1985 5.0 GT Brake Upgrade

**MasterJ** · 10-21-2011, 05:46 PM

I am looking to upgrade my 1985 5.0 GT brakes while keeping the 4-lug all around. I am not looking to race my car, just drive it moderately hard on the streets. I want to change the rear to disk and upgrade the front disk brakes. First i would like to attack the rear. I am considering purchasing the kit in this link "http://www.latemodelrestoration.com/item/SS-A112/1979-86-Mustang-4-Lug-Rear-Disk-Brake-Conversion-Kit". Beyond this kit will i need to change out anything else? I have a brand new stock master cylinder so would i need to replace that?

As far as the front brakes go, would increasing the size of the rotors do? any recommendations about the parts or which ones i would need? I am willing to spend the money but don't want to buy something and then find it doesn't fit or won't work.

I know there is a lot of info out there on this subject but i am getting more confused as i go. can anyone help consolidate for me?

**celeste** · 10-21-2011, 09:08 PM

This is totally my opinion but from experience I went five lug but regardless (4 lug or 5) when I added rear discs to my 89 I also went with a 93 cobra mc which required gutting the stock proportioning valve and adding an ajustable proportioning valve so I would not have a stiff pedal and could get the rear to work correctly. When I was done with the swap I still had to swap in a 93 brake booster too which finally made the pedal feel right. I upgraded the front by using hawk pads, braided lines and ss sleeves from maximum motorsports rather than doing the sn95 spindle swap. Honestly if you are not looking for anything serious I would just upgrade the front. The rear is an easy swap but the supporting mods for it can get costly, complicated and and sometimes a mystery/guess to solve to get the car to feel right again. My car stopped tremendously better with just the upgraded front. Let me know if you have any questions.

**MasterJ** · 10-21-2011, 09:36 PM

thanks for the information. i think i may just upgrade the front brakes first and see how it feels. do i need to upgrade the size of the rotors or did you just use the stock rotors and got the hawk pads? on maximum motor sports website i only found mustang big brake kits and it says you need to do the SN95 upgrade.
If i do the rear, do you keep the stock proportioning valve and convert it to adjustable or do you just gut the stock and add another proportioning valve that is adjustable? I also have read that putting on a different brake booster can be a pain because you need to offset it from the firewall somehow. I may not want to get into that.

Can i keep the stock master cylinder with any of these changes?

I appreciate it

**Donstang86** · 10-21-2011, 09:55 PM

I may have the rear disc setup in the garage from a 87-88 Turbocoupe!

**celeste** · 10-21-2011, 10:04 PM

Same rotor size but I am sure vented or slotted would help.... Everyone has an opinion on that. If you just upgrade thefront the stock mc and booster is fine You have to gut the stock and buy a plug from MM (MM-2450-A) and splice a proportional in where there is a union on the passenger side firewall. You will also need to make some hard line changes to go to the cobra mc. Mine was a 3 to 2 port conversion. Not sure of 85 may be different. Brake booster is supposedly easier on newer foxes (91 I think) and it was said you have to BFH the shock tower to get the cobra in on the older. I just elongated two holes and it was fairly easy without a BFH.

**Donstang86** · 10-21-2011, 10:15 PM

If you go with the 13" rotors you will need to do the complete sn95 swap and go to 17" five lug wheels. Its a few buck but is not that bad!

**gpfarrell** · 10-24-2011, 12:36 AM

I did this years ago... the details have blurred, but the '85s had tiny rotors. I think they were the same 10" rotors the 4 cyl and V6 cars had. You can easily step up to the 87+ 11 rotors. Hell, better Nikes would be step up! You should be able to find slotted, drilled, or slotted & drilled rotors anywhere. Race cars have drilled but race cars get new rotors long before stress cracks form. I went with slotted as I'm told they aren't prone to cracking. I'm sure some drilled rotors are fine, but I've never heard of problems with just slotted rotors. Then find yourself some Lincoln Mark VII calipers. They're much beefier than the Mustang stuff. Between the bigger rotors and bigger calipers your brakes will be able to absorb much more heat before they fade away.

Also, since it's all FoMoCo parts, you should be able to find anything you need at any auto parts store for a long, long time.

My 10-hole wheels clear the Lincoln calipers.

Oh, the Turbo Coupe rear end is a great way to go from a 7.5 with 2.73s or 3.08s to an 8.8 with 3.55s or 3.73s, keep your quad-shock stuff and get discs at the same time. I'm using an adj. proportioning valve to make mine work, and mine has worked fine for 10+ years now.

The car is lots of fun at BeaveRun. I can't say they won't fade, but they've never faded on me!

**Mark Aubele** · 10-24-2011, 02:02 AM

Don't waste your money on drilled or slotted rotors. Race cars rarely have drilled rotors. Take it from someone who has broken a drilled rotor (car came with them, ran them, regretted it), stay away, they will provide you with zero advantage over standard cheap blanks. Drilled rotors are for looks, that's it. It is so guys who buy new Porches and Corvettes can feel really racey when they drive to car shows.

I would go with a five lug swap and SN95 stuff, but as has been said above, swapping to the 87-93 V8 front brakes is a cheap (free?) and easy solution, that is much better than the woefully inadequate 79-86 stuff. Get some decent pads and you are done. I personally wouldn't bother with front discs unless you plan on going to the SN95 stuff or bigger, with the stock four link the rear tires are practically off the ground under braking anyway.

