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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" I can sit at a stop and literally feel the brakes yield letting the car creep forward"

That tells me your master could be leaking. The plumbing looks fine as long as you are not using the original dist. block. Are yo using the proper disk/disk prop valve?

I changed my front drums to disk and used a 1" master in a manual system. Everything feels good and I lock up the drum rears before the fronts on brake checks and it stops well. I tried to find a 7/8" master since i was going manual, but those are hard to find in a replacement master. Wilwood may have one, tho. Most disk masters I have seen use a 1-1/8" bore since they assume it's used in a booster system where the booster compensates for the additional effort needed with the larger diam. master.

As inferred, I really need to do some more brake checks to see if i can lock up the fronts. The brakes seem to work correctly given the rear end tends to lift and lock up more easily with the fronts grabbing. A future mod would be to use a 7/8" master in this manual system.I stayed with manual to declutter the firewall and clutch linkage.

george

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.

Braking is better (not great) at higher RPM but in a panic stop, the brakes won't lock up (front or rear). In stop and go, stopping power is diminished to the point I wouldn't trust sitting on a steep hill at a stoplight relying on the brakes. I found myself in this position once and had to bring the RPM up against the convertor to keep the car from rolling backwards.

Oof, that sounds nerve wracking.

You need at least 18" at idle.. Unless your in the Mickey Mouse club.. Frankly I'd use a better cam, one thats designed around street driving or it will be a drag to ride around in. Like that 041 cam, that has to be the worst cam to have on the street, its a lesson in misery..

Keep us posted as you go through your list, will be interested to hear the final outcome

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More vacuum always helps, but it's simply untrue that you need 18" or better of idle vacuum for vacuum assisted brakes to work.

I live in colorado where we lose 20-30% of pressure as it is and getting anything even with stock cams to produce that much vacuum is almost impossible.

My Wife's chevelle has the exact same parts as the OP does with exception of ditching the e-brake rear calipers because they are a **** design. The car has a bone stock GM Goodwrench 350. Stock cam, stock heads. Only mods are an Edelbrock performer intake manifold and headers. At the altitude the car is operated at, it only makes 15" of vacuum. The brakes work wonderfully in that car, as doe the brakes in my bird which are hooked to an engine that only makes about 11" of vacuum.

When I went to buy a 4-wheel manual disc brake setup (C6 Z06) for my ‘64 Tempest the two master cylinders that were recommended had a 7/8” bore (Wilwood) and a 15/16” bore (GM).

I had this issue but with expensive Aerospace 4 piston brakes. My vacuum was 11" and I used to run a basic Cadillac vacuum pump and it was OK at best and usually really scary.

Hella UP28 pump, set to 22" of vacuum, dual diaphragm booster and I pressure bled the brakes with a custom master cap and bug sprayer. Stops better than my 3 other cars and my GTO weighs the most.

I have stainless hard lines etc but the Hella pump and bleeding the brakes via pressure and not pumping to the floor really helped. I think i was ripping boosters after the swap by flooring the brake pedal during bleeds.

This was my my brake bleeding experience after installation... a 3/4 full Mityvac (probably 2 gallons) with a pedal that would hold one moment and dive to the floor the next after installing. I borrowed a buddy's shop Mityvac but it was so filthy, I couldn't re-use the fluid! Basic bleeding procedure until bubbles were no longer present and the pedal was high and firm. Start the car, a couple pumps of the pedal and it was back on the floor again. Rinse and repeat.

I had bent and flared all the lines myself and had no leaks anywhere but I finally just took a claw hammer and yanked every line off the car and ordered lines from Inline Tube and started over. ... same result. I was told to do the "rotate the rear calipers while bleeding routine" but still had a low, hard pedal. I have never had such a poor return on my investment (time and money) than this disc brake conversion project. It rapidly degenerated into parts swapping diagnostics which just throws good money after bad at some underlying issue that defies discovery.

https://imagizer.imageshack.com/v2/6...923/bAirPK.jpg

What calipers did you replace the Eldorado ones with?

