Soft pedal on modified 79 MGB : MG Engine Swaps Forum : MG Experience Forums : The MG Experience

Soft pedal on modified 79 MGB #1
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 02:05PM Registered: 8 years ago Posts: 1,124

I posted a similar thread on the UK MG BBS but thought I would try and get opinions here as well. Background is as follows: I have a SC'ed 1979 MGB with a FastCars (Ted Lathrup) front coil over suspension with Wilwood calipers and a Hoyle rear IRS with Ford Sierra disc brakes. I recently redid my engine bay which included a new MC and professionaly rebuilt servo as well as new SS lines throughout the car, both hard and flex lines. After bleeding both from a standard foward as well as from the bleed screws themselves backward I still have a soft pedal for the first 2/3 to 3/4 travel. The car will stop but the soft pedal does not breed a lot of confidence from the driver. Looking for any and all ideas. Ted Lathrup suggested installing 2lb residual pressure valves near the MC in all three lines. As I am hoping not to have to cut my new SS lines if I can help it am looking for any suggestions from the conversion crowd that may have crossed this bridge before. BTW before the new lines I did have a firmer pedal, although, not anything like what you would expect for all my upgrades. One poster on the UK BBS suggesting removing the rear calipers during bleeding as the bleed screw is not pointing straight up when installed on the car and this may be allowing air to remain in the cylinder, which I plan on doing but have not done yet.
Frank

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Re: Soft pedal on modified 79 MGB #2
Jim Stabe San Diego, USA	Posted: February 24, 2012 03:13PM Registered: 4 years ago Posts: 1,228

Residual pressure valves should not be necessary with high mounted master cylinders, they are generally used when the cylinders are at or below the level of the calipers. I assume you have used non-expanding flex lines and they are kept as short as possible and there are no air leaks in the plumbing. If the lines are not expanding, a soft pedal has to be from air in the lines so you need to find out where that is and get rid of it. Do the lines run downhill all the way from the master to the caliper with no high loops? As mentioned above, is the bleed screw at the highest point on the caliper? Air has to be able to either rise up the line to the master reservoir or be captured at the top of the caliper so it can be bled out.

Jim

"If you want me to agree with you then we would both be wrong"

'66 MGB widened 11" with LT1 Chevy and 6 speed, C4 Corvette suspension
Pictures here Part 1 http://forum.britishv8.org/read.php?13,7581
Continued in Part 2 http://forum.britishv8.org/read.php?13,22422
Continued in Part 3 http://forum.britishv8.org/read.php?13,33108

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Re: Soft pedal on modified 79 MGB #3
rficalora Rob rficalora Cypress, TX, USA 1976 MG MGB V8 Conversion "MG MUTT"	Posted: February 24, 2012 03:17PM Registered: 7 years ago Posts: 1,678

Check out Larry Shimp's write up on BritishV8.org (http://www.britishv8.org/MG/LarryShimp.htm). He has hoyle front & rear but should be close I'd think. He changed his MC using a Willwood one if I recall but details should be in the write up. I also recall a tech write up he did; you might search the archives.

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Re: Soft pedal on modified 79 MGB #4
1744 Bill Guzman California, USA 1973 MG MGB GT "Green GT" 1974 MG MGB "Punking"	Posted: February 24, 2012 07:57PM Registered: 7 years ago Posts: 4,820

what size MC in your B.

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Re: Soft pedal on modified 79 MGB #5
mowog1 Rick Ingram Saint Joseph, Illinois, USA	Posted: February 24, 2012 09:02PM Registered: 8 years ago Posts: 20,370

I'm having the same dilemna with my V8 and talked with Ted Lathrop, Bill Guzman, and Bill Young.

(I've got Ted's front end and Guzman's four-link rear suspension.)

I'm running a stock MGB brake m/c with servo; a Wilwood proportioning valve; Wilwood four-pot calipers.

Ted recommends the installation of residual valves and elimination of the proportioning valve.

Bill G. recommends changing out the brake m/c to a GM style with a GM proportioning valve.

Bill Y. recommends same as Bill G.

I'm not sure which way to go...Ted does feel that the residual valves will cure the problem at the lowest expense.

1968 MGC - 1969 MGC - 1972 MGB - 1974&1/2 MGB/GT V8 conversion - 1978 MGB

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Re: Soft pedal on modified 79 MGB #6
danmas Dan Masters Alcoa, Tennessee, USA 1974 MG MGB GT "Powered By Ford"	Posted: February 24, 2012 09:15PM Registered: 8 years ago Posts: 1,193

In reply to # 1993991 by mowog1
I'm running a stock MGB brake [without servo]; a Wilwood proportioning valve; Wilwood four-pot calipers.

Ted recommends the installation of residual valves and elimination of the proportioning valve.

This is the setup I have in my car. I'm satisfied with the brakes, but then I'm not really qualified to judge. Jim Blackwood, Steve DeGroat, Ken Hiebert, and Kelly Stephenson have all driven my car - maybe they could comment on the brakes.

Edit: I just remembered - these guys are having a party in Florence, KY this weekend, so we may not hear from them until Monday.

Edited 1 time(s). Last edit at 02/24/2012 09:35PM by danmas.

