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I have a question. I converted my OEM drum brakes to factory-style discs all around. Before the engine swap the car stopped extremely well for what the brakes were. Now, with the new engine and aggressive cam, the brakes SUCK. Like, manual brakes would do better. It's scary.
I know it has to do with the difference in engine vacuum with the large cam, etc.
First of all, what proportioning valve do you have?
This could be a huge deal and you may still have a residual pressure valve on the front discs brake line(s)which you don’t want or need with discs.
You will likely need a proper front disc/rear drum proportioning valve like factory would have installed.
Is the bore of your master cylinder a good match for your calipers and wheel cylinders or the wrong size?
Bigger is not better on bore size if you can’t get proper pressure to your calipers without excessive pedal pressure.
Second, check to see that you have a good one way vacuum check valve on or going to the booster where you hook into the main vacuum source.
Also, get a vacuum reservoir can to hook in line or an electric vacuum pump if your engine vacuum won’t run the brake booster.
Does it just suck for stopping because of caliper force or It feels like your pads aren’t doing anything? Or the pedal is bad no matter how much you bleed It?
Your pads may be made of chinesium dust, which is not a good friction material.
First of all, what proportioning valve do you have?
This could be a huge deal and you may still have a residual pressure valve on the front discs brake line(s)which you don’t want or need with discs.
You will likely need a proper front disc/rear drum proportioning valve like factory would have installed.
Is the bore of your master cylinder a good match for your calipers and wheel cylinders or the wrong size?
Bigger is not better on bore size if you can’t get proper pressure to your calipers without excessive pedal pressure.
Second, check to see that you have a good one way vacuum check valve on or going to the booster where you hook into the main vacuum source.
Also, get a vacuum reservoir can to hook in line or an electric vacuum pump if your engine vacuum won’t run the brake booster.
Does it just suck for stopping because of caliper force or It feels like your pads aren’t doing anything? Or the pedal is bad no matter how much you bleed It?
Your pads may be made of chinesium dust, which is not a good friction material.
Did you try to bed the brakes in?
Hello,
Thanks for the reply.
1. I have this proportioning valve, for disc/disc as I have disc brakes all around:
2. How do I know if I have a residual pressure valve on the front discs? I'm somewhat new to this - but the disc brakes worked great before the engine swap - so I figured it was vacuum related.
3. OK, yeah the pedal is firm but I have to really press on it hard for the car to stop, and even then it feels like I have manual brakes. It does not stop well at all now - before the disc brakes were very nice actually.
4. I bed the brakes in, yes. The pedal feels ok, a bit firm, but nothing happens and I can just tell the pads aren't grabbing the discs like they used to - but I'm sure getting a lot of brake dust now which doesn't make sense either...?
5. I'm thinking of getting better pads for the front calipers than what with the kit came with, but other members on here said they also use this kit with good results.
2. How do I know if I have a residual pressure valve on the front discs? I'm somewhat new to this - but the disc brakes worked great before the engine swap - so I figured it was vacuum related.
3. OK, yeah the pedal is firm but I have to really press on it hard for the car to stop, and even then it feels like I have manual brakes. It does not stop well at all now - before the disc brakes were very nice actually.
4. I bed the brakes in, yes. The pedal feels ok, a bit firm, but nothing happens and I can just tell the pads aren't grabbing the discs like they used to - but I'm sure getting a lot of brake dust now which doesn't make sense either...?
5. I'm thinking of getting better pads for the front calipers than what with the kit came with, but other members on here said they also use this kit with good results.
The problem is lack of vacuum. When I installed 463 I had to switch to 9" booster to clear the valve covers. My brakes felt like crap, it felt like I was trying to push the pedal through the floor just to stop completely at a stop sign. They were fine before I replaced the booster.
I've tried different boosters, dual diaphragm etc, nothing worked. Installed hydro boost and it brakes better than ever. Hands down best upgrade I've done to the brakes.
What are you running for rear brakes ? How much engine vacuum do you have ? All our cars (Trans Ams) have been converted to hydroboost.