The good news is the low pedal is probably from having the booster rod in the top hole of the pedal; the bad news is that when fitted to the lower hole [ for use with a booster ], pedal will be higher [ good news ], but pedal even harder [ bad news ].

The hard pedal indicates no air in the lines, that is good.

Your symptoms point to a bad booster, or m/c.

I'll start by saying I feel your pain by having the same disc/disc conversion you have except mine are from Master Power Brakes. I was in the exact same situation as you, don't give up! I have 11" of vac, it's just not enough to sufficiently operate a booster, no matter what anyone says. I tried big single booster, dual boosters but had one pump brakes, no wheel lock and would scare the crap out of you. I have the same Mighty Vac, I know I ran probably 2 gallons through my system with no change. I dug in and was determined to make them work. After talking with Wilwood tech and giving them my entire system specs, here is what I did and now I can wheel lock & have great brakes. The pedal will travel further, but you have a much better feel and will not run out of brake.

1) Install 1" Wilwood master with adjustable prop valve. Convert to manual. Upper hole on the brake pedal(You need at least 6.1 ratio. 6.5 or 7.1 is better). You'll have to lengthen your pushrod more than likely so you can get entire stroke on the master. My brake pedal sits about 1" higher due to this.
2) Scrap the junk pads that come with the kits & replaced with Hawk HPS + pads. Be sure to bed them in correctly.
3) The Eldo calipers can be a pain in the ass. They have to be 100% adjusted or they don't work. You have to adjust them to scrub the rotors and use the e-brake consistently to keep them adjusted. Here is the correct way to adjust: https://www.classicperform.com/Instr...structions.pdf

You can skip on the Wilwood master and use a stock Corvette style 1" master also. Along the way I have upgraded all rubber lines to Russell stainless. Mine stops almost as hard as friend's full Wilwood systems now. I love manual brakes now and will never look back.

FWIW, in reference to another caliper that will fit the rear (eldorado caliper) without the emergency brake hardware.

The D154 which was used on the front of G bodies beginning in 1978-1987, can be used to replace the rear 4 wheel calipers with the emergency brake provision. There are some other applications for the D154, also known as the "metric" caliper.

It's commonly used on 4 wheel disc conversion on dirt track cars where emergency brakes aren't needed.

This is the booster I'm using after I switched from manual drum to 4 piston power disk. I'm very happy with my Wilwood setup.
https://www.jegs.com/i/Tuff-Stuff/908/2123NA/10002/-1

Greetings Geoff! Join the pity party!

I don't know. When I pull the check valve/fitting out of the booster, it sounds just like disconnecting an air compressor hose quick coupling as the air rushes in to fill the booster.

Good point on the the upper hole pivot rod location. While increasing the leverage of the pedal ... why would you need to do that if you have a brake booster? I just assumed the longer stroke was required as a larger displaced fluid volume is needed for the power brakes in addition to a higher line pressure.

Thanks so much for this info. I like having the eBrake but may just swap them out if I haven't solved my problems with the other fixes.

Maybe you mentioned it previously, but are you still running a GM rear axle?

In general, I find that manual brake applications use 3/4 to 1" bore MC, and Power brakes are 1-1/8 on up. When I did the manual drum/drum to manual drum/disc swap on my Studebaker, I used a 7/8 master cylinder.

food for thought:

https://techtalk.mpbrakes.com/master...isk-conversion
" In general - the smaller the bore size, the more line pressure you will have in the system at a particular pedal effort. "

Yeah. 8.2 BOP.

Just got this delivered today ... hope I don't have t use it but at least I can march through my checklist now. Self contained, 2 wire + 1 hose connection. Installs in any orientation desired. Will hide nicely on the rad core support behind the battery ... if needed.

https://i.ebayimg.com/images/g/-7UAA...p~/s-l1600.png

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..

Chinese Vacuum Booster?
 

