LS4/F40 swap, but it also had to take into consideration spline placement and engagement since the input shaft is about 1" into the bellhousing. Not an issue for the F23.

 
quote
Originally posted by fieroguru:
There has been lots of discussions lately about the proper measurement of the range of travel for the F40 HTOB. So here are the following measurements - all measurements are distance from the Bellhousing Flange:
End of Input shaft: 1.121"
End of Splines: 1.502"
HTOB fully extended: 2.675"
HTOB fully compressed as delivered: 3.218"
HTOB fully compressed with the bleeder screw opened: 3.582'

The F40 HTOB has a check valve inside it. So the amount of fluid in the HTOB from the factory is trapped and will not allow the HTOB to fully collapse until the bleeder assembly is installed and the bleeder screw opened. Once you bleed off the factory fill, you get an extra .364" of travel to the back side and the overall range of travel increases to .907" (from .543").
Here is the setup I used to get these measurements with my digital calipers:

[This message has been edited by fieroguru (edited 05-27-2013).]

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FieroGT42
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Report this Post05-27-2013 07:57 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
"I see" said the blind carpenter, as he picked up his hammer and saw. Thanks, it seems pretty obvious now. My trip through KY has been cancelled or I'd buy you a beer, so I'll just have to owe you one.
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joshua riedl
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Report this Post05-28-2013 10:57 AM Click Here to See the Profile for joshua riedlSend a Private Message to joshua riedlEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm going through the same thing right now so ill post my numbers. It would be great if you put yours up when you get them to compare. For the tob I have 1.89 extended and 2.75 compressed for .86" available travel. Cutch fingers to mounting surface I have about 2.19". The fingers measure different on every one so I picked an average number. I'm thinking about a .25" spacer added to the 2.19" clutch reading is 2.44". Subtract the extended number gives me .55" available TOB travel. I could probably go thicker on the spacer but I was having an over travel issue with the spec clutch before so I don't see the point on pushing the limits. Ill be curious to see what you come up with.
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FieroGT42
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Report this Post05-28-2013 06:48 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
Will do but it might take me a week or so to get to that point. I'll post and PM you when I do.
Never mind. The rest of what I needed came in the mail. BTW, this is on a stock 2.8 with a flywheel #6505 from Standard Flywheels and replacement pressure plate.

F23 HTOB measurements
1. Engine side, Pressure plate fingers to bellhousing face 2.260” 2.310"
2. Trans side, HTOB extended to bellhousing face 1.900”
3. Trans side, HTOB compressed to bellhousing face 2.675
Derived measurements:
A. 2.675 – 1.900 = 0.775” travel
B. 0.775 / 3 = 0.258333 per third of the travel
C. 0.245 * 2 = 0.51666 for 2/3 travel

The HTOB should not extend (on my car, with my measurements) more than 0.775” from its compressed state, which is 1.900” from the where the engine & transmission bellhousing faces mate.

Is the disengagement travel calculated from where the HTOB makes contact with the fingers?
2.310 - 1.900 = 0.410" HTOB-fingers clearance when compressed.
0.775 - 0.410 = 0.365"of throw for disengaging
0.445" / 0.775 = 47% of the total HTOB throw is after the HTOB meets the fingers.

With 1/4" spacer:
0.410 - 0.250" spacer = 0.160 air gap & clutch wear
0.615 of throw for disengaging
0.615 / 0.775 = 79%. 2/3 would need 0.152" spacer

Jason

[This message has been edited by FieroGT42 (edited 06-01-2013).]

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Report this Post05-28-2013 08:44 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
There are other clutch plates which have fingers that are higher than one from a Fiero. A pressure plate from a Chevy 2.2 bolts to the same flywheel as a fiero but has fingers about 1/4 to 5/8 highter, same diamerter disc. There are probably a lot of ways to solve this problem without resorting to shims. Larry
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Report this Post05-28-2013 08:55 PM Click Here to See the Profile for joshua riedlSend a Private Message to joshua riedlEdit/Delete MessageReply w/QuoteDirect Link to This Post
At least the measurements are fairly consistent. I actually think I could get away without a spacer but just barely and I'm not going the chance it. TOB's are expensive for these transmissions. I called today to order one but they were closed for the holiday. I don't know if you got that far but autozone had a 12mm x1.0 coupler that I'm going to braze to the hydraulics to hook up the stock line.
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Report this Post05-28-2013 09:54 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
I just figured out what I'm doing for that the other day. I'm just waiting on the part to arrive so I can confirm it fits before I go running my mouth about it and having people upset that it doesn't fit.

