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66' GT with Manual Disc Brakes good pedal, no stop

3K views 14 replies 9 participants last post by  baylensmanfl 
#1 ·
Hey Folks!


Well after a bit of forum searching I'm wondering if I have a common problem.


My 66' GT [auto trans, 289, manual front disk/rear drum brakes]


Pretty much from day 1 of the restoration, I've never had good brakes. Very hard/good feel pedal but no stopping power.
I had to replace the entire system, all of it. At first I went back stockish, with the large single res M/C, had to add a Wildwood preportion valve
[removed the old crusty original one] new SS lines, calipers, cylenders, hoses, etc.


This was done back in 94'. I added the silicone dot 5 fluid because I figured the car may sit some untill I got it all finished.
Well, in the past few months, it started pulling to one side, hard. So I figured the front calipers were stuck,
in process of working on them one of the calipers stripped the crossover tube threads, and I couldn't fix it, so I ended up
buying a replacement pair.


Went and upgraded to the dual res M/C as well, with new hoses too, The brake pads and the rear cyl's I've not replaced yet.
But, the brakes hardly have 14k on them over a 22year period.


So I'm wondering, were these cars just so-so with the brake systems?
Or do I have another issue??


I thought it may be the per-portioning valve or maybe the rear brakes that seem to keep staying out of adjustment, putting all the braking effort on the front discs,
but, It's scary when you go past where you want to stop when you're "giving it all she's got" and it just wont stop!


So, hopefully this weekend I can get it all back together and see if it makes any difference.


My only other guess is it's my type of brake pads (think they were Raybestos) but it's been 20+ years, they still look new though.


Anyone had this issue and remedied it with just changing brand of brake pads or some other method?


Saw a brand called "Hawk" but they were like $100+ for a set of pads.
Napa has pads for under $20, few of the Mustang parts houses have them in the $30 range.


I didn't upgrade to power brakes yet, not sure I have enough vaccume to run the booster [someone suggested 18'' of vac for their booster].


Any suggestions anyone?
Anything that helps would be greatly appreciated!


T
 
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#2 ·
Sounds like a typical manual disc brake setup.
Marginally better then power drum brakes.
I'd go PDB, world of difference. My ex 71 Roadrunner
had 8"-10"Hg and no probs running vacuum assist
brakes. Just my .02.
 
#3 ·
The brake system on these cars are very, very good provided you are using the proper spec'd components which I'm swagging is the issue......

Braking co-efficient iswhat identifies the bite rating of the linings- you want the CE to be no less than that of the OEM....., (the replacement liningsat most parts houses have a braking co-efficient of around .25, that is about50% less than what the oem called for in the 60's) this will drive most e-base distributors & big boxstore "experts" right out of their mind because they either cannot verify this info or you will find the spec is less than oem....and I'm thinking this is part of the issue...........look for a CE that is .49 or greater. IMHO, I really doubt if you are going to find any brake lining (pads) that is of any quality until you hit the $100 mark or higher.....

With regards to brake linings in general,

Ceramics: They are good but do not develop any more friction than good quality OEM linings

Performance Friction & Hawk: Good braking, but like any performance lining they have to be carefully selected in addition to chewing up a drum/rotor, they can be very dirty compared to OEM.

Wagner & Raybestos: a line of products that is 100% marketing and mfg fromvery low quality/inexpensive and/or imported products with the mfg's notproviding any back-up or support on product failures (and I mean real uglyspontaneous, catestropihic failures)

VelveTouch lining- Used for manydecades and was the original lining used in all Shelby Mustangs in the 60’s (Ipersonally have used the Velvetouch lining since 1960’s until brake liningproduction ceased in 1986), then switched to Carbo. Wellman has been thebuilder of braking linings for Formula 1 race teams for more than 30years and VT is now available again.

Bendix- TitaniuMetallic™ II, a newer lining (semi-metallic) and although I havenot personally used this, I have always been impressed with Bendix brakelinings and this particular lining IIMHO would be a low dust, excellent oemupgrade/mild performance type brake lining.

CarboTech Engineering lining, which I have usedfor about 20+ years and been very happy on multiple full size (V8) cars and trucks. This particular lining has a high friction co-efficient,excellent pedal feel, wears (typically 50,000 to 75,000 miles beforereplacement is required) and produces less dust than OEM linings.

I highly recommend speaking to them by phone for linings that would be best foryour application.
 
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#5 ·
Hey folks,

Thanks for the responses!

Power disk brakes are still on the table, but that was some good info on the brake linings themselves.

and drum brakes, when all working right, do stop pretty good.


I didn't get as far along as I wanted, got the Pass side disc roughed up, repacked the bearings and mounted the caliper with the old pads for now.
going to try to do the same to the driver side next.

still need to flush out the dot 5 silicone from the lines and the rears.
then mount the dual res M/C and see how this thing drives and stops.

IF nothing changes, then new brake pads and possibly the power option (esp since I've already bought the calipers and dual res M/C).

the only other possibility is the perportion valve is out of adjustment.

Well, any other ideas are welcomed, I'll try to update as I go along.

Thank you all for the suggestions!

T
 
#6 ·
FYI, power brakes don't get you better braking only less effort in applying the brakes. Efficient braking is a function of friction materials, proper break-in, hydraulic system in proper working order, and properly prepared braking surfaces.
IMHO, ECB and Porterfield are top brands for good friction materials. Yes they are twice to 3 times more, but, are well respected for offering quality friction materials.
 
#7 ·
#9 ·
There was a thread a few weeks ago along the same topic. Not sure how it turned out, but you might take a look.

