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repro Bendix-style brake booster issue #1603322 04/05/14 10:51 AM 04/05/14 10:51 AM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	I installed the new reproduction dual tandem brake booster/MC/rod assembly in my '68 Coronet. The MC was bled while in the car using the manual method. Engine was started and I have no pedal. When shutting off the engine I hear hissing on the cabin side of the booster. After a few seconds when the hissing stops, presumably when pressure equalizes in the booster, the pedal is rock hard. I repeated this 3 times and noticed the same result. The Ram Man has been helpful and responsive until I noticed this issue last weekend. I need to know if the booster needs to come out or if it's something minor like replacing the check valve. With winter behind us it's killing me not being able to take it out for a drive. Thanks

Re: repro Bendix-style brake booster issue [Re: 68red440] #1603323 04/05/14 10:58 AM 04/05/14 10:58 AM
Joined: Jan 2003 Posts: 10,714 North Dakota 6PakBee I Live Here
6PakBee I Live Here Joined: Jan 2003 Posts: 10,714 North Dakota	First, what do you mean by "have no pedal"? Goes to the floor without resistance but with brakes, goes to the floor without resistance with no brakes, goes to the floor with resistance but with brakes, goes to the floor with resistance with no brakes, doesn't move at all????? "We live in a time when intelligent people are being silenced so that stupid people won't be offended".

Re: repro Bendix-style brake booster issue [Re: 68red440] #1603324 04/05/14 11:02 AM 04/05/14 11:02 AM
Joined: Dec 2007 Posts: 18,157 Mass DAYCLONA I Live Here
DAYCLONA I Live Here Joined: Dec 2007 Posts: 18,157 Mass	Start with the easiest possible solution, the check valve, buy a quality unit, a lot of the cheap aftermarket check valves either don't work right out of the box or fail shortly there after...DAMHIK

Re: repro Bendix-style brake booster issue [Re: 6PakBee] #1603325 04/05/14 12:17 PM 04/05/14 12:17 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	By having "no pedal" I mean it goes to the floor with no resistance. Before putting it in the car, I removed the MC from the booster to verify ~.030" clearance between the adjustable rod & MC piston. I also planned to bench bleed the MC, but later decided to do it in the car. I then noticed the disclaimer saying not to remove the MC from the booster because it needs tension otherwise it'll break a seal inside. It seems that disclaimer would only apply after it's been in the car and the engine run because what do people do if they only buy the booster or only replace the MC? Also, the rod had clearance with the MC piston so I can't see how that could've ruined it. Anybody install one of these new units? They flow 7% more air and "may require enlarging the hole in the firewall" to eliminate linkage interference. The sketch shows as much as an 1/8" being removed. I had to grind off 1/4".

Re: repro Bendix-style brake booster issue [Re: DAYCLONA] #1603326 04/05/14 12:22 PM 04/05/14 12:22 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	I agree, a new check valve would be worth trying. Thanks

Re: repro Bendix-style brake booster issue [Re: 68red440] #1603327 04/05/14 02:19 PM 04/05/14 02:19 PM
Joined: Jan 2003 Posts: 10,714 North Dakota 6PakBee I Live Here
6PakBee I Live Here Joined: Jan 2003 Posts: 10,714 North Dakota	Quote: By having "no pedal" I mean it goes to the floor with no resistance..... So you have no brakes? First thing I would think would be to bleed the brakes. I'm afraid though that won't be the end of your problems. The hissing sound you hear is ambient air being admitted to the rear portion of the booster to get the booster to move forward. I'm guessing you have a defective booster. But first things first. "We live in a time when intelligent people are being silenced so that stupid people won't be offended".

Re: repro Bendix-style brake booster issue [Re: 6PakBee] #1603328 04/05/14 02:35 PM 04/05/14 02:35 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	Brakes were bled prior to firing the engine. The pedal is hard when the engine is off. When the engine is on, the pedal has no resistance and easily pushes to the floor. Yes, I believe air is being sucked into the booster when I turn the engine off. Since air should not pass through the back of the booster, the booster is probably bad. Not sure how or why at this point.

