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Old 11-24-2005, 01:07 PM
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Will Rear Disc's Stop Better Than Rear Drums??

I did a search on this but didn't get a definitive answer. Is it worth the time & money to convert my rear drum brakes over to disc? My rod has 11" front disc's, with a Ford 9" rear end & drums, power booster, combination valve and 205/65-15 tires in front, 235/70-15 rears.

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Old 11-24-2005, 02:44 PM
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As a general rule YES......

That's why Ford and GM have went to 4 wheel disc brakes on most of the newer vehicles.

The lighter the vehicle....the less difference you will see between disc rears and drum rears. You will also need a different master cylinder for a 4 wheel disc brake setup.

It is generally accepted that the front brakes does 60 % of the braking and the rear does the rest ( 40 % ) .....on most vehicles.
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Old 11-24-2005, 02:47 PM
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It depends on how you define "better". It sounds to me that you have a fairly light weight car that you run on the street. If you're having no problems stopping I have to ask: Why change anything if it ain't broke?
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Old 11-24-2005, 02:50 PM
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Quote:
Originally Posted by acr
I did a search on this but didn't get a definitive answer. Is it worth the time & money to convert my rear drum brakes over to disc? My rod has 11" front disc's, with a Ford 9" rear end & drums, power booster, combination valve and 205/65-15 tires in front, 235/70-15 rears.
Probably not.

The rear drum brakes that you have at present are originally designed for a much heavier car than what you have and assuming they are adjusted correctly will work great.

Some advantages of disc brake rear (for your consideration):

Will not fade as quickly as drum brakes.
Not easily affected when wet.
Ease of replacing pads versus doing a complete brake job with drum brakes.

Just for a side note. My latest project has 4 wheel disc brakes (9" Ford rear) and I am using GM rear disc brake calipers that have the emergency brake as part of the caliper. Running GM calipers on the front. Below the floor dual diaphragm booster and 1" bore Master cylinder. 2# residual valves in front and rear lines and adjustable proportioning valve on the rear line. So far I have been unable to get a good pedal. Takes two pumps. I don't think I have any air in the lines and recently read an article where it said to use a 10# residual on the rear with those calipers to correct the low pedal. I haven't tried that yet. My point here is that if I had left the stock drum brakes in place I would have good brakes and have saved a few hundred dollars. The rear calipers are $100 each.

As always, the final choice is yours to make. ENJOY!!!
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Old 11-24-2005, 03:17 PM
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Quote:
Originally Posted by Frisco
Probably not.

The rear drum brakes that you have at present are originally designed for a much heavier car than what you have and assuming they are adjusted correctly will work great.

Some advantages of disc brake rear (for your consideration):

Will not fade as quickly as drum brakes.
Not easily affected when wet.
Ease of replacing pads versus doing a complete brake job with drum brakes.

Just for a side note. My latest project has 4 wheel disc brakes (9" Ford rear) and I am using GM rear disc brake calipers that have the emergency brake as part of the caliper. Running GM calipers on the front. Below the floor dual diaphragm booster and 1" bore Master cylinder. 2# residual valves in front and rear lines and adjustable proportioning valve on the rear line. So far I have been unable to get a good pedal. Takes two pumps. I don't think I have any air in the lines and recently read an article where it said to use a 10# residual on the rear with those calipers to correct the low pedal. I haven't tried that yet. My point here is that if I had left the stock drum brakes in place I would have good brakes and have saved a few hundred dollars. The rear calipers are $100 each.

As always, the final choice is yours to make. ENJOY!!!
I have seen 10 # valves on discs, but in general it is not recommended since it makes the brakes drag.

Could be air or bad master cylinder.

I also have heard that an adjustable proportioning valve to rear disc brakes will cause that. Try removing the prop valve just to see if the problem goes away.

