Power brake push rod adjustment

[1970 CST Short Wide]

What is the correct way to adjust the power brake booster push rod? I just installed an 8 " power booster and while it does stop the truck it just doesnt feel like power brakes. I have vacuum and the booster is working (it holds pressure) but the pedal feels hard?? Any suggestions.

Thanks in advance
Steve

[MusicMan70]

ttt

[1970 CST Short Wide]

Anybody??

[oldblue1968chevy]

inside the cab there is an adj.

did you 'switch' to power brakes if yes, did you get the rod that goes into the cab also and put it on your truck?

[Murphy IRE]

I'll have to find an old thread of mine (like 3 or 4), same problem! Longhorn Man said it wasn't the push rod and he was right. I checked it anyway and it was perfect. I have replaced just about everything and I've got the best brakes I've ever had but still not great. In the city they are fine, but they are bad in the mountain 4x4 roads. How many inches of Hg to you have? I'm finally up to 13, but the booster needs 18. I have installed a canister (JEGS), but that won't increase the vacuum only the volume. So I have ordered a vacuum pump (ebay). I'm going to hook the pump to the canister, so that it will cycle off/on and then "T" into the original line with a check valve. The pump arrives this week and I'm trying to find the correct one way check valves. The pump is supposed to build 18-20 inches. I hope that helps and I'll update you on the install.

[1970 CST Short Wide]

Thanks Murphy, Please keep me updated. Like I said it stops the truck but dosent feel like power brakes. I'll check the Hg tonight. I do have a Jegs canister and a lumpy cam. It my well be thats all I'm going to get.

The truck had PB when I got it so I dont know for sure if it was added but I suspect it was.

[MusicMan70]

Here's a link from CPP with info...


http://www.classicperform.com/TechBo...hoot.htm#pedal

[Autoblueprint]

Originally Posted by 1970 CST Short Wide

What is the correct way to adjust the power brake booster push rod?

Another member had the same question. Check out my reply with factory service manual illustration at thread:

http://67-72chevytrucks.com/vboard/s...d.php?t=460923

[Ryan5O]

If your confident you installed correctly, I would make sure there's no air in the lines. If that doesn't resolve it, I would swap out the booster. Even though its holding a vacuum, it could have bad internals. If the truck was stopping fine w/out the booster, is it safe to assume that the master cylinder is fine? I'm adding power to my truck next week; curious to see what your problem is.

[slikside]

subscribed

[1970 CST Short Wide]

Originally Posted by Autoblueprint

Another member had the same question. Check out my reply with factory service manual illustration at thread:

http://67-72chevytrucks.com/vboard/s...d.php?t=460923

My adjustment here is good. Just to be clear I had power brakes with an 11" booster. I replaced it with a 8" booster and new master. Bench bleed it and adjusted all brakes. It stops the truck it just dosnt feel like power it takes too much leg pressure on the pedal if that makes since. I still need to see what my Ng is which could be the whole problem I'm thinking?????????????

[Ryan5O]

Any luck?

[1970 CST Short Wide]

Talking with a buddy and told him I didn't use the proportioning valve that came with the unit, I used my old one. He said that could make a difference?????. I'll plumb the new valve in tomorrow and let you know if it fixes it.

[1970 CST Short Wide]

Originally Posted by 1970 CST Short Wide

Talking with a buddy and told him I didn't use the proportioning valve that came with the unit, I used my old one. He said that could make a difference?????. I'll plumb the new valve in tomorrow and let you know if it fixes it.

Well that didn't make any difference. It still doesn't feel like power brakes. Done for the day I'm going to bleed the hell out of the system AGAIN tomorrow just on the off chance that will help. I'm at a real lose here Guys, don't know what else to do except change back to the old booster and Master

HELP

[MusicMan70]

You did mention you had a lumpy cam and that you went to a smaller booster(11 to 8). As stated previously by Murph; you need at least 18 inches of vacuum for the booster to work properly. Is the 8 inch booster a dual diaphram type?
I did an upgrade on a 61 GMC V-6. It too did not stop as well as I thought it should. I had more than enough vacuum, or so I thought but...I added a vacuum reservoir and vacuum pump to boost it anyways. Still wasn't happy with it.
I changed out my dual diaphram S-10 booster, for a power drum brake unit from a 1970 GMC; master cylinder and Booster. Turns out, I may not have Bench bled the first master cylinder properly because that pedal feels 100% better. My two cents....