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Re: Soft pedal on modified 79 MGB #7
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 09:25PM Registered: 8 years ago Posts: 1,124

Dan,
Do I read your post correctly in that you installed the residual pressure valves as per Ted's recommendation?
Thanks,
Frank

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Re: Soft pedal on modified 79 MGB #8
ex-tyke Graham Creswick Chatham, Ontario, Canada 1976 MG MGB	Posted: February 24, 2012 09:26PM Registered: 5 years ago Posts: 777

The stock MGB servo brakes never gave me that confident crisp feeling that a good braking system should have.
Rick, now that you've added more brake system fluid requirement with the Wilwoods, you probably need to upgrade to a larger bore M/C.

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Re: Soft pedal on modified 79 MGB #9
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 09:29PM Registered: 8 years ago Posts: 1,124

Jim,
I have the stock high loop at the rear where the line curves up along the arch of the rear wheelwell near the fuel pump.

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Re: Soft pedal on modified 79 MGB #10
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 09:30PM Registered: 8 years ago Posts: 1,124

Bill,
I have the stock late model MC.

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Re: Soft pedal on modified 79 MGB #11
danmas Dan Masters Alcoa, Tennessee, USA 1974 MG MGB GT "Powered By Ford"	Posted: February 24, 2012 09:33PM Registered: 8 years ago Posts: 1,193

Frank,

Ted installed them when he built the car.

Edit: I just realized my first response made no sense. I have a stock M/C, no servo, no proportioning valve, residual valves front and rear, Wilwood 4-pot calipers.

Edited 1 time(s). Last edit at 02/24/2012 09:47PM by danmas.

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Re: Soft pedal on modified 79 MGB #12
mowog1 Rick Ingram Saint Joseph, Illinois, USA	Posted: February 24, 2012 10:11PM Registered: 8 years ago Posts: 20,370

Dan....I'm guessing those are the two-pound residual valves?

1968 MGC - 1969 MGC - 1972 MGB - 1974&1/2 MGB/GT V8 conversion - 1978 MGB

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Re: Soft pedal on modified 79 MGB #13
mowog1 Rick Ingram Saint Joseph, Illinois, USA	Posted: February 24, 2012 10:13PM Registered: 8 years ago Posts: 20,370

In reply to # 1994001 by danmas

Edit: I just remembered - these guys are having a party in Florence, KY this weekend, so we may not hear from them until Monday.

My money would be a week from Monday with these guys!

devil smiley

1968 MGC - 1969 MGC - 1972 MGB - 1974&1/2 MGB/GT V8 conversion - 1978 MGB

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Re: Soft pedal on modified 79 MGB #14
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 10:29PM Registered: 8 years ago Posts: 1,124

Question for the residual pressure valve guys. Is there any increased Pad wear with these?

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Re: Soft pedal on modified 79 MGB #15
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 24, 2012 10:33PM Registered: 8 years ago Posts: 1,124

Link to Larry Shimp's brake upgrade write-up:

http://www.britishv8.org/Articles/MGB-Power-Brakes.htm

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Re: Soft pedal on modified 79 MGB #16
ex-tyke Graham Creswick Chatham, Ontario, Canada 1976 MG MGB	Posted: February 25, 2012 11:04AM Registered: 5 years ago Posts: 777

Notes from the Wilwood website:

1. On four wheel disc brake applications, where the fluid reservoir is mounted higher than the caliper bleed screws, a residual pressure valve is usually not required.

2. On disc brake applications where the fluid reservoir is mounted lower than the caliper bleed screws may require a 2 pound residual pressure valve. This can prevent fluid drain back and excessive pedal travel on initial engagement.

3. Use an adjustable proportioning valve to set the front to rear brake bias (That's if an automatic proportioning valve isn't used)

4.All drum brake applications require an inline 10 pound residual pressure valve

Edited 1 time(s). Last edit at 02/25/2012 11:04AM by ex-tyke.

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Re: Soft pedal on modified 79 MGB #17
danmas Dan Masters Alcoa, Tennessee, USA 1974 MG MGB GT "Powered By Ford"	Posted: February 26, 2012 07:03PM Registered: 8 years ago Posts: 1,193

In reply to # 1994057 by mowog1 Dan....I'm guessing those are the two-pound residual valves?

Yes.

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Re: Soft pedal on modified 79 MGB #18
9146 rick dentel yardley, pa, USA 1970 Porsche 914 1978 MG MGB 2002 Mini Cooper	Posted: February 26, 2012 07:12PM Registered: 1 year ago Posts: 1,353

Have you pressure bleed the system while tapping on the calipers?

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Re: Soft pedal on modified 79 MGB #19
mowog1 Rick Ingram Saint Joseph, Illinois, USA	Posted: February 26, 2012 08:20PM Registered: 8 years ago Posts: 20,370

In reply to # 1995728 by 9146 Have you pressure bleed the system while tapping on the calipers?

In my case....yes.

1968 MGC - 1969 MGC - 1972 MGB - 1974&1/2 MGB/GT V8 conversion - 1978 MGB

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Re: Soft pedal on modified 79 MGB #20
Frank J. Mooring Frank Mooring Rutherfordton, NC, USA	Posted: February 26, 2012 08:37PM Registered: 8 years ago Posts: 1,124

Rick D,
Not yet, but will do this as well as removing the rear calipers and making the bleed screw point to the sky to have it at the highest point.
Frank

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