Hydraulic clutch retrofit slave system, Chevy bellhousings, 7/8 slave cylinder.

Hydraulic Clutch Slave Retrofit Kit for Chevrolet Bellhousings

Hydraulic clutch release systems have gained wide acceptance in the aftermarket as a keen solution to both engine conversion and stock clutch linkage replacement scenarios.

Novak's Hydraulic Clutch Slave Retrofit has evolved into its third and best rendition, as our #HCRC. It bolts to the popular Chevrolet 90 degree style bellhousings - typically Small Block V8 & V6 and Big Block V8, I6 and Iron Duke style bellhousing flanges.

Product & Features

7/8” Slave Version

• e.g., Jeep CJ vehicles with factory hydraulic release though our usual recommendation is to use the 3/4” version for adequate throw. The 7/8” slave with stock CJ master cylinder will have to be adjusted and set up to exact minimum clearance specifications to function properly
• Other types of factory or custom vehicles

Applications & Compatibility

Available Kit Versions

Hydraulic clutch release systems are typically engineered to have a 1:1, master-to-slave ratio, where the leverage is not obtained through differential hydraulics. The force is obtained through the leverage provided by the clutch pedal and then the release arm / fork at the throwout bearing, like a conventional mechanical clutch - the method of transmitting the force is the only difference. These principles are discussed here.

As such, the installer will generally choose between our 3/4" bore version or our 7/8" bore version to best match the diameter of their master cylinder.

• Choosing a larger slave for a smaller master may create a situation where the pedal pressure is reduce, but the lessened travel may not fully release a clutch.
• Choosing a smaller slave for a larger master may create a situation where there is excessive pedal pressure. However, the Novak 3/4" bore slave has more travel than OEM units and typically work with 7/8" master cylinders without blowing out. This is helpful if the throwout bearing needs more travel for release, but note that this is not a substitute for not choosing the right length throwout bearing.
• Keep in mind these ratios are based on the area of the bores, not the diameter so, πr² to calculate either master or slave area. Small changes in the bore size can yield a large change in distance or force. 3/4” bore yields .442 sq. in. whereas the 7/8” is .601 sq. in. Travel is a linear function of the area x the distance equals volume. The volume of fluid moved is the key and the same on either end no matter what changes are made so long as the system is sealed and no air is present.

For your best benefit, read and understand the principles of working with hydraulic clutch release systems and determine the applicability for your vehicle.

* Note that Full Size Jeeps (Wagoneer, Cherokee, J Truck) vehicles do not accommodate conventional, firewall mounted master cylinders due to the brake booster and the electrical bulkhead connector. If converting one of these Jeeps to hydraulic clutch release, the installer will need to custom configure a master cylinder accordingly.

Bellhousing Compatibilities

The Novak #HCRC has been proven to work on big clutch & small clutch as well as big bore and small bore Chevy bellhousings. We have verified that the following GM bellhousing part numbers have the necessary block / bellhousing flange style that the #HCRC utilizes for mounting:

3840383
3788421
3858403
3899621
462606
460486
464697
6263756
15998496 (NV4500)
14010202 
6263756

There are surely more Chevy bellhousings not yet listed, but these are the major ones. If you are not sure of applicability, send us a digital picture or two via e-mail, and we will let you know. See our contact page.

Many aftermarket bellhousings such as Lakewood, McLeod and others have thus far proven compatible with this system, excepting the Lakewood #15003, which positions the release fork pivot and window too high.

We have customers with drag and other racing setups running this system, as well as various other Jeep, GM and custom applications.

Chevrolet Cast Iron Bellhousings 

The classic cast iron bellhousing as found on so many Chevrolet engines from 1955 through the early seventies can be made to be compatible with this kit with two modifications:

• The through-boss at about 9 o'clock (see highlight in image, right) must be milled down to the same height as the through-bosses at 10 o'clock and 11 o'clock. This is a simple machining procedure and we would expect most machine shops to be able to bill it out at around 20 minutes. 

Alternatively, one could install a spacer on the boss at 11 o’clock and adjust the pushrod shorter, accordingly. This cylindrical thru-spacer can measure 0.385” - 0.410” ID x 7/8” OD x 0.925” tall. 

Once completed, our mounting bracket will sit at the same level as it does on the later aluminum bellhousings. 

• The clutch fork window is too narrow for the provided, hydraulic style release arm. Widening this window will be required.

Big Block Installations 

Installers with Chevy Big Blocks should be aware that the line fitting is very close to the oil filter boss and may require grinding.

Clearance for the standard diameter oil filters is sufficient without modifications.

Incompatible Bellhousings

• Buick, Olds, Pontiac or Cadillac style bellhousings
• The Iron Duke bellhousing as made by Jeep for the 1980 - 1981 CJ's
• The Advance Adapter's conversion Chevy bellhousing is not compatible without clearancing two aluminum recesses in the bellhousing-to-block bolt areas
• GM bellhousing #3849309