[1970 CST Short Wide]

I checked my vacuum and at idle get only ~8 at 1000 rpm it goes to ~16 and holds that in the canister. So at first push I get the ~16 so I believe I have enough vacuum???? I did bench bleed but at this point will do it again and then bleed the hell out of the whole system. That's today's plan , I'll let you know the outcome later. I don't give up easy.

[1970 CST Short Wide]

OK I'm happy now. I re-bench bled the Master on the truck and found a bit of air. I then bled the whole system AGAIN. I also put hose clams on the vacuum hoses just in case. With the canister if you rev up a bit you'll get ~16-18 Hg for the 1st push of the pedal if you are on and off the brakes with out revving up, the pedal gets real hard so If I'm in stop and go traffic it will suck other wise it stops real nice, just have to make sure the canister is full.

[Murphy IRE]

In the finishing stages, Here is a pic. The canister is behind the booster and the pump is in the forefront. The pressure valve and relay are behind the pump. I just have to finish the electrical and hook up the vacuum lines. But I'm wondering about the tee connection to the original vacuum line from the carb. I can't find a 3/8" check valve any where. I was thinking of "teeing" in for redendancy (back-up) if the pump fails. At least that way, I'll still have 11-13 inches of Hg.
So, if I "Tee" straight into the old line, will that affect the current vacuum to the engine? The only check valve that I can find is a small Dorman (#47149 1/4" x 1/8"). If I install that, I will have to "Gerry rig" the conections( No big deal. Last question, which way should I set the one way valve?

[1970 CST Short Wide]

Where did you get the pump and how many $'s did you have to give up. I'm real courious to see what that pump does for you with out going into the old line. You dont need to tee in right? you just want to for back up. I dont know how that might affect things. One way to find out , hook it up both ways and what works best. Let me know

[MusicMan70]

Hey Murph....

Nice clean installation. Have you hooked up the electrics yet? I had a different style pump and it was very nice; built in relay and vacuum level sensor and no switch need but too noisy. I did it from Summit but I contacted the manufacturer directly and they told me not to "T" the connection. Just plug it in direct or the way you have it with the reservoir in line.

[Murphy IRE]

Not yet! I'm hoping to finish in the next week. I had a hard time locating the 3/8" one way valve. That's the secret to the "Tee". I couldn't find one for a USA car. Dorman only makes a 1/8 x 1/4" valve. So I located one from VW and Mercedes. They call it a brake booster check valve. I got one from a salvage vehicle. I checked it and it works just fine. As soon as I'm done, I post the results. The photo doesn't show the shut off solenoid/valve, but it will cycle the pump off when the canister is full. With my flow masters, I will probably only hear the pump at a stop.

[1970 CST Short Wide]

Where did you get the pump and how many $'s did you have to give up ?????????????????

[MusicMan70]

I believe he got it off of Ebay?!! I've seen similar from Summit and CPP I believe. The pricing range is about $225 and more. Here is a link to one I used...Canadian Made; no switch or relay necessary, just connect two wires and hook up to the Brake Booster.
$300 from Summit...

http://cvrproducts.com/12-volt-billet-electric/

[Murphy IRE]

AARRRAAAUUUGGGHHH!!
Everything is hooked up and working. It is only minimal improvement. I went straight from the vacuum/canister into the booster and the performance of the brakes dropped way off. The vacuum is pulling 20", but it must need more volume. So, I "Tee'd" back into the line. The first hit on the pedal is delivering more stopping. When I pump the pedal, it isn't as effective. Looking back, I have replaced everything except for the portioning valve and the booster. The PO indicated that the booster had been replaced. When I bought the truck, the breaks were really bad. One of these days...

[1970 CST Short Wide]

Originally Posted by Murphy IRE

AARRRAAAUUUGGGHHH!!
Everything is hooked up and working. It is only minimal improvement. I went straight from the vacuum/canister into the booster and the performance of the brakes dropped way off. The vacuum is pulling 20", but it must need more volume. So, I "Tee'd" back into the line. The first hit on the pedal is delivering more stopping. When I pump the pedal, it isn't as effective. Looking back, I have replaced everything except for the portioning valve and the booster. The PO indicated that the booster had been replaced. When I bought the truck, the breaks were really bad. One of these days...

If it will help you out you can have my old booster, I'll send it to you for shipping cost. Its an 11" and worked fine I wanted a smaller one to clear my valve covers on the BB. Let me know if you want it and well work out the details later
I know how frustrating this can be