If you are using the screw actuated rear parking brake all in one calipers those are extremely fussy and cause hard pedal issues. Many aftermarket systems used these and common now that china is mass producing them. They sucked on the 79-81 trans ams and like to know what rear discs you have. The best kits come from Kore3 (17” wheels needed) or get a kit from scarebird. Tobin at Kore3 is probably one of the best brake guys I have used and his stuff isn’t cheap, but works great
The problem is lack of vacuum. When I installed 463 I had to switch to 9" booster to clear the valve covers. My brakes felt like crap, it felt like I was trying to push the pedal through the floor just to stop completely at a stop sign. They were fine before I replaced the booster.
I've tried different boosters, dual diaphragm etc, nothing worked. Installed hydro boost and it brakes better than ever. Hands down best upgrade I've done to the brakes.
Do you have a link to the hydroboost system you have?
Originally Posted by olds403
What are you running for rear brakes ? How much engine vacuum do you have ? All our cars (Trans Ams) have been converted to hydroboost.
If you are using the screw actuated rear parking brake all in one calipers those are extremely fussy and cause hard pedal issues. Many aftermarket systems used these and common now that china is mass producing them. They sucked on the 79-81 trans ams and like to know what rear discs you have. The best kits come from Kore3 (17” wheels needed) or get a kit from scarebird. Tobin at Kore3 is probably one of the best brake guys I have used and his stuff isn’t cheap, but works great
This is the rear end I have - purchased with the optional "11" Disc Brakes w/ Park Brake [+$69.00]"
I put mine together my self. Pulled one out of a Suburban, modify the pushrod to bolt on universal GM clevis pin, Aeroquip lines. Not that hard to do. All together I have about $200 in it.
what do the rear calipers look like. I know QP as I have his posi/rebuid kits my self
70 Cutty - Kore3 sells Hydratech as part of his packages. I have a complete Kore3 with Hydratech all from Tobin.
what do the rear calipers look like. I know QP as I have his posi/rebuid kits my self
70 Cutty - Kore3 sells Hydratech as part of his packages. I have a complete Kore3 with Hydratech all from Tobin.
Seriously, what's your vacuum reading at idle and in gear?
Wait, wait. Just looked at that Summit page. Is that a single 9" booster? TONS of vacuum for those to work well. Since the engine is a small block you should have plenty of room to go back to an 11" converter. Or you can try a dual diaphragm 9".
Regardless, the pedal should feel pretty firm with the engine off. If the pedal is still spongy or can easily get to the floor then you still have air in the system. Bleed, bleed, and bleed again. Hint - the Earl's Solo Bleeds are simply magical.
Hydroboost is a good option, but the swap can be pretty involved. I went that route years ago and don't regret it, but I've been tweaking it ever since. Still have a lot of noise - the unit can resonate with the pump pulses and use the firewall as a speaker. You have to be careful on the plumbing due to the pressures. There's ways to patch together OE hoses from various places, or you can use the Aeroquip teflon or High Pressure hose - both rated to 2,000 psi.
There's a seller on ebay -sterlingworth..something - that sells units with brackets, just search for "chevelle hydroboost". The Chevelle stuff is the same as Cutlass for most years. I've bought stuff from him - good guy.
Good morning! I also agree with Battenrunner.....I installed this particular electric vacuum pump (see link below) on my 550HP 455 engine because of my high performance camshaft and the brakes pump up nicely now. It's got a very nice pedal and you can't really hear these new style pumps. It was a great addition to my resto and keeps things neat and clean in the engine compartment. Here's a pic of mine and where I installed it on my resto. They cycle as needed and compensate for the low engine vacuum issues. Good luck.
What does the back of caliper look like ? Where is the ebrake ? That is what i am trying to understand. Drum in hat ?
What I suggest is put a pressure guage on each caliper. I bought a gauge from mp brakes when i was fighting this on a trans am, Then that led me to the hydroboost/kore3/hydratech system. I agree with the post above hydroboost has its own quirks and spent a fair amount on custom hoses and a dual return pump. Works.