I can start this by telling you my original booster (67 GTO) passed the tests for working properly...barely! I borrowed a new booster from a buddy and installed it. My brakes improved a little bit, but not enough to make me happy. I had already rebuilt my wheel cylinders and and had a new master, new shoes and fluid, it should've stopped hard and fast like it has for the 40 years I have owned the car. It didn't! I sent my original booster out for rebuild to Power Brake Booster Exchange in Portland, OR. That is all they do! I received my booster and installed it that day and "Oh my God" that car stops like it never has before. Booster Steve said it had a small hole in it and was also collecting moisture causing it to fail. Well that got me thinking about the new booster I installed in my other 67 Pontiac. It always had a hissing sound when it was cold and seemed to go away when it warmed up. One day I needed brakes pretty bad because of an idiot in front of me and I almost planted my headlights into his tail lights...Not good? I found another original and had it rebuilt and the same story. It stops like it never has before. Moral of the story DO NOT THROW AWAY ORIGINAL RE-BUILDABLE PARTS. Both of those "New" boosters were aftermarket and are now melted down to make bottle caps!

Fought the same problem for 7 years but with front disc conversion and rear drums. Could never lock up the front brakes no matter how hard I tried, rears would lock up a little bit. I have a factory 9” booster car with 15” of vacuum. I replaced the booster a few times, no change. Added a vacuum canister, no change. I finally purchased a 9” dual diaphragm booster and installed it 2 weeks ago, front wheels locked up at 30 mph panic stop but after a trip around the block the wheels started dragging. Removed the push rod between master and booster, shortened it by 1/8 of an inch and drove again with an even better result. The front brakes now work and feel exactly like my factory power front disc 73. Two weeks of driving with working brakes, I couldn’t be happier. I hope this helps someone.

Well, after reading how one poster shortened his pushrod and it improved his braking, I tried that first. I slipped a flat washer between the MC and booster and braking improved. I added a second and braking actually feels normal with brake lockup occuring on panic stops like it never did before. Not content with the flat washers, I ground the push shorter and it's done and stopping like a normal power disc brake car.

I didn't have to make a single other change though I installed the vacuum can afterwards so I still have some boost if the motor stalls. If anyone needs a brand new hi-tech vacuum pump, I'm your huckleberry as the return period is past.

Nice to hear, always the simple things, right?

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You need to be sure you have the correct booster pin depth. Best way is to use a pin depth tool:

https://www.ebay.com/i/254608893852?...iABEgLek_D_BwE

For others, reference:

Put a hand vacuum pump on the booster and make sure it holds vacuum. Make sure you can blow thru the vacuum break that goes into the booster in one direction, and not the other.

More than once I've had bad boosters out of box.

Yes, the eldo calipers are critically dependent on the e-brake, to take up piston/disc free play. Bleeding is a pain, when you think you're done, do it 2 more times.

Just to ask, you bench-bled the master, correct?

The 1 1/16 bore is correct for your system.

As for pedal/pedal hole, etc, key is to have the rod be a square, straight-shot into the back of the booster. Also have the 'slack' taken up by adjusting the clevis. Power brakes = bottom hole in pedal.

General brake troubleshooting tech at Pirate jack's:

https://piratejack.net/tech-support/

Make sure you go to the bottom and look at other troubleshooting sections for different areas of the system.

If all else fails, replace the combo valve, they are know to be defective. Get the one from Pirate Jack.

I had pretty much the exact same setup as you, and originally had issues, and after going thru everything multiple times, turned out to be a bad booster.

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I would put the right cam in that motor for street use. It would be faster, run smoother, not destroy motor mounts and sound better.. 12" of vacuum is a lot of overlap! That power band is way too high for street use... Back when I was hard headed and the 041 in my 455 I used to hate these posts but they were right. The last motor I had I listened to Jim Hand and swapped out the 041 for the Summit 2801, WOW what a difference!!!!

Nah. 2801 is a towing cam in a 455.

I picked my Crane cam because it has the same duration, lift and LSA as the Wolverine cam Jim Hand favors. Good street manners and with my 3.55 gears and GM25 convertor, it has no soft spot and drives like a normal car but with a very choppy idle. Even off-idle it pulls like a freight train.

What's the specs on that Crane cam? Curious...


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