Builds Weenie 3 - Bringing another 40 back from the dead (2 Viewers)

[RWBeringer4x4]

Could it be the LACK of a residual valve? Proportioning valve certainly balances the flow to adjust brake engagement relative to one another (for front bias in most cases), but the residual valve, (I think) maintains slight residual pressure in the line instead of letting it all bleed off when you release the brake. As I recall drums need that slight residual pressure to keep the return springs from backing the shoes all the way off. Might that be why you need to double pump the brakes to build pressure? Once to push the shoes back out and once to engage them?

If that’s an early 80 Master cylinder (believe it is) then it was designed to work with front discs and rear drums but I’m honestly not sure how 80’s were “valved” to balance and operate the drums. Perhaps there was a change to the drum mechanism that did away with the need for residual pressure that the 40 drums don’t have?

Either way, if you’ve isolated the front circuit and the brakes are soft, and when the whole thing’s plumbed normally, the brakes are soft, that seems to imply not enough pressure to the front brakes. I think we can safely eliminate air in the lines - so assuming the pushrod is fully engaging the master piston, I’m not sure what could be causing it...

I’m thinking out loud/grasping at straws too...

 

[wngrog]

I’ve got the same master and booster on both my 40 and 55. The 40 has the old dial type City Racer prop valve and it will toss you into the steering wheel the brakes are so good. (Disc/drum)

My 5800# FJ55 has the same master, same booster. No prop valve at all. 4 wheel lock up. (Disc/drum)

That’s why I’m so puzzled. I’ve got two just like it. Both are different in that one has a prop valve. One does not.
Both work great.

 

[middlecalf]

4 is furthest, not as the crow flies but as the rabbit runs.

 

[wngrog]

Could it be the LACK of a residual valve? Proportioning valve certainly balances the flow to adjust brake engagement relative to one another (for front bias in most cases), but the residual valve, (I think) maintains slight residual pressure in the line instead of letting it all bleed off when you release the brake. As I recall drums need that slight residual pressure to keep the return springs from backing the shoes all the way off. Might that be why you need to double pump the brakes to build pressure? Once to push the shoes back out and once to engage them?

If that’s an early 80 Master cylinder (believe it is) then it was designed to work with front discs and rear drums but I’m honestly not sure how 80’s were “valved” to balance and operate the drums. Perhaps there was a change to the drum mechanism that did away with the need for residual pressure that the 40 drums don’t have?

Either way, if you’ve isolated the front circuit and the brakes are soft, and when the whole thing’s plumbed normally, the brakes are soft, that seems to imply not enough pressure to the front brakes. I think we can safely eliminate air in the lines - so assuming the pushrod is fully engaging the master piston, I’m not sure what could be causing it...

I’m thinking out loud/grasping at straws too...

where does one get a residual valve?

 

[RWBeringer4x4]

where does one get a residual valve?

I have no idea...when I converted to 4 wheel discs I used a 60-series master cylinder. It was supposed to have a residual valve in the rear circuit. When I took the (rebuilt) master apart the valve was MIA.

Further that valve relies on the big adapter “nut” at the connection points on the old MC’s to retain it - not sure it’d work in your case with the 80 MC...

 

[RWBeringer4x4]

Wilwood makes an inline one - I think I read somewhere that the stock 40-series residual valve held about 2 pounds of pressure:

Wilwood Disc Brakes 260-13706 Wilwood Residual Pressure Valves | Summit Racing

Free Shipping - Wilwood Residual Pressure Valves with qualifying orders of $109. Shop Residual Pressure Valves at Summit Racing.

www.summitracing.com

Not sure they have one with the appropriate connections - I also feel like I might be sending you on a wild goose chase...if this setup works on 2 different trucks, I might go back to the drawing board and replacing the "new" components to see if something was bad out of the box...

This is frustrating to read about...let alone work through!

 

[MOTOV8R]

Stock disk brakes is 2lbs, drum is 10lbs for residual valves.

May want to verify your part number. Maybe you got sent the abs unit instead of the non-abs which wouldn't have the right valve or maybe the valve is just missing or bad.

 

[whitey45]

I would change out the master, or pull it apart and check the seals and correct assembly.

 

[Mark Jennings]

You need the residual valves. Put them in both circuits. If you’re running 4 wheel disks, use 2 lbs valves in both circuits. If you’re running drums in the back I think it’s a 10 lbs residual. Go to the Willwood web site...there are several articles on the subject.

The photo below I use a 1” Tacoma master cylinder to 4 D154 GM brake calipers, no booster, stops awesome. The blue things in the brake lines are the residual valves. The residual valves are like check valves that maintain a minimum pressure at the calipers. Keeps the pedal rock solid....no pumps.

I got the valves on Amazon believe it or not. They were pretty inexpensive from what I remember.