Thanks for the help everyone. Seems like we have all the information needed besides what my vacuum is at idle. I'm confident that is the issue since it started with the new engine w/ more aggressive cam.
I'll report back when I have that information and anything else that may be applicable.
Seriously, what's your vacuum reading at idle and in gear?
Wait, wait. Just looked at that Summit page. Is that a single 9" booster? TONS of vacuum for those to work well. Since the engine is a small block you should have plenty of room to go back to an 11" converter. Or you can try a dual diaphragm 9".
Regardless, the pedal should feel pretty firm with the engine off. If the pedal is still spongy or can easily get to the floor then you still have air in the system. Bleed, bleed, and bleed again. Hint - the Earl's Solo Bleeds are simply magical.
Hydroboost is a good option, but the swap can be pretty involved. I went that route years ago and don't regret it, but I've been tweaking it ever since. Still have a lot of noise - the unit can resonate with the pump pulses and use the firewall as a speaker. You have to be careful on the plumbing due to the pressures. There's ways to patch together OE hoses from various places, or you can use the Aeroquip teflon or High Pressure hose - both rated to 2,000 psi.
There's a seller on ebay -sterlingworth..something - that sells units with brackets, just search for "chevelle hydroboost". The Chevelle stuff is the same as Cutlass for most years. I've bought stuff from him - good guy.
Originally Posted by Battenrunner
I would try an electric vacuum pump hooked to your booster and see what you think about it before dumping hours and more money into it...
I also strongly suggest some high quality pads once you get the pedal feel right.
Originally Posted by olds403
That is a drum in hat set up. It a good set up. Put a gauge on it. That will tell you.
And this is my booster/set up. 9-in. Some say an 11in would help out and others say larger booster is worse for low volume? I'm a novice on braking systems...
Yeah you've got the worst possible combination.
Bigger boosters apply more pressure given the same vacuum. It's generally recommended to have 18" vacuum at idle for power brakes, although they'll work fine with big boosters at somewhat lower levels.
A single diaphragm 9", which that appears to be, will provide very little boost even with ample vacuum.
11" vacuum at idle is very low for vacuum brakes.
You can get a dual 8" or dual 9" pretty cheap from Pirate Jack. They're the retailer for MBM, who is the actual manufacturer for most of the muscle car era brake parts out there. A 8" dual is more-or-less equivalent to the stock 11". It'll push the master cylinder forward just a bit. Or you can get an 11". Looks like you don't have a clearance problem.
11" is pretty low. I just added a vane vacuum pump and it was quite easy. Got all the parts off Amazon - generic $70 vacuum pump that's a replacement for, I think, a Ford part, got the vacuum switch/relay for $30, two check valves and an assortment of tees and fittings. Make sure to use actual vacuum brake hose, 11/32".
Yeah you've got the worst possible combination.
Bigger boosters apply more pressure given the same vacuum. It's generally recommended to have 18" vacuum at idle for power brakes, although they'll work fine with big boosters at somewhat lower levels.
A single diaphragm 9", which that appears to be, will provide very little boost even with ample vacuum.
11" vacuum at idle is very low for vacuum brakes.
You can get a dual 8" or dual 9" pretty cheap from Pirate Jack. They're the retailer for MBM, who is the actual manufacturer for most of the muscle car era brake parts out there. A 8" dual is more-or-less equivalent to the stock 11". It'll push the master cylinder forward just a bit. Or you can get an 11". Looks like you don't have a clearance problem.
11" is pretty low. I just added a vane vacuum pump and it was quite easy. Got all the parts off Amazon - generic $70 vacuum pump that's a replacement for, I think, a Ford part, got the vacuum switch/relay for $30, two check valves and an assortment of tees and fittings. Make sure to use actual vacuum brake hose, 11/32".
Thank you for the response.
So a stock 11in or a dual 9in - which would you go with? Looks like either way I'll need to get a new booster in the first place.