I think I found a one-piece German OEM part that has the quick disconnect we need on one end and a threaded fitting on the other (undoubtedly metric, maybe even 12mm x 1.0) connected with flex hose. Plus it was about $25 vs $40 for one made by a PFF member or the $80 that I saw some J-body enthusiasts paying. I plan to run my own clutch line since I'm swapping auto-to-stick, so I'm hoping that will take care of my flex hose and HTOB hydralics in one shot. Plus hey, it's German OEM quality. That's hard to beat.

Edit: Should know Thursday

[This message has been edited by FieroGT42 (edited 05-28-2013).]

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Report this Post05-28-2013 11:10 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have this sitting here, on the floor not bolted down the fingers are 2.050 from the cement. bore is 2.080 or so. It is close to new, I could bolt it to a FW with a plate and measure the height, it is yours for the shipping it will fit a large flat rate box which I think ships for about $16.00. Larry

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Report this Post05-29-2013 11:56 AM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
That's very generous of you, thanks! I'll have to measure my PP to the flywheel to see if it works for me. I'll let you know.
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Report this Post05-29-2013 01:07 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
I can bolt it down to a FW with a disc in it to get a measurement, just not sure where to measure to, fingers to the flywheel surface? Larry
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Report this Post05-29-2013 01:21 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
Yeah, I measured from the transmission side of the fingers to flywheel surface.
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Report this Post05-29-2013 05:23 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
OK, with a clutch disc in it that measures .275 thick, the height from the flywheel face that the pressure plate bolts on to the top of the clutch fingers that the throwout bearing runs on ranges between 1.960 to 2.005. I laid a file across the fingers to measure at the edge where I could get to the flywheel face. Hope this works, would be really nice to find a pressure plate that would eleminate shims on this project. Larry

[This message has been edited by trotterlg (edited 05-29-2013).]

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Report this Post05-29-2013 05:27 PM Click Here to See the Profile for joshua riedlSend a Private Message to joshua riedlEdit/Delete MessageReply w/QuoteDirect Link to This Post
That seems pretty close to the measurements I was getting. I just ordered the spacer and the salesman said he only saw one part number and it happened to be .250", so I didn't say anything but I imagine any different thicknesses would take a conversation with more than a salesman.
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Report this Post05-29-2013 06:27 PM Click Here to See the Profile for fieroaddictedClick Here to Email fieroaddictedSend a Private Message to fieroaddictedEdit/Delete MessageReply w/QuoteDirect Link to This Post


I am at this stage as well, so i am very interested. I will check later on tonight to see if i can come up with some #'s myself. I don't have my "new" HTOB yet, but the old one should do for some measuring. I'll see if i can figure it out. Although i am not 100% sure how you are coming up with a couple of the measurements. Maybe it will be clear when i look at it

EDIT: Opps i just re read the first post and realized it was being installed to a 2.8, not a 3800....guess my measurements would be different anyways.

[This message has been edited by fieroaddicted (edited 05-29-2013).]

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Report this Post05-29-2013 06:35 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
If my memory is correct, the Spec pressure plate for the 3800/F40 combo had the pressure plate fingers designed to extend past the pressure plate by some amount when the clutch was engaged. They were trying to make up the extra 1" of depth within the F40 by using the thicker camaro flywheel (un cut) and this pressure plate with extended fingers. The initial mockup didn't release the excess fluid in the HTOB and was off by 1/4" so spec made the spacer for that application, but it has been used numerous times on the F23 as well.

The pressure plate for the 3800/F40 combo might be the ticket for use w/o a spacer, but it might not clear the differential bulge or the fingers could be extended too far.
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Report this Post05-29-2013 07:26 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
My brain has fallen out and I'm wondering if my math is correct. I know the measurements are good though.

What stops the HTOB from over extending and blowing out if I don't have a pedal stop and happen to put my foot down too far?

And how do I measure for the pedal stop? Do I have to connect everything and carefully hit the pedal while I measure the HTOB?

[This message has been edited by FieroGT42 (edited 05-29-2013).]

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Report this Post05-29-2013 07:36 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Never seen the system, but I would guess there is a clip that will not let the piston fly out of the system. Larry
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Report this Post05-29-2013 07:41 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
I haven't seen it apart, but then why are people blowing the piston seals all the time? Too much pressure because the master cyl is allowed to compress too far past the point when the slave (HTOB) is fully extended?

