[NeighborsComplaint]

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.

[AG]

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.

[NeighborsComplaint]

Originally Posted by AG

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.

[JUDGE3]

Originally Posted by AG

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.

yes heave the ugly NOT NEEDED brake booster. I have used the manual front disc rear DRUM manual brakes on my last 2 cars and love it. I have a corvette manual master cylinder from master power brakes. they have the kit for manual conversion.

not knocking those who like high end brake equipment, to each his own, but if your car is as 90% most are, a lengthy cruise now and then and some quarter mile fun manual brakes are plenty.

I always wonder with all the big brake equipment are those guys going to an indy type track a lot and hammering their brakes and jerking the steering wheel into hard turns? nope lol but I get it, nice automotive equipment is cool.

manual brakes have great pedal feel, cure big cam low vacuum issues, provide clearance for nice tall valve covers for stud girdles, and clean up the engine bay. -brake boosters are ugly- and the hydro boost thing really tickles me. just sayin.....

[ZeGermanHam]

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?

[JLMounce]

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.

[NeighborsComplaint]

Originally Posted by JLMounce

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.

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).

[AG]

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.

[FrankieT/A]

Hydraboost...$300.00 bucks...Done

[NeighborsComplaint]

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.

[ZeGermanHam]

Originally Posted by NeighborsComplaint

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.

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...

[NeighborsComplaint]

Originally Posted by ZeGermanHam

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...

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.

[ZeGermanHam]

Originally Posted by NeighborsComplaint

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.

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.

[FrankieT/A]

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.

[mf67gto]

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.

[patox]

Originally Posted by mf67gto

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.

Any chances you can grab a pic to check?
I feel so very interpreted by everyones pain in this this tread... kind feel we need a group hug!

Only to add I have swaped 3 rear disk convertion kits because my wheel vintiques rally I 15x8 will hit every caliper installed...

Trying scarebird adapters for the eldo calipers... hope this will be the one... at least on fitment!!! then will see how they brake..

[JLMounce]

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).

[Goatracer1]

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.

[ZeGermanHam]

Originally Posted by JLMounce

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.

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.

[NeighborsComplaint]

Originally Posted by JLMounce

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).

Pushrod is in the top hole.

Braking improved slightly (still marginal stopping) when I shortened the pushrod slightly. Additional shortening/lengthening mase no improvement. As regards "a hodgepodge of parts", what I have is no different than the components furnished in complete kits and the booster is an improvement over the "throw-away flowerpot" 9" boosters that come in most kits.

I have suspected the master cylinder is inclined too far and the fluid volume in the master is diminished by the angle but others on the board said not an issue.

My plan is as follows with road test after each change:

1) Swap the angled booster brackets for straight ones, verify change

2) Add a vacuum can, verify

3) Add vacuum pump, verify

4) Install 1" MC w. current booster, verify

5) Convert to manual brakes, verify

6. Give up and retire the car to storage until a cure can be found.