Sooo tired of lousy braking and pedal feel!
 

Well I finally threw in the towel and ordered a vacuum pump as a fix for my hard pedal and unresponsive 4 wheel disc conversion. I've tried everything but stand on my head to get the brakes to feel like a "normal car" including swapping to a dual diaphragm booster from a Turbo TA. 12" of vacuum is 12" of vacuum and just doesn't cut it apparently.

I ordered a prewired, self-contained unit from Leed Brakes that utilizes a Hella rotary vane pump similar to what late model GM's are using. The maker says it completely replaces engine vacuum as the vacuum source though I plan on installing a T and check valve so the engine vacuum is available in the event of a pump failure and will probably add a vacuum storage canister if the pump volume doesn't keep up.

One interesting thing I encountered from dialog with multiple "techs" is the claim that "All you really need is a vacuum reserve canister ...". Am I the only guy that thinks "if 12" of vacuum won't operate my brake booster now, why would a larger reserve of 12" of vacuum be any better?"

Wish me luck because the next step will be a complete do-over as the car just does not stop like it should. Any ideas? The low engine vacuum has persisted through 3 different camshaft/intake/carburetor combinations. It is what it is.

I know someone will recommend a Hydroboost but that's not an option. I don't like the way they look on a classic car.

I would go manual and get rid of the big ugly booster. Just did this on my brother's car with front disc and a Wilwood master. Looks great and works great.

You read my mind if this pump doesn't work out.

Remind me/us... What conversion kit do you have installed? And do you still have a 1/4" line running from front to back of car?

I have a feeling something else isn’t right. 12” of vacuum at idle should be plenty to run power brakes. Heck I run power brakes without issue with about 10” of vacuum. I’ve got to get down to about 9” before I start feeling an issue.

One thing to note about the vacuum reservoirs is that you are absolutely pulling more vacuum than 12” during low load driving operation. Probably over 15” of vacuum, if not more. That’s what you would actually have in reserve. That’s also the vacuum level your booster is going to be seeing as you decelerate and break.

That’s what specifically leads me to believe you have something else going on.

Are you running an actual vacuum hose to your booster and not fuel hose? Vacuum hose is specifically designed not to collapse. While fuel hose is not. If that hose collapses, there goes your vacuum assist.

As mentioned already I’d also be looking at line size, verifying the combination valve is setup for disc/disc operation. Disc brakes need more fluid volume than drums. I’ve seen a lot of people try to reuse the original drum/drum combination valves and that’ll be a recipe for poor braking performance.

Right Stuff kit and stayed with all the born with brake lines. Wilwood 1" master/prop valve recommended by Wilwood for the big D52 calipers.

Hydraboost...$300.00 bucks...Done

I have reman OEM calipers up front, reman Cadillac Eldorado calipers in back, with parking brake pre-loaded per the manual, Reman '81 Turbo TA dual diaphragm booster (holds vacuum, hisses like a scalded cat when you pull the hose and fitting), check valve is (was}new and obviously working. Master is a 1-1/8" bore Corvette style (oem for '69 Z28/ZL1 disc/disc). GM disc/disc prop/combo valve and Inline Tube brake lines for disc/disc w. under-master cylinder prop valve mount. Basically, it just doesn't stop. I couldn't lock up the brakes if my life depended on it. Pedal has long travel with rock hard engagement, drop slightly when started. Everything has been bled multiple times even though the pedal is rock hard and not the problem. The brakes have been awful since installed. Brake shops won't touch it because it is not OEM.

This pump is the last straw. After that, it all comes off and I start over with a Wilwood manual 1" bore master and Wilwood calipers.

If this helps you....

A little background:
I have had Pontiacs for forty years. I've always built them up with porting and cams and stuff. I've always had a hard pedal or get one good stop, then the next quick one; hard pedal and no stop. Well I got tired of that in my mid fifties and decided to go to Hydraboost. Did the research and here is my set up in order.

First was rear wheel disc from an S10 and an aluminum master, booster and proportioning valve from an 81 T/A with four wheel disc . That was a worthy upgrade. Then the hydaboost from an Astrovan and hoses from an '81 Cadillac Seville diesel. Instant amazing brakes.

Then after that 12" rotors front and rear and Wilwood calipers all the way around.

I had a problem on a '68 GTO like this that drove me crazy - even had a new reman'd booster on it. Could not get the tires to lock up and almost felt like manual brakes by how much pressure I had to put on the peddle. As last resort I went up under the dash and where the connecting rod comes out of the booster there was a felt pad or filter around it to keep junk from being pulled into the booster as the diaphragm moved back and forth. After removing it and hitting the brakes it almost put me thru the windshield. I think the filter was acting like a plug and not letting the booster do its job or allowing the diaphragm to move. Easy to check from sticking your head under the dash. This "tip" has helped out several folks in the past.

Hope this helps.

Yes, running Gates vacuum hose, also combo valve is disc/disc. Line kit for 4 wheel disc conversion from Inline Tube. I would have to check the line size but the line sizes and flare fittings matched the the disc/disc proportioning valve. BTW, the front brakes suck with no lockup also.

Here is what it looks like. Pretty but works only marginally better than the junk I took off (drum/drum master, original drum booster) extended drum brake lines and used GM calipers the prior owner had done).

https://imagizer.imageshack.com/v2/6...923/nZI4UR.jpg
https://imagizer.imageshack.com/v2/6...924/dRnHWA.jpg
https://imagizer.imageshack.com/v2/6...922/XH9X6U.jpg

Not sure this applies in your case, but with my disc/disc conversion kit with Eldo rears, the distribution block (on frame) outlet for the rear brake line is plugged and the 1/4" line instead connects directly to the prop valve under the master cylinder. Perhaps you haven't got your system plumbed correctly? I was surprised that the kit did not want the rear brake fluid passing through the distribution block and could easily have been installed wrong had I not read the instructions a million times to verify.

