has anyone successfully fixed a rear wheel lock-up scenario under hard braking?

[roma042987]

Keep in mind, when you back off the rear brake adjustment it effects pedal height.

I'm not backing off the rear adjustment don't worry I know better.

 

[roma042987]

FJ60’s have the same front brakes. I think @mattressking is on it

@roma042987 what master cylinders are you using? I like to use the FJ60 / 80-84 FJ40 master cylinder

I did a 40 with this setup but with stretched wheelbase and it wasn’t an issue.. about to do two more but with stock wheelbase. Should be interesting to see if it’s different

Fj80 non abs master. I agree on the design aspect just not something I want to alter by stretching the wheel base.

 

[JohnnyC]

Disclaimer…

I have not done the 4Runner calipers in the front but am contemplating one day doing it … they will rub on 15” rims so they need some grinding

The upgrade comes recommended by mark w and fj40jim to aid in bias issues

 

[roma042987]

Could try the larger front calipers from a 4Runner … give you more stopping power up front

Had you got a good grippy semi metallic pads on the front? Your not running ceramic up front are you

And the rear shoes use the worst lol

I don’t think you can get ceramic for the shoes but cheapo hard organic shoes would have less bite if your running semi in the rear

O.E. pads and shoes Johnny. I've considered upgrading calipers but these are reman Toyota calipers and my understanding is that with 4 runner calipers you have to do something to the dust shields...i could be wrong on that.

I am actually building up a new axle for this 40 with large pattern knuckles, cable locker, and aisin hubs. Since the o.e. calipers aren't available any more I'll need to make a decision soon on what calipers to put on it. I'll look into options for caliper upgrades. Still would like to figure this out though since my current axle will be going in another one of my 40s.

 

[roma042987]

Disclaimer…

I have not done the 4Runner calipers in the front but am contemplating one day doing it … they will rub on 15” rims so they need some grinding

The upgrade comes recommended by mark w and fj40jim to aid in bias issues

I have 16"s so perhaps I may have clearance.

 

[raisinhell2]

80 series disc/drum non abs master.
View attachment 3237593
View attachment 3237594

The ports are a good question....I've been reading some threads with mixed opinions as to which port is for which circuit. I ran my front port to my front circuit.

Adjustment on the rear isn't the issue. I promise

I didnt know you were using an aftermarket valve what kind of fluid pressure are you getting at the wheel cyls? I have always used 76+ disk drum master with oem valve. never had an issue. The oem ones like to stick

 

[sggoat]

Are you using the 77 master cylinder or later model? If using the 77 but then the single rear wheel cylinders, sounds like you effectively halved the fluid volume needed for the rear to work but are still providing the same amount?

Is the proper port on master cylinder going to the proper axle?

I could lock up my rears before the fronts, but then I backed off the rear adjusters until they locked up all 4 evenly (77 style double rear drums and 4Runner front discs). I don’t consider that a band aid fix, I consider it proper adjustment for the system.

I am not sure of this "volume" issue. If the master has a full reservoir, and the master stroke pushes -for example 10 cc''s of fluid into the system, the wheel cylinders should move 10ccs of fluid(front/rear--if they don't the wheel cylinders have a volume greater than the master--This would indicate required adjustment of the wheel cylinders to affect contact with the shoes/calipers for the amount of fluid produced by the master. The proportioning valve in my mind is un-necessary--this is a closed system, and as such when it is pressurized. the pressure is applied equally in all circuits that are connected.--If the pedal goes too far , there is a maladjustment of either the shoes or the calipers(assuming no leaks)

 

[roma042987]

I didnt know you were using an aftermarket valve what kind of fluid pressure are you getting at the wheel cyls? I have always used 76+ disk drum master with oem valve. never had an issue. The oem ones like to stick

I don't have any way to check pressures. O.E. valve was froze and I chunked it in 2012.

 

[sggoat]

They're adjusted properly. With the single wheel cylinder set up there is no guess work. Loosening them may yield a "band-aid" improvement while sacrificing parking brake performance. Not my goal here.

Parking brake is purely mechanical and has no connection to the fluid wheel brakes

 

[roma042987]

I am not sure of this "volume" issue. If the master has a full reservoir, and the master stroke pushes -for example 10 cc''s of fluid into the system, the wheel cylinders should move 10ccs of fluid(front/rear--if they don't the wheel cylinders have a volume greater than the master--This would indicate required adjustment of the wheel cylinders to affect contact with the shoes/calipers for the amount of fluid produced by the master. The proportioning valve in my mind is un-necessary--this is a closed system, and as such when it is pressurized. the pressure is applied equally in all circuits that are connected.--If the pedal goes too far , there is a maladjustment of either the shoes or the calipers(assuming no leaks)

You make sense to a point...calipers don't have adjustment and the rear shoe adjustment should not cause inadvertant lock up unless they are grossly over tightened to the point of dragging...which is not the case. Prop valves are necessary for precisely the reason I started this thread. Mine is just not effective "enough".

