After 34+ years and 379,000 kilometers (235,500 miles) the hydraulic clutch system seems to be wanting attention.
For years, (maybe 15?) the clutch would gradually engage despite keeping the pedal down. I always shift to neutral and take my foot off the pedal when I'm stopped anyway, so I didn't do anything about it. Recently, the clutch occasionally wouldn't disengage; preventing shifting. Most of the time it would work "normally" and if it didn't, a couple of tries would get it to work.
Suspecting the traditional culprit - the slave cylinder, I pulled the piston out. It and the seal look good; but may not be... Then I thought if the slave cylinder seal was at fault, fluid would have to pass by and leak from the slave boot, and the level in the master reservoir would decrease. Since neither of those are occurring, I'm thinking that the master cylinder seal is letting fluid by but it stays in the system. So, I'm thinking I should get new seal kits for both cylinders to ensure a successful outcome since I've already pulled out the slave piston.
Anyone else ever have a clutch that would gradually engage with the pedal depressed?
I have had this on an 85GT. Different slave than the 84 but same principals. It's possible you really just have air in the system. A good gravity bleed might give some answers. Also, check closely where the master pushrod comes through the firewall. Pull the carpet and padding back to see if there are signs of fluid.
Air can be created in the system because the clutch fluid line passes close to coolant lines on the driver's side. Secure a length of the ribbed plastic wiring cover as used on your Fiero wiring. Slide it down on the fluid line until it bottoms out, then cut it just below the slave line nut. This will help to insulate that portion of the fluid line. This is especially helpful on the V6's. j
As for rebuilding the MC. I don't think the rebuild kits are available any more.
Mine turned out to be a master cylinder problem. The clutch master and slave cylinders are both available at Autozone but they may or may not be good quality. I use them and they work well in my 85. Rodney Dickman has the best units they are about $60 for each unit. With that much time on them I would replace both. It only takes about 20 minutes to change them. Bleeding them can be a pain to get all of the air out however.
This is the first time in 34 years I've needed to address a hydraulic clutch issue. 51 "Fiero years", including the other two I drive as well... I think OEM stuff is frequently superior to typical replacements, so I tend to get the more expensive of the available options. I'm not sure that's the best value, but I can't blame myself for getting an inferior part based on price...
I'm getting Rodney's stuff at a considerable premium over Rock Auto selections... I'm confident it'll be top quality.
Question regarding the 2nd seal: isn't it redundant until the first seal fails?
Question regarding the 2nd seal: isn't it redundant until the first seal fails?
It's not like the second seal is held in reserve until the first one fails and then it takes over. Both seals work together to ensure a better overall seal against fluid leaking out, and just as importantly, air being sucked in.
Fiero owners went through years of misery bleeding bleeding bleeding their clutch hydraulic systems prior to the availability of a dual-seal piston for the slave cylinder. It's been a game changer!
You master has a bad umbrella seal in it. My 84 had the same issue. The umbrella seal sits at the back of the master has has a spring between it and the Piston. When you press the pedal, the piston pushes the spring into the seal and it blocks off the clutch reservoir so you don't just back feed. As the seal starts to fail it will slowly let some pressure by and the clutch will release with the pedal still pressed in We At one point you could get rebuild kits but it is easier, and cheaper it seems, to just get a complete unit.
$128 Cdn for Rodney's clutch master cylinder and slave piston. Rec'd shipment in mail 8 days after order placement. $18 Cdn for 946 ml (1 US quart) of "OEM formulated" () DOT 3 fluid. Installed the master cylinder and slave piston 7 days later (today). Bench bled master per Rodney's instructions; gravity bled system per Fiero Factory instructions. Only had 1/2" travel, so bled the slave end a little more aggressively and finished off with the traditional 'depress the clutch while opening the bleeder screw' method. Had a successful test drive including holding the clutch pedal down for over a minute with no clutch engagement. Woohoo!
You master has a bad umbrella seal in it. My 84 had the same issue. The umbrella seal sits at the back of the master has has a spring between it and the Piston. When you press the pedal, the piston pushes the spring into the seal and it blocks off the clutch reservoir so you don't just back feed. As the seal starts to fail it will slowly let some pressure by and the clutch will release with the pedal still pressed in We At one point you could get rebuild kits but it is easier, and cheaper it seems, to just get a complete unit.
Here's a (poor quality) pic to illustrate your explanation. The round black seal edges were only sealing where they're shiny. The seal is eroded away between those shiny areas.
Edit to add better (?) pics of the eroded seal:
[This message has been edited by David Hambleton (edited 08-09-2018).]
) DOT 3 fluid. 
