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Author Topic: Booster sizing  (Read 609 times)

Offline RA61Kurt

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Booster sizing
« on: May 01, 2020, 12:13:06 am »
Hi guys, got an odd issue in my RA60 that i need to rectify.

For a bit of backstory, i drive a RHD RA60 (F-Disc, R-Drum, SRA) and my brake booster and MC are on the right hand side of the engine bay, where the column sits. Opposite to USDM models.

Quite some time ago, I purchased the 20R/21R dual sidedraft Weber kit from Toyhead Auto, and it fits the engine great -- but it doesn't fit the car, due to the booster/MC assembly being in the way on RHD cars.

Image for reference (not my car)

Images of how far my webers foul on the prop valve and booster:

First weber image is reference on how far into the booster area it portrudes, second image is showing how far back it needs to go.

So my options are either
a) remote booster, which requires a shitload of legal f*ckery
b) go without the booster altogether and run a bigger bore master cylinder
c) find a smaller booster from another car that fits to clear the webers.

I'm too far in the hole on a set of webers i can't return due to how long I've owned them and how long shipping takes with covid19, so i want to make them work.
Full-time daily/part-time project: 1983 Toyota Celica 2.0 XT

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Offline ozzie

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Re: Booster sizing
« Reply #1 on: May 01, 2020, 03:30:39 am »
I'd start by relocating the proportioning valve, assuming it's a separate piece from the MC. From there you might be able to trim the trumpet to fit next to the booster. Not an ideal solution, but better then spending mega hours scouring junkyards for boosters that are the same bolt pattern as our cars, but more compact.
'84 Celica GT - 261k mi

Offline sirdan

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Re: Booster sizing
« Reply #2 on: May 01, 2020, 04:05:18 am »
Apples to oranges but I converted my 73 dart from power brake to manual. Honestly barely even notice its not power and its got front disc rear drums. If you sized the master properly im sure it would feel and work fine. I wonder if any of the 70s celicas had manual masters? I think there is a small toyota booster but idk what it came on. Other options you have are adapting gm hydroboost but I bet that would probably not be legal.

probably manual brakes would be your best bet although not sure if that is a legal issue or not where you live.
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Offline ozzie

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Re: Booster sizing
« Reply #3 on: May 01, 2020, 05:20:14 am »
Other options you have are adapting gm hydroboost but I bet that would probably not be legal.

Why not? I don't know much about hydroboost, even though I have it on my pickup.
'84 Celica GT - 261k mi

Offline Teranfirbt

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Re: Booster sizing
« Reply #4 on: May 01, 2020, 03:57:06 pm »
One thing to be aware of is that if you remove the booster you need a smaller master cylinder, not a larger one. This is because pressure = force divided by area. If you increase the area, it takes a lot more force to get the same pressure. The downfall to a smaller master cylinder is that you have to move the pedal more to take up changes in fluid volume as the pistons move and calipers flex. This is the reason that boosters exist in the first place.

As for sizing the booster, a good place to start is measuring the diameter, finding the area, and multiplying by 10PSI to get the force level of the booster.
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Offline 85GTS

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Re: Booster sizing
« Reply #5 on: Aug 01, 2020, 05:22:05 am »
A little late to the party, but if you havent resolved this you might look at the booster from an ma61 supra. The ones in the US anyway had a deeper, but smaller diameter booster (dual diaphragm id guess)
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Offline Sigma Projects

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Re: Booster sizing
« Reply #6 on: Aug 06, 2020, 10:51:17 pm »
Speak of the Devil, I saw an ad for T3's mini brake booster for AE86. Not sure if it's something you can swap onto a 3rd gen.
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Offline TotallyBroke

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Re: Booster sizing
« Reply #7 on: Aug 27, 2020, 06:20:41 am »
I agree with sigma. Id try to get in touch with T3. They've been doing alot of fitment r and d for the mini master theyre now selling. Could be a great option for these cars down the road
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