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Residual brake pressure valve question.

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MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
When I was buying all my bits for the GT's two master cylinder set up Wilwood suggested I get a Residual Pressure Valve for the rear circuit so I did. Their instructions (in the hot link) suggest putting the valve as close as possible to the m/c. I can do this but I was wondering what happens if I place it where the stock system has the joiner #6?

Edit: I did not Underline the Bold Italics but it happened automatically. Some folks don't like Underlined Bold so I was trying to be more compliant; IDK how to fix. smiling smiley



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.



Edited 2 time(s). Last edit at 2017-12-06 01:32 AM by MGB567.

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spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Ocean Shores, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
Barrie, your master cylinder is not below the caliper or wheel cylinder, why would you need this?



Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.


Member Services:
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MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
I only had Wilwood's advice to go on:

"Since you’re using rear drums we strongly recommend adding a 10 lb residual pressure valve within 12” of the master cylinder on the rear brake line. This will help prevent your shoes/springs from closing the wheel cylinder at rest."



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Ocean Shores, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
In reply to a post by Wildwood A residual pressure valve is used when a master cylinder is mounted equal to or below the
horizontal plane of the calipers or drum brake wheel cylinders. This valve prevents fluid flow-back
to the master cylinder reservoir which can cause excessive brake travel or “pumping” of the pedal
to engage brakes.



Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.



Edited 1 time(s). Last edit at 2017-12-06 02:15 AM by spikemichael.


Member Services:
Pre-Order NOW for shipping in early December! Call me at 978-249-5760 PST for help with your Weber DGV Carburetor, questions about the calendar or just to talk MGBs!
MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
Mmm. Perhaps I should have read their blurb (and before posting) rather than relying on their advice (seems in retrospect just a ploy for me to have spent more $). Oh well another $20 to help US balance of payments and another thing for the trinket box. Thanks for reading for me.



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

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melbaver Avatar
melbaver Gold Member Chris Howells
Broadwater NSW, Australia   AUS
1968 MG MGB "Moneypit"
1996 Jeep Cherokee "Shopping Trolley"
I think we need a competition, here in Australia, to design and manufacture an object out of excess MGB parts. Will not be very costly for the parts, but the combined freight cost would be astronomical.



Chris Howells

1968 MGB Purchased already dis-assembled but which is largely back together so I'm a lot less ignorant.

tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
Most twin circuit MG master cylinders have such valves built in, which causes it to be a pain to gravity bleed them. "Trap Valve" as they are called. Without such a device, first time you press the brakes, it is a longer travel. Rest of the trip is fine.

Try it without and see how it works. If you have a long petal, put it in. I am not sure where in the circuit makes that much difference.



Cogito ergo sum periculoso

Wachtmans Avatar
Wachtmans Wouter Strodijk
OVERVEEN, Noord Holland, Netherlands   NLD
1974 MG MGB "The Bee"
1974 MG MGB "The Bee"
1974 MG MGB MkIII "The Bee"
I tried that once (without trap valve). Pedal gets real long without. The springs in the brake drums tend to retract the brake cylinders far in, especially when new, which makes the pedal long.

geezer Avatar
geezer Silver Member charles durning
Magee, Mississippi, USA   USA
1958 MG Magnette ZB "Chick Magnette (sold)"
1967 Morris Minor 1000 Saloon (2-door) "Marvin"
1974 MG MGB GT
I can attest that the residual pressure valve is needed when the M/C is below the floor of the car. When I did my disc brake conversion on the Morris Minor I had a very long pedal before installing the valve.

I just completed a rear disc conversion on the '74 GT and am contemplating on removing the trap valves from the M/C. I do have a good pedal feel as is. The problem is I'm not getting pressure/flow to the rear brakes. What is the purpose of the "trap valves" and are they the same value for the front and rear circuit in the stock dual M/C?



Who's version of right are we talking about? When you get 10 LBC owners in a room you'll get 12 different answers.

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Wachtmans Avatar
Wachtmans Wouter Strodijk
OVERVEEN, Noord Holland, Netherlands   NLD
1974 MG MGB "The Bee"
1974 MG MGB "The Bee"
1974 MG MGB MkIII "The Bee"
No, this trap valve is standard for the rear on a dual brake system. Has nothing to do with bleeding. Start with bleeding the right rear, then left rear then right front and last left front.

spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Ocean Shores, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
oh boy another brake bleeding thread haven't seen one of those in a while!



Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.


Member Services:
Pre-Order NOW for shipping in early December! Call me at 978-249-5760 PST for help with your Weber DGV Carburetor, questions about the calendar or just to talk MGBs!
tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
I believe this was directed my way. I think you miss-read my comment. It makes GRAVITY bleeding more difficult. Other methods are no different.
As you can see from the Moss diagram, the valves are in both circuits.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/dual-line-non-servo-brake-master-cylinder-1968-74-5 ( item # 21)

In reply to # 3640883 by Wachtmans No, this trap valve is standard for the rear on a dual brake system. Has nothing to do with bleeding. Start with bleeding the right rear, then left rear then right front and last left front.



Cogito ergo sum periculoso

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Paul755 Paul H
Richmond, Virginia, USA   USA
1974 MG MGB MkIII
1979 MG MGB MkIV "Nemesis"
The residual pressure valve also keeps some pressure on the rear wheel cylinder piston seals and is supposed to also prevent the cylinders weeping brake fluid. Or at least that is what my MG TF workshop manual claims.
The rear brake adjuster prevents the rear shoe springs retracting the rear wheel cylinder piston beyond the set running clearance.



Bigamy is having one wife too many.
Monogamy is pretty much the same thing.

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Barrie it is normal on production cars that have disc / drum setup to have a residual pressure valve in the "drum circuit" built into the master cylinder. Cant do any harm and will improve the pedal feel.

Denis.



68 B roadster, Daffodil yellow, Moss supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in 2016 with high comp pistons and a few other nice bits. Started on the body late 2016 and found Its a lot of work and expense starting from scratch. Did the work myself, mechanical, body. paint etc all except the interior trim.
Finished and going well, great to drive and quick. Future mods, maybe an increase in gearing but not for a while.

MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
So I should take Wilwood's advice and insert it around 12" or less from their M/C?

It makes a difference because I'll be getting HEL to fabricate lines so at present I'm determining brake line length and position (using 7mm OD clear plastic tube).



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

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