Manual Brake Conversion with Pictures

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
This week I put on the Wilwood big bore calipers. I got them bled and immediately had less pedal pressure when using the 7/8” G-Body manual brake master cylinder. The pedal almost went to the floor. I assume it is from the increased piston diameter over the Speedwaymotors.com “Big Bore” calipers (2.704” Wilwood v 2.565” Speedwaymotors/CCP) that I replaced. When driving with the Wilwood big bore calipers, I could pump the pedal 3 or 4 times and get the pressure I needed and would lock up the right rear tire and stop the car just like the other calipers. I suspect now I will need a 24mm bore G-body master cylinder (from a power, vacuum boosted G-body).
 

ElCaturbo

Weekend Racer
Jul 17, 2012
57
0
0
meridian, ms
Interesting... I currently have a 'Mopar'(spit!) 15/16" bore manual master on mine, and with stock calipers/wheel cylinders the pedal effort is insane, to the point it's scary. Instead of changing the master I may try these big calipers instead.

Just curious, as you've done more research on this than I have, but what led you to these iron calipers instead of the Wilwood aluminum single/dual piston calipers? Just cost, or something else?
 

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
ElCaturbo said:
Interesting... I currently have a 'Mopar'(spit!) 15/16" bore manual master on mine, and with stock calipers/wheel cylinders the pedal effort is insane, to the point it's scary. Instead of changing the master I may try these big calipers instead.

What is you manual brake setup now? What plate are you using? What are the outlet line sizes on your master cylinder? Do you have any pedal travel at all or do you have a hard pedal from the beginning of the pedal stroke?
 

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
ElCaturbo said:
Just curious, as you've done more research on this than I have, but what led you to these iron calipers instead of the Wilwood aluminum single/dual piston calipers? Just cost, or something else?

I tried the CCP/Speedwaymotors “big bore” calipers with a stock 24mm (roughly 15/16”) bore master cylinder and the stopping was not there. The effort was not bad, but I never got enough pressure to the front “big bore” caliper. It did stop the car, but it did not give a lot of confidence if I drove every day.

I went with the Wilwood 2.75” big bore calipers because it looks to be a better designed caliper and from the way it is built and the design seems to lend itself to have less caliper deflection. There also should be an increase in clamping force with the bigger 2.704” caliper piston. A smaller master cylinder bore gives greater pressure at the cost of volume. With a bigger piston area, more fluid volume is required and I don’t think the 7/8” bore master cylinder can keep up. There was another person that had this problem when he used the Wilwood 2.75” bore calipers with the 7/8” bore master cylinder, but I decided to try the calipers since they would be easier to change out compared to another master cylinder.

Which direction should I go? I have 4 choices with my setup.
1. Upsize the master cylinder to a 24mm and keep the Wilwood big bore calipers.
2. Replace the Wilwood calipers with the CCP calipers and start testing different brake pads.
3. Downsize the caliper to the Wilwood 2.38” bore aluminum caliper and keep the 7/8” bore master cylinder I have now.
4. Go with the Wilwood 1.62” bores dual piston aluminum caliper and keep the 7/8” bore master cylinder.

I am going to try option one first, because I like the Wilwood 2.75” calipers and I want to try and make them work. I would be loosing some clamping force going up in master cylinder size to a 24mm (because of pressure loss), but I hope to make it up in less caliper deflection from the better designed Wilwood caliper. From here I will test different front pads.

Option 2 will be next. I have an extra set of the CCP “big bore” calipers to use and I can then revert back to the 7/8” bore master cylinder and then start testing pads.
 

ElCaturbo

Weekend Racer
Jul 17, 2012
57
0
0
meridian, ms
malibudave1978 said:
What is you manual brake setup now? What plate are you using? What are the outlet line sizes on your master cylinder? Do you have any pedal travel at all or do you have a hard pedal from the beginning of the pedal stroke?

Mopar master mounted to the upper two holes in the firewall (with just a flat block off plate over the hole, no angled adapter) and pushrod in the upper hole in the pedal. Everything else on the brake system is 1980 factory stock - brake lines, prop valve, etc. The old power master was just plain stock replacement variety cast iron non-stepped bore.

The stock power brake master was 15/16" bore, I didn't bother to check the bore on the Mopar master until after I found it didn't work very well... and it's the same size bore. So even with the added pedal leverage, it's not enough pressure (well, at least at an acceptable pedal effort) to overcome the loss of the power assist.

