Hot Rods WOW--- Where did the brakes go?

Oops .. I picked the wrong key prematurely sent the message anyway as I was saying my buddy had the same problem when he told me he had braided stainless lines I knew what it was and this is very common braided steel lines are all a in 37° flare .all plumbing for brakes uses an inverted flare that is 45° flare. This is a common mistake and will cause an air leak that is not detectable. He would think he would see fluid leaking out but not always the problem is the threads are the same so you can thread a AN-3 braided line into a regular inverted OEM or auto parts fitting , tighten it up and think everything is great kick back and marvel at what a beautiful job you just did only to find out you cannot believe the brakes. You pump over and over and over bleed all the air out get a hard pedal let it sit for a minute and the pedal goes to the floor


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I need to proof read before sending!! I meant to say Bleed not believe the brakes. You will need adaptors for AN-3 to inverted flare. Speedway motors has all you need and a good tech line for any questions. If you already have the flare adaptors then you are using the wrong master piston diameter.


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How about reversing the lines on the mc...front feeding rear and vice versa. ..does the problem follow the mc or stick with the axle?

 

I don't even use fluid in the sprayer. I just use the garden sprayer to provide pressure after the master cylinder is topped off and refill the master cylinder if needed. I couldn't get my OT pickup bled before I picked up the $10 garden sprayer and a fitting to put in the master cylinder cap. Then stopped at an auto parts store and picked up a replacement master cylinder cap. It doesn't take much pressure. Maybe 5 ps1.

I was able to bleed it without having to refill the master cylinder reservoir but that has a reservoir that you can see the level without opening it.

 

With the booster you could probably use a 1-1/8 bore master to provide more volume.

 

OK-- I went back over all the work. Changed to a 1 1/8" M/C, put fresh Teflon tape on the bleeders. Put a real tights clear hose on the bleeder and into my clear bottle. Went through a lot of fluid until I was SURE I saw zero bubbles. Got a pretty decent hard pedal...
TEST DRIVE: pretty decent feel at first application then-- the more brake I need the harder the pedal was to push.
Back in the shop-- tested booster-- it holds vacuum. Checked engine vacuum,, yep 18+ Yep the booster check valve holds... I'm back to zero---

 

That sounds like the problem is opposite now.

 

Anyone have issues with the GM calipers? Park Brake ratchet not taking up slack? Or the 7" boosters commonly available to the aftermarket?

 

I had a similar problem with early GM calipers that used the parking brake to both adjust the pads and apply the parking brake. Several long time mechanics who worked on them all told me they hated them for exactly the problem you're having. One, only one, old timer told me they needed a 10lbs residual, and the "adjustment" mechanism would slowly bleed back thru the usual 2lb residual for disc. I was disgusted and replaced them with a late model unit with little internal drums for the parking brake, so I don't know for sure. At this point, changing the residual might at least give you a read on that.

 

A bigger bore master is going to require more pedal effort for the same clamping force at the calipers.

 

OK-- Update: Replaced the single dia. booster with a dual. Had to make room for this to happen, seems this is an early TCI chassis that the dual booster would not fit until a small mod was made. Did that and got the dual booster mounted. Got rid of the rear GM calipers and went with the rear disc set from Currie. So now I have the dual diaphragm 7" booster, the new 2# residual valves, the TCI stainless lines all as supplied, 1 1/8 master (new) Engine vacuum 15" to 20" drops to 15 when brakes applied- raises UP as throttle is lifts and braking starts. Car stops OK. But pedal gets real hard and impossible to skid tires.... SO--- I put the 1" master on..About same brake situation.. Put the pressure gauges on and have 500 psi front and back-- This is the exact SAME pressure I had with the single diaphragm booster.
So-- Now what? I should have MORE pressure with the dual booster but do not. The cars does stop AND I have had three otehr guys drive the car and tell me it drives as good or better than their cars--- BUT the OWNER says the car is not safe to drive-- Keep in mind he has a 32 Ford Street Rod-- but that one has Jag brakes. His daily driver is a new Mercedes AMG CL55-- No comparison here-- But I think he wants brakes same as the CL55--
OK-- Comments????

 

Check for caliper flexing under pressure and causing "pad knock-off" when released

 

It was suggested to try a 10 lb residual valve for the rear. Did you try that?

 

You should easily have more than 500 psi without any boost, and well over 1000 with. The booster may be faulty with early "run out", causing the hard pedal. Are you sure the pedal is not binding or interfering with body or chassis, because that's what I found on two cars with a similar problem as yours.

 

Mashed the pedal hard MYSELF-- Got 875 at rear calipers. Vacuum never dropped below 15#. All adjustments are good, pedal free-- good solid pedal - zero air bubbles seen when bleeding- pumping pedal does not come up as if there was still air in the lines. Three guys drive it that have similar cars all tell me this one has better brakes-- Owner of the car says he will not drive it like this "unsafe" --- One of the guys wants to buy the 40 like it is. Yep, he drove it more than once. Likes it, and he already has a 34 coupe and sedan, a 40 pickup and a 32 roadster, so he has plenty of cars to compare this one to-- He offered to trade his 32 Roadster for this 40 coupe.