86 F-150 clutch question - hydraulics

My old 86 is having a bit of a problem, clutch does not slip at all but pedal is weak and must be pushed all the way to floor to disengage clutch. I would assume it is either the master cylinder or slave unit. It was a little low on fluid but not much. I see no signs of leakage. Does either of these fail more often than the other? Any way to test properly? Maybe another problem??

Here is some addtional information on the truck. 300 engine, 4 speed tranny (has 3 speeds plus OD) and is 2 wheel drive. Has 134K on it. I have owned it about a year and do not drive it a lot as a rule. I use it to tow a small pop up camper from time to time and for fishing trips. I have put about 4K on it so far. Just started the weak pedal about 2 days ago.

well a quick update... I had to take the truck out a short time ago, barely made it home. Now to the point you can't shift into gear when parked and running. the clutch does not seem to want to disengage although it does, but apprently something is hanging up. I could upshift and downshift in 2nd, 3rd, and 4th but only if the truck was moving at a fair speed. Was able to get it home though and still puzzled. Had the wife push the clutch pedal anf noticed the slave cylinder was moving about an inch or two, as far as the arm is concerned. No sign of leaks.

OK I found I was wrong on the fluid. The slave cylinder IS leaking, will need replaced. The master cylinder seems OK, but will know better afterwards. I made a major goof when checking the level before, was lower than I thought. I can get it to hold for a while by refilling but that is the culprit.

This can be a real self help forum at times!!!

well I did read some earler posts and read what information I could find in books. The problem is I mis diagnosed the problem to begin with since I was unfamiliar with this setup. have not owned a manual tranny vehicle for many years and never dealt with a hydraulic clutch. Thought there might be something bad wrong but turns out there was a problem but I blame myself for making it worse. anyway, I know what is ailing it. Will say though, that I have put other posts on the F-150 site and they generally went unanswered. I would guess this is because my truck is old and I am learning Ford has a lot of different options and types of things and part numbers(such as fluids) that will drive you crazy when trying to buy parts. But the forum has helped a lot as it has others.

"I am learning Ford has a lot of different options and types of things and part numbers(such as fluids) "

Never, ever look for a fluid that has a specific part number.

part number was a slip of the tongue. I was referring to Ford SPECIFICATIONS, which are a pain in the butt, even to Ford people. My transmission has two types that were approved by Ford and no one could identify one, and the other was a synthetic I finally found at Motorcraft. Even Jiffy Lube was confused on the type as their system showed a type SLP which they did not have or recognize. They do have part numbers too in the owners manual, but yes, you are right there. The truck I have also i hard to buy parts for as they made more than two types of ignition systems for it so I have 2 -3 different distributor caps, buttons, modules, etc. Still love the old truck though, just have to be sure what I am getting.

Tying right into my fluid part number caution:

"Even Jiffy Lube"

Never ever use Jiffy Lube.

Tying right into my fluid part number caution:

"Even Jiffy Lube"

Never ever use Jiffy Lube.

No, i do not use them at all... I do my own and have for years. However they do service our companies vehicles and unlike many other Jiffy lubes this one has good people in it. I called them and asked and their records were unclear on what type of fluid this old manual transmisison used... To make my point NO ONE here knew either.... But your point is well taken. I have heard horror stories about many of these quickie oil change places for sure.