I still haven't decided yet which direction to go with it - smaller master or bigger calipers. Probably bigger calipers, as it feels like now it's got more brake bias towards the rear than it did before, needs some shifted to the front (and I don't want anything to do with adjustable proportioning valves - K.I.S.S., whenever possible!).
 

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
Before you go buying the $90 a piece front Wilwood calipers, let me see if I can get them to work with the 24mm bore master cylinder.  I wouldn’t want you to spend $200 and it still didn’t fix your hard pedal problem.
 
I also didn’t know if you needed to use an adapter to mate you stock lines with the mopar master cylinder or if you had to rerun different size lines from the master cylinder to the prop valve.  How are your lines run?  What is the part number for that mopar master cylinder?
 
The reason I ask is there are smaller mopar master cylinders that will work better with stock size front brakes, but they have the 3/16” lines instead of the ½-20 and 9/16-20 outlets on the 15/16” and larger bore mopar master cylinders.  The smaller master cylinders come in 7/8” and a smaller 21mm bore.  The 21mm would be the best choice if you can find them.  The ones I have bought that say 21mm, end up being 7/8” bore. They come in 1993 dodge shadows and derivatives.
 

ElCaturbo

Weekend Racer
Jul 17, 2012
57
0
0
meridian, ms
Yes, that's why I'm watching what you do here, to see how the big calipers work (both pedal effort & bias-wise) with the same size master I have.

I don't have the p/n on the Mopar piece, it was years and years ago and the box got lost long before I had a chance to use it on anything. But, it was the one commonly sold for the 'universal'* manual brake conversion, I don't think this same one is still sold thru Mopar, but it's the same as any of the other kits on the market now with 15/16" bore, as far as I know.

It came with new inverted flare fittings, but I didn't use them... with the stock line fittings, one was an exact match and fit fine, the other was just a slight difference in thread pitch, with a little monkeying I was able to get the flare seated and it's now tweaked the threads in the m/c so that it fits like it was built that way.

Don't get me wrong, the brakes work - I can lock the wheels, but it just takes too much pedal effort to be confidence-inspiring in normal driving (standing on the pedal, pulling like crazy on the steering wheel - in all your travels down this road, I'm sure you've tried a combo that acted the same, lol). It's not just the difference in manual vs. power, as I used to have an S10 with the factory manual brakes and it wasn't much different than a power setup, other than a less squishy pedal feel.


*'universal' = doesn't fit anything :lol:
 

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
I am done testing the manual brake setup with a stock, aluminum, rebuilt, 24mm bore, 1980 El Camino master cylinder. With only this change, I got back the brake fluid pressure that I lost when I upgraded to the Wilwood 2.75” metric calipers using the 7/8” bore master cylinder. I bench bleed the master cylinder installed it in place of the 7/8” bore master cylinder, bled the line at the master cylinder, and then bled the car at all four wheels.

On the test drive, using the 24mm master, I did a few hard stops from about 30 mph. I was rewarded with both rear wheels locking up, but the front braking system felt as if it still wasn’t grabbing. After the testing, I jacked the front of the car and removed the wheels and I unbolted the calipers so I can take a look at the pads. I suppose during my very first manual brake test, I did not bed the brakes in properly and I glazed the brake pads over. I do not know why I did not notice this when I put on the Wilwood calipers other than not recognizing what glazed pads look like. The glazing most likely happened because I had a large master cylinder and small calipers on my first manual brake test and, at the time, I wasn’t getting enough pressure to the pads to do accomplish correct bedding. The moral of the story is to bed your pads properly.

Good news is that I found out what the issue is with the front brakes not grabbing. Bad news is that I didn’t deglaze my pads and retest. I didn’t deglaze the pads I originally used because went ahead and upgraded to a Wilwood Polymatrix A brake pad.

I went to the Wilwood PolymatrixA pad because of its good, cold clamping properties and, before I realized about the glazing pads, I had thought this would help with front brakes. **As a warning from Wilwood to any one using these pads, Wilwood considers these race pads**. These are aggressive pads and will most likely wear the front rotors prematurely and are intended for race use only. These pads have almost twice the friction coefficient as a “stock” type pad. I am using this aggressive pad because the front rotors are small, the brake pads are small, the front calipers are a floating design, and the car is now has manual brakes. These pads are also a wallet buster at $150 a set.

The braking test with these pads where a noticeable night a day difference. I felt very comfortable and confident while driving and stopping. On hard stops, the nose of the car would “dive” down and the rear wheels still locked up. Only time will tell if these front pads are good for everyday use with this manual brake setup.

