Slave cylinder overextended?? 3800 w/F40 (Page 1/3)
dnthmn87 AUG 25, 05:11 AM
I found a new old stock F40 transmission on the local classifieds. It has never been used and came with a 6 puck clutch and flywheel, which weren't used either but it seems that at least the transmission was left out in the weather a fair bit. I installed this setup on my 2006 Grand prix and started to bleed the clutch master cylinder and slave, but was quickly disappointed when the clutch pedal gave way when still trying to bleed the system. That was followed by a steady stream of fluid coming out the bottom of the trans. So either the slave cylinder gave way because it was 15 years old but never used??? Or possibly the slave cylinder had to overextend because my flywheel is to thin? Or was there supposed to be some spacer between the throwout bearing and clutch fingers? Any suggestions are welcome. I'm hoping to drop the trans this thursday night and I have a new slave on its way to install. But maybe I need to do some measuring first??

Thanks

Dan
fieroguru AUG 25, 08:15 AM
Never install a HTOB transmission without measuring the stack height to the fingers and the range of motion for the HTOB. Lots of people have over extended them due to not measuring first.

Specs solution for the F40/3800 was based on a full thickness Camaro flywheel, clutch disk with a flipped hub (to increase spline engagement), a pressure plate with altered finger placement, and a HTOB spacer. Far from an ideal setup and easy to accidentally swap out any of the 4 parts for similar but not the same and run into issues.

dnthmn87 AUG 25, 03:31 PM
Thanks for responding Fieroguru. That's all new info to me, guess I lacked the research. Another piece of the puzzle is that I originally installed a 5 speed 282 from an 89 Grand Prix, and am still using that master cylinder. Not sure if that displaces too much fluid or not. But I definitely need get an HTOB spacer, and didn't flip the clutch around for better spline engagement. I believe it is a stock camaro flywheel with the spec clutch. Where do you recommend getting the spacer? Is the air gap the same as stack height? Just watched a video on measuring the air gap (working manual transmissions is new to me).

[This message has been edited by dnthmn87 (edited 08-25-2021).]

dnthmn87 SEP 02, 05:29 PM
So I got the transmission out last night and measured from the clutch fingers to the block, 3'' exactly. Bellhousing to TOB was 2'' 7/8 with the slave cylinder compressed with the bleeder installed and open. So 1/8" of an inch is actually ideal, right? Could the seal of the original one just have just blown out because it was 15 years old and sat out in the sun for a couple years?
note, my throwout bearing didn't compress even half as much as the one in the video that I watched on how to do this, but it was a different transmission. But it does compress at least 1/4'', using the new slave.
dnthmn87 SEP 08, 03:09 AM
Forget my last post, it is 3.5 inches from the bell housing mating service to the compressed slave cylinder, only 3” from the pressure plate fingers to the block, so I’ve got 1/2”… I’ve found 1/4” spacer so hopefully that’ll be good enough 🤷‍♂️.
fieroguru SEP 08, 08:25 PM
A stock F40 HTOB has about 0.90" of available travel. You want about 25% of this to be for wear (gap between pressure plate fingers and fully compressed HTOB) and 75% of this for travel to release the clutch.

You want something around 0.225" for wear so you have about .675" for clutch release travel. Having 0.5" for wear is a bad thing.
dnthmn87 OCT 21, 01:09 AM
So shouldn't the .25" spacer make it good enough? I installed that spacer with a new slave and put it together. I was bleeding the clutch and it was starting to feel pretty good, then POP!!! The slave blew out again!!! Grrr
Now what?

[This message has been edited by dnthmn87 (edited 10-21-2021).]

fieroguru OCT 21, 08:14 PM
Time to pull it apart again and remeasure. Something isn't right.
dnthmn87 OCT 21, 09:07 PM
For sure. I’ll probably rope someone else in to help measure this time too. Is it possible that my master cylinder is displacing to much fluid? Pushing the slave out too far? Or should the clutch fingers bottom out on something?
kennn OCT 28, 09:23 PM
I'd like to join this conversation if I may. I too have an F40 6 speed. I was not aware of the 0.90" of travel assigned to the TOB. With no hydraulic fluid in the bearing it appears spring loaded and upon compression will collapse 1/2". Where is the 0.90 dimension measured from? The face of the bearing before it is collapsed? The understanding that I'm taking away from this conversation is that the fingers of the clutch should be depressing the bearing 1/4 of its travel, or 0.225". So for setting up the location of the clutch fingers, would it be accurate to say that the fingers should be 0.675"away from the face of the TOB before any fluid is added? I would really appreciate some clarity here. Thanks.

Ken

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'88 Formula V6
'88 GT TPI V8