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Hydraulic clutch Complete!


Well-known member
Jul 3, 2001
Auburndale, Florida
1969 Killer Shark
Okay, here is the 411 on how to convert your mechanical linkage clutch to a smooth hydraulic action. As you guys know, this has been part of my project. It was not until last night however that I was able to finally see it work. It is so schweeeeeet!

Parts you need.

1. Quatermaster "Street" Hydraulic release bearing ($180-$220 depending on where you get it).
2. 1985 Chevy full size truck clutch master cylinder, resevior, cap, and main hose (MC $45, resevoir/cap $10, hose (Napa $28)).
3. One custom compression AN #4 female adapter to replace the 5/16" MIP flare on the slave cylinder end of the hose kit. ($1.00)
4. Two rubber insulated hose mount clips ($1.99)-to secure the hose to the firewall.
5. One ball stud swivel to install in the clutch pedal where the original pin goes through the pedal holding the mechanical linkage (5/16" fine thread with lock nut $20 Napa)
6. One hacksaw and 5/16" fine die to cut down the clutch rod from the master cylinder and thread it to fit the Napa Ball Stud ($10).
7. A scrap piece of 3/16" aluminum or steel to build a backing plate to secure the master cylinder in the firewall (you put it through the original clutch rod hole, drill a hole on each side to bolt it in, and make an oval plate to back it up for strength ($$free if you have the scrap metal and time).
8. Two 3/8" hardened bolts, washers, nuts to secure m/c ($5)

You have to have the trans out of the car to install the hydraulic release bearing as it goes over the trans shaft just like a release bearing. You have to take a couple of measurments and shim it to make sure it is about 1/4" away from the clutch fingers when disengaged. The kit comes with the shims and they are easy to install.

You can use any master cylinder you want. Wildwood and others make racing version that are less than $100 and come with standard AN style connectors that allow you to make up a line. Also, the rod to pedal assembly could be done 100 other ways I am sure.

If you decide to make this mod, feel free to get in touch with me if you have any questions. It is really cool!!!!!!!!!!

Finally, I don't know why at this point, you could not just install the complete hydraulic assembly as you would find on a 1985 full size chevy truck. I did not explore that avenue, but I imagine you would just need some brackets to mount the slave cylinder to the trans housing and do the install. That would probably be a less expensive mod, and the parts would be external, but it would never be as cool looking as this is from underneath.
Whats the difference about mechanical and hydraulic, in terms of functionality?
How about performance?

I don't know to much about trannys and clutches.

sscam69 said:
Whats the difference about mechanical and hydraulic, in terms of functionality?
How about performance?

I don't know to much about trannys and clutches.


They both obviously do the same job in the end. That is, the clutch pedal will activate the release bearing that contacts the clutch fingers on the pressure plate to release the clutch for shifting gears and coasting, moving the car/spinning the engine without it turning the trans.

The mechancial version does it by rods and levers. In fact, it has a pivot point on the engine block just above and forward of the oil filter area. It can be adjusted as needed to control the release point realative to the pedal position as the main rod is threaded and the pivot point can be adjusted higher or lower.

The plus is, it is very reliable, simple, and of course, the stock configuration for all stick shift vettes up to 84.

The minus is that the linkage can wear out and get noisy, and the driver feels the vibrations/torque of the engine in the clutch pedal since it is basically connected to the engine block. The effort to push is also significant.

Hydraulic uses a master cylinder much like your brakes. When you push the clutch pedal the rod attached to the clutch pedal will depress into the master cylinder forcing fluid to travel through a hose down to the clutch assembly. At the clutch you will either have an external slave cylinder, or internal hydraulic release bearing that will expand to push on the pressure plate fingers and release the clutch.

The benefit is smooth easy operation, less pedal effort, no vibrations in the clutch pedal, and less moving parts to wear/break adjust. It is also "self" adjusting from the perspective of the hydraulic system, much like your brakes.

The minus to hydraulic would be the time and expense involved if there is a leak, or failure in the system. In my case, the trans would have to be removed to access the hydraulic release bearing.

For performance purposes, it really does not make a difference. Different people will have different opinions on this one. Most circle track cars I see as well as high speed Nascar/Winston Cup and SCCA road race cars are hydraulic. Many drag race cars are mechanical. Ford put cable mechanical operated clutchs on the Mustang for years and years.
69MyWay said:
Ford put cable mechanical operated clutchs on the Mustang for years and years.

:eek Ford also used plastic gears! My brother had an '83 GT and we lost the clutch pedal in Northern CA; drove back without it (even got stopped for speeding once :)).

