Clutch Hydraulics Improvements

As has been discussed elsewhere there are several of us who have had clutch disengagement issues on both factory S10/Blazer transmission as well as T56 swaps. I'll just quote it all here to have it all in one place for easier reference (skip past the quotes for the new info).

The clutch doesn't seem to be fully engaging. It typically shifts with 0 issues, but sometimes can't get into second when downshifting and from a stop, starting with the pedal up I'm having to use the synchros in 1st or second to slow/stop the input shaft before sliding it into gear. My leading theory is a bit of air in the remote bleeder hose as the transmission, slave, pressure plate, flywheel, etc. are all setup as the would have been from the factory on a Camaro. I really should just grab a friend and a wrench and confirm/fix that.

clutch: i think you meant to say it isnt fully DISengaging.
As for that issue, I have a feeling the stock s10 clutch master/pedal system doesn't have quite the travel it "should" have from a mechanical design perspective.
with the 2 clutch swaps (3 if you count re-doing it once with the same parts) I'm convinced that a brand new clutch is going to drag for the first several hundred miles of "wear" which knocks down the high points on the friction disk
(i had the same issue every time, regardless of how much bleeding and stackup measurements i did, but it eventually fixed itself (i think from wear as mentioned))

Yup. Not fully disengaging. Sometimes just writing my thoughts down has me thinking through it more. The pedal is firm, so a bad bleed doesn't really line up. Leaves,  I figure,  a master that doesn't push enough like you said or a slave that needs to be shimmed, but with all the s truck clutch disengagement issues I have run across or heard of I'm leaning toward the master. Al and I discussed running some numbers comparing to the other cars that use this slave.

I'm 6000 miles in on this clutch and it hasn't gotten better. Matter of fact it got worse from the beginning and settled in where it is now, which is why I was thinking it was a bleeding issue.

My experience with a t56 swapped blazer is also a firm clutch pedal and a 2nd gear that grinds more with time. On mine i had to cut out the firewall for the stock s10 master, since it was also an auto to manual swap. Im interested in running the numbers on the clutch system to see how much force, pressure, throw we're expecting.

2nd seems to be the most unhappy, but I get 1st and 3rd problems too. Anything 4th or above has shown no signs of an issue yet.

hmmm 6k miles should have worn down any high spots for sure.

I'm curious on the fluid volume displacement compared to other cars too. the blazer definitely has the heaviest stock clutch pedal in any cars ive ever driven, which backs up the theory that there wasn't enough pedal stroke room to the floor/firewall to start with.

Al and I did some clutch Master Cylinder comparisons. Didn't worry about the rest of the system as it is identical to the T56 Camaro including the clutch on my truck. S10 Master has 18mm bore with 35.9mm stroke. Camaro is 19/36, so the S10 doesn't push as much volume as the Camaro. The internet says the 7/8" bore aftermarket slaves are popular; 19mm is essentially 3/4", but have to find another solution for the clutch start and cruise switches on the factory master. Any other GM masters that fit the square hole are the same part number as the S10. Al did some internet sleuthing and looks like a 94-97 Ram may have a square attachment hole too with a larger bore, so hopefully I can find the right combo in the yard to test fit.

Another thought floated was to extend the master push rod. Both Al and I are shoving the pedal all the way to the floor to catch the start switch on our respective T56 swaps. It's so far down both of us ditched floor mats independently, so it might be a matter of not enough travel available for the pedal. Or it's just another result of the smaller volume available.