I don't think you're going to get enough booster assist with a vacuum booster and 11" of manifold vacuum. Going from a single 8" booster to a single 11" would almost double your booster assist (90% increase). Installing a dual 9" would increase booster assist by 153% assuming 85% efficiency of the booster. The stock 11" booster adds about 684 lbs of assist at the master cylinder with 18" of manifold vacuum. The dual 9" will only put out 586 lbs of assist at 11" of manifold vacuum. That's still 100 lbs short of the stock system.
All of the above calculations assume you are using the power brake hole on the brake pedal arm. You could add more mechanical leverage by using the manual brake hole on the pedal arm but you increase the pedal travel so the pedal will travel further before you get enough pressure. A smaller bore master cylinder will also increase the line pressure to the calipers and wheel cylinders. By my calculations a 1" master cylinder with a dual 9" booster, using the stock power brake hole on the pedal arm would net you a 13% increase in brake line pressure over the stock system.
Hydro-boost may be the better solution and will provide lots of brake force, although it can be too much of a good thing if you have too much assist. Installing a dedicated vacuum pump as suggested previously would be an easier install.
So a stock 11in or a dual 9in - which would you go with? Looks like either way I'll need to get a new booster in the first place.
Dealer's choice. Stick with the dual 9" if you like having the room around the unit like the current one. There's plenty of room with a small block, so either is fine.
Location: Colorado Springs Colorado/Thousand Oaks Ca
Posts: 1,721
Maybe a factory brake booster with the correct camshaft is in order. Its very possible there could be problems with the way the cam was ground, I see this extremely often with the Isky cams, one thing that WILL effect idle vacuum is the relationship from one base circle height to the next base circle height. For reference one of my 228/238 @ .050 cams will idle @ 16 plus inches of vacuum @ sea level, and make 600 plus HP, but again this is 467 Cu in.
VORTEC PRO “For reference one of my 228/238 @ .050 cams will idle @ 16 plus inches of vacuum @ sea level, and make 600 plus HP, but again this is 467 Cu in.” [/QUOTE]
How much vacuum @idle would the same camshaft make in a 434 CID engine?
Anyone have a link to a recommended dual 9 or single 11in booster? Whatever would work best quality-wise.
I chose a dual 9" with a 1" master cylinder from Tuff Stuff. Lots of side clearance to the valve covers, but the dual booster is longer than the single 11" and sticks out a good bit farther than the stock boost/MC combo.
I chose a dual 9" with a 1" master cylinder from Tuff Stuff. Lots of side clearance to the valve covers, but the dual booster is longer than the single 11" and sticks out a good bit farther than the stock boost/MC combo.
Thank you. What engine do you have and how does it work?
I have a small block Olds in a '72 442 convertible so clearance to the valve covers wasn't a big deal to begin with. My manifold vacuum is 17-18" so I have much more booster assist than you, but my brakes are not stock. I have C5 Vette discs on the front and the rear discs are from a '01 Blazer. At 1.59" dia. the apply area of the Vette calipers is smaller than the stock Olds calipers which are almost 2x larger at 2.94" dia. I had to make up for the lost caliper force with a bigger booster and smaller dia. master cylinder. The car is still under construction so I don't have any miles on it, but I hope to get it into the body shop in the next 2 months. The drive train and chassis are complete just waiting on the paint & body work now.
Here's a few pics:
And some pics of the Vette front brakes. Z06 calipers from a C5 Vette. Rotor is 12.8" dia.
Only one I could find that advertises 10-12in of vacuum minimum needed. Mine is 11in at idle.
Thoughts?
I just talked with this company, and they said they use this on lots of their LS builds with only 10in vacuum at idle etc, with great results - that they made this unit specifically for low vacuum builds. Seems like the first, easiest and relatively cheapest route to try first to see if I can get my power brakes to actually work, even if not at OEM levels.
Just curious on everyone else's thoughts on this product?
Electric vacuum pump = problem solved using the setup you currently have. Get the one that 442Dude recommended.
Thanks, looks like that is the way I'm going to go for sure. Hopefully it works well even just directly attached to my little 9in booster.
If it still isn't good enough with the vacuum pump, I'll try an 11in booster with it and go from there. I don't want to get too invasive with a hydro-boost system.
May 15th, 2021, 06:50 AM
