Moparts
Rear disc conversion= low pedal, any suggestions.
Posted By: hunterstroble
Rear disc conversion= low pedal, any suggestions. - 12/24/11 06:54 AM
Hello all! My dad and I have '69 dart. It has manual brakes. 73 Dart discs up front and always had a great pedal. We got a summit rear disc brake conversion, single piston calipers w/ built in parking brake. Since the swap the pedal needed two pumps to get a good firm pedal. fluid shoots out, no air. Blead it, used a pressure bleeder ect. It got better when I tensioned the e/brake cable a bit. It is not dragging or anything. The master cylinder is a drum rear, disc front m/c from a 73 dart. After all my goofing around the pedal finally gets firm on one pump, but i'm still not satisifed with it. I was thinking of a 2 lb res. valve for the rear. Also I do have the bleeder mounted upright. Thank you so much! Happy holidays.
Posted By: Kern Dog
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:05 AM
Some may tell you that you need a dedicated 4 wheel disc master cylinder, but I have a disc/drum master cylinder on my Charger with 4 wheel discs and it works fantastic. Your situation may come down to an issue of brake bias. Maybe the rear caliper pistons are too large, requiring a LOT of fluid, too much for the master cylinder to pump them to the right amount of pressure. If this is the case, it would be cheaper to swap master cylinders rather than to switch to a caliper with smaller pistons.
Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:07 AM
I've heard of people going to cordoba m/c's? Was hoping to get away with my factory disc/drum. But if I have to brakes are rather important to have. thank you for your input.
Posted By: Kern Dog
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:14 AM
My Charger has the Cordoba 12" front rotors and a rear disc conversion from Moparts member Dr Diff. The rear kit uses Toyota rotors with Mustang calipers and a custom fabbed bracket to attach to a Mopar 8 3/4 axle. Also in the mix, a lumpy '509 cammed 493 engine to feed the power boosted master cylinder! Somehow it all works, defying logic. I think that the smallish rear caliper piston is a factor.
Posted By: MR_P_BODY
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:19 AM
You need more volume in the master(bigger bore)
Posted By: DoctorDiff
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:23 AM
Are the rear bleeder valves facing upward?
Posted By: RapidRobert
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:32 AM
1st get a pair of brass male inverted flare end plugs from the Edelman section at your parts house and cap both M/C bores and if the M/C is good & bled out the pedal will be high and tight w virtually no travel. Then hookup the fronts & see if they pump up (air) & if so bleed em out till they're good then hookup the rears & repeat. Now see if they're all good. Holler w any news. If need be, bleed out the fronts & get em tight then cap em & bleed out the rears & get them tight then hook the fronts back up & see if everything is now all good. This'll help you determine if it is air (common) or lack of M/C capacity (less likely)
Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:32 AM
rear bleeders are facing upward. Any recconmendations on what m/c to use at what parts I need to make it work? I/e m/c pushrod ect... It is a manual brake set up I have now. Thanks all! If I don't replay for a while my computer is not to relaible and i'm down for a day sometimes. Thanks!
Posted By: MR_P_BODY
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:33 AM
Quote:
Are the rear bleeder valves facing upward?
Doc he does say they are up
Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:34 AM
Robert, I did do that. Everything checks out. No air whatsoever. Thanks! The suggestions and help is much appreciated all.
The summit tech guy said they were mustang calipers if that helps at all.
Posted By: RapidRobert
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:41 AM
Holler what it ends up being as I want to do a 4 wheel disc deal too (homemade so I need some ballpark bore dia #'s to work w) or avoid
Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:42 AM
Sure thing, I'm sure i'm not the first person to come across this.
Posted By: MR_P_BODY
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:47 AM
Quote:
Sure thing, I'm sure i'm not the first person to come across this.
I will assume this kit came with rotors that matched
the calipers...the reason I ask is... if you have a
1/4 thick rotor and the caliper requires a 3/8 thick
rotor then you would have to hit the pedal a couple
of times to move the piston enough to contact the rotor
Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:50 AM
Yes it came as a complete kit. It is the summit set up. I told my dad to contact dr diff before buying anything but....stubborn old man.
Posted By: MR_P_BODY
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 08:05 AM
Quote:
Yes it came as a complete kit. It is the summit set up. I told my dad to contact dr diff before buying anything but....stubborn old man.
Then I believe you just need a bigger bore master
(more volume)
Posted By: hooziewhatsit
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 08:17 AM
I agree with going to a bigger bore. I had to go to an 1 1/4" MC with my 4 wheel disk conversion. It's still not great, but I'm thinking now that may be the booster.
