Putting booster on 66 drum brakes driving me crazy

[buildinga55]

Adding a booster to the original drum brake setup. Split the lines and went with a 67 dual reservioir. Also put on new shoes and wheel cylinders. Bench bleed mc and installed. Drilled hole lower on brake pedal as instructed. Left just about a 1/4 play in pedal to prevent pushing on mc. Here is the result. The pedal seems to get very hard about half way down and you can stand on it and it will slow the truck but not like it should. It kind of coasts to a stop i tried moving the pedal rod back to the original spot thinking this feels like the mc is not getting fully pushed in. That just made the pedal feel spongey but did not help the stoping. So I took the booster back off and you can lock the truck up if you don't care to really stand on it. I cannot figure out why my braking is worse with the booster than without. It is my father in laws truck and he needs the power assist. . Any other ideas.

[geezer#99]

You don't have enough engine vacuum to make the booster work. Might need a vac can or a vac pump.

[buildinga55]

It's got 14inches of vacuum at idle. It does have a very mild cam but nothing at all radical.

[geezer#99]

14's obviously not enough. Likely borderline.

[LostMy65]

Is the rod from the pedal to the booster adjustable? Try adjusting the rod so it engages the booster sooner.
Also check how far the intermediate rod (between the mc and the booster) protrudes into the master cylinder.

[Captainfab]

Is the booster known to be good?

[buildinga55]

It is all new. I think I will try the additional canister. Wonder if oreilly or anyone carrys a cheap one locally. Don't need chromed out or anything fancy. This old engine smokes a little and has some miles on it. Don't know if that would make any difference in vacuum.

[Captainfab]

What is the application for the booster? Does it have the long intermediate pushrod that is required with the '67-'70 truck master cylinder?

[luvbowties]

Here's practically a bolt-on for our trucks with that mc, if it has a void, about 1-inch deep, drilled into its piston-rear. If no void, then even better, as no need to make the 'plug' described below. AutoZone Booster Part Number: 54-71108, found on AutoZone.com., & made to fit a '79 Chevy truck.

You'll have to buy 3 parts from Lowe's to adjust the pedal length to fit: a *clevis, a threaded rod, and a coupling nut, about $10-$12. *Clevis should be wide enough to accept brake pedal linkage between its holes. May hafta buy one slightly too snug and widen its ears a tad.

You'll also have to make a *"plug"[about the shape and size of a .38 bullet] to fill the void in the rear of the mc, so the booster rod will begin its push where the plug's rear lies approx. flush with the rearmost surface of the mc-piston. *This plug is made from the threadless shoulder portion of a bolt--or a rod--whose size lets it slide around easily inside & is close to the diameter of the 'void' drilled into rear of mc.-piston. This plug takes about 30 minutes to make. Cost approaches $zero, if you can find a proper sized bolt in your junk bin to cut, grind, & fit.

If you don't have a booster core, just go by a garage-or-two until you find a discarded, for free booster--most any model, I've found--and AZ will accept it for the core value when neatly closed up in their original box.

Just another method that skins this particular cat....... Have fun.
Sam

[buildinga55]

It was a kit you buy on eBay for this truck. It has a bullet to fill the space in the mc.

[LostMy65]

Does anyone know the exact length of the 'bullet' ?

[old cool]

I can't get too mechanical or technical here but I may have some info that will help.
1. I have a "66 with an older power booster and dual circuit upgrade. From what I see in the catalogs and on-line, it appears I have a Cardone booster to fit a 67-70 truck.
2. If I recall, I get 15-17" vacuum with carb set at max vacuum read
3. I have a 250 inline 6
4. My brake pedal is almost as high as clutch pedal so I have a pretty long push before pb engages. Different from new cars for sure.
5. My brake pedal touch and stopping is very easy. Stops great. Almost too good. A first time driver always needs to drive a couple of times to avoid sending someone at windshield. Not sure if it's right, but I have no problems now that I'm familiar with braking.
6.Brakes will lock up if sudden stop is needed. (my MC looks a little dingy inside so it may be on its way out)

I sense your frustration and I'm sharing for 4 reasons.
1. My pedal is not firm whatsoever and the booster is prob the same as the one you picked up - though I've read somewhere there is a 2nd generation booster for 67-72's that may be slightly diff in size and color. Mine came flat black.
2. I've read that if you put a hose to back of booster from inside truck, near push rod (vehicle running) and you hear air hissing that gets louder as you depress brake pedal, your booster is leaking and this causes a firm pedal. FYI, I have a very light hiss that is continuous whether brake is being pushed or not. Not sure if that's ok yet although my pedal is NOT firm at all.
3. I went all over my engine for vacuum leaks and did pick up a couple of connections that sounded of leak. Resolved where needed. I also changed check valve and grommet at the booster as the grommet was old and did hear minor hiss. In other words, vacuum leaks can be the culprit in your case.
4. I think my pedal is factory setting for a non power brake system and one of the previous owners used existing push rod and made it work by fabricating the booster bracket on the firewall.

So, I don't have your experiences but I do have your modifications. Good luck. Please let us know how you resolved your issue. Hope this feedback is helpful.