You might step back and take a look at all the components you have installed and make sure they work with each other. Do you have the correct pedal assembly, pedal to MC rod, and all the other stuff? Is everything adjusted?
 
#10 ·
I had a similar arrangement to yours a while back that never seemed to stop well. Pedal felt OK, a bit mushy. But I think it was mostly the rear drums being out of adjustment. Once I changed to rear discs (no more adjustment needed), it stopped incredibly well! And this was with Kelsey-Hayes style fronts. I was using Hawk HP+ pads in the front, and Wilwood Polymatrix E in the rear. Lots of brake dust, not very good stopping power under 50 degrees, but once it warms up and the brakes dry off, it could send someone through a windshield if they weren't buckled in.

First thing for your system: Check your drum adjustment. Second: Check your pedal pushrod length. It may not be engaging the master cylinder entirely. It'll feel like it inside, but it almost needs preload. Then start worrying about pad materials.
 
#11 ·
Hey all,
That's a good question on was everything adjusted, and having correct pedal /rod items...

best guess is yes as far as I know. But I'm betting my rear drums were prob out of adjustment, the backup, hit the brakes method don't work so well on adjusting them as I'd like.

When I started this resto, the car had been sitting since 77' when I found it in 88'. Whatever was on the car at that time was replaced, (if it was ok). I believe I used
the same MC rod but with a new replacement large single bore MC at the time.

Now yall got me thinking it may have been my rear's being out of adjustment causing the problem, I don't drive this car as much as I like, it's very
possible that was a majority of my issue, that and the stripped threads on my pass side caliper.
Of course I found a few other issues that "at the time" I didn't have the correct flare tool and had to Teflon a few line connections to get them to stop leaking.

I'll muck with it more this week/weekend and report back any updates.

Thanks all for the suggestions,
I like the idea of rear disk brakes too, may need to look a that as a future option.

T
 
#12 ·
It comes back to fluid pressure and lining materials. A 3/4 to 15/16 bore MC will generate the fluid pressure you need for adequate stopping along with a good pad. Many aftermarket or even the wrong part as far as a master cylinder even though it may bolt right up precipitates many problems. you get a 1&1/16 mc that moves tons of fluid but at low pressure like 750psi where as the 3/4" bore moves less volume but easily generates
1200-1300 psi. Take yours off and use a micrometer or caliper and measure the hole the piston goes into - that is the size you have as the hole is a machined tube the piston rod travels in. Dealt with this a couple times myself...dont give up.
 
#13 ·
finally finished!

Hey Folks,

I do have an update:

Apparently I had a few issues going on.

First off, I decided to go back to Dot 3.
The dot5 did work and I realize now that I should have flushed the system every 4-5 years.
I didn't do that and after about 24 years, I was surprised to see how little rust was in the system. [just in the front calipers].

The rear brakes were out of adjustment and when I pulled the cylinders I had a heck of a time getting the pistons out, kinda like they were stuck. But once they came out, the bores were like new.
Not sure why they were stuck but once I washed them out good and re-assembled it with a good dot 3 soaking, they work like new.

My other issue was I could not get the system to gravity bleed---at all.
That was caused by multiple nut/flare mini-leaks.

The Stainless lines were being a bit*ch to fix but doing the [tighten-loosen-tighten-loosen-tighten] I managed to fix all of them so far and get a good seal on
the flare/nut connections.

That really helped, once I got that done the fronts gravity bled good, the rears not so good, but I eventually got them to grav bleed after a few rounds with using the 1-man brake bleeder tool
and some pump/bleed action.
Also, I got me some "Line wrenches" to do this, they def help when you gotta get them tight so you don't round the nuts. Harbor Freight had a set for like $13 bucks, I really recommend
using a line wrench, they can be fun to get on verses the regular type but I had to put the gorilla grip on some of these stainless lines in the tight-loosen method, I know i'd have
beggared them and probably my hand using a non line wrench.

First test drive, man I got good brakes now! And at first I had a bit of left hand pull, but after a few brake tests it cleared.
I May even leave the proportioning valve set as is. But needs more test drives, been too hot/rainy here to do that so maybe next weekend.

Also, there was some discussion about adjusting the MC rod length, my M/C rod is not adjustable, It's a 1 piece rod.
But, I seem to have good pedal movement and it seems to be doing a full stroke on the MC best I can tell.

One other note, I did buy some denatured alcohol but never used it, I ended up flushing the system with enough dot 3 I didn't get to use it.

On the first pump/bleed, the MC did a backwash and pulled some dot 5 into the MC from the remnants in the front lines[which had dripped dry I thought],
I just drained it down as low as possible without exposing the MC drain holes to air refilled and did it again. It's flushed now!

You can actually see if it's mixed as the remaining dot 5 made the dot 3 fluid somewhat cloudy, not "white cloudy" but you could tell "something else was mixed in it". I did use a flashlight to illuminate it good.

I think i'm ok for now, I'll do more test driving and check for any other leaks and make sure the MC fluid stays "clean/clear".

Thank you all for the suggestions & ideas and such, it was a big help, wish it didn't take a month of Saturdays to fix but it's done for now.

T
 
#15 ·
Thanks for getting back, and its a good reminder for the rest of us. Little bits here and there can add up. On brakes and electrical, bad ground here weak connection there chase it for months. Same with the brakes especially drums, easy to get out of adjustment. Ford does self adjust. Back up slowly and stab the brake, then back up another 10 ft and stab the brake repeat 3 or 4 times. Also with new pads most OE's recommend going from 30 to full stop with fairly heavy pedal pressure around 5 times leaving a 30 second cool down between decel's to avoid warping, this helps the pads to "SEAT".
 
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