 

[wngrog]

You need the residual valves. Put them in both circuits. If you’re running 4 wheel disks, use 2 lbs valves in both circuits. If you’re running drums in the back I think it’s a 10 lbs residual. Go to the Willwood web site...there are several articles on the subject.

The photo below I use a 1” Tacoma master cylinder to 4 D154 GM brake calipers, no booster, stops awesome. The blue things in the brake lines are the residual valves. The residual valves are like check valves that maintain a minimum pressure at the calipers. Keeps the pedal rock solid....no pumps.

I got the valves on Amazon believe it or not. They were pretty inexpensive from what I remember.



View attachment 2166855

I really glad you posted that because I’m going to ditch the 4 wheel drums on my FJ45 at some point soon and that’s what I want to hear.

 

[wngrog]

Stock disk brakes is 2lbs, drum is 10lbs for residual valves.

May want to verify your part number. Maybe you got sent the abs unit instead of the non-abs which wouldn't have the right valve or maybe the valve is just missing or bad.

That’s what I have been thinking. I actually ordered the old style 2 res style that would have been period correct for the brakes I’m doing but this one was substituted by Cruiser Outfitters and I just assumed it was the 80 series non ABS.

I’ll see if I can dig up the PN.

 

[wngrog]

Looks like I have the proper master. Non ABS 1” bore just like on my 40 and 55. These have a built in residual for drum rears.

This photo is from the City Racer site

The bottom pic is the ABS type

 

[Mark Jennings]

That master cylinder looks like a non-abs and Non residual unit used on Forerunners, T100’s, etc... they are pretty common and pretty inexpensive. I think those trucks used some sort of load sensing proportioning valve instead of a residual to the rear circuit.

 

[wngrog]

I pulled it apart at the master and did the measurements to ensure my plunger was correct between the master and booster.

reinstalled the proportion valve and used the pressure bleeder to push out the air.

Sameness. Pedal feels Great.

3 pumps then it locks up all 4.

I’ll try the 2 person pump/pump hold method with a friend and at that point if I can’t get it to work I’ll be ordering a new master. That’s all it can be at this point unless all my fancy one man bleeding gadgets don’t work which just does not make sense.

 

[ToyotaDon]

What's up with that rear line at the MC? It looks like it's been ground down, so could it be leaking?

As I understand it, the residual valves are for the wheel cylinder cup seals, especially those without cup expanders. The return springs should only pull the shoes back as far as the adjustment will allow.

Shoe adjustment will definitely affect pedal travel, so that's also something to double check.

 

[wngrog]

No leaks. I can leave 20 psi on the Power Bleeder overnight and no pressure is lost.

I’ve got the rears where they will turn 1/2 spin so they are tight.

 

[wngrog]

@USMC22 is going to ride up tomorrow and we will get this thing done. I have no doubt.

In the mean time I installed the @ToyotaMatt

choke

CaBle

in WEenie ThREe

Getting the old one out was fun. FYI. Pull the instrument cluster and it’s a 17mm backing nut.

The @FJ40Jim carb does not need choke in Mississippi but it might where it’s going

 

[FJ40Jim]

What was accomplished by removing the OEM Toyota booster, and 1" bore MC with built in residual valves; and replacing with unknown, incorrect booster and short stroke 1" MC without RPVs?

The above is equivalent to the math teacher saying "It's not enough to guess the right answer, show your work."

 

[wngrog]

What was accomplished by removing the OEM Toyota booster, and 1" bore MC with built in residual valves; and replacing with unknown, incorrect booster and short stroke 1" MC without RPVs?

The above is equivalent to the math teacher saying "It's not enough to guess the right answer, show your work."

Well.....it was old. The truck sat up for years. It was a “drum” booster.

When I did the front axle, I rebuilt with 60 series calipers and discs.

The rear I used all new cylinders (harvested the sloped ramps like you taught me) with new Toyota drums.

I basically tried to make it a 77 brake system. This formula has worked great in my 5800# FJ55 and in my FJ40. Both have the exact same setup.

I also built another trucks brakes out just like this and I had no issues.

The sad thing is that I had good brakes before i decided to swap the old front calipers with new rebuilt calipers.......I still have those. Maybe these “new” front calipers are crap.......

 

[Jdc1]

Well.....it was old. The truck sat up for years. It was a “drum” booster.

When I did the front axle, I rebuilt with 60 series calipers and discs.

The rear I used all new cylinders (harvested the sloped ramps like you taught me) with new Toyota drums.

I basically tried to make it a 77 brake system. This formula has worked great in my 5800# FJ55 and in my FJ40. Both have the exact same setup.

I also built another trucks brakes out just like this and I had no issues.

The sad thing is that I had good brakes before i decided to swap the old front calipers with new rebuilt calipers.......I still have those. Maybe these “new” front calipers are crap.......

One of the Toyota rebuilt 60 calipers on my build was clogged and had to be replaced. Don’t rule out anything.