"FrankenBrakes" power booster (1 Viewer)

[offrd63]

Hello All,
Like a lot of you I have cobbled brakes together. Mine, Fj40, 4 wheel discs with V6 4-runner calipers up front and Monte Carlo's in the rear. I'm using a fj80 non ABS master cylinder mated to a mini truck power booster. And there lies my question. How much boost is enough. I've been running this set up for years, but I've never thought it was working as it should. Ten years ago I think things felt to touchy. Very sensitive. Now, not so much. It stops good, but I couldn't lock them up if I wanted to. Ive done some of the tests that ive read about on the booster, and It seems good, just not enough.

What booster's do any of you use with this application? I just don't think it's an adjustment issue. I also didn't think that residual valves helped either. Any thoughts would be appreciated.



aw

 

[mr jits]

What year 40?

 

[offrd63]

It started life as a 1963

 

[mr jits]

How did you deal with the rib on the firewall? I've been planning to just run manual brakes with the FJ80 master .

 

[offrd63]

Years ago a gentleman from CA named Danny Warden used to mill a spacer from billet alum. Then there is an adjustable push rod that fits in the spacer. Sometimes I wish I had gone the same route as my friend did. I believe its a Chev s-10 non boosted master designed for 4-wheel disc. There was also one for a vete. I am running a sbc 350, and he's got a 2F. Clearance wasn't an issue for me like it is for the 2F guys.
Was there a FJ80 master that was for a non boosted application?

 

[mr jits]

No, but using one of the disc brake calculators (it's on one of the circle track sites, I'll dig it up) I found that the 80 master should work with the 4runner front calipers and monte carlo rears. If it doesn't work I'll look at hydroboost.

 

[srgould41]

I am in the same boat as you. I can't lock up the tires on pavement. Moving up to 36" tires made it even worse. My original issue was a hard pedal and took both feet to stop the truck. I now have a 10" dual diaphragm GM booster (started out with a 7"). I originally ran a 1" GM master, moved to a 15/16" GM master and now a 7/8" master from an MR2. The 7/8" master made the brakes work with one foot, but still won't lock all 4. I can lock the rear in dirt with bias dialed all the way, but not the front.

One thing I have read is that two vehicles with seemingly identical setups can have very different results. Go figure.

With 4 wheel disk I see 3 primary issues. Pedal effort, ability to lock the tires if needed, proper bias.

Monte Carlo calipers have a 2.5" piston. The surface area exceeds that of the fronts which causes the bias issue. Most forum posters agree that their bias can't be adjusted enough. Larger diameter front pistons really isn't viable which leaves the rear as the area to work on. There are smaller piston diameter calipers available that help with bias such as the El Dorado and Camaro rears. You can also buy 2" Willwood calipers which is what I plan to do when I re-work my brakes in a year or two. I worked on bias calculations a while back and a perfect bias was somewhere around 1.7" pistons (basing bias calculations on 4 wheel disk brake Jeeps). 2" is still too much, but the proportioning valve should work better.

I think pedal effort and the ability to lock the tires go hand-in-hand. If a vacuum booster isn't enough to do the job then hydroboost is the only way around it unless you want to invest in exotic solutions.

 

[offrd63]

"I think pedal effort and the ability to lock the tires go hand-in-hand. If a vacuum booster isn't enough to do the job then hydroboost is the only way around it unless you want to invest in exotic solutions."

Well, this gets me back to the boosters, has any one tried a fj80 booster with the fj80 Master cylinder on a fj40,or just a larger booster. As I said earlier I'm using a 83 mini truck booster now. with the price of power boosters its hard to just start trying out different (fj40,60,80) boosters. Although that may have to be my next step. I did at one point try two proportioning valves in line and it did work, but I still never got the 4-runner fronts to where I wanted them, and i'm now back to just one. I have had brakes that were just to touchy and that really sucks too! Oh the joys of doing your own R&D. I guess if I didn't enjoy this I would have just bought a jeep and started bolting parts on to it 24 years ago.

 

[Tapage]

have you consider the Hidroboost route .?

 

[offrd63]

Ya know I really hadn't, I can't say that I've heard of anyone doing it to their fj40. I had hydroboost in my Dodge 3/4 ton, but I've never even thought about what it mite take to make it work in the 40. Can hydroboost be fine tuned like you can with proportioning valves?

