HOW TO MAKE POWER BRAKES SENSITIVE

ARPM · Jan 20, 2008

After doing my 65 vert with new brakes and working out the problems of the new installation i decided to change my 66GT brake system to exactly the same setup i did on my 65 vert. I installed the 7" MBM Universal booster, a new 1 1/8" GM disc/disc Master Cyl. Original 66GT 4 pistons Front disc brakes, universal GM disc/disc combination/dist valve and Crown Vic rear calipers setup. It works as good as my 65 vert. Now my wife wants to drive the 66GT and she finds the brake not sensitive enough for her taste. After all she's driving a 2005 Cadillac CTS and that car has super sensitive brakes and stops on a dime. I need recomendations in order to increase the sensitivity of my 66GT setup to acomplish the same as the Cady. Any sugestions?......................Thanks

10secgoal · Jan 20, 2008

Does the caddy have Hydro boost ? If you don't have P/S, it's out of the question anyways though.

12sec67 · Jan 20, 2008

I had to do this after installing a Cobra brake conversion to P/B and to a P/B conversion (stock style booster).
you can adjust it slightly in the booster. disconnect the master cylinder from the booster. there should be a small adjustable rod sticking out of the booster that puts pressure to the master cylinder. you can re-adjust that out just a bit to get a quicker response at the pedal. Just make sure not to adjust it too much or the front brakes wont release all the way. you should be able to pull the master cylinder away from the Power Booster just enough to adjust the rod. Adjust it ever so slightly (1 turn at a time getting the rod further in the master cylinder) little by little and drive it around the block a few times while getting on and off the brakes.

either that... like 10secgoal said, Power steering and hydro boost

wild70stang · Jan 20, 2008

12sec67, wont that prematurely activate the brakes by having it adjusted further than recommended? I guess you could then adjust the brakes themselves but im curious if that extra length might rupture the seals on the master cylinder if you need to apply full force against the pedal?

C0V3R · Jan 20, 2008

Does hydro boost really assist that much more than a vacuum booster that there is a really tangible difference in pedal feel

ultrastang · Jan 20, 2008

C0V3R said:
Does hydro boost really assist that much more than a vacuum booster that there is a really tangible difference in pedal feel

Brake boosters, whether vacuum-operated or hydraulically-operated, are force multipliers. For a given amount of input (from the driver), there will be a multiplied output force to the brake MC.

The best vacuum boosters will have an output of ~800-1,000 psi. Depending on the power steering pump used, --since that's what a hydroboost system runs off of, the output will be ~2,500-3,500 psi.

Input force to actuate brakes of hydroboosted systems is generally less than vacuum systems and modulation of the brakes is grenerally much better with a hydroboosted brake setup.

ARPM · Jan 21, 2008

10secgoal said:
Does the caddy have Hydro boost ? If you don't have P/S, it's out of the question anyways though.

No Hydro Boost on the Cady and yes the 66GT has Power Steering.

ARPM · Jan 21, 2008

12sec67 said:
I had to do this after installing a Cobra brake conversion to P/B and to a P/B conversion (stock style booster).
you can adjust it slightly in the booster. disconnect the master cylinder from the booster. there should be a small adjustable rod sticking out of the booster that puts pressure to the master cylinder. you can re-adjust that out just a bit to get a quicker response at the pedal. Just make sure not to adjust it too much or the front brakes wont release all the way. you should be able to pull the master cylinder away from the Power Booster just enough to adjust the rod. Adjust it ever so slightly (1 turn at a time getting the rod further in the master cylinder) little by little and drive it around the block a few times while getting on and off the brakes.

either that... like 10secgoal said, Power steering and hydro boost

That adjustment was done with the tool that MPbrakes sell's and is as close as 1/32".

PUNISHER RACING · Jan 21, 2008

put an adjustable prop. valve on it

ARPM · Jan 21, 2008

ultrastang said:
Brake boosters, whether vacuum-operated or hydraulically-operated, are force multipliers. For a given amount of input (from the driver), there will be a multiplied output force to the brake MC.