I calculated the surface area of the old drum pistons compared to the old MC bore, then figured the percentage larger I had to go given the new disk piston surface area.
Posted By: DAYCLONA
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 11:20 AM
Quote:
Hello all! My dad and I have '69 dart. It has manual brakes. 73 Dart discs up front and always had a great pedal. We got a summit rear disc brake conversion, single piston calipers w/ built in parking brake. Since the swap the pedal needed two pumps to get a good firm pedal. fluid shoots out, no air. Blead it, used a pressure bleeder ect. It got better when I tensioned the e/brake cable a bit. It is not dragging or anything. The master cylinder is a drum rear, disc front m/c from a 73 dart. After all my goofing around the pedal finally gets firm on one pump, but i'm still not satisifed with it. I was thinking of a 2 lb res. valve for the rear. Also I do have the bleeder mounted upright. Thank you so much! Happy holidays.
I've done my share of 4 wheel disc brake set-ups over the years for myself and customers cars....so I know what your going thru, the Summit kit is basically a cheap chinese version of the SSBC set-up...
If the master your using is the correct 73 A body vintage, the casting number will be 3461187 this master has 1 1/32" bore, but has a limited stroke on the piston/bore, your not getting the volume you need to the rear, I'd recommend you use a 1970 B body MANUAL master, casting number 2225621, this master has 1 1/8" bore and amble travel in the piston/bore, I'd also recommend you get rid of the factory proportioning valve if your still using it, 4 wheel disc don't require a PV or distribution block, the front lines can be teed off left and right respectively, the rear line can be plumbed directly off the master
The Fenco line of rebuilt masters (AutoZone,CarQuest,NAPA, etc) are better quality than the Cardone line IMHO...Fenco PN# M1404 should be your ideal choice, the lines exit the master from the fender side, if you require the lines to exit the master from the engine side, Fenco PN# M1475 these are both 70 B Body only applications with 1 1/8" bore and disc/drum masters, bolt on, you MAY need adapters, or change and reflare the fittings/lines that attach to the master's ports...maybe
Mike
Posted By: upnover
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 03:25 PM
put a residual valve on it, ssbc has them, buythe bigger one
Posted By: DoctorDiff
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 04:25 PM
Are the lines routed correctly? The front line should run ot the rear brakes and vise-versa.
A '73 Dart (MANUAL disc) 1 1/32" bore master should yield a firm pedal with that system. A larger bore will give you a harder pedal, but lower line pressure and less clamping force at the pads.
I would run a simple, drum brake distribution valve. You can always add an adjustable prop valve if the rear brakes lock up before the fronts.
Posted By: dogdays
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 05:57 PM
And I don't think it is good to run a residual pressure valve on disks.
R.
Posted By: MR_P_BODY
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 06:09 PM
Quote:
And I don't think it is good to run a residual pressure valve on disks.
R.
If the master is above the calipers then theres no
reason for them
Posted By: Greentween
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 06:14 PM
I've got that rear kit in a 74 challenger, stock rebuilt m/c, gutted prop valve, stock front disks. Rear calipers are small so no rear valve needed. Maybe the fluid drained out from the master during install, and now the master needs bench bleeding.
What did you use for parking brake cables? I havent hooked up those yet.
Posted By: justinp61
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 06:25 PM
Quote:
I'd also recommend you get rid of the factory proportioning valve if your still using it, 4 wheel disc don't require a PV or distribution block, the front lines can be teed off left and right respectively, the rear line can be plumbed directly off the master
If you are using a proportining valve from the 73 donor car you can remove all the internal parts and use it as a distribution block. Thats what I did when I installed my aluminum mc and it works fine, plus I didn't have to re-do my brake lines.
Posted By: Todd
Re: Rear disc conversion= low pedal, any suggestions. - 12/24/11 07:43 PM
Hey I got the same kit from summit and had the same problem. What I found was that one of the piston seals were pulling the piston back to far when releasing the pedal. It was pulling back .090
from the pad. The seal was some how twisted when it was assembled. Was in the same situation you have. After multiple phone calls and e-mails, Got the caliper replaced and works great.
I know, The bleeder is on the bottom in the picture but the directions and the tech support said to install this way. There is a bleeder in the banjo fitting on the line.
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Posted By: hunterstroble
Re: Rear disc conversion= low pedal, any suggestions. - 12/28/11 07:00 PM
Thanks all, I have some family stuff to get back to but I will let everyone know what fixes it.