Yeah, sounds like you can’t afford a lick of vacuum leakage and easy enough to check. There are options on how to preserve vacuum more and less. I installed a reserve canister, rather inexpensive to do finding a nice-hidden spot for it below the battery tray. They aren’t good for much reserve, but in my case with a mild cam, a couple inches was all I was looking for. Lol, don’t ask me if I think this is/was a deal breaker. I had so many hassles with getting my conversion right (root cause issue) there wasn’t much I wasn’t going to try. It was compounded by converting manual to power as well.
Brake issues
- Thread starter TheCouzin
- Start date
New booster is the way. I went through this on my car. Also running Wilwood front disc, stock rear drum. I tried 15/16" MC and 1-1/8" MC. The 15/16" had the pedal travel too low to the floor. Once I got the correct booster (8" dual diaphragm as posted above), with the 1-1/8" MC, pedal travel was fine and stopping power was DRASTICALLY improved. Pedal feel is very light, almost too light, so I would not want to go with a 1" MC with this setup and make it even more so. Change one part at a time and a booster change is my recommendation. It was the last thing I changed in my brake saga and I wish it had been the first.
By the way, even though the 1" MC generates more pressure, the Wilwood discs require a bit more fluid that the 1-1/8" provides (so I was told). I also cannot believe how much effect the vacuum booster has on pedal feel. After installing the new booster, make sure you use feeler gauges or the H-shaped adjustment tool to set the booster pushrod to MC engagement to .050". Incorrect adjustment of this gap greatly affects pedal sensitivity and proper function.
By the way, even though the 1" MC generates more pressure, the Wilwood discs require a bit more fluid that the 1-1/8" provides (so I was told). I also cannot believe how much effect the vacuum booster has on pedal feel. After installing the new booster, make sure you use feeler gauges or the H-shaped adjustment tool to set the booster pushrod to MC engagement to .050". Incorrect adjustment of this gap greatly affects pedal sensitivity and proper function.
tjdriscoll
Member
I'm having the same issue here with my brake setup. I have soft pedal travel and no panic stopping capability. The car will roll to a stop eventually but it almost feels like it has to build pressure to eventually stop. I've bled everything multiple times in the right order with both a vacuum bleeder and the pump and bottle method. I've probably gone through more than a gallon of brake fluid at this point bleeding the system. Triple checked all fittings, no leaks. Could it still be air?? I've heard the calipers can be a nightmare to fully bleed. I'm looking at trying a different master cylinders from other posts I've read here (1 1/32" - 15/16) to find my right combo.
Setup:
- Otherwise stock 440 engine and cam making 18" vacuum
- Wilwood 4 piston calipers up front on 10" rotors (Stage 2 Plus kit)
- Wilwood 1 1/8" Master Cylinder (pin adjustment was checked when I removed the master to re-bench bleed)
- Bendix style dual-diaphram booster purchased from Dr. Diff
- 1 piece proportioning valve (texas valve) purchased from Dr. Diff
- 10" rear drums with brand new hardware
- 7/8" small bore wheel cylinders for rear drums purchased from Dr. Diff
- All brake lines and hoses are brand new.
Setup:
- Otherwise stock 440 engine and cam making 18" vacuum
- Wilwood 4 piston calipers up front on 10" rotors (Stage 2 Plus kit)
- Wilwood 1 1/8" Master Cylinder (pin adjustment was checked when I removed the master to re-bench bleed)
- Bendix style dual-diaphram booster purchased from Dr. Diff
- 1 piece proportioning valve (texas valve) purchased from Dr. Diff
- 10" rear drums with brand new hardware
- 7/8" small bore wheel cylinders for rear drums purchased from Dr. Diff
- All brake lines and hoses are brand new.
TheCouzin
Member
***UPDATE***
So I checked manifold vacuum its at 9" hahaha. There is a reserve vacuum tank but I dont think 9" would bring down the reserve tank enough. Also checked the booster and its not holding vacuum for very long. Soooo. Ill order a vacuum pump to wire in and probably a booster.
Does that sound right to all you veterans?
All your help is greatly appreciated.
So I checked manifold vacuum its at 9" hahaha. There is a reserve vacuum tank but I dont think 9" would bring down the reserve tank enough. Also checked the booster and its not holding vacuum for very long. Soooo. Ill order a vacuum pump to wire in and probably a booster.
Does that sound right to all you veterans?
All your help is greatly appreciated.
You may have done this, but don’t think you mentioned it – bleed the MC? ONLY way to get any trapped air out of it. Bleeding the brakes alone won’t do it. looking at all the posts, tons has been covered, though if you are converting to power from manual, there’s what’s called ‘pedal ratio’. In many older rides, the pedal arm has two holes for connecting the linkage, if recall the top is for manual and the lower for power. This was one of the hassles I encountered having to machine a new rod. May not be relevant, though since my setup wasn’t fully compatible this was among the – hassles. They included my rear drums being maxed out and getting new ones, rears need to be adjusted of course.
As Ron H says, did you bleed the MC? If so, all should in theory be working correctly. The 1-1/8" MC should be fine - same as my car, except I'm running a Raybestos Blue. After installing MC and booster, did you set the MC pushrod gap to .050"?
tjdriscoll
Member
Yes. MC was gapped using the "H" tool and verified with feeler gauge. MC was bench bled twice, and bled again after bolting back on the car.
Sixpactogo
Well-Known Member
The Dual diaphragm booster will be a big improvement. Not so sure about 9" of vacuum. If you can double it somehow I think you will be Okay.
With a race engine maybe manual brakes are the ticket.
With a race engine maybe manual brakes are the ticket.
Geoff 2
Well-Known Member
9" of vacuum is iffy.......
A vacuum canister does NOT increase vacuum, it only stores it. In this case, 9", so will still have 9" of vac. If the low vacuum is due to a big cam, then the engine needs a LOT of idle timing, perhaps 40+*. If the current timing is 10-15*, then increasing the timing to what the engine wants could add 2-3* of timing, with no other changes.
A vacuum canister does NOT increase vacuum, it only stores it. In this case, 9", so will still have 9" of vac. If the low vacuum is due to a big cam, then the engine needs a LOT of idle timing, perhaps 40+*. If the current timing is 10-15*, then increasing the timing to what the engine wants could add 2-3* of timing, with no other changes.
TheCouzin
Member
Greatly appreciated! When I get some time I will add some timing to it to see if I can get enough. Haha I've been thinking of just going to manual brakes now. But would still like to mess around a bit. That's how you learn.
Again thank you for the reply and any info is awesome.
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