Brake Help

[RalphN]

Anyone have issues with 70-72 brakes? I just can't seen to get this thing to stop on a dime. Or even close. 

I've replaced the rear shoes, turned the drums. Found out my rotors were under the serviceable limits replaced them, new calipers, new pads, new master cylinder, new booster. New flexible lines to the calipers. Still not good stopping power. I'm getting good fluid at the bleeders.  Only thing left is the proportioning valve, which I'm getting good fluid when bleeding so i don't see it being that. I've never been able to "lock them up" as they say. 

Any suggestions?  Or is this a good as I'm going to get? 

[GRAY 70 Monte Carlo]

Only 2 things come to mind. First have you adjusted rear brake shoes after replacing them. Second I would check vacuum to booster and see how much vacuum is at the booster 

[Dtret]

Without out actually feeling it, it will be hard to tell. But remember these 50 year old cars were not built like the cars of today,  pedal pressure and feel are going to be different than what you’re used to on your daily driver. 

[RalphN]

Dtret. That Just may be what it is. Just seems like it should be better. 

[Marks71]

I noticed the check valve wasn’t mentioned. Couldn’t hurt, they’re cheap. 

[RalphN]

The check valve on the brake booster?  Yes  checked

 Thx

[BobW]

Before I changed motors, I had the same impression of the braking ability. Good vacuum, new calipers, new booster, rotors, rear cyclinders and shoes. It was competent but not slam into the windshield power.

New motor installed, cam radical enougth that it only makes 14" of vacuum, barely had any assist. Used a vacuum pump and reservoir for 2 months, better pedal, but no more stopping power, and vacuum pump ran more frequently than I was comfortable with.

Just installed a Hydroboost, and WOW! Now I can lock up the brakes!

[Scott S.]

Factory systems weren't what they are today....

I've got my '70 and an '04. 

Night and day difference in braking, that's why I've been looking into multi pistoned calipers. 

And there's always the 4 wheel disc option.

I swapped to steel braided when I replaced the booster and cylinders. Less swell in the hose under pressure.

Made some improvements. 

QQ... Did you set the rod correctly ?? 

I noticed being out even a little bit can leave the pedal feeling spongy. 

[BobW]

3 minutes ago, Scott S. said:

QQ... Did you set the rod correctly ?? 

With the vacuum booster, yes, I have one of the magnetic tools that measures the MC depth on one side and gives you the booster rod set  on the other side.

The Hydroboost apparently is self setting, the pushrod does not adjust and I haven't found any reference to setting it. I was pleasantly surprised when it worked perfectly with just bolting the existing MC on.

[Scott S.]

Being called "Hydroboost", I'm assuming that there's some sort of fluid in it as opposed to just using vacuum operated ??

[BobW]

8 minutes ago, Scott S. said:

Being called "Hydroboost", I'm assuming that there's some sort of fluid in it as opposed to just using vacuum operated ??

Google 'Hydroboost, how it works'. You'll find that quite a few GM products use it, mainly trucks. It basically uses hydraulic power from the power steering pump to creat/add significant boost to the pedal. The hydraulics run through the Hydroboost to the power steering box then back to the pump.

It mounts in place of the vacuum booster. I used my existing master cylinder, just unbolted it, pushed it forward, replaced the vac booster with the Hydroboost and bolted the MC back in place.

This is the kit I used from Ebay: https://www.ebay.com/itm/196877579361

 

[Leghome]

if you have a photo what the connection for the preasure hose look like on the pump?

[BobW]

20 minutes ago, Leghome said:

if you have a photo what the connection for the preasure hose look like on the pump?

 

21 minutes ago, Leghome said:

if you have a photo what the connection for the preasure hose look like on the pump?

The hose kit has a fitting with an inverted flare on one end like the stock hose, and an AN6 on the other end that the new hose attaches to. You can just see the hose coming off the back of the PS pump in my pic above. Look at the eBay link and you can see the fittings. There is also a fitting that goes into the steering box pressure side for the new hose from the Hydroboost.

[Scott S.]

Similar theory as the electric pumps on the Grand Nationals and T-Types.

Just using a mechanical pump instead of an electric one.

Nice idea.  

[BobW]

On 7/18/2025 at 3:56 PM, BobW said:

Google 'Hydroboost, how it works'. You'll find that quite a few GM products use it, mainly trucks. It basically uses hydraulic power from the power steering pump to creat/add significant boost to the pedal. The hydraulics run through the Hydroboost to the power steering box then back to the pump.

It mounts in place of the vacuum booster. I used my existing master cylinder, just unbolted it, pushed it forward, replaced the vac booster with the Hydroboost and bolted the MC back in place.

This is the kit I used from Ebay: https://www.ebay.com/itm/196877579361

 

Here's an update on my Hydroboost installation.

First, I'm completely pleased with how the system works, braking power is exceptional!

Second, I had an issue with the hose kit that came with the unit. I had a hose blow out while leaving my friends house! No owner to the brakes or steering and PS fluid everywhere! Fortunatly I was still on his property. The hose that comes with this kit has no reinforcement! See the pic below. Took the hoses to a local shop and had steel reinforced hoses made. Installed, bled and everything works as it should!