We didn't jump into the slave cylinder side of the equation. The internal style slave uses a hollow tube of fluid instead of a solid cylinder like a push rod style, so it's not as easy to find dimensions for. I have an extra slave on the shelf and might have one in the scrap bin too that I will try and get measurements for. I know that the Gen 1 CTS V owners often uses later slave cylinders on clutch/flywheel swaps (C6 vette slaves for example), so there might be something bolt in out there for the slave side of the equation.

how about moving the clutch MC pushrod pivot on the clutch pedal down a touch? i don't know where in the misalignment the pushrod is sitting stock, but maybe moving it down 1/4" would be enough to get you more stroke and possibly retain the start safety switch? (this is assuming the pedal touching carpet/mat/floor is the stroke limitation and not the MC bottoming. I cut away my mat and my carpet is worn pretty much all the way through under the clutch pedal which makes me think the MC may not be getting full stroke.

interesting to hear the gen1V owners use something different for the slave.
I know the ls1/6 vs the ls2/3 have different flywheel/clutch geometries so i wonder if they changed the PP spring rates and stroke required too.
I never had an issue on the rx7 running the ls2/3/7 style clutch/flywheel with the ls1 t56 slave, but then again i was running a totally different MC/pedal setup too.

Isn't moving the pivot point up what we want? Goal would be to move the pedal further from the floor/firewall to gain more clearance for more stroke.  Sounds like you're in the same boat as both Al and I with the clutch to the floor.

I keep reading about shims or shimming slave cylinders, different torque values for pressure plates affecting where the spring fingers are located, as well as some sort of difference between the C6 slave cylinder and earlier applications with the T56.

https://ls1tech.com/forums/cadillac-cts-v-2004-2007-gen-i/1642218-cts-v-ls7-clutch-upgrade-how-confused-read.html

This thread has a bunch of info for the LS7 clutch into a gen1V that may or may not be related or helpful. I'm definitely curious what the dimensional differences are between the 2 slaves and if it may be another solution path. The fact that the 2 options for the V are the earlier slave + spacer vs C6 slave makes me think the C6 is longer or has more travel or something along those lines.

moving the pedal pivot point upward (longer pedal) would also work, but i was originally saying moving the pushrod point on the pedal lower. (longer pushrod stroke per pedal face stroke)

I did all the reading and measuring on the shimming of slaves (nv3500, stock setup) and i was definitely in the correct spot. I'd be hesitant to shim it because you might lose out on full clamp force if you go too far.

No, I wasn't talking about the pedal pivot, but I was also wrong in my thinking in my last post.

Moving the master pushrod down on the pedal shortens the pedal stroke for the same master stroke. I think we're on the same page there, now. Drawback will be more force required to move the pedal.

There's a ton of information and probably misinformation to sort through in that thread. To start out with I want to get the pedal out of carpet at full stroke and play with the pedal ratio, master size and/or slave size from there. I'm with you on the shimming, at least on the T56 I'm setup exactly as the LS1 Camaro would have been from the factory using all factory or factory replacement parts.

I need to sit in the truck and actuate the pedal again as well as look under the dash. I keep thinking I'd prefer lengthening the pushrod or the more attractive option of moving the pushrod mounting point on the pedal forward in vehicle. I've got a bracket design in my head that seems pretty simple to do without chopping up the pedal and could even add in extra holes to adjust the point up/down for pedal feel/travel preference. It would however bring the pedal position toward the driver and I'm not sure how that would feel in real world driving.

Al and I did some deep diving comparing the hydraulic setups between S10s and other vehicles that use similar, if not the same components. The NV3500 & NV1500 found in the S Trucks use the exact same internal slave as the T56, so that really helped narrow down where the potential issues may be, which... well... is the master cylinder.

Getting this chart together made it obvious the S10 master is pushing less volume than the Camaro, which in turn is less displacement at the Slave. We ended up looking at the Ram & Medium Duty master cylinders because they appeared to have a similar mounting flange to the S10.



As you can see both the MD and the Ram push plenty of fluid to match the Camaro's output and turns out the MD flange is nearly spot on to the S10 too. I did order up both the OEM and the Centric masters to compare the bore size - the 13/16 would have been just about perfect, but they are instead the exact same part. The casings have identical markings and the cylinder seal is the same p/n. I did some rough measurements and I'm quite positive the bore is the size GM spec'd out in their drawings.



