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Hydroboost conversions

Started by 403CADILLAC, March 17, 2023, 09:47:49 PM

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403CADILLAC

Anyone here done a hydraulic assist power brake conversion on 69-70 or similar model years? I see the caddy daddy conversion kit but would rather swap or fabricate one to keep costs reasonable. These are common swaps on muscle cars of the same Era using truck/van boosters but I can't find info for the cadillacs / c body platform.

I am building the engine and converting to rear discs. I worry the vacuum booster will not preform well once modified. If anyone out there is running a larger cam and/or disc brakes how are your power brakes?

Cheers🇨🇦

C. Malcolm

Dave Shepherd

If you have an engine with 15" of idle vacuum, Hydro Boost is unnecessary. Just need a properly sized vacuum booster. Obviously  a "big" cam would most likely  have less vacuum.

bcroe

Quote from: 403CADILLACAnyone here done a hydraulic assist power brake conversion on 69-70 or similar model years? I see the caddy daddy conversion kit but would rather swap or fabricate one to keep costs reasonable. These are common swaps on muscle cars of the same Era using truck/van boosters but I can't find info for the cadillacs / c body platform. C. Malcolm

I have taken them off diesel cars, 2 still in service
here. Of course the power steering is involved.  Fitting
style changed in 1980 just to make it more complex.  I
am not a fan of rear disc brakes, though extreme
performance might need them. 

I though I had the only 403 powered Cadillac.  Bruce Roe

fishnjim

You have to be real careful here and make sure the right pressure and amount of brake fluid is applied ie, match the master and calipers.  It not simple plug and play.   A rear drum wheel cylinder has a different requirement than a disc.  Some had smaller bore than the fronts, some proportioning to adjust.  That's why I like to get something already figured out and have someone else install it, so it doesn't come back on me and my work.   Something to consider, when "saving" a few bucks.  What's you car or life worth?
The size of the rotors will be important, the rear doesn't need as much stopping as the front, the 60/40 rule.  That ratio can be changed with chassis mods, so it all works together or has to.  Depending on how much horsepower you intend to make the factory frame may not hold it either.  Making it vs hooking it to the ground to benefit is another twist.   Back then, there wasn't the HP available today, so people could change things without much consequence, but today double, triple, or more is possible.  Frame changes aren't cheap. 
Probably a mild cam won't need a fancy brake system, if the factory is functioning well/replaced with new.  One can add an electric vacuum pump booster too if the cam eats into the vacuum.  No parasitic loss either.
If you just assume things, you'll end up worse than what is on it.

403CADILLAC

Quote from: bcroe on March 17, 2023, 11:16:11 PMI though I had the only 403 powered Cadillac.  Bruce Roe

You still might be the only one. Its got a 472, guess the names a little misleading

403CADILLAC

Quote from: fishnjim on March 18, 2023, 10:34:25 AMYou have to be real careful here and make sure the right pressure and amount of brake fluid is applied ie, match the master and calipers.  It not simple plug and play.   A rear drum wheel cylinder has a different requirement than a disc.  Some had smaller bore than the fronts, some proportioning to adjust.  That's why I like to get something already figured out and have someone else install it, so it doesn't come back on me and my work.   Something to consider, when "saving" a few bucks.  What's you car or life worth?
The size of the rotors will be important, the rear doesn't need as much stopping as the front, the 60/40 rule.  That ratio can be changed with chassis mods, so it all works together or has to.  Depending on how much horsepower you intend to make the factory frame may not hold it either.  Making it vs hooking it to the ground to benefit is another twist.   Back then, there wasn't the HP available today, so people could change things without much consequence, but today double, triple, or more is possible.  Frame changes aren't cheap. 
Probably a mild cam won't need a fancy brake system, if the factory is functioning well/replaced with new.  One can add an electric vacuum pump booster too if the cam eats into the vacuum.  No parasitic loss either.
If you just assume things, you'll end up worse than what is on it.

Good points and no triple power or frame modification in the plans. I can't even bring myself to cut the hood. It might be overkill but I'd like to increase brake pressure for 4 wheel discs. Fit new lines and preportioning valve same time (a future winter). This fall my master seals went and took out the booster so I need to buy replacements this year. I just pulled and tore down engine to rebuild and wake it up some so I've got room for working on firewall now.