'77 MC Diagnosis confirm?

[TheHardWay]

When I test drove Zeke, I knew right away the brakes needed pumping to stop him and would need to be bled . So, the second thing (after replacing the clutch master that was leaking into the cab) I did was bleed the rear drums and front discs. Still required three pumps to stop. No problem. Read many brake threads and decided to adjust the rear shoes.


None of the adjusters would budge. No problem. Ordered four cylinder rebuild kits. Those f*****g cylinder pistons fought me every step of the way until I got them out, cleaned up and installed the kits. Bled the brakes and went for a drive. Still required three pumps to stop. Read more threads. Aha, pumped the brake pedal, started engine and the pedal softened a little. Probably not the booster (yet).


This morning I opened the bleed valve on the left rear and watched bubbles come out of the bleed hose. Critical piece of info - no leaks anywhere in the system, and after topping up both reservoirs there's been no loss of fluid.


And so, my new family of personally experienced experts, here's my best educated guess - the master cylinder is allowing air into the system. I'm ready to order a rebuild kit from FJParts, but would appreciate a second opinion before pulling the trigger.


To entice you, I have attached a photo of Zeke's rearend.

 

[Weber Sarge]

Since these use dual rear cylinders it's an absolute pain to get them bled fully , almost nearly impossible . I have , on bigger trucks taken the time to unbolt the backing plate with the axle removed (or just the wheel cylinder) and spent the time with clamps on the cylinders to rotate them and bleed until every bit of air is out . It sucks , but works .
Use plenty of good quality anti-seize on those adjusters , too .
Sarge

 

[edwjmcgrath]

Agree with Weber. It seems to take forever to bleed rear cylinders when they're replaced.
AND, are your cylinders adjusted so that the wheel won't turn and then backed off 2 clicks?

If the shoes are too far from the drums (as they will be if you follow the FSM), they'll not get there in one pump.

 

[TheHardWay]

Agree with Weber. It seems to take forever to bleed rear cylinders when they're replaced.
AND, are your cylinders adjusted so that the wheel won't turn and then backed off 2 clicks?

If the shoes are too far from the drums (as they will be if you follow the FSM), they'll not get there in one pump.

Thanks for the help guys. Yeah, the first time I tightened them REAL tight I backed off two clicks, and could hardly get Zeke to move forward, so I backed off one more click and could feel just a slight drag. Bled them again and still had to pump them to get decent braking power. I believe there are no leaks in the system because neither reservoir is losing fluid, yet when I did the bleed test yesterday and got a lot of bubbles that seemed to be a clue that air is getting into the system, leaving the MC as prime suspect.


Correct me if I'm wrong, but can't the MC allow air to get in, yet not lose fluid?

 

[edwjmcgrath]

When you're adjusting, it's good to make sure the shoes are centered. I usually hit the brakes once after each adjustment. When it's right, you should be able to just barely spin the wheel by hand one revolution with a strong effort. If you are just feeling a slight drag, that sounds too loose. It really makes a difference. There's not a lot of "throw' in the cylinders. If they're loose, you need to pump a few times to get the shoes to seat.

When you first bleed a wheel, there's air in the bleed hose, so you'll always get bubbles at first. And the usual way that MC's fail is that they let fluid some fluid by on the pressure stroke. This doesn't let air in. However, if your MC is failing, it will take FOREVER to bleed your brakes. Been there-done that.

 

[TheHardWay]

Thanks for the tips. It seems too simple that the drum adjustment can make such a difference in how the pedal feels when the brakes are applied, but then it's been so long since I've owned a vehicle WITH drum brakes that alot's been forgotten.

I ordered a replacement MC, but I'm going to methodically follow the adjust/bleed procedure to rule out the MC before I try an installation. SAFETY FIRST...save money second.

 

[Howard705]

I bleed-many hundreds-by myself-open bleeder at wheel-begin slowly pumping-never letting m/c get below around 1/2. do it for 20-30 pumps-no hoses or anything. then (keeping m/c full)-watch bleeder for around 1 minute as slight amount of air drawn in as pedal is raised bubbles out. after it stops- tighten. then do other wheel with only around 10 pumps same way. you are only needing it bled from T to wheel.

 

[TheHardWay]

I bleed-many hundreds-by myself-open bleeder at wheel-begin slowly pumping-never letting m/c get below around 1/2. do it for 20-30 pumps-no hoses or anything. then (keeping m/c full)-watch bleeder for around 1 minute as slight amount of air drawn in as pedal is raised bubbles out. after it stops- tighten. then do other wheel with only around 10 pumps same way. you are only needing it bled from T to wheel.

Hmmm. Do you bleed them this way because you do it by yourself?

 

[sggoat]

Agree w/Weber & edwjmcgrath - It's a pain. As long as the reservoir is full(or thereabouts) it's a closed system-no air can get in--bleed/bleed/bleed.

 

[sterling]

LasCrucer
I use a one man brake bleeder kit I got from Autozone I beleive. I have had it a few years, cheap and works good for me.

