gm metric calipers/disc brakes front and rear...what master?

[84montesc]

I know someone is going to tell me to use the search function and i have time and time again and find a lot of threads but most of them just confuse me more!!!

i have stock gm metric calipers front AND rear. also have a manual plate for firewall/manual conversion. i have an adjustable bias valve in line with rear brake lines already setup.

i know i can buy the trz kit for master cylinder but want to avoid it if i can. i want a cheap CHEAP cheap master cylinder that will work here.

i read that a step bore master wont work is this correct? and from what i read a 1.000 inch straight bore would be best for these calipers or am i wrong? what master cylinder/what car does it come on that i can take and order from a local parts place to just bolt into place and plumb up?

 

[malibudave1978]

Re: gm metric calipers/disc brakes front and rear...what mas

What are the specs of the calipers front and rear? New, used, rebuild, brand, size of caliper bore, etc?

 

[84montesc]

Re: gm metric calipers/disc brakes front and rear...what mas

not sure to be honest i dont have receipts for the new front ones anymore either.

i have a set of USED ones off of a 1984 monte carlo on the REAR end. they were the front ones on my car before i tore it down for resto and i had them on and used them and they are about 10 years old id say.
i used those front ones for the rear because i had them around when i got my rear so i used them.

then went to oreileys and got a NEW set of calipers for the front. all i told him was 84 monte carlo front calipers id have to go and take them off to measure them if you really need bore size.

 

[84montesc]

Re: gm metric calipers/disc brakes front and rear...what mas

i dont have the time to go out and tear them apart now to measure so just for now let pretend they were all the same size. whether its 2.38 then what master cylinder? or 2.75 diameter bore then what master cylinder?


and if in the case that i did happen to have a 2.38 on rear and 2.75 on front then what master cylinder? and should i leave them they way they are or change the 2.75 to rear and 2.38 in front?

 

[malibudave1978]

Re: gm metric calipers/disc brakes front and rear...what mas

How well do your brakes work now with the vacuum power assist and the brake setup you have now?
How does your brake pedal “feel” with the vacuum power assist and the brake setup you have now?

 

[84montesc]

Re: gm metric calipers/disc brakes front and rear...what mas

It's not assembled yet as I dOnt know what master to buy. All I have is calipers all mounted and plumbed up to rough area I'll need it where I just need to bolt on whatever master I decide. I sold off the stocker cause I knew I couldn't use it cause I want manual brakes

 

[malibudave1978]

Re: gm metric calipers/disc brakes front and rear...what mas

The cheapest master cylinder for current setup would be a rebuilt manual brake master cylinder from an s10 truck (1982 to 1987 ish). This is a step bore design. I say go with a step bore because I think your new calipers on the front are more than likely 2.5” bore low drag calipers and your rears are very likely 2.5” bore low drag calipers. A step bore master cylinder will most certainly be needed for these calipers because it was designed for these calipers. These calipers need more volume of fluid that only a step bore master cylinder can provide along with increase pressure. A strait bore master cylinder will NOT work well with low drag calipers.

In my opinion, you have a lot of variables in your brake system that may cause you problems.
-Same size front and rear calipers (potential front and rear bias problems)
-Low drag calipers (can only use step bore master cylinder and were never designed for the rear calipers)
-Step bore master cylinder (has a 100 psi bypass valve that can go bad and this master cylinder is harder to bleed)

To try and remedy the front to rear bias and the low drag caliper issue you need to “invest” in aftermarket brake calipers. “Invest” in U.S. Brake or Afco metric calipers. Other brands may be out there, but these are the only ones that I know of that do not have the low drag feature of the stock calipers. Lowest priced calipers I found are at http://www.speedwaymotors.com . They are direct bolt in to your calipers that you have now. They come in big 2.75” bore, stock 2.5” bore, and small 2” bore. I would use the 2.75” for the front and the 2” bore for the rear if you are going to use the metric calipers for the rear. I haven’t run this system so I cannot guarantee that the rear brake system you are using will work well with the front. I would research online for people using metric calipers for rear disc brake systems. From my research, most of the problems stem from using rebuilt parts store low drag calipers on the rear and a strait bore master cylinder. This equals to spongy brakes.

I would also use a strait bore 7/8” master cylinder if you upgrade the calipers to the aftermarket units. The cheapest are rebuilt units for a 1978 to 1980 ish g-body cars. Only drawbacks to the rebuilt master cylinders are that they are unreliable rebuilds (don’t always work out of the box) and the front reservoir doesn’t hold a lot of fluid (the front reservoir is for the rear brakes). I would buy new, brand name master cylinder ($65 to $75 shipped for stock and over $200 plus shipping for Wilwood). The 2.5” bore rear (and front) calipers require 3.25 fluid ounces of fluid in the reservoir and the 2” calipers require 2.1 fluid ounces of fluid in the reservoir to operate. Because of the angle of a g-body firewall and the angle of the stock reservoir on the master there is less fluid in the front reservoir (front reservoir is used for the rear brakes). I can’t tell you if there is enough fluid in the front reservoir of a stock master cylinder to operate those rear calipers effectively, but my guess it is right at the limit. As a comparison, the stock rear drum brakes require less than 1 fluid ounce of brake fluid in the reservoir for them to operate.

Bottom line is there is no cheap way to convert these cars to manual brakes and them operate effectively. Your brake components need to be matched for proper operation.

 

[gman415]

Re: gm metric calipers/disc brakes front and rear...what mas

Good read, malibudave1978.
What about a Wilwood front and metric (front) calipers on the rear?
What would you suggest?

 

[malibudave1978]

Re: gm metric calipers/disc brakes front and rear...what mas

Good read, malibudave1978.
What about a Wilwood front and metric (front) calipers on the rear?
What would you suggest?

I will always suggest any thing other than stock replacement calipers from the auto parts stores. Rebuilds calipers are low drag and will come with headaches when trying to convert to manual brakes and trying to get a good pedal pressure with out having a hard pedal or mushy/spongy brakes. I am not sure of the how the new calipers are built that and sold in the auto parts stores. Are they low drag or are they regular? I actually don’t know. The metric dirt track calipers in 2.75”, 2.5”, and 2” made by U.S. Brake and/or Afco are NON low drag calipers and will work well with regular master cylinders. I think Wilwood has a cast iron metric caliper that will work and I am sure that it is a NON low drag caliper. The Wilwood metric aluminum caliper will also work, but I have no experience with these.

For master cylinders, always go the smallest you can that can support the volume of fluid you need. A stock manual brake master cylinder from a g-body can support most aftermarket calipers, but the stock master cylinder has a small capacity of fluid for the rear brakes (it was made for rear drum brakes which requires less than an ounce of brake fluid to be effective). When you start going to rear disc brakes, I think another alternative master cylinder with a larger fluid capacity and a 7/8” bore for the rear brakes should be used.

What are your options? Not many. 7/8” bore Wilwood master cylinder 260-9439 (expensive, but has the correct brake line outlets, will be at an angle when bolted to a g-body firewall, but it will work), 1993 Dodge Shadow (cheap but has 3/8” brake lines, looks like a Strange master cylinder, light weight, has a pushrod retention hole, and has an angled reservoir).

I really like the 1993 Dodge Shadow master cylinder. The really only downside is the brake line outlets. There are no adapters, that I found, that will mate the master cylinder outlets with the stock g-body brake lines.

 

[gman415]

Re: gm metric calipers/disc brakes front and rear...what mas

Thanks