Weird brake issue (1 Viewer)

[bad_religion_au]

ok the background:

hj45 troopcarrier, 1980, drum brakes all round. got sick of adjusting the drums every other weekend.

converted to disks using FJ60 knuckles, new calipers, pads and rotors.

i pulled the front one of these valves

https://forum.ih8mud.com/40-55-series-tech/185090-what-these.html

shown in post #10, from the front circuit, due to reading poser's/others opinion in this thread that they will cause drag.

https://forum.ih8mud.com/40-55-series-tech/267373-how-remove-residual-valve-disk-brakes-2.html

master cylinder is a factory replacement for the hj45, with a single resevour, but dual circuit.

i followed the bedding in proceedure outlined by the brake component manufacturer.

the brakes probably have 500 kilometers on them now

now the problem is, i have decent stopping under normal conditions, BUT under emergency stopping conditions, the pedal gets to the point of no more travel (not the floor, about 2/3rds of the way through the pedal travel, normally where the drums would lock up), BUT the troopy just "slows to a halt". i cannot lock up the front brakes on dirt or pavement. rears will lock with alot of provocation

i have bled and re-bled the system. the pedal has no "spongeyness" to it. pedal feel is excelent. the booster is doing it's job (disconnected is much worse, and the hold the pedal/start the car test shows it works).

the master/lines are not leaking. all front rubber hoses are new. no kinks in the metal lines.

i have pulled the lot apart and hit it all with brake cleaner to ensure i didn't get grease/oil/crap on anything. i have rechecked caliper bolts for any that may have come loose. all 4 pistons on each caliper appear to be moving freely.

is there anything else to try? i'm about at the stage of putting the valve i mentioned earlier back in to see if that helps, but i'm not holding out much hope it will.

 

[bad_religion_au]

for the record, the drums stopped better when properly adjusted, and would lock up if pushed hard enough, so i knew the components were decent overall before the conversion.

 

[remorris]

You have extensive posts and forgive me for not reading all them. But my thought is fairly simple. If I were having this problem, I would switch to the late model FJ40 mastercylinder that has the lines coming out the top rather than the sides (and has 2 reservoirs).

The other factor with a master cylinder is the amount of fluid it moves. So along that line of thinking, if your MC isn't pushing enough fluid, you will feel the MC stop before the brakes are fully compressed. (another reason to get a different MC).

The late FJ40 MC IS designed for disk brakes on the front, drums on the back. Using it you may also need to get the matching vacuum assist unit. (all available on eBay).

Your symptoms sound to me like you don't have sufficient front pressure, perhaps the same issue on the back. At least give this some thought (that your MC isn't supplying correct pressure, or not moving enough fluid). Once you get the pressure up, you will most likely need a proportioning valve going to the back brakes.

So, there's my shot in the dark, when you finally solve this, please post what it was.

Richard

 

[handcannon]

Your post is vague on whether you are dealing with four wheel or just front discs, but I'm thinking four wheel. If my memory is correct, when I went to four wheel discs I used a MC for an 80 series that was made for four wheel discs. The pistons for discs need greater fluid volume and the 80 MC I think has a slightly larger cylinder than the 40 series does.

With four wheel discs a proportioning valve of some sorts is needed. I used a Wilwood adjustable valve on the rear supply line. To adjust the brake bias I drove on a gravel road and hit the brakes hard enough to lock wheels. Then I'd adjust the valve and re-test. I kept doing this until the front brakes locked just before the rears did. This gave me good front to rear stopping bias.

Don

Don

 

[remorris]

I think the MC is the issue,

Hey, you know what they say.. "even a blind hog can find an acorn now and again"

I feel proud that my 2:26am post was lucid.

Richard

 

[Fast Eddy]

Here's my wild-ass guess. There's a little stud with a bolt head that holds the front circuit piston in place. You can see it in post #9 of the "what is this" thread. It sounds to me like your front circuit piston is not getting past that stud, so you have limited or no front brakes.

If that's not the case, you may, indeed, need a larger bore master cylinder. A rebuilt one from Napa is great quality for a low price.

FWIW, I got a new Aisin master from Toyota for my '78, and it came with residual valves in both circuits. I tried everything to get the front discs to not hang up, but failed until I removed the front circuit residual valve.

I also made the mistake about the little stud at least once. I seem to remember that it was pretty obvious though, so I'm surprised if you got 500mi down the road without noticing.

With four wheel discs a proportioning valve of some sorts is needed. I used a Wilwood adjustable valve on the rear supply line. To adjust the brake bias I drove on a gravel road and hit the brakes hard enough to lock wheels.

I agree you need one, but not necessarily adjustable. I have a narrowed fzj80 rear end with Toyota disc brakes, and the non-adjustable prop. valve that was stock with f. disc r. drums works great. All four tires lock up at the same time on gravel.

 

[bad_religion_au]

sorry i wasn't clear. JUST front discs, rears are standard drums.

the late model, disk master over here in AUS is the same setup as the drum brake one (single res feeding 2 circuits, both lines coming out the side.)

 

[bad_religion_au]

second thought. do brake pads "go off".

pads were new in box... but they were bought for my 40 about 4 years ago and kept in the shed?

 

[Fast Eddy]

sorry i wasn't clear. JUST front discs, rears are standard drums.

I actually got that. I was just responding to him, since I have a similar setup.

the late model, disk master over here in AUS is the same setup as the drum brake one (single res feeding 2 circuits, both lines coming out the side.)

My stock one sounds like that exact one, but with two reservoirs. Pressure switches coming out the bottom, bolt in the side of the cylinder between the two circuits, right? If so mine works great with front discs.

 

[bad_religion_au]

Here's my wild-ass guess. There's a little stud with a bolt head that holds the front circuit piston in place. You can see it in post #9 of the "what is this" thread. It sounds to me like your front circuit piston is not getting past that stud, so you have limited or no front brakes.
.

if i am thinking this through correctly, wouldn't that stud stop the pedal travelling to the floor, even with a bleed nipple cracked open? because my pedal physically can go to the floor during bleeding.

 

[bad_religion_au]

I actually got that. I was just responding to him, since I have a similar setup.



My stock one sounds like that exact one, but with two reservoirs. Pressure switches coming out the bottom, bolt in the side of the cylinder between the two circuits, right? If so mine works great with front discs.

my master appears identical to the one in post 9 in the "what are these" thread.

 

[bad_religion_au]

would seem i solved it. put the flowback cup of controversy thingo (in the "what are these thread) back in and bled the system, and it works properly. no dragging aparent, jacked the fronts up and they spin easily by hand, after a 20km round trip the hubs can be touched and they are not getting hot. fronts will lock up right at the end of pedal travel.

 

[JohnnyC]

would seem i solved it. put the flowback cup of controversy thingo (in the "what are these thread) back in and bled the system, and it works properly. no dragging aparent, jacked the fronts up and they spin easily by hand, after a 20km round trip the hubs can be touched and they are not getting hot. fronts will lock up right at the end of pedal travel.

for what its worth...with my 4 wheel disk conversion I have the "flowback cup of controversy " still in my MC as well

been that way for 18? years...works great...one of the 1st mods I made