Hi all. I just bought a '55 Bel Air - arranging to have it tranported home. The car has 11" GM Intermediate disk brakes (Chevelle, GTO, etc) with a non-descript 7" power booster, dual master cylinder, and combination valve. The brakes were surprisingly horrible. Car is verging on unsafe to drive - every stop is like a panic stop. Pushing the pedal is like pushing on a brick and the car doesn't like to stop. At all. The brakes stop straight - no pulling to either side and no funny noises from the calipers. In short, it drives like a fully loaded gravel truck on a steep grade. Good thing I work out at the gym! Are any of you running this setup and how well does it work when properly set up? Are the GM Intermediate brakes big enough for a '55? I drove a number of GM A-bodies back in the day and my recollection is with drums they weren't great but with disks they stopped well. I am pretty sure the power brake booster is dead. I thought I heard it hissing when I pressed the brake pedal at a stoplight. I didn't think to hold the brake pedal down then start the car to feel if the booster engaged or not - I will do that when the car is here in my shop. If the booster is working then something is even more wrong with the system, but the brakes don't grind or pull. I have no idea what the booster is, nor does the seller. It was put on the car 12 years ago from unknown origin. What kind of power boosters work well on Tri-fives? There isn't a ton of room over the valve covers (standard hight, motor an inch higher than stock), but I am thinking an 8" booster or an 8" dual booster might be a better setup. Would a 9" fit? Any advice appreciated. I'm still figuring out who the good parts suppliers are for '55 Chevys. The ones I was looking at today are CCP (good rep, mid price), Master Power Brakes (expensive!), Eckler (expensive!), Summit Racing (SSBC kit, summit brackets?), and Pirate Jack (very affordable, but total unknown to me as a supplier). Not looking to trade my life to save a few bucks, but the prices are all over the map and there can't be that many booster manufacturers out there. Another website I came across is chevychevy.com. Anyone do buisness with them? Their prices look good, but no clue who they are. Anyone you know of that I should look at? Thanks in advance for any and all help and/or advice. Thanks!
Hi Welcome to Hamb and sorry to say welcome to problems with braking on a 55 Chevy I would first join chevytalk.com and trifive.com and start to read Get a comfortable chair because there is quite a bit written on this topic When in chevytalk go to forums then to the 55-57 section From there go to 55-57 chevys stock and restored and then go to 55-57 modified,pro street,show and read You can also do a search on those 2 threads When in trifive.com go to 55-56-57 forum section and then go to the superstock/pro street modified section Then go to the suspension questions in the next section You can search trifive as well PM me with your home address and I'll send you some links after supper tonight Some of the brake websites have trouble shooting guides which are invaluable There is so much too learn so read lots and ask lots of questions 7" is probably too small for starters Is your engine producing enough vacuum ? Is the stroke in the m/c long enough ? Is it the correct dia ? Are the brake hoses collapsing Air in the lines Theres a lot of us been thru this so theres a wealth of info available Good luck, keep in touch and pm me your home e mail address Ontario55
MuttonHollow.com is the best place i've found for Tri-five parts. Before I discovered them, I bought a cheapo disc brake kit with drop spindles off of Ebay. Sellers name is Fatrodder. It came with the dual diaphram 7" booster and i couldn't ask it to work any better. I have the 10" rotors and the car stops perfectly. So, i don't think the size of your parts is the problem. I think you have a bad booster. You could have yours rebuilt or maybe a better choice would be to replace it with a dual diaphram unit. My kit also came with the 1" bore Corvette master cylinder. The only draw back to my kit is the booster has brakets to mount it to the firewall and it sticks out to far and looks goofey. Is your engine idling rough? a bad booster can be a vacuum leak. All of my master cylinder and booster parts were ccp that came with the kit. Works great.
A hard pedal on a power brake system is usually a sign of no vaccuum to the booster. But it's rare for a booster to go bad. I'd check the lines that go to it and make sure it's getting vaccuum. That may be the entire problem, either way, I would get that working and see how the brakes are before I changed anything else.
