Rear Drum Brakes For Track Use

4955 Views 52 Replies 10 Participants Last post by silverblueBP, Sep 6, 2021

daveoxide

Discussion Starter · Jul 1, 2021

My last HPDE in my 67 involved a lot of excessively long braking zones with me fighting rear brake lockup. On heavy high speed braking zones with less than smooth pavement, the rear axle would get unsettled and start hopping. A quick release of brake pedal pressure would calm it down but another bump while I reapplied brakes and it would start all over again.

I do have an adjustable pressure reducing valve installed, and after every session I gave it another turn or two to reduce rear brake pressure. Unfortunately it never completely cured the problem, and I think I only have a few turns left on the knob before it’s at max pressure reduction. I was able to work around the issue by starting my braking early, ease up over the bumpy stuff, then hard on the brakes again when the pavement smoothed out. I could also just brake less aggressively, which worked too, but my braking zones were twice as long as everybody else out there with modern vehicles

Anyway, my questions are:
1. Is anyone using rear drums successfully for track use? Successfully… as in no excitement high speed braking (100+ down to 30mph).
2. Is the self energizing nature of how drum brakes work part of the problem with modulating brake pressure during heavy braking events?
3. Could my issue be the lack of axle location devices to control axle wrap while slowing down? I have traction bars that work great during acceleration, but have zero effect when slowing down.

I am curious what others are using to control rear brake lockup and axle hop during braking. Comments and input is appreciated!

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patrickstapler

· #21 · Jul 2, 2021

You have some other problem then. I don't recall seeing any vintage car (including mine) at the last two events I have attended experience the issues you describe. If it were me, I would call John at ORP, describe what you are experiencing and see what he prescribes. I agree with Mark's comments on the traction bars. I don't recall seeing any of the vintage road race cars with traction bars installed.

Are you making like 600HP+ or something?

jkg2101

· #22 · Jul 2, 2021

If someone is truly trying to be vintage legal, I think the drums have to be 10”? It sounds like most of us use 11”? Not sure if it matters or anyone cares

patrickstapler

· #23 · Jul 2, 2021

No Sir! Every event/club I have visited permits the 11" rear drums. Rear discs are referred to as cheater brakes, but several still run them.

silverblueBP

· #24 · Jul 2, 2021

daveoxide said:
I’ve run without them on the street and it isn’t pretty, I don’t envision the track will be any kinder! These aren’t the Shelby under riders, they are very similar to the slide-a-links in how they operate; no resistance to axle movement up and down nor at an angle. And they most definitely do the intended job during acceleration… braking not so much, but they weren’t designed for that. Without them, it sounds like I have a 200 lb basketball on the loose back there!

You have problems with your rear. A 65-66 does not need traction bars of any type if you have good springs, shocks and a locating device. Not one single person that I’ve raced with has traction bars.

Mark

Reactions: 1

daveoxide

Discussion Starter · #25 · Jul 2, 2021

silverblueBP said:
You have problems with your rear. A 65-66 does not need traction bars of any type if you have good springs, shocks and a locating device. Not one single person that I’ve raced with has traction bars.

Mark

The more responses I read the more it appears this may be the case. I guess I will have to dive deep into the rear suspension bits and give everything a thorough once over.

Reactions: 2

Russstang

· #26 · Jul 2, 2021

Any chance these under rider bars could cause this? Do you have lowering blocks? I have no answers, only questions.

patrickstapler

· #27 · Jul 2, 2021

I can almost 100% guarantee that eliminating the traction bars, replacing the leafs with a high quality reverse-eye 4 1/2 or 5 leaf and installation of Del-A-Lum bushings and/or PH bar will cure your problems. But you already have a PH bar right?

daveoxide

Discussion Starter · #28 · Jul 3, 2021

I don’t have lowering blocks per se but I do have small angle wedges installed to take care of a pinion angle issue. I’ve wondered if that extra bit of distance from the springs (~1/2”) is adding to the rotational forces the springs need to resist as the axle winds up. Might have to think about this relationship in more detail.

