Stiff brakes with new engine.

[NBC-Steve]

I recently did a major engine & transmission swap on my 72 Satellite along with a whole bunch of other new things. Blue Print 408 Stroker with a 904 transmission. I also rebuilt the brake system with all new rotors, pads, drums, shoes and all new hardware along with new brake lines and master cylinder. (I kept the stock vacuum booster and proportioning valve) I just got my Plymouth running and have taken it out on some test drives and the brakes seem very stiff as if there is not enough vacuum from the intake manifold. The new engine does have a kick *** cam and I know that there can be a loss of vacuum with a radical cam. How can I fix this problem? A few ideas come to my mind.

- Replace the stock vacuum booster with one from Summit Racing?
- Move the vacuum line from the intake to the base of the carburetor?
- Install a vacuum assist pump? (I've only seen one and wasn't impressed.)

Yes I did power bleed the entire system.

What's a post without pictures eh?

 

[toolmanmike]

You probably don't have enough vacuum with your new engine. Does it have a good sized cam?

 

[toolmanmike]

The PCV goes to the front port and the power brakes goes to the rear port.

 

[Don Frelier]

Try moving the PCV to the front and cap the rear port like Mike kinda suggested.
Vacuum booster right off the manifold should be OK.
Also remember the pads need to "bed in" so you need to drive it a bit with some hard stops.
If you have automatic adjusters on the back do some repeated stops in reverse and back forward as well to get them tightened up.
It may improve after you do these couple things but the pedal might still be a bit hard to press.
The problem then becomes if the pedal is variable where sometimes you get assist and others not.
That would suck.

 

[ruffcut]

I agree. Move the PCV to the front of the carb. Hope this cures the vacuum loss, although the cam may be the problem. Let us know your results. RUFFCUT

 

[steve340]

Firstly - is the booster working correctly? There are a few simple tests.
I had one of those pancake boosters and it worked but they need all the vacuum they can get.
It is possible you do not have enough vacuum to get it to work properly.
If you go to the carb as suggested the vacuum will be the strongest it can be.

 

[66 Sat]

Not related to the brakes - but how is the engine? Quality, power, torque? Can you write a review of your experience to date if you don't mind? Cheers

 

[R413]

Is the manifold vacuum he same in the entire system? So moving the hose means nothing?

 

[66Satellite47]

Gee, stiff brakes seem like the opposite of a bad vacuum booster. Seems like that would be real soft. Could be wrong.

 

[toolmanmike]

Is the manifold vacuum he same in the entire system? So moving the hose means nothing?

No, how he has it hooked up know only get's vacuum from that particular intake runner. Base of the carb is pretty much everything.

 

[toolmanmike]

Gee, stiff brakes seem like the opposite of a bad vacuum booster. Seems like that would be real soft. Could be wrong.

Soft and spongy means air in the lines. Unhook and plug your booster and see how hard the pedal is.

 

[NBC-Steve]

OK I made the correct connections. Thanks for the input guys! (I was going off the old stock 318 hook ups) Fired it up and seems better now but I really need to take it on the road to really test it but wait!!!!! My temporary spark plug wire routing failed and the wire broke due to it sitting on the header pipe. Replacement wires already on the way from Summit and..... its raining. I'm going to make a tempo-matic fix and see if I can get her on the road just to test. I'll let you know if its a success or a total fail.

My post engine install fix list keeps getting longer.

 

[ruffcut]

If this doesn't fix, I noticed on another members post that Edelbrock wants the hose for power brakes in the back port on the carb. Just a thought if you would like to try. I think the reasoning is there's more vacuum there. RUFFCUT

 

[NBC-Steve]

Took her out for a spin and moving the hoses helped significantly however at lower RPMs there is just not enough vacuum. If I put it in neutral and rev the engine a little bit then the brakes become more responsive. I clearly don't have enough vacuum for the booster with the radical cam. Will the new boosters like this one help?

https://www.summitracing.com/parts/sum-760171/make/plymouth/model/satellite/year/1972

 

[moparedtn]

Just how much vacuum DO you have at idle?

 

[NBC-Steve]

Out of all the tools I have the one thing I do not have is a vacuum gauge. Time for me to call my Snap On guy!

 

[steve340]

A double diaphragm booster will be more effective but it may be safer to try a hydro boost system - from what I have seen they do always work well and you only spend money once.

 

[moparedtn]

Out of all the tools I have the one thing I do not have is a vacuum gauge. Time for me to call my Snap On guy!

Woah Nelly, doesn't have to be a freaking high-dollar thing here.
Heck, most of us have one of the ancient old gauges they typically sold with "tune up kits"
that included timing lights and dwell meters.
I'm betting @HALIFAXHOPS probably has one he'd send you for quite reasonable $$$.

 

[HALIFAXHOPS]

I am sure I do prob around 20. PM if interested.

 

[NBC-Steve]

Just found a vacuum gauge kit on Amazon for 30 bucks. This should give me some good intel.