Similar to this:

http://shop.advanceautoparts.com/p/...=google&utm_campaign=gpla&utm_content=9020969

 

[TheHardWay]

Read this quote from Lake Rat from Dec. 2011:




'I had a similar problem adjusting and bleeding the brakes on my '68 40. After about 4 gallons of brake fluid (not really, but it seemed like it) I called Spector and asked a few questions. The guy on the other end of the line giggled a little and said "you need to adjust the drum brakes all the way out until they stop, then bleed the air out of the brake lines, then back off the adjustment". So I've done this procedure on each one of my 40's and it works.'


Has anyone tried this method? I'm trying to logic through this, but can't see where locking the drums will get more air bubbles out of the bleed.

 

[Pin_Head]

Not all bleeding methods are equally good when it comes to getting bubbles out. The one man, vacuum and speed bleeder gizmos don't get the difficult bubbles out. They suck and in a commercial shop, you don't have time to fool around with anything that doesn't work 100% of the time.

The one that works all the time is the two person method when properly executed.

1. Have your assistant in the cab pump the pedal until it is firm and then step on the pedal hard like you were trying to stop in an emergency. This pressurizes hydraulic system and compresses all the bubbles until they are teeny tiny. Tiny bubbles are less likely to get stuck than bigger bubbles

2. Rapidly open the bleeder and let fluid and bubbles squirt out and close the valve before the fluid stops flowing. This prevents air from getting sucked in when you let up the pedal. You might consider putting a clear plastic hose on the bleeder or covering the bleeder with a shop rag so the fluid does not squirt across the shop. Yell to the assistant to let up on the pedal.


3. Go back to step 1 and repeat until the pedal is firm without pumping.

 

[Howard705]

I perfected the method because I was always by myself. There are some vehicles it won't work as well on but always on the Land Cruiser. Haven't done it much in the last ten years on newer cars. Perfected some good methods for all the older medium duty hydraulic brake trucks too. As you raise the pedal back up it will pull air back in as the m/c piston retracts to the port. Very slight amount. and gravity pushes it back out-usually by the time you top the cyl and get back under it. . Works well on the LC probably because m/c is much higher. If you don't want to wait 1 minute you can hold pedal down on last pump and use board or whatever against steering wheel to hold pedal down. But like it says above ALWAYS have shoes ADJUSTED -no matter what kind of vehicle it is. Bleeding hydraulic clutches on these is same only easier. Newer vehicles however lots harder w/hyd clutches-they have larger diameter lines that can let fluid go right around trapped air.

 

[TheHardWay]

The one that works all the time is the two person method when properly executed.

1. Have your assistant in the cab pump the pedal until it is firm and then step on the pedal hard like you were trying to stop in an emergency. This pressurizes hydraulic system and compresses all the bubbles until they are teeny tiny. Tiny bubbles are less likely to get stuck than bigger bubbles

2. Rapidly open the bleeder and let fluid and bubbles squirt out and close the valve before the fluid stops flowing. This prevents air from getting sucked in when you let up the pedal. You might consider putting a clear plastic hose on the bleeder or covering the bleeder with a shop rag so the fluid does not squirt across the shop. Yell to the assistant to let up on the pedal.


3. Go back to step 1 and repeat until the pedal is firm without pumping.

I was hoping Pin_head would weigh in My handy assistant (wife!) and I have followed Step 1 except for having her do the hard emergency stop, so I'll have her do that next time (this weekend). In following Step 2 I've used the clear plastic hose, but I put the 'out' end in a glass jar of brake fluid on the floor. As we go through the pump/drain procedure I make sure to top up the reservoir before it gets to halfway empty. Any reason NOT to hit the pedal hard more then once to make sure the shoes are centered?

 

[Howard705]

By the was after any brake bleeding on these- I always hose under backing plate/spring area and usually run some water over M/C area-especially if nicely painted- to flush brake fluid off and avoid paint bubbling.

 

[TheHardWay]

By the was after any brake bleeding on these- I always hose under backing plate/spring area and usually run some water over M/C area-especially if nicely painted- to flush brake fluid off and avoid paint bubbling.

Yeah, found that out already - while soaking one of the cylinders to loosen the frozen piston, some fluid dribbled out the end of the brake line, onto the outside of the backing plate. I must say, though, brake fluid is quite an effective paint remover - think I'll keep some in a jar to use on small parts I want to strip!

 

[TheHardWay]

Today I did the following:
Jacked up rear end and tightened drums two notches. Could hardly move the wheels with great effort. Pumped the brake pedal, then hit it hard as suggested to center the shoes. Time to bleed!
Wife gave pedal two quick pumps, then 'panic' pump. This got some more bubbles out through the bleeder hose.
Mixed short pumps with long, slow pumps while bleeding and keeping the reservoir topped up. Finally no more bubbles.
Drove it down the street and hit the pedal hard. Brakes work BUT if I keep pressure on the pedal, it slowly fades to the floor. Still not losing ANY fluid, so is it time for MC replacement?

 

[Tin basher]

Yes the master needs replacement
you have confirmed no leaks
So it is bypassing the seals in the master causing the sinking pedal
When you pull it off the booster it will probably be wet in the bore of the master
Might not be

 

[Howard705]

X2 above- had to eliminate other things- now replace/rebuild-all bled-can bleed only at master after replacing.

 

[edwjmcgrath]

Ok, you can replace the master now.
Bad news is you'll have to bleed the brakes again.