yet another 5 lug conversion thread

Low86GT · Oct 26, 2009

Hey guys long time no post since I don't have either of my 86s anymore.

I am in the process of helping my nephew gather parts for his 5 lug conversion.

We got a set of SN95 spindles from a 94. We will be installing the 13" rotors with bullitt or cobra calipers. I know I need a line adaptor as well as all the other brake hardware.

The part that I am not sure about is if there is anything I need to do to the proportioning valve if we keeping the rear drums for now. It will get discs in the rear later but the money isn't there for them now.

I know with the rear discs you have to gut it and put an adjustable PV in line.

I am also not sure about which MC to use. I read that the 85 town car is a direct replacement on the 86 and has a 1" bore.

any help would be great.

lancec2c30 · Oct 26, 2009

If you keep the rear drums, I think you will have to leave the P-valve alone for now. I'm not sure on the master cylinder.

54deuce · Oct 27, 2009

I would wait until you get the rear brake parts and put it all on at one time. If you get the bigger mc and just put it on with the new front brakes it may blow out the rear wheel cylinders. I would think you would have to add the adjustable p valve and have it set more towards the front for that. You also could just bolt the fronts on and see what happens with the stock mc. I dont know what year you are working on but on my 87 I used 95 GT brakes all around with the stock mc it worked but not as good as it should. Like I said I would just wait until you have all the stuff.

Low86GT · Oct 27, 2009

Thanks for the info.
This is on an 86.

I know that on one of my 86s. I did the 87-93 brakes with the SVO 73mm calipers and did not change the mc or anything for several years and everything worked great.

I was planning to try it without the mc at first and see what it does but I wanted to be ready to change it out just in case.

The town car wheel cylinders are 15/16 inside and the 86 is 3/4. I know that is a 3/16 difference but I think thas as long as the vp isnt changed or modified it should be fine.

Shaolin Crane · Oct 27, 2009

you should do a GT MC first then then do cobra MC later might be too much pressure for the drums

Mustang5L5 · Oct 27, 2009

Which MC to use is really just a matter of hydraulic ratios.

SInce the rear drums are staying constant, you only need to concern yourself with the front.

Stock brakes on an '86 are 60mm calipers, so that gives you a surface area of 5654mm^2 for both front brakes

Now, if you use the 99+ Cobra/Bullit brakes, they are 40.5mm pistons x 4, so that gives you a surface area of 5152mm^2...which is very close. Your pedal will actually be a tiny bit more firm due to the smaller piston area. You prob would never even notice it (FYI, if you get a set of 94-98 cobra calipers, the piston area is 4536mm^2 and you would notice a firmer pedal with them. I'd do a 1993 cobra booster as well to help in this situation)

So my recommendation....stick with what you have. Your GT has a 21mm (0.82") bore Master cylinder. You may be able to use the booster you have as well. The next size up is a 94-95 Cobra MC (15/16") but it will be too big and your pedal will be hard as a rock. The town car MC is 1" and much too big. These MC's are suited for rear disk setups.

However, minute you change to rear disks, this all goes out the window. With rear SN95 calipers and the bullitt fronts, you will then want the town car 1" MC...and a 1993 Cobra booster.

You should really gut the PV and install the adjustable valve now as well. You can actually add more rear brake pressure since the front brakes are now more powerful

faststang90 · Oct 27, 2009

i was told to look here for a friends car

87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times!

Low86GT · Oct 27, 2009

Mustang5L5 said:
Which MC to use is really just a matter of hydraulic ratios.

SInce the rear drums are staying constant, you only need to concern yourself with the front.

Stock brakes on an '86 are 60mm calipers, so that gives you a surface area of 5654mm^2 for both front brakes

Now, if you use the 99+ Cobra/Bullit brakes, they are 40.5mm pistons x 4, so that gives you a surface area of 5152mm^2...which is very close. Your pedal will actually be a tiny bit more firm due to the smaller piston area. You prob would never even notice it (FYI, if you get a set of 94-98 cobra calipers, the piston area is 4536mm^2 and you would notice a firmer pedal with them. I'd do a 1993 cobra booster as well to help in this situation)

So my recommendation....stick with what you have. Your GT has a 21mm (0.82") bore Master cylinder. You may be able to use the booster you have as well. The next size up is a 94-95 Cobra MC (15/16") but it will be too big and your pedal will be hard as a rock. The town car MC is 1" and much too big. These MC's are suited for rear disk setups.

However, minute you change to rear disks, this all goes out the window. With rear SN95 calipers and the bullitt fronts, you will then want the town car 1" MC...and a 1993 Cobra booster.

You should really gut the PV and install the adjustable valve now as well. You can actually add more rear brake pressure since the front brakes are now more powerful

Thanks for the reply. These are the calipers I am looking to get from Ford Racing. I find it hard to believe that the price is that cheap on them but that is what I am getting either what. Buy Ford Racing Parts!

I didnt know that these were 4 piston I thought that they were only two. I know I used something like it on one of my 86s and they were only 2 piston. The other I had the 4 piston Brembos

Low86GT · Oct 27, 2009

faststang90 said:
i was told to look here for a friends car

87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times!

Thanks for the link. I have already been over that thing a few times.
The 86's are kind of an odd ball to start with so getting good information is difficult.

Mustang5L5 · Oct 27, 2009

Low86GT said:
Thanks for the reply. These are the calipers I am looking to get from Ford Racing. I find it hard to believe that the price is that cheap on them but that is what I am getting either what. Buy Ford Racing Parts!

I didnt know that these were 4 piston I thought that they were only two. I know I used something like it on one of my 86s and they were only 2 piston. The other I had the 4 piston Brembos

That is a good price.

They are dual piston 40.5mm pistons. I meant 4 pistons in both calipers total by my comment before...2 each side. The area of all 4 pistons combined is roughly equal to the stock 60mm calipers you have now.

So because of that, hydraulic ratio shouldn't change much and your current MC should work fine...slightly favoring the firmer side.

yet another 5 lug conversion thread

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