**juice_man_86** · 10-24-2011, 03:16 AM

If you plan on upgrading to the 87-93 V8 brakes, you will also need the spindles too. It is easy. The 86 and older cras had 4 cylinder brakes.

**Donstang86** · 10-24-2011, 07:04 AM

You can do whatever you want to do to get better brakes. The sn95 swap has been interesting but required some extras that I was surprised about. I still can't get the rear brake cabes correct for the application.

I do agree that cross drilled rotors are for show and are not necessary for the street. Mine is a cruiser and will not be driven hard.

My 11" swap was years ago and it did the job for me. I just said you only live once and went for it all.

The Lincoln MK VII setup for five lugs is another nice way to go but you need 87-93 v8 spindles. 11" Four lug is 87-93 V-8 Mustang (or 87-88 Thunderbird Turbocoupe). The turbocoupes have the same spindles set up for 11" rotors.

Four lug rear disc - Thunderbird Turbocoupe rear end or the expensive Ford Motorsport / Racing kit with axles.

One problem to keep in mind, the Turbocoupe rears already have axles and everything installed so you can clean up the rearend and bolt it in. When I was taking the axles out on my 86 GT 8.8, one carrier bolt broke off. I ended up using the carrier from a Ford Explorer and went to 31 spline Moser axles. Throw another $300 into the mix but it will be stronger! With a Turbocoupe rear end you wont have to play with the interior of the 8.8 /swapping axles. 87-88 Turbocoupe 5 speed cars were 3:55 and automatics were 3:73.

Rear disc axles also widens the track .75" on each side. I will have 17" x 9" Cobra Rs. Again the extra width needs to be a concern also

**PaxtonShelby** · 10-24-2011, 11:44 AM

Seems like everyone has nailed down the info in the replies above. I can vouch for gpfarrel's car ( '85 GT Conv ) with the Mk VII fronts and Turbo Coupe rear axle/brakes. His car stops great ( and trust me...sometimes he NEEDS it!!

- but don't we all... ). Also, his car is lowered and he has no rubbing in the rear due to the wider TC axle. That wider axle sure does fill out the rear wheel housing though! Looks great! And has he mentioned, he is running - by choice - the original 10-hole rims, so the car looks pretty much stock. He is a big fan of sleepers. His 13.1 second '03 Marauder ( street tires with 32psi, 3 child car seats in back ) with a Trilogy supercharger is more proof of that.

**Stangman701** · 10-24-2011, 12:30 PM

There is one other option that I didn't see mentioned in here. I also have an 85 GT and I upgraded to 11" front rotors with SVO calipers. I forget the exact #'s, but I think the piston in the SVO calipers is a good bit larger than the standard GT calipers. It may be the same as the lincoln caliper that was mentioned though. Definitely helped out the breaking a lot. The stock 10" brakes are just about worthless at anything above legal highway speeds. I hit them once at about 120 or so and it felt almost like I had no brakes.

I swapped all that stuff about 10 years ago though. If I had to do it all over again now I'd just go with the SN95 stuff with 13" rotors up front. That setup can be had fairly cheap and the car will look and brake a lot better.

**Donstang86** · 10-24-2011, 11:44 PM

The Lincoln and SVO calipers have a 73MM piston if I am correct. I picked up a rebuilt pair of these years ago and never put them on until you reminded me of it. I have got to quit collecting parts lol!

**MasterJ** · 10-25-2011, 08:15 AM

Thanks for the info everyone. When i get a free couple of minutes i will digest everything and see if i have anymore questions.

**Dan B.** · 10-30-2011, 07:03 AM

I have a 1988 Thunderbird Sport Coupe that I am in progress of swapping parts on. It had the 10" front discs and drum rears. The current braking set up is from a Turbo Coupe....11" front disc upgrade and disc rear w/ 3.55's. Before doing the front swap I did try to get the rear discs to work with the stock MC and Turbo Coupe prop valve...no luck. So I am reading your thread with great interest to see what the others have to say.

But, from the reading I have done...still need to pull the trigger on the parts purchase...is that I need to swap in a 1993 Cobra MC, gut the stock prop valve and install an adjustable prop valve. This will be about a $150 investment but if it works, I'll still keep my four lug wheels (like you also wanted to to) and have a substantially better braking set up.

**Martin0660** · 10-30-2011, 11:25 AM

Just to pile on, when you change from the early spindles, to the 87+ V8 spindles (or TC as mentioned), watch your struts. The earlier stuff is wider at the point it bolts on, most vendors proveide a spacer to take up this gap, but you wont have it if you keep your current struts.

I have the SVO calipers (same 73mm as Lincoln) and one of the best upgrades I could imagine was going to the SS caliper bushings. Amazing the change in feel it made to the brakes. Even better than the SS lines IMO, both helped feel, but the bushings was amazing for me.

**Dan B.** · 10-30-2011, 11:31 AM

I'm swapping everyting from the top of the strut to the control arm bolts! Had a TC parts car.

**Donstang86** · 10-30-2011, 02:45 PM

Originally Posted by Martin0660

Just to pile on, when you change from the early spindles, to the 87+ V8 spindles (or TC as mentioned), watch your struts. The earlier stuff is wider at the point it bolts on, most vendors proveide a spacer to take up this gap, but you wont have it if you keep your current struts.

I have the SVO calipers (same 73mm as Lincoln) and one of the best upgrades I could imagine was going to the SS caliper bushings. Amazing the change in feel it made to the brakes. Even better than the SS lines IMO, both helped feel, but the bushings was amazing for me.

You know in my parts stash I actuall have a set of the stainless bushings from Steeda.