Re: repro Bendix-style brake booster issue [Re: 68red440] #1603329 04/05/14 03:24 PM 04/05/14 03:24 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	Holy crap these brakes grab hard! Apparently the brake assist was helping so much with the pedal feel that I thought I had no brakes when idling in park. With the rear wheels off the ground I ran it through the gears and found the brakes actually were working. I drove it around the neighborhood and it feels like it has hydroboost! Time for some road tests!

Re: repro Bendix-style brake booster issue [Re: 68red440] #1603330 04/05/14 05:40 PM 04/05/14 05:40 PM
Joined: Jan 2003 Posts: 10,714 North Dakota 6PakBee I Live Here
6PakBee I Live Here Joined: Jan 2003 Posts: 10,714 North Dakota	Quote: .....Yes, I believe air is being sucked into the booster when I turn the engine off. Since air should not pass through the back of the booster, the booster is probably bad. Not sure how or why at this point. The air inlet into the booster is at the rear of the booster around the pushrod. When you press the brake pedal air is admitted into the rear half of the booster. But it shouldn't be leaking when the brakes are released. Just a question, are you sure the booster pushrod is fully extended with the pedal at rest? You see what I'm getting at? "We live in a time when intelligent people are being silenced so that stupid people won't be offended".

Re: repro Bendix-style brake booster issue [Re: 6PakBee] #1603331 04/05/14 07:11 PM 04/05/14 07:11 PM
Joined: Dec 2007 Posts: 18,157 Mass DAYCLONA I Live Here
DAYCLONA I Live Here Joined: Dec 2007 Posts: 18,157 Mass	Quote: Quote: .....Yes, I believe air is being sucked into the booster when I turn the engine off. Since air should not pass through the back of the booster, the booster is probably bad. Not sure how or why at this point. The air inlet into the booster is at the rear of the booster around the pushrod. When you press the brake pedal air is admitted into the rear half of the booster. But it shouldn't be leaking when the brakes are released. Just a question, are you sure the booster pushrod is fully extended with the pedal at rest? You see what I'm getting at? I hope the OP adjusted the booster to master cylinder clearance gap (generally no more than .060 max) before installing his master? 8102678-boostergap.JPG (112 downloads)

Re: repro Bendix-style brake booster issue - <resolved> [Re: DAYCLONA] #1603332 04/06/14 01:04 AM 04/06/14 01:04 AM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	Before installing, I measured a gap of ~.030. I drove it a lot today, and am really happy with it. It's working way better than I expected! The pedal feel is so different from what I was used to. So I assumed there was something wrong, but there wasn't. Huge relief. Thanks for the input.

Re: repro Bendix-style brake booster issue - <resolved> [Re: 68red440] #1603333 04/06/14 01:56 AM 04/06/14 01:56 AM
Joined: Dec 2007 Posts: 18,157 Mass DAYCLONA I Live Here
DAYCLONA I Live Here Joined: Dec 2007 Posts: 18,157 Mass	Quote: Before installing, I measured a gap of ~.030. I drove it a lot today, and am really happy with it. It's working way better than I expected! The pedal feel is so different from what I was used to. So I assumed there was something wrong, but there wasn't. Huge relief. Thanks for the input. I usually run the dual diaphram Bendix booster on my Mopars, along with 4 wheel discs....pedal feel is drastically different than the single diaphram Midland/Chrysler boosters...my pedal travel with the dual diaphram Bendix and 4 wheel discs is approx 1/2" when the pads are fresh, and 3/4" when the pads are about 1/2 worn, but the pedal/power assist is impressive with the Bendix, but it is a vacuum hog! Glad your system is A-OK! Mike

Re: repro Bendix-style brake booster issue - <resolved> [Re: DAYCLONA] #1603334 04/06/14 10:25 AM 04/06/14 10:25 AM
Joined: Jan 2003 Posts: 10,714 North Dakota 6PakBee I Live Here
6PakBee I Live Here Joined: Jan 2003 Posts: 10,714 North Dakota	Glad to hear it seems to be okay. Not trying to be a wet rag here but keep an eye on it. That hissing sound from the air inlet still doesn't seem right. "We live in a time when intelligent people are being silenced so that stupid people won't be offended".