[old cool]

Oh yea 55, forgot to mention, the previous owner of my truck plugged the check valve which made it a non power brake system. He said he liked the feel better than pb. I found it almost impossible to stop safely and absolutely knew I would crash into someone if I didn't keep a very long distance between me and other drivers. My truck stopped exactly like you are describing and I therefore replaced check valve. That being said, I think its fair to assume your booster is not working or as others have suggested, your rod/modifications are not right.

[buildinga55]

I adjusted the rod today maybe Little better but still not right. I ordered a vacuum canister today and we will see what that does.

[Captainfab]

What is the diameter of the booster? And is it a single diaphragm or dual diaphragm?

Originally Posted by buildinga55

It was a kit you buy on eBay for this truck. It has a bullet to fill the space in the mc.

[old cool]

I don't want to be redundant 55, but I think you should begin looking at simple vacuum parts before spending on pumps. As I indicated above, your brakes are functioning exactly as mine did when the check valve was plugged off. A check valve is cheap. I would make sure that is doing its job. Best wishes.
Fyi, my booster is the least expense of the Cardones. it is rather slim so i assume it is a single diaphram. It is black vs cadium and it averages about 100 bucks.

[buildinga55]

I'm not buying a pump I am putting an extra vacuum canister on it. $35. I checked my check valve and it is new as well and checked out fine. From all I have read the vacuum may be boarderline so I am going to give that try. I will report back midweek when it shows up and we will see how that goes. Thanks all

[buildinga55]

9" appears to be single diapham, not real sure how to tell the difference on diaphragm.

[66pnl]

Originally Posted by LostMy65

Does anyone know the exact length of the 'bullet' ?

I have a couple. One is 1.425. The other is more of a bullet shape so it kinda matches the bottom of the hole. It is 1.522 overall. I recently found that the holes in the aftermarket masters are larger diameter than the oem remans that I've used. The aftermarket (cpp) are slightly over 1/2 in. (The bullet is .535). IIRC I used a 3/8 or 7/16 bolt and sanded the threads down to fit the smaller bore.

[buildinga55]

The one I have made is probably 1.250, I measured the depth and set it up so it does not fit tightly against the booster plunger, but is very close. I know you need to release all the pressure on the MC when the brake is let off and too long of a bullet can be a problem. I think I am about right with that length. The vacuum canister is scheduled to be here on Wednesday so I am anxious to see the results. Thanks

[old cool]

Hey 55. I have a couple of questions as I may be changing MC. First of all, is the bullet needed cuz the push rod does not go deep enough into master? Second, what brand MC did u buy that takes 1.25 fit?
Please share cautions and results. Hope all is well with your efforts.

[buildinga55]

Yes the bullet is to fill the gap because in the manual master cylinder it has a deeper hole. I bought a kit on eBay with a 9 inch booster and what was to have been a disk drum or drum drum set up. That might have been my first mistake. It had a Corvette style master cylinder with it that I installed and was not happy with the brakes about a year ago. So I went and got a 67 Chevy manual drum drum master cylinder and mounted it on the 9 inch booster. I was never really that happy with the set up whenever I gave it back to my father-in-law. Then recently I was riding with him and he was complaining about the breaking and I could see that we needed to improve the brakes. So this last week I put a new master cylinder on it 67 Chevy style as the old one was leaking slightly I also put new brake shoes and wheel cylinders on the front. I have played around with the length of the bullet as well as adjusting the pedal. I feel like I have the bullet where it has no pressure on the master cylinder with the break up but should engage quickly when you start pushing the pedal down I also have a little bit of play in the pedal to the booster. So tonight I installed a vacuum reserve canister that I ordered and I am a little disappointed it does not seem like that has really helped much either. Currently when you're driving the truck and you start to break it feels like you have power brakes and it will slow the truck down but if you needed to stop urgently you have to just stand on the brakes and the pedal gets very hard. I have put brakes on dozens of vehicles over the years and have built several street rods I usually just go with all brand-new disc brakes on those cars but this has been a real problem.

[old cool]

I can sense your pain. Hope you dont have a bad booster. One more thing to buy.
I have an 11" thats about 4 3/4 " wide. I too have a 67-70 MC. My bracket may have been modified. As such, I would have a diff bullet requirement (probably).
if you recall, I can hear air at the back of my booster from under the dash if I put a hose up to it. Im wondering if thats due to an improper rod adjustment (putting pressure on the diaphram) or if its normal.
Learning as I go. Always good to hear the eventual solution.

[buildinga55]

Well, I think I have done all i can do. Bled the brakes again tonight. Drove it and the booster feels like power brakes just to slow down, but if you really want to stop, it will slide the tires, but you have to stand on the pedal. At least that is better than when I got this thing from the father in law. You could not lock it up at all. So I guess new shoes, new wheel cylinders, new MC, extra vacuum canister and multiple pedal adjustments and bleedings, did improve it some, but this is all I can do. If it were my truck, I would put disc brakes on it and call it a day, that is what I always do on stuff I restore but this is not my truck and I guess this is the best we are going to get.

[old cool]

55. I googled this site: How to diagnose hydraulic brake problems - AGCO Automotive.
The site suggested corroded wheel cylinder, return port in MC, and/or hose collapse internally. Other discussion as well. unfortunately, the probs are not visual.