Just spitballing here...

Looking at the first picture of the combination valve, I don’t see a plumbing issue. The valves is backwards from typical mounting but the rear reservoirs is feeding the rear brake and the front reservoirs feeding the front brake.

I’m sure this isn’t the issue, but just to check everything off the list, is the brake pedal clevice installed in the proper hole in the pedal? Or at all?

For quite a while I had literally the exact issue you’re dealing with. Turned out that the pushrod clevice pin was literally not attached. The brakes “worked” because the pushrod would still be pushed by the pedal, but because the clevice was not in the correct position the pedal ratio was terrible.

Another area to look at is the pushrod to piston clearance in the master cylinder. If there is excessive clearance, you’re using a lot of pedal travel before you start applying hydraulic pressure.

You can try moving the pushrod to the top hole in the pedal. If it gets considerably better it’s either a pedal ratio issue or a fluid volume issue (likely pushrod to piston clearance).

Have you ever considered using a 1" bore master cylinder instead of the 1.125" you now have? I replaced my master cylinder with a smaller bore one and cured all my problems. Remember your fat foot makes more pressure with a smaller bore than with a larger one.

In the first photo, I believe you can see the rear brake line from the prop valve (agree it's mounted backwards) connecting directly to the distribution block on the frame. If his disc/disc conversion kit is similar to mine, this is an incorrect configuration. The 1/4" rear hose should connect directly to the prop valve, and not pass through the distribution block at all. The frame distribution block should have the the rear line outlet plugged.

Again, that's just if his kit is similar to my CPP conversion kit, and it might be. If it uses different components, all bets are off.

Proportioning valve replaces the distribution block on the conversions. Yes, on OEM, a distribution block was mounted to the frame rail below the master cylinder. For conversion to disc/drum or disc disc like mine, the distribution block is removed and replaced with the proportion/combination valve mounted under the master cylinder. Some install flat like mine, some install on-edge depending on the bracket used. The Inline Tube brake lines were pre-bent to terminate under the master with the rear brake connection coming off the front. You just have to cross the lines between the master and proportioning block for correct phasing of the brakes. The lines have different sized tube nuts to keep you from routing them backwards.

I've had it in 3 different shops, described the issues, explained the work already done, literally handed each of them my credit card and said fix the brakes, I don't car what it takes. They've all tried and failed. I've done everything I can and just can't trust the car to drive it. I will try the vacuum pump and if that's not the answer, the cover goes on and won't be coming off.

Hmm, that is very much different from how my disc/disc CPP kit is designed and configured. It instructs to retain the distribution block, and gives specific guidance on how to use it in conjunction with (not in lieu of) the prop valve.

Must be some differences between our kits, but mine is just the basic 68-72 Chevelle front calipers and Eldorado rears.

Interesting. My kit did not include any hard lines, only rear soft lines, calipers, rotors, caliper brackets and soft line tabs. I already had front discs on the car (installed by prior owner) with booster and master. Proportioning valve was installed where the distribution block was orig mounted on the frame rail (about 1/4” away from a header downtube lol).

As mentioned, I wound up replacing everything the further I got into it. The line kit from Inline Tube is precut and pre-bent with tube nut terminations. They sell kits for configured for OEM replacement (using existing distribution block) or disc conversion in both bottom or side (relative to master cylinder) mounted combination valve with no distribution block. When I installed, the ends terminated within 1/4” of my bottom mounted combination valve.

Like I said, it’s all by the and doesn’t stop the car. I can sit at a stop and literally feel the brakes yield letting the car creep forward.

No fluid leaks and every hydraulic part has been bought and replaced since I started this ordeal.

I recently went through a similar trial & error process with my manual disc/disc setup and learned a little more while speaking with a wilwood rep.

In another thread here, I think it was "rocktamas prime" (sp) asking about prop valves, and someone accurately stated that the engineers took every factor into consideration when designing a brake system. This includes calipers piston size, rotors, MC bore size, rod position on pedal, prop valve, etc. It was all designed to work together. Makes 100% complete sense.

I think your issue is having a "mashup" of parts, all good in their own respect, but not intended to work together. From everything you have tried so far, the suggestions that stood out for me include verifying which hole the push rod is in. If an upper hole is available, try it. Bore size... often times the smaller 1" bore size is preferred as it takes less pedal effort, which is why wilwood suggested it on my manual brakes.

I had a 66 Chrysler Newport in the early 80s with manual drums, there was a reason that brake pedal was 12" wide!! I thought it would be great to have pwr brakes so threw an OEM booster on it and the braking was no better maybe worse. Looking back, it was likely a push rod location or the booster not intended to work with that particular MC (improper rod length or similar)

You could try removing the booster, but my guess is your larger bore MC bore is not going to be your friend in that scenario. Another thought is to remove the prop valve and connect lines directly to the MC. If you end up with too much rear brake, then install an adjustable valve on rear line.

From everything stated here, my sense is that the vacuum pump is not going to get you where you want to be...





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Another quick test... your engine would be pulling 20+ inches of vacuum while cruising. Leave the car in 1st gear, bring rpm up to 2500 or so then slam on the brakes. Does it stop like it should? If yes, maybe the vacuum pump could help at idle speeds.

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