Re: repro Bendix-style brake booster issue - <resolved> [Re: 6PakBee] #1603335 04/06/14 03:02 PM 04/06/14 03:02 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	You're absolutely right 6PakBee. Even though the brakes work great, the hissing of air into the back of the booster needs to be corrected. It's acting like a small, controlled vacuum leak on the engine. The push rod gap was .030 prior to installation, but the gap AFTER installation is what matters. When I push the pedal in ~1/8", the hissing goes away which tells me my pushrod gap is too large. When installing the booster with the 4 nuts on the cabin side, I partially compressed the new white foam gasket. I was careful not to over tighten the nuts, but maybe they need to be a little tighter. That would draw the booster back to the firewall. If I draw the booster back another 1/16" (compressing the gasket a little more), it should close the pushrod gap by the same amount. A 1/16" at the linkage would translate to more than 1/8" at the pedal. When it stops hissing I'll consider it good. The pedal feel and travel is good as it is, but if the brakes start actuating a little higher in the pedal travel that'd be even better. If tightening the nuts isn't enough, I'll pull the master and adjust the rod. I'll let you know what happens. Seriously, these brakes feel like hydroboost. They're really sensitive like the new Darts that I've test driven recently.

Re: repro Bendix-style brake booster issue - <resolved> [Re: 68red440] #1603336 04/06/14 04:12 PM 04/06/14 04:12 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	Correction: Compressing the gasket doesn't affect push rod gap. If anything, it moves the pedal a small amount. The gasket did compress from all the activity, so the nuts needed snugging up anyway. I need to pull the MC from the booster and extend the push rod to close the gap to ~.020. However, the instructions clearly say not to remove the MC from the booster because it can ruin a seal inside. I'll ask The Ram Man about how to do it without potentially voiding the warranty. As long as vacuum isn't applied to the booster with the MC off, it should be OK. Thanks for your help.

Re: repro Bendix-style brake booster issue - <resolved> [Re: 68red440] #1603337 04/06/14 04:22 PM 04/06/14 04:22 PM
Joined: Dec 2007 Posts: 18,157 Mass DAYCLONA I Live Here
DAYCLONA I Live Here Joined: Dec 2007 Posts: 18,157 Mass	Quote: Correction: Compressing the gasket doesn't affect push rod gap. If anything, it moves the pedal a small amount. The gasket did compress from all the activity, so the nuts needed snugging up anyway. I need to pull the MC from the booster and extend the push rod to close the gap to ~.020. However, the instructions clearly say not to remove the MC from the booster because it can ruin a seal inside. I'll ask The Ram Man about how to do it without potentially voiding the warranty. As long as vacuum isn't applied to the booster with the MC off, it should be OK. Thanks for your help. Horse puckey just remove the master, no need to remove the lines, leave the cover on, the pushrod will/should have a threaded snout, you need to grip the main rod sticking out, and turn the threaded insert in/out for the desired gap, use a set of dial calipers,to measure the depth of the master's bore, and then measure how much rod sticks out from the boosters/master's mounting face and adjust appropriately

Re: repro Bendix-style brake booster issue - <resolved> [Re: 68red440] #1603338 04/06/14 05:38 PM 04/06/14 05:38 PM
Joined: Feb 2012 Posts: 4,452 Morristown Tn. 7 71birdJ68 master
71birdJ68 master 7 Joined: Feb 2012 Posts: 4,452 Morristown Tn.	I have a question. Where is your pedal? Is it down close to the gas pedal, where it belongs, or up almost half way to your knee? I have a reason for asking this.

Re: repro Bendix-style brake booster issue - <resolved> [Re: 71birdJ68] #1603339 04/06/14 09:05 PM 04/06/14 09:05 PM
Joined: Dec 2003 Posts: 329 Cincinnati, OH 6 68red440 OP enthusiast
68red440 OP enthusiast 6 Joined: Dec 2003 Posts: 329 Cincinnati, OH	Pedal position is even with the gas pedal. The pedal assembly is original to the car. It actuates the brake light switch properly. I'll adjust the push rod and move on to the next project.

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