Clutch is spongy when cold? Fluid spec?

[Dave04]

Hey fellas. I have a desert dynamics car with an S4S, small bell housing hooked to an LS. I’m in Michigan and went to move the car out of the trailer (it was about 40F here), and the clutch pedal is super spongy. I noticed last year that it felt a little like this on a colder day when I was prepping the car, but it was fine in the warmer weather so I never messed with it. Looks like I’m full on fluid and there’s no signs of leaks. 
 

Im planning to bleed it as a first step here, any other things you guys can think of that I should check here? Also what fluid is recommended? I haven’t ever needed to mess with this so I’m not sure what’s in there. I know certain types don’t play well when mixed so I’m thinking to just change the fluid out while I’m doing this. I’m working on fixing a few of the quirks I’ve had since our season is over out here, and this is number 1.

Thanks for the help!

-Dave

 

[SeanRitchie]

DOT 3 or 4 is the most common fluid to use. Typically stay away from DOT 5.1

Spongy feel typically means there is air in the system, or bad o-rings in the slave or master cylinders. If you are confident with the bleed, I would start digging into the master and slave and replacing o-rings, checking for scoring in the bores, etc. 

If master and slave cylinders are good, it could be a pressure plate spring starting to go bad, but this would typically happen at any temperature. 

 

[J Alper]

Start off at the beginning, the slave cylinder on the trans, 

• check the adjustment, pull it as far apart as you can to make sure it is not partial way in on the shaft
  
• after the hydraulic slave is as far apart as possible, pull by hand on the lever (like the clutch is going in) and you should have about 1/8 or a 1/4 of space from the jam nut to the bracket on the trans
  
• If it is a hard line, personally i prefer soft line, it will take more vibration over time, change it to a AN fittings with sealant and soft line 
  
• bleed the clutch,  easiest way is with a pressure bleeding cap, 
  
• No leaks and new fluid with no air, new lines, then change the master cylinder,    
  

 

[lincster]

DOT 3 or 4, like Sean said.

Don't worry about changing from hard to soft line.

I have had hard line from the master to the slave for 19 years in my car, no issues.

Usually when slaves go bad, they do it at any temp, but you never know.

If you are going to have to replace one, I would do them both, that way you don't have to bleed twice.  

 

[J Alper]

DOT 3 or 4 is the most common fluid to use. Typically stay away from DOT 5.1

Spongy feel typically means there is air in the system, or bad o-rings in the slave or master cylinders. If you are confident with the bleed, I would start digging into the master and slave and replacing o-rings, checking for scoring in the bores, etc. 

If master and slave cylinders are good, it could be a pressure plate spring starting to go bad, but this would typically happen at any temperature. 

I only use Dot-5, depends on the situation, but for 37 years i have used this in all the rails we prep and all sand cars, Major reason is that it will not eat the paint, same fluid has been in my System now for 5 years same feel, 

If you are not worried about any paint including powder coat then the Dot 4 is a better fluid, only because it has a longer life cycle, and will not collect moisture, most rails have a complete sealed system like a ATV so the Silicone Base will work the same,  If you have a willwood master cylinder  with the clip style cap, they are not a compete sealed system and Dot 4 is the best choice, 

Cars with Hi End paint jobs or nice powder coat, I only run a Silicone Base Brake Fluid, My floor, chassis and panels are all custom paint, so if a like breaks or you spill some fluid it will not tarnish the paint job,