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Topic: 1986 Clutch Master Cylinder Leaks

in Forum: C4 General Discussion


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1986 Clutch Master Cylinder Leaks (1/4)
 5/2/14 2:47pm
DanB 1986
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Mission Viejo, CA - USA

Vette(s):
1986 Red Corvette Convertible. Indy Pace Car


Joined: 8/23/2012
Posts: 1

The clutch master cylinder leaks the fluid.  I have had the cylinder replaced three (3) times over the past 3-4 months. The repair shop has completed the replacement each time under their warranty.The issue is not about cost.  The car has only 46.000 miles. It is just a stock 350 engine with no mods. The clutch, pressure plate, fly wheel, shifting fork, throw out bearing and slave cylinder have all been replaced as well over the last year.

As you can imagine, with each failure I have to have the car towed to the shop. I am just trying to find a solution that returns reliability.

I just don't understand how this cylinder component (both new and re-mfg.) could fail three (3) times. I have discussed this at length with the repair shop and they are emphatic that they are doing the work correctly.

Any thoughts as to what could be causing this failure? 

Any suggestions/recommendations for a Corvette repair shop in Southern Orange County, CA area?



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Dan Burtt

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Re: 1986 Clutch Master Cylinder Leaks (2/4)
 5/3/14 11:10am
REDVETTE85
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NORTON, OH - USA

Vette(s):
1985 C4 red, 1985 C4 Black and dark gray


Joined: 7/9/2012
Posts: 111

I have been there & ruined the carpet from the fluid dripping off the pedal. What I discovered is when you upgraded the clutch  the pressure plate requires more master cylinder. what that means is the bore on our stock M/C is .56  If I remember correctly ?    most of the better clutches need at least a 3/4 bore or BIGGER     and good luck on that   Summit racing has a couple to choose from and none of them are a bolt in  My red 85 now has a Tremic TKO-500 with a Ram power grip clutch that's good for 500 HP in it and I went through 8 M/C before  I found this out and then after the M/C leak is solved the slave cylinder will be the next to go (never ends)   Willwood has a 3/4 clutch M/C for about 50 bucks thats a 3/4 bore and a hydraulic throw out bearing  solved my problems also the factory hose has a constrictor in it so when you get off the clutch it slows down the fluid for a smother launch I replaced mine with a S/S braided line off the shelf nothing custom  GOOD LUCK
Re: 1986 Clutch Master Cylinder Leaks (3/4)
 5/8/14 10:11am
hcbph
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Minneapolis, MN - USA

Vette(s):
Purchased a 1986 Convert August 2013, Bright Red color with a black top, it'd already received a Tremec 5 speed upgrade along with a disc upgrade prior to purchase.


Joined: 8/16/2013
Posts: 53

I don't know if you want a brand or not.  I had the clutch leak out right after I bought it last summer and had my mechanic change both out with parts from NAPA.  Other than being a bear to get the air out of it once replaced, it's been working fine ever since.  My 86 had a Tremec tranny change (oem was the 4+3) done to it before I bought it and unfortunately I can't tell you if the clutch and throwout are oem or not but this has been working very well for me once I got the air out.  It was a direct replacement and everything went in without any mods based on what he told me.  I did end up having to bleed it as he was not able to get all the air out.
IIRC the clutch and master ran around $50 each.

|UPDATED|5/8/2014 7:11:12 AM (AZT)|/UPDATED|
Re: 1986 Clutch Master Cylinder Leaks (4/4)
 5/10/14 7:02pm
C4Shane
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Charlotte, NC - USA

Vette(s):
-1993 LT-1, Coupe, 6speed, white/black -1986 L98, Coupe, 4+3, Black - SCCA TT Racer -1979 L48 Coupe, Auto, Red/doeskin


Joined: 5/15/2010
Posts: 26

Similar to the other reply - I have replaced mine with a NAPA rebuild and it has now held up through 5 years of use and abuse on a car that I drive in competition.  The clutch is a Sachs performance clutch and I have the original 4+3 trans with the OD locked out.  This car does not get driven gently and I have had no issues with this clutch.  Not sure what fluid your mechanic is using, but any good DOT 3 brake fluid should work. I use Valvoline synthetic DOT 3 & 4 fluid which seems to work well.  As also stated above, these suckers are a bear to bleed and I end up bench bleeding it using the little tubes that usually come in the replacement kit before attaching the lines.  The problem is the little uphill bend they put in the tube and it acts as a P-trap for air. Later C4s didn't have this issue and are easy to bleed.

As with any system like that - the key is to keep it clean.  Worst case, and if you don't mind spending the bucks - take it to your GM-Chevy dealer and let them figure it out - they have good warranties on their work.

good luck!



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There is no problem a little horsepower can't fix!

C4s: 1993 LT-1 coupe, 6-Speed, White w/black 1986 L-98 Coupe, 4+3 Trans, Satin Black w/red-black interior - SCCA Time Trial racecar.
C3: 1979 L-48 couple, auto, Red w/doeskin interior.
 
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