Thanks everyone. You have given me a lot to look at and think about. The car is running pretty well and has an RV cam (high lift short duration) so there should be plenty of vaccuum. I won't know for sure until I can get the car here and measure it with a gauge though. I did check the hoses and didn't see any vaccuum leaks and everything was plumbed correctly. I definintely heard something that sounded like a vaccuum leak from under the dash when I was sitting at a light with my foot on the brake and it stopped when I took my foot off. Suspicious. I checked out the Website Ontario55 recommended - thanks! Great wealth of information there. The prevailing opinion seems to be that the 11" GM intermediate brakes that are on the car should work fine - certainly much better than they do on this car. The other prevailing opinion is that a 7" single diaphram booster is too small. Most folks seem to be running 8" dual. If I have to change boosters I will probably go that route. The origin of the booster is a complete unknown. The master cylinder is also an unknown - no clue what the bore size is. I will probably start investigating from the top down - booster leaks / operation, MC size and operation, then go from there. 50mercfan - thanks for the tip on muttonhollow.com. I will check them out. Ontario55 - I will PM you tonight (assuming it is so simple even a newbie can figure it out!) Rustynewyorker - You may very well be right. First check will be with a vaccuum gauge to see if all is as it appears. Lightning 55
I had a 7" booster on a 56 chev. It wouldn't lock up the brakes no matter hard you pushed the pedal. I bought a 8" dual diaphragm booster from summit and it made all of of the difference in the world. GM intermediate brakes should be fine for a tri 5. My GTO is longer and wider than one. Dave
I'm not an expert, but I've been researching this stuff a lot lately. off the cuff, IMHO a 7" dual is marginal for a tri 5. Dual 8" should be good, dual 9" even better if you can fit it. If you want to go into it further, we need the bore on the MC, pedal ratio, and size of booster you want to use. Also need to know what you're working with vacuum wise. Until you measure it, we're just guessing. I ordered the universal 8" dual dia setup from pirate jack(free shipping this month ) and should get it this week. They seem decent enough to me.
When I tried an aftermarket 8" dual diaphragm booster I was told they work best with at least 18" of vacumn. I couldn't get the one I had to work on 16" so I went junkyarding and got one out of a late Chev. If you look at the varius models you'll see ones that around 8". After I put that one on my brakes have been fine and that was almost 50,000 mi ago. A friend had new 8" booster from the same company and had the same problem, he changed out to what I now have and eliminated his bad braking also.
I don't run a booster on my wagon and it has no problem stopping. I'm using the Heidt's spindles and disc kit. When the pedel starts to get soft it's time to adjust the rear drums. The booster won't make the stopping distance any shorter it just makes your leg do less effort.
I second the site Chevytalk.com They have a section for stock, and one for modified, tri 5`s. I have gotten much help there in the past...
I don't run a power booster with disc brakes and it stops very easily. I did have a problem that sounded much like your and it ended up just needing the rear drums to be adjusted by hand. I always thought they were supposed to self adjust when you go in reverse and stomp the brakes. Not the case with mine. Good luck.
I also have a manual master cylinder and 11" chevelle brakes on my 57 and it stops well. I think the booster is your isue.
I run a Master Power 8" booster which 'Just' fits with my BBC. Car stops very well, I believe I have the 1 1/8 bore MC, with 10.5" disks and Ford big car drums on the back. Been running this set up for about 12 years. I concur with others that it is probably either a servo that is too small or faulty. Again, another vote for Chevytalk! P.
That's the same booster my friend and I both replaced with junkyard stuff in order to have good brakes. For the record they were both 8" dual diaphram new right from MPB
Had very similar results with 7" boosters. They require a lot of engine vacuum and a non-power brake pedal ratio to work properly. The original inteded purpose was for the underfloor applications on early cars and their stock pedal systems. Annother avenue to explore, pull the master loose from the booster and measure the bore. If the internal bore is 1 1/8" it is too big. You need a 1" bore master for the combination of parts you have.
