Bramblehart '76 620 Project - trouble bleeding clutch

[Bramblehart]

Hello Ratsun! First time posting! 

I recently acquired a '76 620 that had been rotting away in a field for the last 20 years in eastern Oregon. Suffice to say it needs a lot of work and I have decided to make it my first project car since I am covid-unemployed and have lots of time on my hands, and I've always wanted an excuse to start working on cars... I am fairly clueless when it comes to working on cars but I have been perusing older threads and picked up the Haynes manual, so please bare with me if I'm making an obvious oversight.

 

 

The problem I am having right now is I am trying to bleed the clutch because the pedal gives no resistance, but it is not working. I opened the bleeder valve 1/4 turn, attached a hose going to a bottle with dot-3 and started pressing the clutch in and out 40 times or so to see if any bubbles would come out, but no bubbles. The fluid level in the clutch master cylinder didn't go down at all so I don't think the fluid is cycling. Could the lines be clogged? The clutch master cylinder was bone dry with some dried gunk in it when I pulled the truck out. If anyone has an idea what the issue might be, I'd love to hear it. Thanks!

 

 

 

[]2eDeYe]

Welcome, nice looking 620 you got there 🙂

 

Open that bleeder screw all the way, 1/4 turn may not do it. If no fluid comes out when pushing the pedal and the bleeder screw is removed you may have a clogged master cylinder. 

[Stoffregen Motorsports]

If found dry with gunk in it, the first thing I would do is disconnect both ends of the hard line and blow through it with air. Get yourself a line wrench to make sure you don't round off the tube nuts. Sometimes a little heat from a handheld torch will be needed to get the nuts loose.

 

Once you have the line reconnected, fill the reservoir and open the slave bleeder. Pump it back and forth slowly a couple times to get the fluid moving down the line then close the bleeder. Pump it a couple more times and then crack the bleeder open again. This time, leave the bleeder open and let it gravity bleed for a few minutes. You can tell it's working when the fluid drops in the reservoir.

 

Gravity bleeding should get you 90% there, but a final purging of air may be done by the two person, pump-hold-open-close method.

 

I wouldn't be surprised if both the master and slave are shot after sitting dry for so long. Seven years is the max amount of sitting time in my experience.

[ducky]

We had the same issue bleeding mine. Fought with it for a couple days. I finally decided to just start loosening it and suddenly, we shot brake fluid 6 feet across the driveway. Made us feel like idiots.

[banzai510(hainz)]

loosen as above and also put your finger over the hole when there is fluid in there and have somebody press the pedal and it might help

Edited July 28, 2020 by banzai510(hainz)

[Bramblehart]

Thanks for the help everyone! 

I drained out the master cylinder, blew through the hole with compressed air to see if i could loosen whatever the clog is. Also blew out some gunk blocking the bleeder valve since there was no cap on it. Filled the master cylinder and tried again, still no luck. I am now trying to disconnect both ends of the hard line to blow that out as Stoffregen suggested but man those tube nuts do not want to budge, i sprayed them yesterday with some liquid wrench to try and free them up but they still won't budge, I am afraid of rounding off the edges and then really being screwed. Does anyone know what size the nuts on the hard line are? Seems just a hair bigger than 3/8s but I'm assuming it's metric. 

[banzai510(hainz)]

did you put your finger over the hole and have somebody cycle the pedal. This worked for me once. TRY IT

 

next get a good set of metric wrenches and also brake wrenches!!!!!!!!!!!

 

most bleeder valve lost the cap years ago.

[Bramblehart]

@banzai510(hainz) thank you, I did try it, and still no success.

However I think I found the issue... I managed to get both ends of the hard line off and blow through with compressed air so I know that's not obstucted now. After that I blew through the lower line leading to the slave cylinder and out the bleeder valve, then filled the reservoir back up and tried pumping again, STILL no flow. At this point I am fairly confident it is the master cylinder that is the problem, so I drained it, pulled the line back off and unscrewed it off the firewall and this is what I found... 

 

 

This is the same type of "gunk" I mentioned earlier that was in the resevoir when I first pulled the truck out. The "plunger" (? Part attached to clutch pedal, not sure what the actual name is) is loose and doesn't produce any "pressure" when pushed in and out like I would imagine it should if it were functioning properly. So I'm guessing this is the issue, any thoughts guys? If I'm replacing the master cylinder now should I also replace the slave cylinder?

[5t341tH]

by the looks of your picture, I'd replace them both. They are fairly cheap new

[Bramblehart]

@5t341tH any brands you'd recommend? I've been looking at the Centric ones on Amazon.

[ducky]

10 hours ago, Bramblehart said:

@5t341tH any brands you'd recommend? I've been looking at the Centric ones on Amazon.

 

I've got luk brand on mine I think. Just make sure to get one that has the exact same position for the hard lines. I had to take one back off because I didn't realize it was wrong. Of course, it likely because at the time, I thought my truck was a 74 instead of 76...

 

Still! Make positive before you waste the time waiting.

Edited July 29, 2020 by ducky

[banzai510(hainz)]

when you get new ones keep the one one to measure the shaft length. Most are too long and youll engage too soon putting pressure on the pedal. Most have to be cut down. Youll see it when you install.  I would but 2 set of these chines made master as hey don't last long at all. maybe 5 yrs on  daily driver

[Stoffregen Motorsports]

Yes, keep the old ones for measurements and for the parts box. Those factory parts are not being manufactured anymore and are worth saving.