The pushrod of the MD master is roughly 1-1.25" shorter than the S10, which translates to a pedal 4-5" closer to the floor. If anyone wants to check my numbers I measured 14" from center of pedal pad to the pivot and 3.5" from the pushrod to the pivot.

Seems like that puts the pedal pretty far down, so maybe an extension of the pushrod is in order.

There is also the concern of overtraveling the slave cylinder as I've done it before with this particular slave. Not exactly sure where I want to be on the travel and haven't sat down long enough to understand the numbers in relationship to that. If it's too much a pedal stop will have to be implemented.



The other good news is the MD pushrod shaft is the same diameter as the S10, so the clutch switch clips on perfectly. Just need to add a basic spacer to the base and it will work like it did before. The pushrod to pedal hole is also the same diameter, so it will clip right onto the S10 pedal as is too.

good research!
i think you have a ways to go before worrying about overstroking, assuming the c5 uses the same slave too.
i added a pedal stop to limit pedal down travel to about half of the original travel because there is no reason to have any more stroke than to get full disengagement.

I'm a bit worried because I pretty much overtraveled my slave before when I didn't have it fully bolted on. It makes me a bit gun shy to toss a ton of extra volume at it haha Might be something I can design an adjustable stop and keep turning it out until I hit the disengagement.

Any thoughts on the pedal position? I may try popping it off the slave currently and see where it ends up approximating the shorter pushrod. My concern there is I'm already into the floor with the stock master trying to activate the clutch start switch.

I'd also like to point out that many of the aftermarket masters I saw others using in my previous research were 7/8" bore. The MD master is also about 7/8, so seems like it must be a decent match.

With the slave installed correctly does the clutch assembly mechanically prevent overtravel?

Clutch start switch will be calibrateable based on the spacer between switch and master cyl that you mentioned.

The larger master came with pushrod uninstalled. Any progress on seeing if the s10 pushrod comes out and can be xfered over?

Edit: excellent summary post to start the thread. I dont think ive ever seen as many blockquotes used in a single post anywhere before.

i think the s10 pushrod once you install it into the clip in the MC it's pretty much stuck there forever.

it's been a while since i drove the blazer but i feel like i remember wanting the initial 'rest' position lower.
obviously with the stock bore MC that wasn't an option.

maybe you can get lucky and it will be in a "sweet spot" as-is?

on the rx7 i used a 7/8 bore MC on the wilwood pedal setup and it felt great, definitely on the heavier end, even with just the ls7 clutch though.

With the slave installed correctly does the clutch assembly mechanically prevent overtravel?

Clutch start switch will be calibrateable based on the spacer between switch and master cyl that you mentioned.

The larger master came with pushrod uninstalled. Any progress on seeing if the s10 pushrod comes out and can be xfered over?

Edit: excellent summary post to start the thread. I dont think ive ever seen as many blockquotes used in a single post anywhere before.

When I used the too long bolts on the slave it overtravelled or at least allowed the seal to come out of the slave, so I'm leaning toward it not mechanically limiting it. I also don't want to find out it does because that will require me to pull the transmission to fix it.

It will be calibrated based on the spacer, but it's a 2 position switch. Just at the top of the throw is the cruise disengagement, so as soon as you bump the pedal it shuts off the cruise and at the bottom is the start switch to make sure it is fully depressed. Any preload or adjusting the switch "up" will have the cruise deactivated permanently.

I was able to break down the S10 master and get the pushrod out. It isn't the same shape on the end, so not so lucky there.

i think the s10 pushrod once you install it into the clip in the MC it's pretty much stuck there forever.

it's been a while since i drove the blazer but i feel like i remember wanting the initial 'rest' position lower.
obviously with the stock bore MC that wasn't an option.

maybe you can get lucky and it will be in a "sweet spot" as-is?

on the rx7 i used a 7/8 bore MC on the wilwood pedal setup and it felt great, definitely on the heavier end, even with just the ls7 clutch though.

I was thinking lower wouldn't be terrible, but 4" sounds excessive. I'll definitely be giving it a trial to see what I think.