Phatrat what booster did you end up using? That's why I asked him how much vacuum he had, because if it was only 15 or 16 my suggestion would be to get a 9" dual new or a big 11" new or junkyard to compensate for that. I'd toss that dual 7" right off a cliff unless money is super tight. Word on the street is that the offshore(read: probably all) of the generic boosters don't produce as much boost as the factory ones, even when they're supposedly the same size, like dual 8". Someone smarter than me broke it down why exactly but it was over my head. My other thought is with elpolacko if he's running a 1 1/8 drop it to 1" and it'll really bring up that pressure. But it's all just good general advice unless we have more info on his setup, can't run the numbers with out the numbers And scott 55 brings up antoher good point, I always say first thing to adjust the shit outtta your drum brakes before you do anything else. Might just get lucky and fix it, but at least then you don't have that in the equation to worry about. I'm just a hack, so take my opinion for what you paid for it. EDIT: Here's a link to MP brakes tech on how to test for a bad booster
We have non-power dual cylinder setup and front discs on our 57 BelAir 2door sedan. It stops just fine, the discs are from the early 70s Chevelle. Modern midsize cars actually weight MORE than the 55-57 Chevies, in particular the late Model Trans AM at 150# more than our 57.
No kidding, Pasadena, what does it weigh? My shoebox ford is around 3200#, guesstimate yours is similar? Knowing that, I dunno why I was thinking closer to 3800 for a chebby, unless its true chevy uses thicker steel! ;-) Also how hard is your brake pedal and what mc bore/pedal ratio are you using? I'm just curious to learn more about non power brakes. Is it a stomp to get lockup pressure on them? I'm putting a 8" dual dia on my ford w/1 1/8" mc bore, dunno my vacuum. I'm running a universal pedal so it looks to be a nice 6 or 7 to 1 ratio, which won't hurt, unless I can't get a comfortable location for it!
Both of the replacements came out of Astro vans. I cut the rod to the length I wanted then threaded it so I could use a clevis to provide adjustment.
I just scheduled the transportation for my '55 - it will be to me in about 2 weeks (the first week is lost due to schedule issues with the seller). Looking forward to getting it here and answering some of the nagging questions like how much vaccuum, what size MC bore, rear brake adjustments, etc. At this point it is all speculation, but you have all confirmed my suspicion that this basic setup should work well once I sort out the issues. That helps set my mind at ease. The only thing that surprises me is...how did they drive it every day without rear-ending anyone. This car has the 2nd worse set of brakes I can recall ever driving (Worst was a Fiat with literally metal on metal brakes and leaky calipers. Drove it 3 miles to my shop and held it hostage until we redid all the brakes. Friends dont let friends drive Fiats!) Sorta reminded me of the movie Fletch when Chevy Chase stopped the cadillac by bumping into planters and other parked cars because the brakes didn't work.
Adjusting the rear brakes has nothing to do with a hard pedal. As stated, vacuum is the number one cause of a hard pedal. The 7" booster will work fine with 18" of vacuum, but few cars with any kind of cam have that much. A common issue with tri fives is the pedal ratio. Most pedals have two holes, one for power and one for manual. A lot of aftermarket booster/master cyl. kits mount them at an angle for better valve cover clearance. With this type of set up, you have to use the factory power brake push rod hole in the pedal, which is the furthest one away from the pivot rod. The next problem is lack of vacuum, and the third is a master with too big of a bore, such as 1 1/8". Couple all three of these together, and you have exactly what you are describing.