 

It would be an easy rebuild, if the bore was not pitted.

[Stoffregen Motorsports]

BTW- it's a 10mm nut on the tubing, but you've obviously figured that out already.

[ducky]

9 hours ago, banzai510(hainz) said:

when you get new ones keep the one one to measure the shaft length. Most are too long and youll engage too soon putting pressure on the pedal. Most have to be cut down. Youll see it when you install.  I would but 2 set of these chines made master as hey don't last long at all. maybe 5 yrs on  daily driver

 

Would this cause the popping/clicking/hanging up feeling I get when I'm disengaging the clutch? It's fine going in, but when I let it out, it's like it hits a burr or something, then click/pops out

[datzenmike]

22 hours ago, 5t341tH said:

by the looks of your picture, I'd replace them both. They are fairly cheap new

 

They are cheap alright because Chinese made. Dealer masters are over $90 so if you paid $13 you'll get what you paid for. The dealer mark up is 60% so a $40 one made anywhere else should be OK quality.

 

I recently had to replace my slave and was not impressed with the 'rubber' seal inside. How do I know? Because it was made in China and I took apart to make sure there were no aluminum shavings inside and to wet the seal with brake fluid so it wouldn't start dry. The 'seal' was floppy soft like RTV and not like rubber at all. I don't trust it one bit.

 

I installed it and connected the line, gave one or three pumps and out came the bubbles and then straight dripping of fluid. I've never had a problem with gravity bleeding. Tightened the bleeder. Done.

 

 

When installed you should adjust the pedal play to 1/16". Just push down on the peddle with thumb until the slack is taken up and there's resistance. Then tighten the adjuster nut, put the clevis pin in and use a new cotter pin. Too much play and you risk the slave not disengaging the clutch properly. Too little play and the fluid may not be able to return to the reservoir. Trapped pressure will hold the clutch from fully engaging. 1/8" is fine.

[banzai510(hainz)]

15 hours ago, ducky said:

 

Would this cause the popping/clicking/hanging up feeling I get when I'm disengaging the clutch? It's fine going in, but when I let it out, it's like it hits a burr or something, then click/pops out

Explain better did you cut the threaded rod or not.???

Im not a mind reader what you did if the shaft was perfect size then why would it make the poping sound.

 

the fork with the dowl pin the threaded rod is usually to long and it hits it when fork is inside the pedal it could BIND. get down there and watch and see the fit and make sure the plunger come out all the way so the master releases 100% also

Edited July 30, 2020 by banzai510(hainz)

[Stoffregen Motorsports]

15 hours ago, datzenmike said:

 

 

When installed you should adjust the pedal play to 1/16". Just push down on the peddle with thumb until the slack is taken up and there's resistance. Then tighten the adjuster nut, put the clevis pin in and use a new cotter pin. Too much play and you risk the slave not disengaging the clutch properly. Too little play and the fluid may not be able to return to the reservoir. Trapped pressure will hold the clutch from fully engaging. 1/8" is fine.

Trapped pressure can actually destroy an engine. Pressure on the back of the crank = wiping away the oil at the thrust bearing = worn thrust bearing and even groove worn in crank.

[Stoffregen Motorsports]

2 hours ago, banzai510(hainz) said:

Explain better did you cut the threaded rod or not.???

Im not a mind reader what you did if the shaft was perfect size then why would it make the poping sound.

 

the fork with the dowl pin the threaded rod is usually to long and it hits it when fork is inside the pedal it could BIND. get down there and watch and see the fit and make sure the plunger come out all the way so the master releases 100% also

If the person doing the work follows your first advice - compare the old vs the new before installation - then the installation should be in the ballpark. Fine adjustments are ALWAYS going to be required, for the reasons Mike and I mentioned above.

[datzenmike]

21 hours ago, ducky said:

 

Would this cause the popping/clicking/hanging up feeling I get when I'm disengaging the clutch? It's fine going in, but when I let it out, it's like it hits a burr or something, then click/pops out

 

After the hydraulic slave it's all mechanical linkage. From the slave to the pressure plate diaphragm there's a push rod, (lube both ends) clutch arm on a pivot ball (lube the pivot ball) the release bearing collar (needs the cavity inside packed with grease to slide smoothly on the transmission nose. There is also the release bearing which may be worn. All these should have a smear of grease on them for smooth action.

[silroc]

I’m going through this same process so was glad to find this thread.

 

In my case, if I have the bleeder screw removed, I can pump the pedal and squirt fluid. But when I insert the bleeder screw – even just a little – no squirting.

 

It seems as if the master cylinder is working well enough when there is no pressure (open pipes) but the internal cup? is weak and is leaking fluid around it internally if there is back pressure.

 

I went ahead and did the gravity bleed – letting the fluid flow out, then inserted the screw quickly and fully before the reservoir emptied out. But still there is no actuation of the slave cylinder when I pump the pedal and no resistance.

 

I guess the next step is to disassemble the master cylinder, see what’s going on, repair/replace as needed. Unless there are some suggestions to save me from that effort? Are there rebuild kits for the master cylinder or just the whole thing?

[thisismatt]

If the master went dry for any extended period it's highly likely going to be junk.

[datzenmike]

If the fluid got around the seal when you let up the clutch pedal the fluid would try to come out the back of the master past the dust boot and onto the carpet.

 

Loosen and remove the hydraulic line at the master. Put your thumb over the opening and try it. There may be trapped air in there. Pump it out and put the hydraulic line back on. Bleed the slave as usual.