Let me know. Please.
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Old 11-24-2005, 03:30 PM
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Quote:
Originally Posted by acr
I did a search on this but didn't get a definitive answer. Is it worth the time & money to convert my rear drum brakes over to disc? My rod has 11" front disc's, with a Ford 9" rear end & drums, power booster, combination valve and 205/65-15 tires in front, 235/70-15 rears.
I have to agree with MM and frisco.
Depends on the WOW factor.

Discs will not stop faster..... that is determined by the tire traction and how good you can manipulate the pedal at the verge of sliding the tires = "threshold braking"... (ah anti-lock brakes) ... As for true stopping ability, fat soft front tires are the best. The more traction the faster you will stop.

Discs are easier to modulate and have advantages as per use in water, fade in the mountains, etc.

Newer cars with rear discs tend to stop quicker because the anti-squat is improved allowing more rear bias and consequently more stopping power by the rear tires.

Ever seen a late model mustang jam on the brakes?...... NOSE DIVE = rear tire slide.

Me? I stayed with the rear drums.

check out www.readershotrods.com drag cars/georges drag strip
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Old 11-24-2005, 08:39 PM
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If it stops well enough with rear drums, I wouldn't change. Drums work better as far as a parking brake, and if the hydraulics go out, drums don't take near as much pedal or manual effort to get the car stopped.
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Old 11-25-2005, 09:44 AM
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rear discs

I spent a lot of time and money switching to rear discs and didn't notice any difference on my daily driven streetrod. Maybe if I drove it harder I would have. Bill
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Old 11-26-2005, 05:55 AM
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Thanks to all for your replys, as usual here very informative & helpful. acr
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Old 11-26-2005, 06:42 AM
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Frisco, I have almost the identical setup as you do except I have Wilwwod calipers. I used a 67 Corvette 427 manual 4 wheel disk master cylinder and my pedal feels good, no need to pump. Me thinks you have either some air or a faulty m/c. I don't see the prop valve or the 10# residual causing your problem.

Vince
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Old 11-28-2005, 02:15 PM
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Quote:
Originally Posted by xntrik
Newer cars with rear discs tend to stop quicker because the anti-squat is improved allowing more rear bias and consequently more stopping power by the rear tires.

Ever seen a late model mustang jam on the brakes?...... NOSE DIVE = rear tire slide.
I take it you are talking about anti-dive in the front end?...or are you talking about anti-lift at the back end?


Care to explain any of this to me? Why would the nose diving cause the rear tires to slide? How much anti-dive are we talking about?
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Old 11-28-2005, 02:22 PM
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From what I have seen of rear disks on the newer GM cars, they are a PITA...................
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Old 11-28-2005, 02:39 PM
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Quote:
Originally Posted by poncho62
From what I have seen of rear disks on the newer GM cars, they are a PITA...................
By newer do you mean what GM used up to the mid 90's that had the e-brake as part of the caliper or the newist ones that use a small drum inside the rotor as the e-brake and a standard caliper for the main brake?

What exactly is a PITA about them?
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Old 11-28-2005, 02:42 PM
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YEAH...THE EARLY 90S....NOT SO MUCH TAHT THEY WERE SO HARD TO WORK ON, BUT THE FACT THAT THEY DON'T LAST AND YOU ARE REPLACING THEM EVERY YEAR.

Whoops...cap locks on.................
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Old 11-28-2005, 02:47 PM
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Quote:
Originally Posted by poncho62
YEAH...THE EARLY 90S....NOT SO MUCH TAHT THEY WERE SO HARD TO WORK ON, BUT THE FACT THAT THEY DON'T LAST AND YOU ARE REPLACING THEM EVERY YEAR.

Whoops...cap locks on.................
I wasn't a big fan of those either. I didn't like how the e-brake needed to be used to adjust the brakes.

I have a set of 2000 s-blazer brakes on my s10. I still haven't hooked up the e-brake part but I like the newer design with the "bridge" that holds the pads in place allowing the caliper to float better (no force on the sliding pins).
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