'71 FJ40 with '76 front axle. Brakes?!?!? (1 Viewer)

[Ryguy05]

Hello Masters of fj40 world. Beginner here.
I bought a gorgeous '71 with the original 1f. The seller confirmed he had some resto work done, Including the trans/transfer and front axle out of a '76. Gave him the 4 speed, and front disc brakes. I have had a weird intermittent "dump" of Dot3 fluid from my master cylinder. EMPTY!! I have caught it twice now, doing my inspections before driving. I was able to confirm the left rear is definitely leaking (I'll address this in a minute). I obviously filled it back up, first time I bled the brakes, second time I have not yet. I havent lost braking power, and I dont have a soft pedal.
Things I've noticed now that I'm paranoid and hyper-aware. It feels like I have "two stages" going on when I brake. First stage is a firm stiff pedal, and braking is fine. Second stage, the pedal softens a little and goes toward the floor a few more inches, but braking remains even and constant. Normal? maybe I need to bleed them again? Or...
But here is the big question I am going to replace the 4 rear cylinders (Maybe ill upgrade to discs, depending on cost). But now im curious.... which master cylinder do I have, or should I have?! Or is there a part/piece in between I'm not aware of to accommodate for drum in the rear, disc in the front. OR could this be the cause of my leak, over pressure, etc....

 

[45Dougal]

Photos of your master cylinder would help, and maybe the brakes too.
You probably have a pressure bias valve on the front of the MC to limit pressure to your rear brakes?
Sounds like you're losing a lot of fluid somewhere though. You make it sound like it's sudden? Have you traced the lines looking for leaks?

 

[pb4ugo]

You have to address the leaking wheel cyldr 1st. The rear brakes set pedal height when it comes to brake pressure. I'd recommend going to rear disc's. I run the m/c for 1976 and later and added an adjustable proportion valve on the rear and removed residual valves, others run a m/c from a FJ80 4 wheel disc. non abs. Im sure someone will chime in about this. This setup is pretty much maintenance free. No more rear brake adjustment.

 

[dazerb]

Leak first!
My 74 has knuckles/disc brakes from 83fj60 up front. Original drums on rear. Should be similar to your set up.
MC from a 93 fjz as per city racer along with proportioning valve. New booster too as the original was toast.
Stops on a dime.
I have a full set of rear cylinders NIB if needed. Mine were working fine when i did the brakes so i let them roll.
I also had a bad rear seal that was soaking one side with diff oil. New seals, no problem now.

I bench-filled the MC and used the gravity method to quickly bleed all. I was surprised at how easy it was! Made up for the &%#€ cone washers.

 

[texcwa]

I too upgraded to FJ60 discs up front, running drums in rear. I swapped the master to an FJ80 single reservoir (bolted right on) and have not had to add any adjustable proportion valves. stops great, uses standard Chevy pads.

 

[Ryguy05]

Photos of your master cylinder would help, and maybe the brakes too.
You probably have a pressure bias valve on the front of the MC to limit pressure to your rear brakes?
Sounds like you're losing a lot of fluid somewhere though. You make it sound like it's sudden? Have you traced the lines looking for leaks?

Thanks for replying, Doug.
It was sudden, both times, and spaced pretty far apart, which I find strange. I have a few drips on the garage floor, so I started with trying to clean things underneath to see if I can identify what im leaking.... probably a little bit of everything in small amounts. Nothing is low though, thus far, other than the reservoirs for the brakes. I will take pictures when I get home this week. Ignorant question though, why are there two reservoirs on top of the MC?

 

[pb4ugo]

The frt res is for the frt brakes and rear is for the rear. 2 res are designed for safety, if 1 brake failed, you'll still have some brakes. DOT Required manufacturers to do this sometime in the 60's.

 

[Ryguy05]

You have to address the leaking wheel cyldr 1st. The rear brakes set pedal height when it comes to brake pressure. I'd recommend going to rear disc's. I run the m/c for 1976 and later and added an adjustable proportion valve on the rear and removed residual valves, others run a m/c from a FJ80 4 wheel disc. non abs. Im sure someone will chime in about this. This setup is pretty much maintenance free. No more rear brake adjustment.

That is an option I looked at. I was shopping "brake parts" and thats when I discovered '75 to '76 change over M/C. Thats why I started asking questions. The M/C is the easy parts, what kit did you use for rear discs and prop. valve?

 

[Ryguy05]

Leak first!
My 74 has knuckles/disc brakes from 83fj60 up front. Original drums on rear. Should be similar to your set up.
MC from a 93 fjz as per city racer along with proportioning valve. New booster too as the original was toast.
Stops on a dime.
I have a full set of rear cylinders NIB if needed. Mine were working fine when i did the brakes so i let them roll.
I also had a bad rear seal that was soaking one side with diff oil. New seals, no problem now.

I bench-filled the MC and used the gravity method to quickly bleed all. I was surprised at how easy it was! Made up for the &%#€ cone washers.

View attachment 3412345

View attachment 3412346

That looks great. But do you not run into pressure gradient problems between front discs and rear drums? Or is that what the proportioning valves corrects? Maybe that IS the setup I have, with the >'76 MC.

 

[pb4ugo]

That is an option I looked at. I was shopping "brake parts" and thats when I discovered '75 to '76 change over M/C. Thats why I started asking questions. The M/C is the easy parts, what kit did you use for rear discs and prop. valve?

Alot of folks use @Poser for rear caliper brackets and rotors machined to accommodate the rear axle. Then you'll need an adjustable proportioning valve and alter and adapt flexible brake lines. You use Calipers from a mid to late 70's Monte Carlo. Other vendors offer similar set ups. Maybe @65swb45

Go to FAQ'S at the top of this section and scroll down to maybe rear axles for more info. There's a search function to. I'd start with using your current m/c and remove the residual valves.

 

[Ryguy05]

Gosh, im sorry guys. I feel like I have a lot of beginner questions. This kit looks to me like it indicates that 75-80 have front discs and rear drums. So as long as I have the correct 75-80 MC, which im guessing I do (ill check when I get home wednesday) then I should be fine. Thus, I probably just have a leak or a bad cylinder somewhere.

 

[45Dougal]

Thanks for replying, Doug.
It was sudden, both times, and spaced pretty far apart, which I find strange. I have a few drips on the garage floor, so I started with trying to clean things underneath to see if I can identify what im leaking.... probably a little bit of everything in small amounts. Nothing is low though, thus far, other than the reservoirs for the brakes. I will take pictures when I get home this week. Ignorant question though, why are there two reservoirs on top of the MC?

A sudden loss is due to something opening up which is normally closed. This might be a wheel cylinder or master cylinder seal, or a cracked or split pipe.

I'd try putting maximum pressure on the pedal for 30s and see if you can make it happen. It's a potentially very dangerous fault so avoid driving until you find it.

As I said - photos always help

 

[dazerb]

That looks great. But do you not run into pressure gradient problems between front discs and rear drums? Or is that what the proportioning valves corrects? Maybe that IS the setup I have, with the >'76 MC.

Yessir. That is the PV in the box. I just had to bend a little hard brake line to install it inline. I ground down some old muffler hardware to create a bracket to hold it steady.
My understanding is that 76 has the the disc/drum set up too.
I think one rear side was a little "grabby" at first with new shoes and hardware, but it settled in.