Forum registration by users has been disabled because of many problem registrations from Russia. Email mail @ chalkevalley.info (delete spaces) if you wish to join the forum and an administrator will register you.
If you would like to join the DLOC, please visit the Club's website https://www.dloc.org.uk/
Please don't post someone's email address. Some people don't want to risk it being harvested by spambots and GDPR regulations discourage it.
Always look at "ACTIVE TOPICS" which gives all posts in date & time order if you can't find a post or "Your Posts", as topics are sometimes moved.
Reg. nrs. Please add reg. nr. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.

SP250 Restrictor or non-return valve for brakes

User avatar
John-B
Site Admin
Posts: 1185
Joined: Tue Feb 09, 2016 9:10 pm
Location: Salisbury, UK
Contact:

SP250 Restrictor or non-return valve for brakes

Post by John-B » Wed Apr 25, 2018 10:45 am

I remember a long discussion on the old forum about whether a restrictor or non-return valve was required in the brake circuit.

I don't know whether I've got one. What does it look like and would it be adjacent to the fluid reservoir?

What is the current thinking about whether to have one or not?

timmartin
Posts: 50
Joined: Wed Feb 17, 2016 1:37 pm
Location: Berkshire

Re: SP250 Restrictor or non-return valve for brakes

Post by timmartin » Wed Apr 25, 2018 11:46 am

Oops!
Sorry John, missed your post and just added to the discussion on this subject under the post “Dart Brake Calipers”

It is a small cylindrical fitting normally screwed into the input to the five way brake union. The brake pipe from the brake master cylinder goes directly to it. The five way brake union is bolted to the chassis, more or less below the master cylinder(s).

Theoretically, some might argue that it is on the wrong side of the brake light switch. As a result, residual pressure created by the Restrictor Valve can occasionally hold the brake light on after the foot has been taken off the pedal. I have seen this discussed, but suspect that it is not common.
Tim
Blue 1964 SP250 in Berkshire

User avatar
Vortex O'Plinth
Posts: 826
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: SP250 Restrictor or non-return valve for brakes

Post by Vortex O'Plinth » Wed Apr 25, 2018 12:03 pm

John-B wrote:
Wed Apr 25, 2018 10:45 am
I remember a long discussion on the old forum about whether a restrictor or non-return valve was required in the brake circuit.
I don't know whether I've got one. What does it look like and would it be adjacent to the fluid reservoir?
The original brake line restrictor valve looks like this John....
Image
It's mounted on top of the 5-way union bolted to the chassis and piped directly from the master cylinder. You can just make it out in this rather cluttered picture...
Image[/url]

It's a rarely exchanged item since its failure is not always obvious. Anyone with the original valve still fitted will almost certainly find it's ineffective by now. I suspect that in many cases it may now be missing all together since replacements have been unavailable for a long time.
Nick

"Open the pod bay door Hal".

User avatar
John-B
Site Admin
Posts: 1185
Joined: Tue Feb 09, 2016 9:10 pm
Location: Salisbury, UK
Contact:

Re: SP250 Restrictor or non-return valve for brakes

Post by John-B » Wed Apr 25, 2018 12:21 pm

OK, I'll have a look later.

At the moment I'm in pain when I bend, twist or breathe heavily as I've hurt my ribs. Last Thursday was the most fantastic day, hot and windless so I went out on my mountain bike but hit a rut on a bumpy grass track that threw me off.

Paulkennedy
Posts: 74
Joined: Fri Feb 12, 2016 11:01 pm

Re: SP250 Restrictor or non-return valve for brakes

Post by Paulkennedy » Wed Apr 25, 2018 2:06 pm

As the dart calliper post got a bit muddled with double push pedal, could Kevin post a reply here about brake non return valve.
Thanks Paul

DaveM
Posts: 18
Joined: Thu Oct 27, 2016 3:36 pm
Location: Haslemere, UK

Re: SP250 Restrictor or non-return valve for brakes

Post by DaveM » Wed Apr 25, 2018 2:55 pm

Wilwood brakes do an equivalent residual pressure valve at 2 psi for disk brakes.
CIMG0008.JPG
Try to place as close to master cylinder as possible

More info here
https://www.demon-tweeks.co.uk/motorspo ... sure-valve

timmartin
Posts: 50
Joined: Wed Feb 17, 2016 1:37 pm
Location: Berkshire

Re: SP250 Restrictor or non-return valve for brakes

Post by timmartin » Wed Apr 25, 2018 3:35 pm

Dave. Did you try the brakes with and without the Wilwood residual pressure valve?
How good do you find it?
Tim
Blue 1964 SP250 in Berkshire

User avatar
Kbeal
Posts: 75
Joined: Mon Feb 15, 2016 9:01 pm

Re: SP250 Restrictor or non-return valve for brakes

Post by Kbeal » Wed Apr 25, 2018 4:31 pm

See DaveM's pic for what I was talking about. Siting the non return valve as shown on the photo cured the problem for me, but reading posts above it might just have been that the old valve was knackered!

Kevin

User avatar
Vortex O'Plinth
Posts: 826
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: SP250 Restrictor or non-return valve for brakes

Post by Vortex O'Plinth » Wed Apr 25, 2018 4:52 pm

timmartin wrote:
Wed Apr 25, 2018 3:35 pm
Dave. Did you try the brakes with and without the Wilwood residual pressure valve?
How good do you find it?
I'd be interested to know too, Tim. The SP Service Manual justifies the use of the restrictor valve with the following..
Capture.JPG
The blue Wilwood residual pressure valve is set at 2 psi and designed to prevent gravitational fluid drainback in applications where the master cylinder is mounted below the level of the calipers. Since this is not the case in the SP and the double pump problem is thought to be the result of physical movement between the disc and the caliper - for whatever reason - 2 psi might not be adequate to transfer fluid through the caliper drillings from one piston to the other?

Wilwood do a higher pressure version set at 10 psi, specifically for drum braked systems, intended to balance the brake shoe return spring tension. In the SP application this might be more effective? I can find no data that specifies the pressure setting of the original restrictor valve.

Incidentally the same type of restrictor - possibly even the same one - was originally fitted to Triumph TR's. The general consensus among the TR owners is that any benefit from having it is negligible.
Nick

"Open the pod bay door Hal".

Ian Slade
Posts: 457
Joined: Sat Feb 13, 2016 9:54 am
Location: Akrotiri Cyprus

Re: SP250 Restrictor or non-return valve for brakes

Post by Ian Slade » Wed Apr 25, 2018 5:31 pm

Though I initially had pad ride out on my C spec I eliminated most of it by stripping down the restrictor valve and bleeding the system using the Gunson Auto bleeder, well at least on the road, I have never needed a double pump but that maybe due that I never braked on a single pump anyway always at least two gentle pumps even in a modern car. The A/B spec never had a brake problem even in competition however that cars restrictor was also stripped cleaned and reassembled, both cars were fitted with a modified condition2 axle supplied by the club in 1972, whether this was a reason I can't say but the C spec's rideout was less noticable after the new axle was fitted
Owner since the 70's, Genghis is slightly to my left.

Post Reply