 

[roma042987]

Parking brake is purely mechanical and has no connection to the fluid wheel brakes

Backing off the shoes increases tolerance between the shoes and drums....more tolerance= more fluid has to move to make contact and friction. More tolerance also yields more pedal travel and more pull required on the parking lever.

Rear brakes are adjusted properly.

 

[pb4ugo]

I think your fighting the laws of physics. You brake, the frt dives down and rear lightens up, and the rear brakes lock up because there's minimal weight on the rear. When I 1st went to 4 wheel disc I didn't install a rear adjustable prop valve. You could lock the rear without trying, and the ass end squatted.

 

[sggoat]

More research reveals you have a good point--the dual master on the '77 pushes fluid in two directions--the trick is to get the fluid going to the front discs and the rear cyls in equal proportions--maybe that is the reason for the prop valve--hadn't thought of it in this situation before--just seems to me the pressure in the system would go to where it is needed, but with the dual Master, that complicates my previous reply--seems you have to match up the rear requirements with the front--one is adjustable--one is not--a conundrum for sure--

 

[mattressking]

I wonder the difference between a 40 series and 60 series proportioning valve. Toyota rereleased the 40 series prop recently for about $155usd.

But if you’ve used a wilwood adjustable, my assumption is that you could/would’ve likely had the same effect for more/less flow to the rear. Using different calipers/rotors and drums would only yield more surface area braking so cooler temps and stronger brakes, therefore locking up just as much or more.

I’m just not sure this will truly be fixed without weight changes and/or abs.

 

[h82crash]

80 series disc/drum non abs master.
View attachment 3237593
View attachment 3237594

The ports are a good question....I've been reading some threads with mixed opinions as to which port is for which circuit. I ran my front port to my front circuit.

Adjustment on the rear isn't the issue. I promise

Now I have concerns as well. Looking at almost every diagram of dual circuit master cylinders, the front port goes to the rear brakes. And this shows the same thing and then it doesn't. the confusion is real. Front vs Rear ports on master cylinder? - https://forum.ih8mud.com/threads/front-vs-rear-ports-on-master-cylinder.1244078/

But in a half hour of research, 95% of tech articles say the rear piston is primary and goes to the front brakes. It starts building pressure first then starts moving the secondary piston.

 

[Fast Eddy]

You brake, the frt dives down and rear lightens up, and the rear brakes lock up because there's minimal weight on the rear.

The load-sensing prop valve from a wagon would be pretty easy to retrofit as an experiment. Some or all 60 and 80 series came with them. Not sure if one from a minitruck would work or not, but seems like, and they're dirty-dirt cheap.

I was going to do this, but I have an 80-series master with rear 80-series disc brakes and a stock fj40 prop valve and it just happens to work fine. My fronts will lock just before the rear on pavement and about at the same time on dirt.

 

[JohnnyC]

Nice gaucho I got me one of those as well

On a dual 40 master it is definitely front res goes to front brake lines and the inboard/back reservoir definitely goes to the rear brakes … however…

I did a look around at 80 masters parts diagrams and it does look to be reversed … front to back and back to front … as @h82crash said above

May want to have somebody confirm which line goes where on the 80 master

 

[roma042987]

Now I have concerns as well. Looking at almost every diagram of dual circuit master cylinders, the front port goes to the rear brakes. And this shows the same thing and then it doesn't. the confusion is real. Front vs Rear ports on master cylinder? - https://forum.ih8mud.com/threads/front-vs-rear-ports-on-master-cylinder.1244078/

But in a half hour of research, 95% of tech articles say the rear piston is primary and goes to the front brakes. It starts building pressure first then starts moving the secondary piston.

Yeah, I read that same thread a couple of times before starting this one....it's about as clear as mud

 

[roma042987]

Nice gaucho I got me one of those as well

On a dual 40 master it is definitely front res goes to front brake lines and the inboard/back reservoir definitely goes to the rear brakes … however…

I did a look around at 80 masters parts diagrams and it does look to be reversed … front to back and back to front … as @h82crash said above

May want to have somebody confirm which line goes where on the 80 master

Thanks Johnny that yellow one is a fake gaucho but I have another authentic one that is 24v. They belong to my 2 and 4 year olds. My conclusion of the 80 master debacle is that the abs ones are backward and the non abs are not. My master is non abs so that shouldn't be my issue. I may swap the lines at the ports this weekend and just give it a try for curiosity's sake.

 

[roma042987]

The load-sensing prop valve from a wagon would be pretty easy to retrofit as an experiment. Some or all 60 and 80 series came with them. Not sure if one from a minitruck would work or not, but seems like, and they're dirty-dirt cheap.

I was going to do this, but I have an 80-series master with rear 80-series disc brakes and a stock fj40 prop valve and it just happens to work fine. My fronts will lock just before the rear on pavement and about at the same time on dirt.

Yes Eddy all the later trucks including the 40s got LSPV's for this reason.