If your car is a daily driver and not a drag car, you most likely do not need to change out to larger wheel cylinders on the rear drum brakes like I did. The original stock 3/4” bore wheel cylinders versus the larger 7/8” bore wheel cylinders should reduce rear lock up on hard braking.

For a drag racer with large, wide, sticky tires on the back, the larger 7/8” bore wheel cylinder may be better to keep the rear tires from spinning when your holding the car on the line with just the brakes. An aggressive front pad may also be needed to hold the car on the line (contact one of the major brake pad manufactures for suggestions).

From my experience, to do a manual brake system on a g-body or s-10, some or all of the brake components will have to be replaced. You cannot just remove the vacuum booster and bolt the master cylinder to the firewall and expect your braking to function well. It is a system approach.

Do you need an oversized caliper? In my opinion, no you do not.

Do you need to change out the front calipers? In my opinion, yes you do. Why? Because the stock calipers may or may not be a LOW DRAG design which requires a step bore master cylinder. How do you know that you have LOW DRAG calipers? You actually cannot physically tell, so its best to buy aftermarket calipers to cut down on variables that may cause trouble with your braking system.

Do I recommend rebuilt front calipers from the auto parts store? No. See above.

Do you need to change out the master cylinder? In my opinion, most likely you will need to. Why? It depends on what you are starting with. If you have a GM g-body vehicle that was built from 1978 to 1980, you have a strait bore, 24mm bore master cylinder from the factory and you can just upgrade to Wilwood 2.75” bore calipers if you master cylinder is in good working order. If you have a vehicle built from 1981 through 2003 you most likely have a step bore master cylinder. These master cylinders are too large for almost all manual brake conversions on a g-body or s-10. Now a choice has to be made. How much money do you want to spend on aftermarket front calipers? Cheapest ones that I have found are around $45 each with a stock size bore from U.S. Brakes. You will then need a 7/8” bore master cylinder to match to these front calipers. For a g-body car you can go with a new or rebuilt, stock replacement from a 1978 to 1980 g-body manual brake master cylinder. For an S-10, the only option I have found that readily bolts to the firewall and to the brake lines is a Wilwood 7/8” bore master cylinder. If upgrading to the Wilwood 2.75” bore calipers, you will need a 24mm master cylinder. The g-body options are a new or built stock power brake unit from a 1978 to 1980 g-body car. New ones will be cast iron. Most rebuilt ones will be cast iron. For some reason, the 1980 model years came in aluminum and these can be bought rebuilt (like I have installed in the latest test). For a s-10, you can use a stock replacement manual brake master cylinder from a 1982 to 1992 s-10 truck with manual brakes. These are step bore master cylinders with a primary bore of 1-1/4” and a secondary bore of 24mm. I do not recommend these master cylinders because they are hard to bleed and have a bypass valve that can fail. The other options are a 24mm Wilwood master cylinder and a 1990s 24mm Dodge Dakota master cylinder. Only issue with the Dakota master is the rear brake port is 9/16-20 instead of 9/16-18. I have found no adapter for this conversion yet.

Do I recommend step bore master cylinders? No, because they are generally too large for a stock size front caliper, they are hard to bleed, and they have a bypass valve that may fail. These three issues can be remedied by using a correct size strait bore master cylinder. A 7/8” bore master cylinder for stock bore, aftermarket calipers and 24mm bore master cylinder for a Wilwood 2.75” bore calipers.

Do I recommend other oversized front calipers other than the Wilwood 2.75” front calipers? No, because their piston size in these oversized calipers are not much larger than stock. The Wilwood caliper, visually, looks to be engineered better.

Do I recommend stock size calipers? U.S. Brake is the only caliper, of the aftermarket cast iron replacements I know, that is not a low drag caliper. There may be other aftermarket, “metric” calipers, but I cannot confirm if they are low drag or not. The U.S. Brake calipers are based on a stock casting. The other alternative is a stock, replacement aluminum, “metric” caliper from Wilwood. I have not used or viewed one of these calipers, but from engineering of the 2.75” bore and 2.00” bore calipers I have viewed, I suspect they should be just as well engineered and lighter.

Do I recommend larger wheel cylinders? If the car is street driven, most likely no. If drag raced, most likely yes to keep the rear tires from spinning when doing a brake stand

Do I recommend braided stainless steel flex lines? Yes, for the reduced ballooning and better pedal feel, but is not necessary.
 

Wile E

Dragway Regular
Aug 11, 2003
1,075
0
0
Central WISC
Dave, Awesome write-up!
 

malibudave1978

Amateur Racer
Thread starter
Jun 8, 2004
226
0
0
Houston, TX
Here is a list of strait bore master cylinders that will bolt up to a G-body’s angled firewall when using a flat, manual brake adapter plate. This is a list from smallest to largest.