I’ve got a panhard bar already yes, and it’s addition was very noticeable and very positive to the driving experience. I’ve got poly bushings in the front of the spring eye, and they are VERY hard… not aluminum hard, but stiff nonetheless.

Based on everyone’s input thus far, I am questioning the integrity of my 20 year old leaf springs and couple year old shocks. One thing I noticed recently is when I jack up the rear of the car, by placing the jack under the center diff, the right rear tire lifts off the pavement about an inch before the left rear tire starts coming up. When it’s on the ground, the fender wells are the same distance from the ground, but when the rear end is in the air, the right rear tire is tucked further up in the well (with the jack under the differential). I’d be curious if anyone else sees this phenomenon with their own vehicle…. It could be nothing, but I won’t know until I rip everything apart.

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silverblueBP

· #29 · Jul 3, 2021

I have angle shims and a 1” drop block. No problems. What type rear springs do you have?

Mark

daveoxide

Discussion Starter · #30 · Jul 3, 2021

silverblueBP said:
I have angle shims and a 1” drop block. No problems. What type rear springs do you have?

Mark

Good to know about the spacers/wedges, thanks!

Current rear leafs are “heavy duty” 4 leaf standard eye springs, and are 20 years old with at least 75k of not so kind miles on them. 😇

silverblueBP

· #31 · Jul 3, 2021

daveoxide said:
Good to know about the spacers/wedges, thanks!

Current rear leafs are “heavy duty” 4 leaf standard eye springs, and are 20 years old with at least 75k of not so kind miles on them.

Some mid eye 4 1/2 or 5 leaf springs will fix you up. Or you can call John at ORP and get his wizard spring setup from junkyard cars. He could tell you what to look for to make a custom leaf pack. Me, I’m too lazy to go through all that!

Mark

Reactions: 1

Russstang

· #32 · Jul 3, 2021

My vote is for springs, followed by shocks. Not sure what you said you had but there seems to be some bad compression/damping mojo going on there. Also, what size tire do you have?

daveoxide

Discussion Starter · #33 · Aug 2, 2021

A quick update… I went ahead and replaced the old leaf springs with 5 leaf units. My shocks were still good, so those stayed. It can brake hard now with no more wheel hop, which is great… but the rears still lock up way before the fronts. My proportioning valve knob is cranked all the way decreased, which I presume is least pressure to rear brakes? I will double check this just in case my logic is incorrect.

If I assume my brake bias knob is cranked the correct direction, then my next step is to look at the front brakes. I’m wondering if the front brakes aren’t creating enough friction; cooked pads, glazed rotors? Gonna have to dive into the front brakes and check them out. If somebody knows of a place to get better brake pads for Granada brakes, please let me know!

Also, I didn’t find any cracked leafs or anything major, but I did notice that the drivers side leaf was de-arched more than the passenger side, see pic.

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Reactions: 2

sheza65

· #34 · Aug 24, 2021

@daveoxide I got Granada Porterfield R4-S # D-91 from Opentracker.

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Reactions: 1

jkg2101

· #35 · Aug 24, 2021

i am running the same shoes on my 11" drums. limited experience so far on track but seem good

silverblueBP

· #36 · Aug 24, 2021

Not sure if I’ve mentioned this yet, but when I switched to the 11” drums, I used std brake shoes. They seem to work well paired with the Lincoln caliper front discs and R4 pads.

Mark

bmcgc

· #37 · Aug 24, 2021

What setup did the TransAm Mustangs use?

silverblueBP

· #38 · Aug 25, 2021

The TA cars from 68 up were discs all around.

Mark

TXBoss302

· #39 · Aug 25, 2021

+1 on the Porterfield pads in the R4-S compound. They can put that compound on pretty much any pad plates.

Quick question - Have you ever had good brake balance? Just wondering what the piston area is on the Granada Calipers and if it's enough to balance out with your rear drum setup. You may have to play around with the piston area on the rear cylinders to reduce the rear brake force. Go down in piston area will reduce your brake force for same amount of hydraulic pressure.

Reactions: 1

sheza65

· #40 · Aug 26, 2021

Granada front pistons diameter:

Piston Size (OD) (IN)

2.596

Area is ~ 5.29 sq. in.

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