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Soft pedal on modified 79 MGB

Posted by Frank J. Mooring 
Frank Mooring
Rutherfordton, NC, USA   usa
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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Jim Stabe Avatar
San Diego, USA   usa
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
rficalora Avatar
Rob rficalora
Cypress, TX, USA   usa
1976 MG MGB V8 Conversion "MG MUTT"
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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1744 Avatar
Bill Guzman
California, USA   usa
1973 MG MGB GT "Green GT"
1974 MG MGB "Punking"
what size MC in your B.
Classic Conversions Engineering MG Classic Conversions V6. Wilwood brake dealer.
mowog1 Avatar
Rick Ingram
Saint Joseph, Illinois, USA   usa
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

mowog1@aol.com
Pieces Of Eight: Struts For Your MG Pieces of Eight! has provided gas-charged strut kits for the MGB bonnet, MGB and MGC bootlid, and MGB/GT or MGC/GT hatch since 1996. Contact Rick at: mowog1@aol.com
danmas Avatar
Dan Masters
Alcoa, Tennessee, USA   usa
1974 MG MGB GT "Powered By Ford"
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.
Frank Mooring
Rutherfordton, NC, USA   usa
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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ex-tyke Avatar
Graham Creswick
Chatham, Ontario, Canada   can
1976 MG MGB
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.
Frank Mooring
Rutherfordton, NC, USA   usa
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.

Frank Mooring
Rutherfordton, NC, USA   usa
Bill,
I have the stock late model MC.
danmas Avatar
Dan Masters
Alcoa, Tennessee, USA   usa
1974 MG MGB GT "Powered By Ford"
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.

Attachments:
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mowog1 Avatar
Rick Ingram
Saint Joseph, Illinois, USA   usa
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

mowog1@aol.com
Pieces Of Eight: Struts For Your MG Pieces of Eight! has provided gas-charged strut kits for the MGB bonnet, MGB and MGC bootlid, and MGB/GT or MGC/GT hatch since 1996. Contact Rick at: mowog1@aol.com
mowog1 Avatar
Rick Ingram
Saint Joseph, Illinois, USA   usa
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

mowog1@aol.com
Pieces Of Eight: Struts For Your MG Pieces of Eight! has provided gas-charged strut kits for the MGB bonnet, MGB and MGC bootlid, and MGB/GT or MGC/GT hatch since 1996. Contact Rick at: mowog1@aol.com
Frank Mooring
Rutherfordton, NC, USA   usa
Question for the residual pressure valve guys. Is there any increased Pad wear with these?
Frank Mooring
Rutherfordton, NC, USA   usa
Link to Larry Shimp's brake upgrade write-up:

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

ex-tyke Avatar
Graham Creswick
Chatham, Ontario, Canada   can
1976 MG MGB
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.
danmas Avatar
Dan Masters
Alcoa, Tennessee, USA   usa
1974 MG MGB GT "Powered By Ford"
In reply to # 1994057 by mowog1 Dan....I'm guessing those are the two-pound residual valves?

Yes.

9146 Avatar
rick dentel
yardley, pa, USA   usa
Have you pressure bleed the system while tapping on the calipers?
mowog1 Avatar
Rick Ingram
Saint Joseph, Illinois, USA   usa
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

mowog1@aol.com
Pieces Of Eight: Struts For Your MG Pieces of Eight! has provided gas-charged strut kits for the MGB bonnet, MGB and MGC bootlid, and MGB/GT or MGC/GT hatch since 1996. Contact Rick at: mowog1@aol.com
Frank Mooring
Rutherfordton, NC, USA   usa
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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