Posted By: 68red440
repro Bendix-style brake booster issue - 04/05/14 02:51 PM
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
Posted By: 6PakBee
Re: repro Bendix-style brake booster issue - 04/05/14 02:58 PM
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?????
Posted By: DAYCLONA
Re: repro Bendix-style brake booster issue - 04/05/14 03:02 PM
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
Posted By: 68red440
Re: repro Bendix-style brake booster issue - 04/05/14 04:17 PM
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".
Posted By: 68red440
Re: repro Bendix-style brake booster issue - 04/05/14 04:22 PM
I agree, a new check valve would be worth trying. Thanks
Posted By: 68red440
Re: repro Bendix-style brake booster issue - 04/05/14 06:35 PM
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.
Posted By: 68red440
Re: repro Bendix-style brake booster issue - 04/05/14 07:24 PM
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!
Posted By: 68red440
Re: repro Bendix-style brake booster issue - <resolved> - 04/06/14 05:04 AM
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.
Posted By: 6PakBee
Re: repro Bendix-style brake booster issue - <resolved> - 04/06/14 02:25 PM
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.
Posted By: 68red440
Re: repro Bendix-style brake booster issue - <resolved> - 04/06/14 07:02 PM
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.
Posted By: 68red440
Re: repro Bendix-style brake booster issue - <resolved> - 04/06/14 08:12 PM
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.
Posted By: 71birdJ68
Re: repro Bendix-style brake booster issue - <resolved> - 04/06/14 09:38 PM
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.
Posted By: 68red440
Re: repro Bendix-style brake booster issue - <resolved> - 04/07/14 01:05 AM
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.