 

[srgould41]

I don't know the difference between boosters other than a wide range of cross fit. One thing to check if using a different booster is where the vacuum check valve is located. Some boosters use an external valve.

There are tons of hydroboost writeups on 40's. It has been done many a time.

 

[Tapage]

I did take the HB route after went up to 40" on Tencha .. and my 80 series setup wasn't up to the task .. I gotta upgrade my PS system tho ..

 

[offrd63]

I did some reading. If I were just doing, or redoing my brakes for the 1st or maybe even the 2nd time, I would go the HB route. The Astro van unit looks just right. The thing is all my brake stuff is new except for the booster. And I'm getting tired of throwing parts at this problem I just think that a 5000# cruiser on 37" or 38" shouldn't be to much for that fj80 master and the biggest 4-runner calipers

 

[srgould41]

I know the feeling. The only thing I didn't change on mine were the hard lines. Everything else was brand new. Stops like a big rig. Give me two blocks and I'll make it stop

 

[offrd63]

I've been driving my 40 for a few days now, and it's stopping pretty hard . It still doesn't lock-em up, but it's been worse. I do think I've got the power assist thing figured out tho. If I just come to a complete stop, without letting up on the brakes it keeps braking . If I let up and then re apply them I loose boost. I can't make vacuum any faster (I think) , so it just makes sense (ha ha, to me) that I need to store more of it. I think I'll compare maybe a 4runner, or even a 60 series booster and see what mite fit.
Can any one hear give me size specs of a fj60 booster? Bolt pattern specs would be sweet too!

aw

 

[jstncse]

I have a vacuum reservoir off of a mid 80's Mercedes diesel to help with my brakes, I have the engine out of it also. The reservoir is huge and really helps keep up with the braking demands of the factory '78 FJ40 booster. I am running FJ60 front calipers in the rear and V6 4runner calipers in the front. I can lock all four up on pavement and the combination works great in the rocks.
The Mercedes vacuum pump couldn't keep up with the brakes at all without the reservoir. I even tried the reservoir out of a mid 80's chevy and that was still not enough. The reservoir needs to be big enough to cycle the brake booster a couple of times and have a check valve between the vacuum source and the reservoir, anyway it's working for me.

 

[srgould41]

How much vacuum does your setup produce? Part of my particular trouble is a hot cam that makes little vacuum.

I have a vacuum reservoir off of a mid 80's Mercedes diesel to help with my brakes, I have the engine out of it also. The reservoir is huge and really helps keep up with the braking demands of the factory '78 FJ40 booster. I am running FJ60 front calipers in the rear and V6 4runner calipers in the front. I can lock all four up on pavement and the combination works great in the rocks.
The Mercedes vacuum pump couldn't keep up with the brakes at all without the reservoir. I even tried the reservoir out of a mid 80's chevy and that was still not enough. The reservoir needs to be big enough to cycle the brake booster a couple of times and have a check valve between the vacuum source and the reservoir, anyway it's working for me.

 

[jstncse]

It will make 15" but has a very small piston to do it with.

 

[srgould41]

Now your comment on needing the big canister makes sense. 15" isn't much. 20" would be nice. I make 14 at idle and I can tell you it's not enough

It will make 15" but has a very small piston to do it with.

 

[GLTHFJ60]

Can hydroboost be fine tuned like you can with proportioning valves?

I did take the HB route after went up to 40" on Tencha .. and my 80 series setup wasn't up to the task .. I gotta upgrade my PS system tho ..

I did some reading. If I were just doing, or redoing my brakes for the 1st or maybe even the 2nd time, I would go the HB route. The Astro van unit looks just right. The thing is all my brake stuff is new except for the booster. And I'm getting tired of throwing parts at this problem I just think that a 5000# cruiser on 37" or 38" shouldn't be to much for that fj80 master and the biggest 4-runner calipers

I've got hydroboost in my rig. The hydroboost unit replaces only the vacuum booster. You still use a regular hydraulic brake master cylinder, with or without a proportioning valve as you prefer.

I never ran the 4Runner calipers with hydroboost, but I did run the stock FJ60 front calipers with FZJ80 rear calipers and she stopped well with 37s. No comparison to how she stops now, but it was good.