Hello all, After inheriting my Fathers 1988 F150 (4.9 six w/ T-18 BW) I have been checking things over. I took the cap off the clutch master cylinder, and the diaphragm is very confusing to me. I am used to diaphragms on brake master cylinders that are bellows type that are retracted, so to speak, and then extend when the fluid level drops. Well.... This diaphragm in the clutch MC is completely extended and cone shaped (not sure how to describe it), I removed it and there was a little fluid in the bottom of the MC, I filled up the MC and then tried to "retract" the diaphragm..... No luck, it SEEMS to not be designed to retract, but to stay in the cone shaped position, which means the MC holds very little fluid. I checked the owners manual and two different repair manuals and all that is mentioned is to "remove the internal diaphragm after removing the cap, and then check the fluid level" I have also searched for related threads. Any help would be most welcome

Scott in Dallas

 

I've never seen one that the diaphragm hangs down in the cyl. They always retract. I'm going to say you have a bad rubber. I doubt you can just buy a new cap or rubber from Ford. You might have to buy a new MC, but you could try a JY for the part.

 

My '92s diaphragm is always extended i just replaced it and the new one cam that way too

Is your clutch working? My reservoir doesn't have a buncha fluid in it either about an inch from the top is all and I have no problems

 

Yes, the clutch is working fine. Although..... when I pushed the pedal the other day I heard a "Pop" and now the pedal moves about an inch or so before I feel any resistance. The popping kept on, so I had a look, and the rod going from the pedal into the master cylinder was making the noise. I took the rod loose from the pedal and the whole rod came out of the master cylinder. Never seen one do that before. Put the rod back in and re-connected it to the pedal, and the popping continued. So.... I removed the rod again and put a blob of wheel bearing grease on the end of my finger and pushed it into the back of the master cylinder. The popping has now stopped but like I mentioned earlier the pedal now moves quite a bit before the rod starts pushing on the master cylinder. I love this truck but I really hate the engineering on the hydraulic clutch. I have owned many vehicles with a hydraulic clutch and they are very easy on the old leg. This one is very hard to engage! Can't imagine how difficult it would be if it were not hydraulic