What would you do for booster & rear brakes?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Dec 16, 2018
Hi guys - back for more coaching on the new to me '68 FJ40.

This FJ has a disc brake front conversion already installed but does not have rear brakes installed yet. Seems like a good idea to put some rear brakes on before I try to drive it - grin.

I am expecting I'll use her around town and on fire roads mostly. I do not expect to do any hard core off-roading or max speed adventures (although it does have a 350 V8 installed). I do expect I will drive her to the Palm Springs and Anza Borrego desert areas so she will see highway use from time to time.

I try not to drive like a moron, don't consume huge quantities of Red Bull, I (usually) let people merge in traffic despite my living in SoCal, and don't instead to rob any banks so don't think I will be using the brakes super aggressively.

So with all of that said - factory drum set up or bite the bullet and install a rear disc brake kit?

EDIT - I need to make a choice on the brake master and booster too, assuming dual lines and research the Toyota pick-up truck options.

Thanks in advance for the help!
Last edited:
Just a couple quick questions:

Does the 40 presently have a brake booster?
Single or dual circuit master cylinder?
Just a couple quick questions:

Does the 40 presently have a brake booster?
Single or dual circuit master cylinder?

Hi, thanks for the response.

Well that seems like obvious info to have left out in hindsight. Oops, and sorry.

Right now it does not have a brake MC or booster installed. There are several that come with it (will need to inspect them of course) but they are dual circuit units.

Assuming boosted brakes would be a plus?

EDIT - I need to make a choice on the brake master and booster too, assuming dual lines and research the Toyota pick-up truck options.
Last edited:
For the type of driving you described, rear disk are nice but not a high priority. IMHO, a brake booster and dual circuit M/C are a priority for front disk/rear drum or four-wheel disk brakes.

There are plenty of options out there, I prefer an all-Toyota system just for the compatibility and reliability of Toyota parts, and accessibility aspect of replacement parts.

I have Toyota four-wheel disk brakes (FJ60/80) an FJ40 booster and FJ80 M/C. VERY little effort required to stop the rig, and that's a good feeling.
Thanks for the follow on response, and was also leaning towards an all Toyota set up.

Drum brakes in the back should allow me to use a factory parking brake too, right?

If you still have the original Toyota T-case or an Orion with the OEM parking brake then you'll still have a parking brake with either drum or disks
Good evening, it does have its stock transfer case so apparently I am OK for a parking break then. I had this idea was dependent on the rear brake set up.

Thanks for the tip!
Converting the rear to disc brakes will likely be cheaper in the long run (or even short run) than rebuilding the rear drums.

I’d recommend Toyota 4 piston calliper front brakes and rear discs. (Poser on mud sells brackets that work with GM mini callipers.) I converted long before mud... I used full-size GM callipers in the rear. I’ve got a proportioning valve in the rear circuit to reduce rear braking and limit lockup.

With an 80 series master & booster, it’ll lock up all four wheels if I stab the brake pedal with two fingers. The brakes aren’t grabby, they are difficult to lock... and it’ll stop towing a heavy trailer with minimal effort... and straight.
My brake system isn’t typical, but I really like how it performs on my ‘71:

FJ60 Booster
FZJ80 Master
Front FJ60 disc brakes, calipers and rotors
Rear ~1997 4Runner 297mm rotors; 2012 Mustang GT calipers.

I’d say it works great! I think its worth the upgrade.
Thanks for the responses, if the cost is similar it would seem that discs in the rear would make sense.

Is there a source for the FJ80 master and booster you would recommend? Lots of options but I’ve heard/seen the cheaper rebuilt units can be iffy quality.

With an FJ80 master will I need any brake line adapters to match the trucks hard lines to the master cylinder size fittings?

You will find that it typically becomes much more of a chore adding a booster to the trucks built before 9/70 b/c of the different firewall rib near the brake and clutch master. Spacing the booster and master off the firewall (due to prior mentioned rib) causes issues with the length of the setup when running a typical Toyota engine. You might or might not have a similar issue with your current 350.

If the overal length of the setup is a deciding factor then running the geo metro booster/master is a great option. You can read details of the swap in my build thread for my 67. The metro booster uses the same size and flare as the later 40 series (m10 inverted)...which depending on your current setup would require replacing / adapting the 9mm lines to 10mm.
The 80 series booster is somewhat shorter than my ‘74 fj40 was, but it was a direct bolt on replacement without line changes. It did require tweaking (bending) the lines a bit. The 80 booster has longer bolts to go through the original double firewall and also needs to be rotated 180* (upside down) for easiest install in any 40 I’d recommend a 1/2-1” spacer to make up for the extra length... but since you likely have a spacer to contend with, extra length won’t be a problem.

With a SBC, spacing it out from the firewall won’t cause interference issues with the carb like you’d have with a 2F (or possibly an F also). I’ve got many pictures in my build thread of the engine compartment... although my rib isn’t in the way of a booster:D
Last edited:
Thanks guys - I very much appreciate all the responses.

I wonder if I simply need to order a returnable 80 series master cylinder and booster and offer them up?

I am reasonably handy with a MIG welder if need be but I'd rather leave things alone (obviously) if I can.

The booster shouldn't functionally care if it is upside down, correct?

Where do I pick the vacuum up with a 350 - intake manifold?

Thank you!
Booster doesn’t care if it’s upside down. It’s a diaphragm and a spring... works any direction.

Brakes are strong enough that your 95 year old grandma could drive it... if it’s steering wouldn’t snap her arms. P/S is coming... but not in yet.

It looks like 4Runners are also a commonly used donor. Any reason to go that way versus the FJ 80?

I pinged Poser, thank you for the referral
Last edited:
Before you decide on a MC and booster, you should first consider how you will perform such a conversion. You can't readily plug in a booster on a non-boosted vehicle. It won't clear the ribs on the firewall, and the pedal won't line up with the booster rod.

There are two ways I'm aware of:
1) Mount a mini-truck booster away from the firewall with an adapter like the one sold by JT Outfitters
2) Cut the firewall rib and make a number of mods as shown in this thread

As for the rear disc conversion, consider the fact that majority of the braking is done by the front brakes. The rear brakes usually require a proportioning valve to reduce the hydraulic pressure, or it would lock up. If you put disc in the rear, it will increase the braking power, which needs to be dialed back down with a proportioning valve to prevent lockup. It seems to me that's a self-cancelling proposition.
Is a booster necessary? (it's a rhetorical question. the answer is no.)

Consider using the 3 bolt to 4bolt firewall adapter from JToutfitters, which will accept any Toyota 4-bolt MC. Select an MC to get a reasonable pedal effort. available sizes are 13/16 to 1-1/16" in 1/16" increments. Start with a 7/8".

Use a pair of 88-90sumthin V6 4runner front calipers to get increased clamping power on front axle.
Use the common GM swap on rear axle with cheap ceramic pads for less bite.
F-R brake bias is just about perfect with that setup. On a customer truck, I still install an adjustable prop valve in the rear, but it is dialed out all the way as it is not needed. On my FJ45 there is no prop valve and no premature rear lockup.
Thanks guys - let me research all of that. Thanks for the link the adapter, trying not to cut anything.

Users who are viewing this thread

Top Bottom