_ken :w
Pls explain the reason why a hydraulic one uses less pedal force.
Is the throw out way less ?
Since the system is not using a booster, the pedal pressure should be equal for both systems ?
Just wondering !
Thanks KEN
Nice explanation.
Problem is, it does not explain where the booster force is coming from if you use a master and a slave piston only.
Force will only decrease if the stroke of the slave piston is smaller as the stroke of the manual cable system, but with an external slave piston on the clutch fork, it should have the same stroke to go ?
Hydraulics might be smoother to operate, but less pedal force ?:confused
I wish it would be so as my 68 big block clutch is very hard to push and hold down. The car was actually sold due to this by the previous owner because his wife couldn't drive it.:D

Does the hydraulic bearing have any way of being ajusted for the amount of travel. When I fitted my Quartermaster clutch I should have fitted the hydraulic setup at the same time. The mechanical linkage is difficult to setup so that it has the recommended travel and after 20 years it is all very worn. The first problem was that due to the high peddle pressure the bracket on the chassis broke after making a new bracket the rods have about an 1" of play before the clutch fork moves so I will probably run with it this summer but fit a hydraulic one later.

What put me of was the cost of the release bearing to match my clutch (£385+17.5% tax !!!! thats about $550+tax) and the lack of availability of the other parts.

Do you think a complete C4 setup would work just as well or alternatively could you give me some part numbers of the items you used. Like you I either stall or rip up the tyres when I take off although I have bought a new cam that hopefully will have a bit more bottom end torque compaired to the RPM cam without sacrificing to much top end horsepower.

If you don't want to convert to hydraulics, look into Centerforce clutches; they are easy on the calf muscles, yet as the rpms come up, the centrifugal weights increase the clamping force of the pressure plate to the disc.

I remember the days of 11" (Hayes, Scheifer, Borg & Beck, etc.) clutches and the immense amount of effort it took to engage/disengage the unit. I also remember breaking a lot of pivot points with the extra stress it took from those units. ;)

_ken :w
The old setups used mechanical leverage....the heaver the clutch springs the more force it takes to operate. Hydraulics uses fluid to do the work. You push the pedal it pushes on a rod which pushes a piston that pushes the fluid. the bigger the the area of the piston the less force it takes to do the work. Just like a brake system.
I remember the clutches in my big blocks . You put the heavy ones in for the performance and when you sit at a stop lite your leg starts to shake from the force. But boy did they hook up when you dumped them at 4 grand :dance
The pressure plates that Centerforce sells use a "diaphragm" type of force to exert the pressure on the plate to the disc. The diaphragm type provides for easier leverage than the coil spring type assemblies, although both can still be found on the market; McLeod makes a good set-up.

Each assembly and method of activation is the same as it is for everything else for gearheads like us; it's all open to debate as to which is best ...and which is best is usually determined by the application in which it will mostly be used. ;)

_ken :w

I will eventually post all the part numbers to everything on the entire project. Sounds like you are a bit away from tackling this anyhow, so I am sure I can have it all up in time.

Yes, you can adapt other style OEM hydraulics to the Vette. I know of a fellow that has done it using the same master cylinder I used and the bottom end (slave cylinder) from a mid 80's Camaro.

So far I am very pleased with the feel, effort, and travel of the pedal.

I had a 74 Stingray with a four speed back in high school. That clutch use to kill me. It was part of the reason I lost interest in the car as my daily driver and got rid of it. So, I am looking for the best way to make this an easy rider.

The QM clutch that I am running is a very mild street application. I learned my lesson the hardway with the 90 model and the extreme duty clutch. However the pressure plate has a high clamping force design so the effort to push is increased.

When I took my stock clutch rod linkage out I was surprised to find it had significantly worn where some pivot points where 1/2 the original diameter and not even round anymore.

We need to Check with TZracer when you get ready to order anything from QM. As you see from my first thread there that I was able to get the QM release bearing through him under $200 US.
Thanks Chris

The rods in my clutch are well worn and the attraction of the C4 setup is that it could use the existing clutch fork and release bearing so should be easier to sort out and I can get the parts over here. It looks reasonably straight forward with the right bits.

It may be that my clutch requires something a a bit special in the way of a release bearing hence the price. I dont know how much the existing one cost as it came with the kit when I bought it.

JHL, I talked to Dave (TZracer) tonight. He said he could probably get you some better deals on parts, but shipping them gets expensive.

You might want to look him up next time you need something hardcore that is not readily available through Summit or Jeggs.

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