Truck starts to move when clutch pedal pressed (master/slave cylinder?)

[jaredwins]

Hey guys! It seems my truck problems are coming in pairs

Yesterday when I was driving home, I came to a stop light, and completely stopped. The light was soon to turn green, so I pressed in the clutch, and moved the gear shifter to 2nd... suddenly the truck started to roll and wouldn't stop moving forward! Thankfully the light turned green and I was able to resume driving home. The clutch felt spongy afterward. 

 

I then drove around a small parking lot at low speed, coming to a stop, then taking off...  and found that sometimes from a dead stop, when I pressed in the clutch pedal, shifted into second, and waited, the truck would randomly starting rolling forward even though the clutch pedal was pressed. 

 

After reading and researching, it sounds like this could be a bad maser or slave cylinder or air bubble. Or maybe a clutch "throw out bearing?" Perhaps even the clutch itself???

 

I was going to start by replacing the whole master/slave assembly with one of the Southbend kits unless you had some other insight or suggestions? 

[Silverwolf2691]

Sounds like textbook leakage past the O-rings in the master or slave.

 

Throw out bearing would have growling noises, and unless the bearing was bad enough to move front and back, would have very little impact on the clutch in the way you are describing.

Pilot bearing on the other hand, could cause the lack of dis-engagement. Usually has a grinding/growling noise associated with it though. 

 

 

[jaredwins]

37 minutes ago, Silverwolf2691 said:

Sounds like textbook leakage past the O-rings in the master or slave.

 

Throw out bearing would have growling noises, and unless the bearing was bad enough to move front and back, would have very little impact on the clutch in the way you are describing.

Pilot bearing on the other hand, could cause the lack of dis-engagement. Usually has a grinding/growling noise associated with it though. 

 

 

 

I appreciate the input. So I should probably just replace that whole Master/Slave cylinder unit with something like https://www.genosgarage.com/product/HYD-X-150/engine-replacement-parts-2 ?

[Silverwolf2691]

That, valair, or south bend.

 

Fair warning, the slave cylinder is compressed all the way and tabbed in place on a brand new system. The first time you push the clutch you break the tabs. It feels and sounds weird but is perfectly fine and normal. 

[Mopar1973Man]

Also pre bled systems I've seen them with enough air that it doesn't break the tabs loose. Then you end up pulling it back out to bleed the system again. Being there is typically a high spot after the master.

[jaredwins]

@Silverwolf2691 @Mopar1973Man thanks for all the help so far guys. That video you have on YT really helped. I got everything installed tonight but had one quick question.

 

I bought the south bend kit, and on the slave cylinder(?) there's a black plastic piece on the end... Does this piece need to stay on? Or should I try and remove it? (Of course keeping the white plastic tabs so the piston remains compressed...)

 

Also, is there and Up and Down position? I was just gonna put the writing facing down towards ground.

[Mopar1973Man]

Install just the way it is. Then first pedal application will break the straps. 

Edited April 7, 2022 by Mopar1973Man

[jaredwins]

1 hour ago, Mopar1973Man said:

Install just the way it is. Then first pedal application will break the straps. 

Thanks dude! I'll get er done tonight!

[jaredwins]

I got the new Master+Slave cylinder kit installed without much trouble (that pin above the pedal was a pain...) and the truck is back on the road. Appreciate all the help!

[Mopar1973Man]

No a problem. That what we are here for.