I was also thinking it would be more effort - the fancy equation of less pedal travel = more effort.

Might be a case where adjusting the pushrod location on the pedal helps both?

I've not been slacking on this research even if I haven't been posting. Lots of failure and learning these past couple months. I haven't completely eliminated the issue and have a few more fixes to make, but I think I'm at the point my remaining issue is either synchros or a dragging pilot bearing. I'll get more into that later. This could be a long post or two.

Cliff notes version:

• Installed 7/8" MD master cylinder with Ram Pushrod - not much change in symptoms
• Made some modifications to pedal geometry to get full stroke of the larger master - couldn't shift into gear with the engine running
• Did some research and learning through google - actually measured Pressure Plate position and clutch disengagement
• Also learned that the LS1/6 clutch I'm using has a Self Adjusting Mechanism, which I wasn't accounting for in my mental physics of clutch actuation and the reason for the no shift situation.
• Used that information to build a clutch pedal stop and control the pedal position to not overstroke the pressure plate
• Returned to original symptoms, but seems not quite as bad as before
• Also added a pedal position switch from a Corvette (and many other applications) and I can now also adjust when the start switch engages, so I don't have to smash the pedal to start the engine.

Where we left off I was comparing the 7/8' bore Medium Duty master cylinder to the S10. The pushrod wasn't long enough and I was still curious about the Ram master, so I bought one of those from Autozone to compare with what I had already. Turns out it is practically the same as the MD master, fits in the S10 firewall, and has a pushrod length very similar to the S10.

From top to bottom: Medium Duty, Ram, S10



Medium Duty (top) v Ram Pushrods



Medium Duty master + Ram Pushrod + S10 Clutch Position Switch. Fits like it was made to work together.





I ultimately decided to use the Medium Duty master I had with the Ram Pushrod. The Ram master I purchased was actually a metal body unlike the plastic used for the S10 & MD (they have a metal bore inside). The S10 & MD fit the firewall hole much more snug than the Ram because of this. The Ram did have a soft gasket to help preload and a spacer could be made for a snug fit like the others. With how similar the Ram and MD masters are I wouldn't be suprised if another brand is made from plastic. The Ram cylinder I bought was the Autozone store brand and the MD was a Centric. I also purchased an AC Delco version of the MD cylinder and it was identical to the Centric. RockAuto does sell a Centric version of the Ram master if someone wanted to experiment if they can get the longer pushrod and plastic body in one package. It does look identical to the MD body in their picture.



Apparently I don't have any pictures of the final installation - I'll have to get those at some point - but I used a clutch reservoir from a ~91 S10 and bolted it through the firewall into the cowl area like they did on that same S10.

I had high hopes for the larger bore, but it pretty much changed nothing. I was still having to smash the pedal into the floor to get the truck to start and it often would grind trying to downshift into 2nd or 1st.

While I had everything out I played around with the clutch pedal position switch to understand where that engaged.

With the switch fully unloaded the start circuit is open.



About 2/3 of the way down is when the circuit closes initially.



It stays closed through the rest of the travel.



The cruise portion of the switch circuit is closed in the fully unloaded state, but as soon as the switch is engaged it opens.

Armed with that information I knew the pedal was nowhere near getting the full travel of either of the master cylinders I've had in the truck, so following the train of thought of not enough volume moving in the system I decided to modify where the pushrod attaches to the pedal.

I removed the pushrod mount from the pedal and made a simple bracket to move it forward in vehicle. In essence I moved the pedal further from the floor allowing it to use the entire stroke before bottoming out on the floor.







It was pretty high up after all of this.



I ended up having to do some rearranging/tweaking of the wiring connectors underneath the pedal box to get enough space for the pedal to move upwards. Wasn't anything more than clocking a few mounts, but took some trial and error. I also realized during this process that my moving of the pedal box/column mount outboard had made matters worse for pedal to floor clearance. Instead of striking inboard of the dead pedal, the clutch pedal was striking the side of the dead pedal limiting its travel even more. I ended up bending the pedal inboard to gain it back, but it does seem that modification has been aggravating the pedal travel issue for me.