Yes, adjusting the brakes addresses excessive pedal travel, but IMHO it's the first thing you do because frequently in my experience that can be the source of the problem people are referring to. Not everybody is as clear as TMcG in describing their brake situation. My approach to fixing stuff for other people is I listen to what the problem is, but I have to verify it, as well as double checking what they said they've already done to correct it. I've found that works best for me. There's a dozen ways to skin a cat. If Indeed its a power brake pedal ratio i'm guessing 4:1 with 100 pounds of pressure you've got 400 pounds on a 1 1/8 bore MC and a 7" dual WITH FULL VACUUM you've got 500 # of free pressure. You're looking at a whopping 900 pounds on its best day. Fat chance it's producing that. Guessing at 15-18" of vacuum I'll be optomistic and say 20% loss of booster output and you've got one poor excuse for a brake system. If you stomp on it and get 150# of pressure , which sounds pretty damn fatiguing to me, or at least it was when I had to use that kinda pressure to stop with my manual 4 whl drum brakes(bent the brake pedal!! actually tore the metal, not at once of course but I noticed when I threw it in a creek ;-) ) Then it will get you close to the magic 1000# number. You could drop it down to a 1" MC and bring up your pressure, but I don't think I'd like the result. A 'vette 4wdb MC is like $18 at autozone, might be worth trying. Me? I'm a girl, I want 1000# of brake pressure with only 50 pounds of manual pressure. If you have power steering, I've heard great things about hydroboost and clearance wise as well, and you get that fat 2000# of boost regardless of vacuum. Sounds good to me!
If these are the early GM BIG piston calipers (7 inches center to center on the mounting bolts) the car should stop well unboosted. I don't know if the booster installation changed the pedal ratio or not, that has a drastic affect on pedal effort. The hissing you hear when you step on the brake pedal is one of two things. When you apply the brakes air enters the booster from the back side through the hole(s) in the boot surrounding the pushrod, this is normal and should stop when you hold steady force on the pedal. If it continues that is usually an indication that the booster has expired. Usually this will be accompanied by a change in engine idle, it gets rougher like you have a vacuum leak (because you do). Other thing to check is what is being used for hose from the booster to the engine. You should have what is called VACUUM BRAKE HOSE, anything else runs the risk of inner liner collapse before you reach full vacuum level. You can identify VBH by the writing on the outside of he hose. Some are marked "VB" or "vacuum brake" etc. but the dead giveaway is it will be sized 11/32 in. ID. and it will have a DOT spec. printed on it. They don' t make 3/8 VB hose. Anything else the parts guy tells you will work probably won't. Gates rubber makes it and the NAPA no. is H1450. Don't be surprised if the NAPA guy looks at you like you have three heads when you ask him for some.
Hi all. The car was delivered to my shop last night! I troubleshot the booster, and it is indeed dead. I did the basic booster test (cycle the brake pedal several times to discharge any vaccuum) then hold the pedal and started the car. No boost, no pedal movement. I have confirmed that it is leaking vaccuum in from the pushrod / clevis when the brake pedal is depressed (and the engine starts running rough as well). Typically it stops when the brake pedal is released, but not always. The booster is definitely dead. I also checked the clevis location on the brake arm and it is in the stock hole. I have some additional tests I want to run before switching out the booster and master cylinder. I don't know the size of the MC bore yet (will measure in the next few days), but I am also questioning the health of the combination valve. It may be fine, maybe not. The pintle at the end (to reset the valve if it is un-centered) does not have a rubber boot on it and the pintle does not move. I am going to ultimately be replacing it anyway, but am very curious if half of the hydraulic system is cut off or not. A dead booster could explain the bad brakes, but they still seem worse than just an unboosted system. There are 2 pieces of good news I did come up with since the last posting. First, I have been working with CPP on a sweetheart deal, and they cut me one. I won't post the details here, but suffice to say they are in the range of 'the Pirate'. If you are shopping for a booster / MC I will PM the details. The 2nd piece of good news is that I discovered the car has a 12 bolt rear end - looks like from an A-body. The seller didn't mention that, and I didn't realize when I was checking out the car before I bought it. 9" self adjusting brakes (and stout as heck!). I'm smiling!
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