How To Tell If Your Brake Power Booster Is Bad – Pit Stop with Marlon Davis: How hard is a hydroboost brake system conversion with low idle vacuum on a 1940 Ford Fender Coupe with a Chevy 350 engine that won’t stall? Are there other solutions?
Q: My 1940 Ford coupe’s cam does not vacuum much. I would like to put power steering and hydroboost brakes on the car. My son has an early 2000 Chevy Tahoe with hydroboost brakes. There must be a lot of people in the junkyard. Can I remove the power steering pump, hydroboost unit and hoses and install them in my car? I know the hoses won’t fit, but there is a place in town that can make almost any hydraulic hose.
How To Tell If Your Brake Power Booster Is Bad
From 1999 to 2007 many GM trucks and SUVs came with Hydroboost hydraulic brakes operated by the power steering pump in place of the vacuum-assisted brakes connected to the engine vacuum. Kinderman wants to use a hydroboost brake system on his 1940 Ford Street dipstick.
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Power comes from a Chevy 350 small block with a healthy Comp Cam Extreme Energy flat tappet hydraulic cam. Running at 230/236 degrees at 0.050-inch tappet lift, there isn’t enough low-power vacuum for a conventional vacuum-assisted power brake.
Comp Cams Xtreme Energy XE274H Hydraulic Flat Tappet, 230/236 Span at 0.050″ Tappet Lift, 0.490″/0.490″ Lift (1.5:1 Rockers), 110 LSA
Stock Mustang II front end “cut from a Mustang and welded to a 1940 chassis”, new coilovers and tubular control arms
For reliable vacuum-assisted brake operation, engine idle vacuum must be at least 14 inches (and preferably 16 inches or more). With only 8 to 10 inches of idle on the Kinderman’s 350, there’s no way a giant vacuum booster could pull out all the stops—but the Kinderman only has room under the floor for this tiny 8-inch booster. He says the big master cylinder is from a 1979 Corvette.
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Wilwood four-piston Dynalite calipers with an outside diameter of 11 inches. The rotors should be fit for the job, assuming sufficient brake pressure. They are paired with 11 x 2 inch Ford drums in the back. Kinderman cut a rack-and-pinion Mustang II from a real Mustang and grafted it onto a 1940, later enhanced with tubular control arms and coilovers.
Dhani, we see problems like yours quite often in many cars, and there are several solutions, including the proposed “hydroboost” brake system. Technically known as a hydraulic instead of vacuum driven brake system, a hydroboost uses hydraulic fluid supplied by the same power steering pump that pumps fluid to the steering gear or steering rack to increase brake pedal force. supplies. Typically, an accumulator provides some short-term backup boost in the event of an engine stall or pump failure.
Before you start replacing parts, I strongly recommend that you double check that your current vacuum brake system setup is as good as it can be. The Comp XE274H is pretty healthy for a Camera 350 engine, but its reported vacuum output still seems low. You can achieve a vacuum of 2 to 3 inches with a professional dynamometer. On one of Comp Cam’s 350 test engines, an XE274H-10 hydraulic flat tappet (PN: 12-246-3) was 11 inches at 800 rpm at no load and 14 inches at 1000 rpm. Interestingly, an XR282HR-10 hydraulic roller (PN 12-432-8) with the same 0.050 length but greater lift was 9 inches at 800 rpm and 11.5 inches at 1000 rpm. Comp’s Billy Godbold reports, “At low altitude [the roller cam’s] slightly smoother ramp and more area under the curve serve to make the head and cam larger.” On the other hand, “this engine also cost the Roller about 30 more horsepower”.
Have you tried advancing the start timing to see if the idle vacuum improves? If yes, but now there’s a lot of time at the top end, you’ll have to go through the distributor and play with the centrifugal advance curve.
Cadillac Delco Moraine Brake Booster
Adding more base time can improve engine vacuum and idle quality, but if the engine likes a lot of head start, you may need to lower the advance curve to avoid top-end knock.