I started up the truck and went to test drive it only to find that now I could no longer shift gears at all. I could only shift without grinding the gears mercilessly if the engine was not running. It wasn't fully engaged with the pedal down because the truck wouldn't move, but it was an ugly and frustrating situation regardless.

The next week I pulled out the transmission.



Nothing seemed wrong, broken, or out of place and I couldn't rationalize what was wrong so I decided to give google a go. Pretty quickly came on this LS1Tech thread discussing how to properly setup a clutch during install.

https://ls1tech.com/forums/manual-transmission/1805906-t56-clutch-adjustment-tips.html

OK. Good to know information, but still didn't really explain what I was experiencing with the all grind no shift. I kept going down the rabbit hole armed with new information and found this post talking about the Self Adjusting mechanism in the clutch I had.

https://ls1tech.com/forums/manual-transmission/1030815-does-your-clutch-setup-need-shim-6.html#post13249039

A few more thoughts were making sense, so I slapped the pressure plate on the press to observe how it operated. The more I pressed in the more it adjusted tighter to the friction disc. It became obvious that with the extra stroke on the larger bore master I had basically adjusted the Self Adjusting mechanism as tight as it could go (and this was the position I found it in upon removal), so it was now engaging the friction material constantly even with the pedal depressed.

Wanting to observe how it all worked on the truck I went down another rabbit hole and built a jig for the slave cylinder, so I could peer inside the bellhousing while the pedal is being depressed.

Well first I built a jig for my jig.





Slapped some more scrap steel together.



And I can bolt this to the transmission with the slave cylinder installed instead of having the transmission in the way.



Also added an inspection hole and cover to the bellhousing.





It's right where the friction disc, flywheel, and pressure plate all come together.





Precision guessing at its finest



Next up I built in an adjustable pedal stop and adapted the Corvette clutch start switch to the pedal box. Knowing I can overtravel the clutch I didn't want to be smashing the pedal any further than required to release the friction disc, so adding in the stop and the adjustable start switch allows me to start the truck and prevent overtravel. They're both nice luxuries to have...

1 part pancake bumpstop + 1 part Corvette start switch + 2 parts adjustable bolts.











That was all a bit more precision guessing and drilling holes. My engineering mind wishes it could go back and redesign it more thoughtfully, but it all works as intended even if the packaging is rough.

That all got me to where I am now. Used the slave jig and inspection port and adjusted the pedal stop to get the recommended .025" gap between the friction disc and the flywheel/pressure plate, so I know the clutch and hydraulics are doing what they are supposed to. I'm actually still all the way into the floor at that point with the 7/8" master. My clutch pedal is actually slightly below the brake pedal, so I'm thinking I will modify this or another pedal some more to bring the pedal up and actually use the pedal stop instead of the floor as my travel limiter.

While I'm at that I will also need to revise how the pushrod attaches to the pedal because the factory style bushing keeps disintegrating on me. I've gone through 2 or 3 since I've installed the 7/8" bore. I think it is a combination of the higher force from the larger bore as well as the extra angle sliding the pedal box outboard has added between the master and the pedal.


I believe that wraps up all I have done and the thought process along the way.

If I were to go back and do it again.... I'd start with checking clutch disengagement. I imagine the factory S10 master wants a bit more travel, but won't know unless I know what the clutch is doing in the bellhousing. From there modify the pedal travel, add in a stop, and probably the Corvette start switch too. If that isn't enough the Centric Ram master is nearly a bolt in and the pedal stop/switch can be adjusted to adapt.

frustrating work, but i'm cheering you on to find us a simple solution!