The best vacuum boosters will have an output of ~800-1,000 psi. Depending on the power steering pump used, --since that's what a hydroboost system runs off of, the output will be ~2,500-3,500 psi.

Input force to actuate brakes of hydroboosted systems is generally less than vacuum systems and modulation of the brakes is grenerally much better with a hydroboosted brake setup.

Thanks for your input Steve. I have always seen the Small 7" Factory Bendix booster as a very small unit for it's operation but MBM claims that with a 1" Master Cylinder their unit will provide 950 psi with 18" of vacuum. Do you think a larger size booster setup like this one http://www.mustangsteve.com/BRAKES.html will improve sensitivity?

ARPM · Jan 21, 2008

PUNISHER RACING said:
put an adjustable prop. valve on it

In my quest for sensitivity i removed the combinaton valve, installed a 2 way brass "T" to the front brakes and a willwood adjustable prop Valve to the rear and it was worst, cuz reducing the rear brakes pressure made the pedal harder.

ultrastang · Jan 21, 2008

The 5.0L booster is a dual-diaphram unit, and has good output (but not as much as a hydroboost system, of coarse).

You mentioned that you have a 1-1/8" bore MC. That may be the key to the whole problem. It takes quite a bit more effort to actuate the 1-1/8" MC compared to a 1" bore MC. Dropping back to a 1" bore will give you more output pressure to the brakes for the same given amount of input force on the brake pedal.

The trade-off will be a little more pedal travel, but shouldn't be significant.

ultrastang · Jan 21, 2008

Additionally, if the output rod of the booster is adjustable, here's an article on how to set the rod depth into the MC to get the best reaction/response out of the booster/brake system:

http://www.maximummotorsports.com/content/install/pdf/brakes/MMBAK-2r3.pdf

ARPM · Jan 21, 2008

ultrastang said:
The 5.0L booster is a dual-diaphram unit, and has good output (but not as much as a hydroboost system, of coarse).

You mentioned that you have a 1-1/8" bore MC. That may be the key to the whole problem. It takes quite a bit more effort to actuate the 1-1/8" MC compared to a 1" bore MC. Dropping back to a 1" bore will give you more output pressure to the brakes for the same given amount of input force on the brake pedal.

The trade-off will be a little more pedal travel, but shouldn't be significant.

One of the 1st things i did was to use the MBM 1" Chrome Aluminum disc/disc master cyl and while braking effort decrease the pedal travel was quite a bit long stoping the car with the pedal almost to the floor. I was recomended to change the pedal ratio by lowering it 1". That will bring it down to 4.5 (13"/3") since the 66 GT factory pedal ratio is 6.5 (13"/2") but i was wondering "How much pedal travel will that decrease?".

By the way i have a crane cams Vacuum reserve can installed and my vacuum port gives 18" at idle and about 22" at 2000 RPM.

CraigMBA · Jan 21, 2008

Here's the link to the kit so you can modify your pedal for the correct ratio:

http://www.mustangsteve.com/BRAKES.html

If that doesn't solve it, use a 1" master cylinder.

bnickel · Jan 22, 2008

brake pads can also have an effect on how sensitive the system "feels" , check into a different pad for the car while you're messing around with other stuff and you might find that solves some problems just doing that.

gsxrken · Jan 24, 2008

bnickel said:
brake pads can also have an effect on how sensitive the system "feels" , check into a different pad for the car while you're messing around with other stuff and you might find that solves some problems just doing that.

Beat me to it. If the 1" MC didn't work out, I'd get some pads that bite better initially. When I first went down the big-brake road, I was running the Wilwood Q pads and they were horrible. I could barely lock the brakes up. A switch to E pads and then BP20s and it felt like a different car.

whlnut_Ed · Jan 25, 2008

Teflon-lined stainless braided brake lines will add more line pressure to improve feel somewhat.

HOW TO MAKE POWER BRAKES SENSITIVE

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