1976 - 1980 FJ40 Brake Booster Replacement List

[Racer65]

I doubt any booster manufacturer can supply the Toyota kit that Dewey wants, except for possibly Toyota itself. As I mentioned, I am willing to make the diaphragms if that's all Dewey needs, but they've confirmed that it doesn't fully address the problem.

 

[Vae Victus]

I'll pimp my friend's brake lines he is making if you need to do that. He's quite the artist: https://forum.ih8mud.com/threads/fj40-brake-lines-and-the-potential-source.800737/

 

[bikersmurf]

It's a good point that it's more than just diaphragms... I've got two stock boosters which both have good diaphragms (as far as I can tell) which weren't boosting properly, one which sat on a shelf for 20 years. It could be that the Master Cylinder was really the problem, because the brakes weren't working 100% right until I installed a new master, or there could be something else internally wrong with them. I had a thread on it at the time, and consensus seemed to be a booster problem, but neither hissed or had a problem holding vacuum.

In 1993 I replaced my 'stock' 1974 booster with one I pulled from a 1977 Fj40 at the wreckers. Roughly. a year ago the brakes started acting up. The booster seemed to be the most likely culprit. I replaced it with one I pulled from a 1977 Fj45 back in 1994ish. The brakes were somewhat better, symptoms changed a bit, but still not right. I replaced that booster with one from a JDM diesel 80 (known to be good) and the brakes were better, but still not right. It wasn't till I replaced the 22+ year old remanufactured master, that the brakes were 100% again. It could be that the boosters weren't the real issue, or it could be something else internal wrong with them. If I had time and energy to burn, I'd try them out again, but I don't. (sorry for the rambling post)

 

[numby]

Bikersmurf - Yeah, that does heavily point to MC problems rather than booster issues. It is possible that internal dirt, rust, and corrosion adds an element of impairment to booster function which may or may not be correctable with a simple internal clean-up.

There's a lot of bright folks here and, despite the obvious safety concerns, this ain't rocket science. I'd like to see someone pull one of these broken boosters apart and reassemble it with new diaphragms to see what we get. 15+ years ago there was a crude tutorial on dual booster disassembly/assembly on the internet (can't find it now). I spoke to Dewey at the time and what I seem to remember was his cavalier attitude to these boosters. He indicated that 1) They weren't very complicated and 2) I could probably rebuild one myself but that an appropriate jig made it a heck of a lot easier.

Dewey's reluctance may also have much to do with reputation/return percentage issues and I would think it wise that they would insist on new replacement pieces (like the crimp-on metal ring) to address their business concerns. As I pointed out elsewhere there was somewhere on the order of 25,000 76-80 US spec cruisers produced which implies that there are likely 1500 to 3000 40/55s still on the road with original braking systems - maybe more. Is there a hobby business opportunity for someone here to do simple test/restore/rebuilds on these for Mud members?. Without a full on assembly oriented shop space it wouldn't be a real money maker but I think one person at their garage bench could turn a few extra dollars.

Also - I have two spares of unknown condition that were guaranteed to be working at time of purchase. Without a current shop space I can't easily swap things out to test them. Knowing that only a complete tear down will give me an accurate assessment of the boosters' condition, what will hooking up manifold vacuum to these things tell me? I think I could rig up a simple wooden press to mimic a brake pedal and run through the standard tests. If they held vacuum overnight would that be an indication of viability?

 

[Fast Eddy]

I'd say it can be made to work, but it's not a direct bolt-in. The diameter is bigger so it covers up the clutch bolt. It requires a different MC. It's also thinner, so you need to bend your brake lines. Actually, you need to modify your brake lines due to the different MC.

For me these reasons would be a no go. I'm not messing with my stock brake lines unless I absolutely have to.

Bah. You just have to bend the brake lines a little. It can easily be done by hand. They are very flexible. The clutch master bolt problem is only a PITA once in a great while when you need to remove the clutch master. You don't have to remove the brake booster to get to it, just loosen the four firewall bolts.

 

[Vae Victus]

I was reading the '72 (75?) Chassis FSM today from TrollHole's thread, and there was a section on rebuilding the booster.

3-4 pages of details. Interesting. Hadn't seen this before.

 

[tls3601]

Could a bad booster make my rig want to stumble at idle when braking, especially hard? Or is this most likely a check valve issue? Toyota tech's supposedly felt my booster was not the problem. Could they have misdiagnosed???

 

[Racer65]

Check valve or the booster hose that connects to the check valve could be leaking.

 

[tls3601]

Thanks Racer65, will post up pics

 

[tls3601]

I have a stock '78, how would I know if mine is a single or tandem unit?

 

[Racer65]

I have a stock '78, how would I know if mine is a single or tandem unit?

If it's a stock USA model, it's a tandem booster. You can tell because it's a "fat" booster as opposed to a thin booster. It looks like the Centric booster shown in this thread.

 

[tls3601]

Thanks Racer65

 

[Fast Eddy]

Could a bad booster make my rig want to stumble at idle when braking, especially hard?

This is the classic sign of a bad booster. It is a crack in the diaphram, leaking vacuum into the engine.

 

[tls3601]

So time to start shopping? What do you recommend? Also planning on replacing the fuel filter, possibly the fuel pump too( I believe it is mechanical on the '78?), going to be an expensive month.................

 

[Racer65]

So time to start shopping? What do you recommend? Also planning on replacing the fuel filter, possibly the fuel pump too( I believe it is mechanical on the '78?), going to be an expensive month.................

As suggested in this thread, the Centric booster would be a direct fit. The last I checked Rock Auto still has a few units in the inventory at a good price.

I'd recommend replacing your master cylinder at the same time if you haven't done so already. Often times the booster fails because the MC leaks fluid into it.

Also a note about removal. Replacing this fat booster is kind of a pain due to the limited working space. You almost certainly have to move the clutch MC to the side in order to make room for the booster to come out. You'll know what I mean when you get there.

 

[tls3601]

Yes, got my clutch master at Rock Auto, will check them out............

 

[tls3601]

At Fast Eddy; a while back I had to replace rear wheel cylinder on passenger side. Upon bleeding out the system, the brake fluid I forced out looked as though it had oil in it, have a pic of this somewhere. It was seperated in my plastic collection container. Could a failing brake booster suck oil into the master????

 

[Fast Eddy]

I don't see how. It's more likely to be water. (?) If you used DOT 4, it wouldn't mix and you'd end up with separated old brown DOT3 fluid at the bottom of the collection container.

The internals of the booster don't connect with the high-pressure brake fluid system. Worst that happens is that a leaking master can leak into the booster and the fluid will eventually ruin the diaphrams.

 

[tls3601]

Thanks Eddy, I used DOT 3, what the manual reccomended, but not sure what PO used

 

[Arabian Cruiser]

Very helpful read. Just going through issues with my 82 booster for my fj40 after the disc brake conversion.

Have decided to go with a FJ 80 booster and master. Hope that fixes the issues.