An out of tune or bad carburetor can contribute to poor vacuum output. It could be as simple as properly adjusting the idle mixture or checking that you have installed the correct power valve. If the “PV” opens at idle, it will dump raw fuel into the intake manifold. It will mess up your vacuum and probability for sure! A rough fix for this is a 3.5-inch power valve with richer main jets, but this can eliminate cruise mileage. For a fine-grained approach, tune master Norm Brands (Westec Automotive of Wisconsin) is practically within walking distance of your location. Full service shops take a holistic or “systems” approach to problems like yours. If – and it’s a big “if”, based on the vacuum readings reported by Comp Cam with its camera – a good tune can get that idle vacuum up to 14 inches, you’ll be able to top it off with an external vacuum canister. May be able to (backup tank of vacuum).
Adjust the carburetor idle mixture screws to obtain the highest possible vacuum reading. Turn the idle screw clockwise only if necessary to stop the car while doing so. A 15-in-Hg gauge reading here isn’t too bad for a hot rod, but make sure the vacuum brake booster can operate at that level. (Hint: don’t rely on MiniBooster.)
I know it sounds corny, but: are you absolutely sure you’re bleeding the brake system properly? It is sometimes difficult to get all the air out of the system, especially with a floor or frame mounted master cylinder. Ideally, the master cylinder reservoir should be the highest point in the brake system, so brake fluid flows downward (thanks to gravity!).
Power Brake Booster Firewall Mount Kit, Fits 1949 1954 Chevy
Another thing we see on many hot rods is that the vacuum booster is too small and/or mismatched with the master cylinder which is too big for the small booster. Yes, 1970s Corvettes had 1-1/8-inch master cylinders (as did many GM power brake systems of that era), but they also had a larger, longer-length, dual-diaphragm vacuum booster. There’s no room for that kind of reinforced tread, but Scarbird brake expert Mark Janis says 9 inches is plenty of brakes. The dual diaphragm vacuum boosters used in GM cars in the 1980s that you have now will offer a noticeable improvement. Many of these installations had a square mounting bolt/vertical mounting bracket pattern which made them suitable for custom installations. A common unit is the “BK” code booster found on many 1982-1987 Chevy S10/GM S15 pickup trucks, Jimmys and Blazers.
You told me the brakes work fine at the end of the drag strip, but not at low speeds. This is sometimes caused by overly hard brake pads that don’t grip well until they’re really hot. Great for running, not necessarily everyday street wear. Consider “soft” pads that work best in moderate outdoor temperatures. Brake pads are usually marked with code letters on their backing pads or on the sides of the pads that provide a guide to the pad’s characteristics; For more information, see “Disc Brake Pad Friction Code Explanation”. If you change to a different pad material, be sure to turn the rotors to remove any polish and/or compound from the pad friction material that may have transferred to the face. Otherwise it’s like an engine cylinder bore where the piston rings never seated.
For a master cylinder, consider lowering the unit by 1 inch. Make sure the pedal ratio is correct and that you are reaching the full stroke of the master cylinder without going off center. Typically, hydraulic brake systems want a pedal ratio of 4:1 and manual brakes like 6:1, but a larger “ratio number” is usually not a problem.
There’s also the option of reverting to full manual brakes. Janice explains, “A little power boost from setting the full manual brake properly is bad.” “I think a 7/8 inch diameter manual master will do a great job for you. But watch the pedal ratio!”
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Now, let’s take a look at what it might take to implement your plan to use the GM hydraulically advanced brake system based on the early 2000 trucks. Generally speaking, hydroboost brake systems provide excellent stopping ability, although some describe the brakes as overly sensitive or positive; In other words, the pedals may lack the linear modularity that’s important for a canyon carver or road racer, not so much for a daily cruiser. On the other hand, many like the “extremely positive” pedal application sensitivity provided by the hydraulically reinforced dial-up brake system. Like most hot rod mods, on a non-stock install, you should be prepared to tweak and overcome unexpected issues.
To get started, you’ll need a rack and pinion unit with a power steering to replace the manual rack assembly. The 1974-1978 Mustang II power rack doesn’t go up on trees – if there are trees in the wrecking yard. At RockAuto, a rebuilt Mustang II power rack is in the $120 range, while new ones are $235 and up. There are two- and three-mount screw designs, but manufacturers say they are interchangeable.
Virtually the same hydroboost brake system was used on many small block 1999 to 2007 Generation III (LS type) Chevy and GMC 1/2-, 3/4- and 1-ton pickup trucks, Tahoes, Yukons, Silverados and related relatives and clones. it was done. , Although these systems are mostly similar, insurance
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