I don't think frustrating even quite describes it! haha

Another thought: aftermarket clutches can be had without the self adjusting mechanics. That would cure one of the issues I had and I suspect it played a part in some of the earlier issues I had too. It seems the mechanism can be overadjusted with overtravel of the pressure plate, so without a pedal stop or smashing the pedal further into the floor than it was meant to the friction disc ends up with a pre load from the pressure plate when disengaged.

I picked up a second pedal from the junkyard today, so I'll start playing with a new mounting solution and work that into a different pushrod position to pull the pedal up slightly and hopefully out of the floor for my release point.

Was browsing through some pictures today and found a few from my first test fit of the MD master.



This is the clutch pedal position with the shorter MD pushrod. Toooo low.

So I gave this another shot and I'm much happier with the results.

I did some browsing at the junkyard while looking for the connector for my current clutch start switch and found a combo clutch pedal stop/switch in a manual Grand Am. It's super similar to the Corvette part I used before, but has the integrated stop, so I grabbed it.

Thinking about this part helped me realize that I could set the pedal stop wherever I want it - in my case I'll move it 0.5-1.0" above the floor - and then adjust the pushrod length or pivot position on the pedal to obtain the correct clutch release.

I had been writing off using a heim joint at the pushrod pedal pivot because I didn't have room to package a threaded adjuster sleeve. Was talking other and far more complicated adjustment mechanisms with a friend and when he suggested a heim again it set off a light bulb in my head; the pushrod itself rotates in the master cylinder, so all I needed was to thread the end of the pushrod and it would be easily adjustable.

So after some measuring, running some numbers, and finding a heim I could purchase locally I dusted off the boring tool - if only I had a lathe - cut off the eyelet and turned down the diameter.









Some careful work with the 5/16-24 die and the pushrod was ready.





The 5/16-24 heim joint is about the perfect size for this without taking too much diameter out of the pushrod. An M8-1.25 would also be a good choice if you prefer metric. Online they're like $3-5 each, so definitely not costly.

Next up was packaging the Grand Am switch. It was tight in there, so I started grinding away at the casting flues in the way. I ended up having to take the blend out of the corner too, but it was just enough to fit the switch on the right side of the clutch pedal. These first pictures were just the start of it.





Welded a simple bracket onto the pedal arm to hit the stop and activate the switch. So much less going on than my first attempt.









Last task was to cut off the factory pivot stud and replace it with a stud to fit the heim. Here I did use an M8 fastener and it fit nice and tight to the 5/16 as it's a touch larger in major diameter. I found a socket head flange bolt and turned the head down with the boring head to fit snugly in the hole left by orignal stud. Threw a couple welds on the back side to secure it.





You'll see in that last picture that I left the flange on the bolt head to help space the heim away from the pedal arm for some extra articulation. I think I mentioned above that moving the pedal box outward was causing binding issues with the original bushing setup, so this should help with that too.

Test fit went well. I was overly cautious in my placement of the stop position, so I'll have to space the stop out with a shim to get the pedal further off the floor, but I'm heading in the right direction.

I'll also need to notch the bracket out for the switch as it activates well before the pedal reaches the stop. I had a feeling I might have to do that based on how the old switch worked. Just some fine tuning left to get it working how I want and I'll have the truck back together for a test drive.

progress is good but this is starting to get to be a fairly involved process!

I'm not super happy with the time all the iterations are taking total, but the final result can be copied without such a consumption of time. Like it could be done in a motivated Saturday or weekend. Hopefully you other manual guys can take what I'm learning and apply it. I think the stock master could be adpated with the same techniques to adjust everything in.

Shimmed the stop/switch before hitting the road last month and modified the pedal stop to engage the switch further down.



Could have gone with more shim, but it's not too bad and I'm getting used to it. Clutch engages pretty high up in the travel and with the larger bore it can be a quick engagement. I like it better than way down at the floor though.

Still getting some grinding in 1-3 gears depending on the situation, trans temps, and a few other factors I'm sure. At this point I'm thinking I have a couple not so great synchros and/or a dragging pilot bearing? I consider myself happy with the performance of the clutch hydraulics at this point.