That leads me to the question of how much is acceptable, or too much, and still how far down to place a pedal stop. :/
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Report this Post05-29-2013 09:57 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the pressure plate clutch finger positions the HTOB in the right place, then pressing the pedal to the floor does not provide sufficient travel to over extend the bearing.... no pedal stop required. My F40 swap uses a very similar (if not the same HTOB) and the stock factory clutch master and I can press the clutch pedal to the floor w/o over extending the HTOB. If you do want to restrict the travel, loosen the bolts holding the clutch master to the firewall and add some spacers to shim it further away... but if you do it right, this step isn't needed at all.

The older style HTOB (92-94) did not have any snap ring to limit travel, so they would just come apart. The F23 and F40 versions do have a snap ring or some other means of keeping the HTOB from over extending itself w/o any significant pressure, but the ring is easily overcome by pressing on the pedal. I have been running various HTOB transmission in swapped Fieros since 2005.
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Report this Post05-30-2013 06:11 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by joshua riedl:
I don't know if you got that far but autozone had a 12mm x1.0 coupler that I'm going to braze to the hydraulics to hook up the stock line.


Just FYI, I got my part today and it fits. I'll post something as soon as I get the photos from my phone.
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Report this Post05-30-2013 07:45 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
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Report this Post05-31-2013 01:45 AM Click Here to See the Profile for FieroNateClick Here to visit FieroNate's HomePageClick Here to Email FieroNateSend a Private Message to FieroNateEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have dimensions as well if you need them. I'll see if they match FieroGURUs. But those look like what you need. I've found its easiest to visualize if you draw it. I can post a diagram of the side view if you want.
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Report this Post05-31-2013 07:41 PM Click Here to See the Profile for FieroGT42Click Here to Email FieroGT42Send a Private Message to FieroGT42Edit/Delete MessageReply w/QuoteDirect Link to This Post
After some sleep, confirming that the "straight" edge I loaned out was returned to me as a wavy edge, and re-evaluating everything, I changed my numbers. I think I'm very close to where I need to be already, and a .25" spacer would leave only 0.08" for clutch wear and air gap.

Like I said, I'm new to clutches so if anyone would like to go over the logic of my math and the calculations, that would be great. BTW, I'd have to dig through some papers to confirm, but I think I'm already using a pressure plate intended for a Cavalier but supposedly compatible with a stock Fiero.

[This message has been edited by FieroGT42 (edited 05-31-2013).]

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Report this Post06-01-2013 07:02 AM Click Here to See the Profile for joshua riedlSend a Private Message to joshua riedlEdit/Delete MessageReply w/QuoteDirect Link to This Post
It is still .200" shorter than the stock clutch, using the numbers posted in another thread. And leaves .410" for extension. My guess is it will work but I accept no responsibility for that statement. A .250" spacer should leave .115" for clutch wear.
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Report this Post10-13-2014 07:16 PM Click Here to See the Profile for mcguiver3Send a Private Message to mcguiver3Edit/Delete MessageReply w/QuoteDirect Link to This Post
Just saw this thread and have a question.
Can a HTOB spacer be fabricated with the appropriate thickness of steel washer welded to a piece of appropriately sized pipe to center and hold it on the bearing?
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Report this Post10-13-2014 07:32 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by mcguiver3:

Just saw this thread and have a question.
Can a HTOB spacer be fabricated with the appropriate thickness of steel washer welded to a piece of appropriately sized pipe to center and hold it on the bearing?


Before you measure for your spacer, make sure the bleeder assembly is installed on the HTOB. The HTOB has a built in check valve that will trap fluid and not give you the right fully retracted dimension.

The face needs to have a radius on it so that the edge of it does not make contact with the middle of the clutch release fingers once they break the transition from convex to concave. Besides that, there are lots of ways you can make one. Some people even use a junk HTOB assy and cut the cylinder part off so they can shim the base of the HTOB from the transmission (the HTOB has the input shaft seal). Here is a picture of the F40 HTOB removed.

[This message has been edited by fieroguru (edited 10-13-2014).]

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Report this Post10-13-2014 07:58 PM Click Here to See the Profile for mcguiver3Send a Private Message to mcguiver3Edit/Delete MessageReply w/QuoteDirect Link to This Post
Great info.
I think I will try to fabricate the spacer.
It looks like I need something in the .275 range
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