Manual brake conversion

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L67ss

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Dec 8, 2016
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What all parts would be needed for a manual brake conversion on an 86 cutlass?
 
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Texas82GP

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manualbrakes.com

Not-quite-so-new-guy
Feb 11, 2016
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What all parts would be needed for a manual brake conversion on an 86 cutlass?

Any of the KITs that you buy will convert you car to manual brakes will work. Here are the things you have to think about.

*The correct size master cylinder
*The best pedal ratio
*LOW drag calipers
*Old rubber brake lines
*Brake pad matched to your braking needs

Most manual brake conversions will do best with a smaller 7/8” bore master cylinder. Smaller bore master cylinders create more line pressure giving more clamping force at the caliper. The only time you will need to go to a larger diameter bore master cylinder is if you use a front caliper that has a larger piston area than the stock metric caliper and if you go with a rear disc system with a larger than stock size caliper. All rear drums systems will do fine with the 7/8" bore master cylinder for manual brakes. Most rebuilt calipers should be NON low drag (normal) calipers. AFCO has a new stock replacement caliper (PN# 6635003 and 6635004) are also NON low drag (normal) calipers.

There are very few calipers that have a larger piston area than a stock metric caliper. Some of these are the GM D52 caliper, the Blazer twin piston caliper, and a big bore metric caliper. Most other front calipers, even multi piston calipers, have a smaller piston area and will be fine with a 7/8” bore master cylinder.

Stock rear calipers run about 1.9” in diameter for a single piston for the popular GM calipers and I believe the Ford Explorer rear calpers. Anything about 2.0” (around 3.14 square inch piston area) or less, you will be fine with a 7/8” bore master cylinder if using a stock size front caliper. Anything larger than 2” diameter piston will most likely need to go up one size in master cylinder bore diameter.

I high pedal ratio is good because it gives better leverage and it is easier for the driver to stop the car. Matched with the proper size master cylinder you will not be standing on the brakes to get them to stop. Stock G-body pedal ratio is 6 to 1. All vacuum booster brake pedals have the hole for the manual brakes above the booster pin in the pedal. That is the optimal point for manual brakes.

From 1982 to 1988, stock G-body cars came with LOW drag calipers which require a step bore master cylinder to have proper working brakes. If you calipers have been changed recently, they are mostly NON low drag (normal) calipers and will work with a step bore master cylinder and a normal, strait bore master cylinder. In my opinion, there is no step bore master cylinder that will work with LOW drag calipers and manual brakes. The pressure bore on most GM master cylinders are 24mm, which is a little too large for stock manual brake systems.

Rubber deteriorates over time. Old 30 year old rubber lines will balloon with pressure reducing you braking performance. Best options are to replace them with new rubber lines or stainless steel braided flex lines front and rear.

For brake pads, you will need to choose a pad suited for what you are using your car for. For most applications (street and drag strip), a pad with better cold frictions properties will be best. Organics are usually the cheapest and have good cold friction properties. I am in the process of testing the Wagner Thermoquiet pads (I have to get the El Camino running), but I have the Thermoquiet shoes on the rear and they work well. If you want to contact one of the aftermarket companies (EBC, Hawk, Porterfield, etc.) they will better suggest a brake pad suited to your needs.

Please let me know if you have any additional questions. Anyone can contact me about their manual brake questions.

David Schultz
[email protected]
832-264-5566
 
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L67ss

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I'm planning to swap to blazer brakes all the way around
 
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manualbrakes.com

Not-quite-so-new-guy
Feb 11, 2016
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I'm planning to swap to blazer brakes all the way around
Good rule of thumb for manual brake master cylinder sizing is stepping down one size from the factory vacuum boosted master cylinder size.

The 4 wheel disc, twin piston front caliper blazer comes with a 1.0" bore master cylinder. I would recommend a 24mm or 15/16" bore master cylinder for manual brakes with this setup. I don't think a 7/8" bore master cylinder will supply the volume to fill all 4 of the Blazer calipers.
 
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manualbrakes.com

Not-quite-so-new-guy
Feb 11, 2016
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What would be a good 15/16" donor?

That's the million dollar question and it will be based on what manual brake system you choose.

The manualbrakes.com KIT comes with everything to convert to manual brakes.
1. Adapter plate with push rod retention cup
2. Matching firewall gasket
3. Stainless steel mounting hardware
4. Custom push rod assembly made for the G-body
5. NEW 7/8" bore master cylinder (upgrade to 24mm at no extra charge)
6. Brake line adapters to mate stock master cylinder brake lines to the supplied master cylinder in the KIT.

If you go with 4 wheel disc brakes, you will need a 4 wheel disc brake prop valve. Most universal ones on the market SHOULD bolt into the stock location on the frame as they are based on the GM design.

While you are doing the swap, upgrade to stainless steel braided flexible lines front and rear or New rubber lines.
 
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