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External Hydraulics FAQ’s & Troubleshooting Solutions


Some of the questions we get here at MDL are listed below with the answers we provide as a solution or advice on procedure.

We hope you find it helpful.

Which is better, the internal slave or the external slave?

It is really a matter of personal preference and your physical setup. The external slave is less expensive than a internal slave. Some people want to push the cylinder away from the header so the internal is their preference. Other people want the external so if anything goes wrong it does not require pulling the trans.

What is the difference between an internal and external slave cylinder kit?

Internal slave cylinder is located inside the bellhousing and is mounted either on or in place of the bearing retainer. It replaces the throwout bearing. External slave cylinders push or pull a clutch lever from outside the bellhousing.

How hard is it to install a hydraulic system?

Compared to a cable system the hydraulic system requires more labor and time to install for alignment and bleeding of the system.

How do I know if I have the internal slave cylinder setup correctly?

Internal slave cylinders should be resting about .120″ – .150″ off the pressure plate fingers and disengage the clutch fully with .450” – .500″ travel at the clutch fingers.

Can I use my stock master cylinder with an aftermarket slave?

In most cases the factory master cylinder can be used with a aftermarket slave cylinder if so equipped.

The slave cylinder piston popped out – why?

  • The only reason a slave cylinder piston pops out is improper set-up and initial adjustment. The slave cylinder rod must be adjusted to “Zero Lash”. This means the piston of the slave cylinder is completely compressed in the bore of the slave cylinder AND the fork (lever) is pushed all the way forward so the throw-out bearing is making contact (not preloaded) with the fingers on the pressure plate. Adjust the supplied slave cylinder rod to achieve this configuration. See installation instructional paragraph starting with the words “Set-up”.

 

Can I get a replacement piston or rebuild kit for my master or slave cylinder?

  • These are not rebuildable units if they are damaged. Modern DriveLine does offer replacement cylinders for purchased kits and comes with new fittings and o-rings.

 

My clutch does not release – what do I check?

  • Make sure the slave cylinder ROD is traveling 1.2” as indicated in the installation instructional paragraph starting with “Important”.
  • Make sure the master cylinder rod attached to the lever under the dash travels 1.4” as indicated in the installation instructional paragraph called “verify actuation”.

 

My clutch fork (lever) is moving 1.2” but my clutch still won’t release.

  • Make sure you are measuring the rod movement and not measuring at the end of the fork.
  • What kind of pressure plate are you running? – This system requires a diaphragm style pressure plate with a “quick release” rate of 3/8”. 3-finger clutch pressure plates have a longer ½” release and must be replaced to work with this system.
  • You have some sort of misalignment or binding condition of the transmission unrelated to the hydraulics. Check for input shaft length/clearance to crank, disk to bearing retainer, and splines to bushing/bearing – all must have clearance.
  • Check the thrust bearing on your crank. Verify this by pushing/pulling on harmonic balancer or flywheel – the crank thrust must fall within spec requirements – usually .008 or less.
  • Make sure all bolts are tight. Bell to block, and bell to trans.
  • Check bolts holding slave cylinder and bracket to transmission are tight.

 

I can’t get the slave cylinder rod to travel 1.2” when moving the pedal.

  • Make sure the master cylinder rod attached to the lever under the dash travels 1.4”.
  • You still have air in the system if the clutch pedal is spongy at the top. You must have immediate movement of the slave cylinder when the pedal is actuated.
  • Check the firewall for flexing where the master cylinder is mounted – damaged, custom or extremely rusty cars may have firewall flex.
  • Bleed the system per the master cylinder instructions. Use the Bleeder kit instructions supplied with the master cylinder kit. These instructions can also be found on-line.

 

I can’t get my system to gravity bleed.

  • Accomplish gravity bleeding by making sure the reservoir cap and bladder are removed and there is no pressure on the master cylinder rod. To make sure of this, disconnect the master cylinder linkage from the pedal.

 

I have leaks at the fittings.

  • The elbow fittings in the master and slave are not tight. Once you have positioned the steel braided line in the vehicle, tighten the fittings making sure the o-rings do not protrude out. The bleeder screw on the slave cylinder is seating steel against aluminum. If you have trouble with this joint sealing… open and close the bleeder screw several times until there is no more leak; it should seat more with each tightening and loosening until a complete seat is formed.

 

For more information see our hydraulics page. or call us 208-453-9800

 

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