My 49 Chevy has a 57 rear end and its drum brakes. The front brakes are the GM metric calipers with oversize pistons. The master cylinder is a 1 inch Corvette style with a small vacuum booster. I was having problems with rear brake lock up and finally deduced that the shoes sold to me by my local auto parts stores were of equal length. So, I cut the material down on the leading shoes and that helped the premature rear lockup. My problem now is that the brakes are still overly sensitive. I have a 57 Chevy with the same rear brakes and the Chevelle front calipers and it is well balanced. My instincts tell me the rear shoes are still a problem. Any ideas? This is making me really uncomfortable in heavy traffic.
Put an adjustable proportioning valve in the rear brake circuit. Adjust the bias until you feel comfy with it.
As above or you can also use smaller diameter rear wheel cylinders to achieve the same effect. Use the square area of the cylinder to make proportional diameter changes. Some early boosted disc brake and drum combinations used 9/16" rear wheel cylinders to get them balanced.
You may also want to measure the rod in the front of the booster against the master cylinder for compatibility.Some MC’s have a longer body where they match up to the booster.If they are mismatched you can get the situation you describe- push on the brakes and with heavy pedal effort- brakes are so-so then ‘bam’ the brakes are on hard.
As Greybeard360 said .... get yourself a Wilwood valve like this. Stay away from the other cheaper units on the market, we have removed dozens of them that have went bad or failed at our Hot Rod Shoppe.
I have one off these in the circuit. Why is the rear brake so much more sensitive than in my 57 with same components? I still suspect brake shoes. https://www.summitracing.com/parts/clp-pv-2
Has this car always had this issue from Day 1 ? We have found allot of the brake shoe replacements sold today over the counter are NOT exactly as the originals. Man I wish we had a old Brake Shoe Grinder What is the "Brake Pedal Ratio" of this car and the other car you say is the same? Are the brake pad and shoe brands & part numbers exactly the same on both cars?
This ^^^^ except for the "As Above" comment. Get the brake balance/bias sorted before adding the patch-up valve Some S10 Chevys were 5/8" wheel cylinders but most were 3/4" [depending on year and manual vs power brakes]
Pedal ratio is 5:1. Most likely, this is a 3/4" wheel cylinder....but so is my 57. I bought the car and the brakes were terrible. I changed the front calipers to the "big bore" ones and then trimmed the front shoes to stop the rear premature lockup. I'm sure. They shoes and pads are not the same. Still, the brake system is too sensitive.
There are 2 different pivot points on some brake pedal or 2 different pedal depending on power and non power brakes.Try and disconnect the vacuum to the booster.
I had the exact opposite problem with my DeSoto project, I had essentially NO rear brakes. I like the separate proportioning valve idea, that's one of the things I changed. Whether it really was that, or going to a 1" master, or an 8" booster, or getting the CORRECT rear rotors, calipers and pads, I can't say, but the car stops now. My wallet is considerably thinner and more comfortable as well, so, winning.
I had people suggest that I get calipers with larger bores than I had to try to correct the problem I was having. My question is, where, or how, does one get wheel cylinders or calipers with other than whatever the standard bore is for a specific application? In the case of my car, I had an '03 Explorer Sport Trac, there is only one caliper for that, and it is NOT interchangeable, nor compatible with Explorer parts.
"Same parts, different braking?" It's more than just M/C and similar corner components Car weight and balance tire sizes engine vacuum booster size and check valve pedal ratio, as mentioned suspension stiffness and geometry (anti-dive) I'm sure there are others. You could measure and confirm each part, but the concern is "overly sensitive". Does this mean apply with one toe rather than your whole foot? If so, you can decrease input - booster (as you mentioned), pedal ratio and/or M/C size.
Yes. Apply with one toe. How do i reduce the booster output? I will get to rhe bottome of this eventually. It isnt that complicated.
Smaller booster. Vacuum applied to one side multiplied by the surface area is the assist. Smaller area = less boost. You could put a big cam in also to lower vacuum. That would be the hot rod method!
When you say overly sensitive, combined with what you have stated earlier, I am assuming you mean rear lock up, not that the entire car stops with minimal effort. Two totally different directions on a repair with the definition of the complaint. If you are having rear brake lock up with minimal effort, (car still rolling with rear tires skidding) it tells me that the brakes are self- energizing. This usually happens with contaminated shoes, improper shoes, or poor adjustment. The scenario happens when the shoe has to much traction on the drum. Look for coarse finish on the drum, improperly arced shoes, contaminated shoes(oil/grease/brake fluid) or loose/ worn anchor pins. My guess with the info provided would be an improper shoe arc. Remove the drums, remove the shoes and place the shoe in the drum. The shoe should contact the drum: 1 On the entire surface Ideal 2 On the center of the arc Acceptable 3 On the outer edges Bad My suggestions are based on a car designed with the brakes in a problem scenario. Being that this is a pieced together system, you may need to replace hydraulic components, but it seems to me that it is more of a mechanical issue.
While working @ a dodge dealer as a young man,I was given by the dispatcher a new dodge van to install a power brake kit. It came with a brake pedal with I did not install at first. I installed all the kit and tried to test drive it and the brakes locked up with very little application.Some on pointed out to me and I changed the pedal,then all ways good. On a 1966 chevy I noticed it had 2 holes in the pedal for the push rod.
trendz beat me to it....sure there's no oil on the linings? Rather than make them slipperier, they'll grab like hell, worse as they heat up.
Sounds like one or more of the brake shoes has become contaminated with oil or some other oil. Once you get oil on shoes or pads pitch them.. That brake cleaner seems to just make things worse, though I have had it work on a few occasions on contaminated metallic brake shoes...
57's have 1" bore wheel cylinders. He needs to go smaller to reduce rear clamping pressures. (Or larger bore front calipers) The front to rear brake bias needs sorting first before he plays with line pressures
I'm on the road right now at Run To The Sun. When I get back next week, I will do more investigating. I don't think the shoes are contaminated but they could be.
Rock, I had a 64 Bonneville that was driving me nuts with pulling to the right. The front wheels and shoes were prefect, it had those Pontiac 8 lugs. Turns out the back right shoes kept getting contaminated from a rear bearing seal that was installed backwards (actually that's an easy thing to do).. I changed the seal and sprayed the shoes down with Brake Clean thinking that was that but it kept pulling. I went through all kinds of fixes until I pulled everything apart, changed both seals and put new shoes on and it finally worked..
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