21mm (0.826”) bore 1993 Dodge Shadow master cylinder (other years and models may work)
• Requires adapters to mate master cylinder outlet to stock lines. The adapter Part number is MC-SF at

• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Hard to find.
• Light in weight.
• Advertised as 21mm, but may be delivered in 7/8” or 24mm bores. Measure bore size before you buy. Rebuilt/Used ones will have a “1” cast into the front of the aluminium body under the reservoir.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.

7/8” (0.875”) bore 1978-1980 GM G-body manual brake master cylinders.
• Can buy new or used. Rebuilt are fairly cheap. New are fairly expensive.
• Reservoir too small for rear disc brakes. The reservoir from 1979 Buick Riviera with four wheel disc brakes can be retrofitted to this master cylinder.
• Advertised as manual brake units, but may be delivered as a 24mm, vacuum power boosted unit. Measure bore size before you buy.
• Bolt in.
• Cast iron body – new, used, or rebuilt. (no aluminium)

7/8” (0.875”) bore 1993 Dodge Shadow master cylinder (other years and models may work)
• Requires adapters to mate master cylinder outlet to stock lines. The adapter Part number is MC-SF at
Disc Brake, Steering and Suspension Products for classic Chevy and Ford cars and trucks
• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Easier to find.
• Light in weight.
• Advertised as 7/8”, but may be delivered in a 24mm bore. Measure bore size before you buy.
• Rebuilt/Used ones will have an “8” cast into the front of the aluminium body under the reservoir.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.

24mm (0.944”) bore 1978-1980 GM G-body power brake master cylinders.
• Can buy new or used. Used are fairly cheap. New are fairly expensive.
• Reservoir too small for rear disc brakes. The reservoir from 1979 Buick Riviera with four wheel disc brakes can be retrofitted to this master cylinder.
• Bolt in.
• Come in cast iron and aluminium. 1978-1979 are cast iron. 1980 is aluminium (some models i.e. El Camino).
• New master cylinders will most likely be cast iron regardless of year.
• Rebuilt units come in cast iron and aluminium (1980 – some models).

24mm (0.944”) bore 1993 Dodge Shadow master cylinder (other years and models may work)
• Requires adapters to mate master cylinder outlet to stock lines. The adapter Part number is MC-SF at
Disc Brake, Steering and Suspension Products for classic Chevy and Ford cars and trucks

• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Easiest to find.
• Light in weight.
• Advertised as 24mm, but may be delivered in a 7/8” bore. Measure bore size before you buy.
• Rebuilt/Used ones will have a “4” cast into the front of the aluminium body under the reservoir.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.

24mm (0.944”) bore 1993 Dodge Dakota master cylinder (other years and models may work)
• Rear brake line outlet is 9/16-20 versus GM rear brake line fitting of 9/16-18. The fitting for GM brake line may be used to “rethread” the master cylinder’s outlet.
• Front brake lines bolt up.
• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.
• Reservoir not angled like above Dodge and GM master cylinders.

1.0” bore 1979 Buick Riviera with 4 Wheel Disc Brakes.
• Can buy new or used. Used are fairly cheap. New are fairly expensive.
• Reservoir is made for rear disc brakes.
• Bolt in.
• Come in cast iron and aluminium.
• New master cylinders will most likely be cast iron.
• Rebuilt units usually come in aluminium.

1 1/32” (1.03”) bore 1985 Dodge Diplomat master cylinder (other years and models may work)
• Rear brake line outlet is 9/16-20 versus GM rear brake line fitting of 9/16-18. Fitting for GM brake line may be used to “rethread” the master cylinder’s outlet.
• Front brake lines bolt up.
• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.
• Reservoir not angled like above Dodge and GM master cylinders.

1 1/8” (1.125”) bore 1985 Dodge Ram master cylinder (other years and models may work)
• Rear brake line outlet is 9/16-20 versus GM rear brake line fitting of 9/16-18. Fitting for GM brake line may be used to “rethread” the master cylinder’s outlet.
• Front brake lines bolt up.
• Mounting holes spaced 3.25” versus GM master cylinder’s 3.375”.
• Can buy new or used. New ones are fairly cheap to purchase.
• Aluminium body – new, used, or rebuilt.
• Large reservoir can hold enough fluid for rear disc brakes.
• Reservoir not angled like above Dodge and GM master cylinders.
 
Last edited by a moderator:

MalibuRacing.com Gear

Stickers & Shirts!!