Cant figure clutch hydraulic issue out

[Flash]

Been working on cars for 15 years now, and e30s since 2007 and am no stranger to bleeding hydraulic systems via backbleeding pumping the slave manually, using a syringe to force fluid back up the slave nipple, gravity bleeding (i dont do that).
Basically in hot weather or hot temps such as sitting in traffic for prolonged periods the clutch pedal gets soft and *eventually* will not come back on its own. It NEVER happens driving it hard and normal traffic conditions.
I replaced the master with two other used ones i had on the shelf and they all have the same symptom, so i refuse to believe they are all problematic. I havent touched the slave yet but i did pull it from the transmission via the two nuts and its dry and shows no sign of leaking.
I googled for a bit and while they are not an e30, various people pointed to the heat causing the slave to fail intermittently, and some needed a heat shield to solve the problem for it.
I know the slave is a simple design and just a piston, but not sure it is the slave.


I need to fix this asap as a tech has to drive the car to inspect the exhaust emissions in 3 days, last time he warmed the car up it sat there for 10 mins, which is fine normally but it caused the clutch to go to the floor.
Any help is appreciated.

[flyboyx]

you mention something about the clutch pedal not returning? there is supposed a return spring inside under the dash. bmw used 2 types. one is a plunger type device that goes behind the pedal and the other is just a regular spring like the one on the brake pedal.

since you didn't mention anything about not being able to shift when the pedal is depressed, i can only assume this would be your problem.

[Flash]

Yep, i made sure the return spring sits in the little slot/horizontally, the tab welded to the sheet metal.

[RobDog]

Check and make sure that your clutch pedal assembly is not cracked. I replaced my sisters leaking clutch line and slave cylinder, but the dam pedal still felt weird. The pedal only had 1 inch of travel and did not want to return. The return spring kept jumping out of the slot when the pedal was pressed a few times. Also the clutch master pushrod was binding at an angle and not straight shot when pushing the clutch pedal in. All of this was because the pedal assembly was cracked on the side facing the gas pedal (hidden good).

[jhaurimn]

You should always replace the master and the slave at the same time.

Either your brake pedal box is cracked, the clutch pedal is bent, the slave is bad, or it was not properly bled. Or there is an issue with a clutch line but I am guessing you would of seen a leak if you inspected the slave. Bleeding the slave can be a pain and sometimes the only way to do it is bleed it is by taking it off the trans and pushing the shaft physically with your hand.

[Flash]

The master hole where the bolt goes through was not lined up properly, i think you are right about the bracket being bent. It was also EXTREMELY hard to bolt the master in with the two bolt holes. Ive done the job many times over the years on other's cars and it always just slipped right in and the two i just installed on mine felt like the bolt holes were mysteriously not lined up, was literally sweating in 50 degree weather trying to get them in....When i get back to the car i will check it out. Appreciate the responses.

[AndrewBird]

Might try bleeding it like this:

https://www.youtube.com/watch?v=wdf--suwqw0