'78 FJ40 Brake Booster (the fat booster) Swap (1 Viewer)

[davespider]

I know the brake booster threads have been beaten to death...but I just finished mine and I thought I'd share what I found out. And maybe answer some questions that may still be floating around out there.

My '78 has the really fat booster (7" deep). Went to the junk yard with a list of possible booster doner vehicles gleaned from searches done here. ('85 mini truck, '89 4-runner, '85 supra, T100 truck)....and ALL of them had the skinny booster (~4" deep). I was really hoping to find a fat one because I was trying to avoid having to use a tube bender. I went ahead and got the skinny booster off of a mini truck one since that seems to be most popular.

Went ahead and took out the old, fat booster and mounted the skinny one. Mounted the MC. Now came the part I was worried about - bending the brake lines. I even got a tube bender - turns out I didn't need it. I was able to reconnect/relocate the brake lines fairly easily. I very carefully either slightly widened or slightly narrowed the bends that were already there. After some careful experimenting, I was able to relocate the lines. If you do it this way, just take your time. ALOT easier than I thought it'd be. I did have to trim about 1/4" off the booster rod and adjust it by about 1/4" closer to the booster.

Super easy, actually. Oh...and be sure to get the check valve from the doner vehicle.

Brakes already work better...even before I've bled them.

Dave.
'78 FJ40

 

[lostmarbles]

Interesting stuff Dave.

I always assumed the fat booster is fat because it is "two stage" (compared to the skinny ones like mine that I know are "single stage").

So I would have assumed swapping from fat to skinny would have required more pedal pressure to achieve the same degree of braking. Very interesting to hear that this didn't turn out to be the case for you.

And I thought perhaps a diesel (like mine) may have got the skinny one because the alternator-mounted vacuum pump was better at achieving a "consistant good vacuum" compared to sourcing the vacuum from the intake manifold of a petrol engine.
So this kind-of destroys that idea of mine too.

Thanks for sharing your experience.



PS. Maybe I'm misinterpretting what you are saying. I'm assuming you are saying the skinny booster is providing better braking than you got from the fat one EVEN WHEN THE FAT ONE WAS WORKING PROPERLY. (Or are you just saying the skinny booster provides better braking that your fat one did when it was stuffed?)

 

[CHOCODILE]

you said stuffed










Great info on the booster swap....


Did you find this on the truck or was it already removed?

Reason being is that the Mini trucks use a .250" spacer between the booster and the bulkhead...


Just wondering if you found that piece when you removed the booster, or if you did not grab that....

 

[85roktoy]

Thanks a lot for the info Dave! I'll have to try the swap soon

 

[davespider]

All the ones I looked at were from the mid-late 80's model vehicles. I'm kinda assuming that they would be dual diaphragm ones. But, to be honest, I'm not sure. I thought maybe the technology was better and they could just make them skinner...but, again, I don't know.

As far as my braking power goes...it seems pretty similar, maybe a bit better. I'll know for sure once I get the brakes fully bled and will update then. The difference kinda seems huge since I've been driving around for the past week with a 'stuffed' booster.

This junk yard was kinda weird. I went out to the yard with the guy...looked at several different ones...chose the one I wanted. Then we went back to the office and he had his helper pull it. I didn't see a spacer when I looked at it on the truck...but I could have easily missed it. That's probably why I had to trim 1/4" off the booster rod. Makes sense. I've seen where some guys have added 1/4" spacers between the booster and the fire wall. I just went ahead and trimmed the rod. Maybe a bit sturdier this way.

Dave
'78FJ40

 

[dgangle]

figure all this out on your own

This has been done eleventy billion times in every conceivable combination. If Toyota made the booster, chances are it's been retrofitted on a Cruiser a cazillion times long before I even knew what one was. The internet just makes the share of info more readily available. BTW, the correct terminology is "dual diaphram' and 'single diaphram'.

Reinvent the wheel - UsingEnglish.com

Oh, and

 

[lostmarbles]

This has been done eleventy billion times in every conceivable combination. If Toyota made the booster, chances are it's been retrofitted on a Cruiser a cazillion times long before I even knew what one was. The internet just makes the share of info more readily available. BTW, the correct terminology is "dual diaphram' and 'single diaphram'.

Reinvent the wheel - UsingEnglish.com

Oh, and

I'm puzzled by your motives in writing the first few sentences here dgangle! Surely you're not trying to discourage people from posting their experiences?

Dave wasn't asking for help. He was simply sharing his experience. (But personally -I wouldn't have objected even if he had been asking for help.)

Like you I do appreciate photos (but then not everyone has a digital camera or compatible up-to-date computer).

But I know I'm sloppy with my terminology at times. (And it is definitely confusing to everyone concerned when people use the wrong terms.) So I promise to TRY and be more careful there. (That's a GOOD point you made.)

 

[AKcruiserfreak]

Good writeup. Helpful for those of us trying to figure out what to do with our brake booster issues.

TK

 

[davespider]

I read cazillion threads on this and after reading them it seemed like some people, including myself, still had some questions. I posted this thread in an effort to help the people that may still have had some questions. I used the fat/skinny term because I thought it may have been easier to understand...but I also did refer to it as a dual diaphragm. I probably should have been more clear on it, that true.

Thanks to all the people who posted their experiences swaping out a booster - made it ALOT easier for me. Great group of people here, that's for sure!

Cheers.

 

[hi5tothaface]

what was your list of donor vehicles? i have to do something with my brake boosetr too and i dont know which would fit on it i have a 72' fj, would the same ones work as your 78'?

thankss

 

[handcannon]

what was your list of donor vehicles? i have to do something with my brake boosetr too and i dont know which would fit on it i have a 72' fj, would the same ones work as your 78'?

thankss

hi5tothaface

In davespiders' starting post he listed several model years/vehicles and I know there are more, probably most any Toy booster will fit. I have a 71 FJ40 and used a booster off of a mid/late 80's mini p'up. I saw a 3/4 inch spacer between the booster and firewall, didn't get it with the booster and ended up needing it.

Just make sure if you see a spacer when you pull the booster, get it. Also, get the vacuum lines that go between the booster and the manifold, you may be able to use all or part of them. The check valve will be somewhere on that vacuum line.

Good Luck
Don

 

[starman]

I have a 78 fj40 that I replaced the dual diaphragm booster with a single diaphragm booster off a toyota mini-truck. The only problem has been my brakes are way too sensitive. I've gotten used to them, but you have to be careful or they'll jerk the rig to a full stop.
Anybody have this experience on a booster swap?