Datsun Roadster Forum-311s.org

23yrRebuild wrote:Can a proportioning valve somehow be used to make the rear drums brake more? I'm under the impression these valves reduce pressure, so in order to increase rear braking, it would need to be in the front brake circuit. Any comment?

I'm getting off the topic, but as far as I know, there is no pressure reduction in the factory combo valve, so it would be for fine tuning. Might be good with a disc rear (Mazda or Nissan).

You're correct, they only reduce pressure. The roadster uses non-servo brakes, so the leading shoe does most of the braking. Servo brakes have a floating adjuster, so when the leading shoe grips, the force also wedges the trailing shoe increasing the brake force. Servo brakes usually need the pressure reduced to prevent lockup. Also, most other cars don't have half the car's weight on the rear wheels and dive more than Roadsters, both of which would need less rear pressure. I had an MG kitcar with a Pinto drivetrain and no proportioning valve. Anything above normal braking would immediately lock the rear wheels. I added a Wilwood valve under the dash, cut the pressure 50% and problem solved. That car had a very light rear and large (for a 1500 pound car) servo rear brakes.
On my 69, the rear wheels will lock if I totally mash the brakes. My front calipers haven't been rebuilt and the pads are older, so I'm sure they aren't 100%, and the rear shoes and cylinders are new, so that may be a factor.

Excellent description Dave!

We add the proportional valve to the rear brake circuit to keep things a little more balanced when we do our 'big brake' conversion in the front. Since 90% of your braking is done by the front brakes, we would experience premature lockup on the rear brakes-- the proportional valve cured that issue with a few hard stops to get the adjustment right.


Michael

spriso wrote:Excellent description Dave!

Michael

Odds are if I ramble on enough, which I do, something useful would come out eventually.

23yrRebuild wrote:Can a proportioning valve somehow be used to make the rear drums brake more? I'm under the impression these valves reduce pressure, so in order to increase rear braking, it would need to be in the front brake circuit. Any comment?

Usually when the front brakes are grabbing or causing the front to dive you install a delay valve. It allows the pressure to build in the rear brakes before the fronts.

Speedway Motors


BRAKE METERING/HOLD-OFF VALVE
Item #: 91031363 Price: EA $49.99

Metering valves are used to equalize the braking action of a Disc/Drum brake system by preventing
the front disc brakes from applying until approximately 75-125 psi has built up in the rear brake lines.
This delays the front brakes and allows the rear drums to engage first. This provides more stability on
wet surfaces, reduces front end dive in panic braking and reduces front brake pad wear in stop and
go driving.

Here's more info on brakes and brake valves:
http://www.mbmbrakeboosters.com/F.A.Q.- ... alves.html
http://www.mbmbrakeboosters.com/Tech-Su ... Pedal.html

spriso wrote:Excellent description Dave!

We add the proportional valve to the rear brake circuit to keep things a little more balanced when we do our 'big brake' conversion in the front. Since 90% of your braking is done by the front brakes, we would experience premature lockup on the rear brakes-- the proportional valve cured that issue with a few hard stops to get the adjustment right.


Michael

What about changing the size of the stock 13/16" rear wheel cylinders?

I considered buying the oversized SS pistons from Hyedracyl.

http://www.hyedracyl.com/datsun.html

I bought the bridge pipes but they were not the same as stock and seem to hit the wheel.

ppeters914 wrote: What about changing the size of the stock 13/16" rear wheel cylinders?

That is the factory method to balance the brakes, I guess you could change cylinder size for maximum braking and use the valve to dial it back.

I'm anxious to see how you do the rear line and the passenger side line routing. I've always thought that the lines could be cleaned up.

Indeed, this is clean work. I appreciate Mike sharing it with us! That he has done many, and those cars have been driven and serviced attests to the fact that the re-routing is not only clean-appearing but functional.

With wiring, brake lines, or whatever, sometimes the "hidden" approach makes things less servicable or more complicated to "work on", but I'll bet that's not a problem with his routing!

Really, it takes time, thought, and often, a few other folks to bounce ideas off of. I, for one, appreciate the contribution Mike CONTINUES to make.

Monkey see what Mikey do!

The RHD to LHD switch was the final explanation I came upon for the non-crossflow L-series head (U20 too) for having EVERYTHING YOU DIDN"T WANT over on the drivers side (in a LHD car).

Gosh, once we add sidedraft carbs, headers, and larger exhaust, it seems like it would be nice if all that stuff was over on the passenger side... oh wait - that's how it was in Japan -ahh wakarimas! jo-zu!

(sorry, but my english phonetics of my distant, dusty japanese is pitiful. Spent a half-year there in 1989 - I think I didn't USE IT so I LOST IT!)

OK Michael:
Solvaang is over - you've had maybe 5 minutes to recover.

Can you please continue your tutorial?
I have the engine out of mine and would love to clean this spaghetti nightmare up!
Please? Pretty Please?
Inquiring minds need to know!
Thanks!!
Tom

I would like to suggest that non-technical/topic-specific posts be PM's to Michael. Too easy to have a 10-page thread with only 2 pages worth of useful info....and not all together. Just a thought.

Pete

pete wrote:

I would like to suggest that non-technical/topic-specific posts be PM's to Michael. Too easy to have a 10-page thread with only 2 pages worth of useful info....and not all together. Just a thought.

I am actually going to edit this thread and pull all the posts out so I can show what we do, and we can discuss brake theory somewhere else. Not that there have not been relevant questions brought up, but it does cloud what I had originally intended to put together. I just built a set of lines for a customer and have taken a bunch of photos, the trick will be finding time to get all of this posted... darn real job anyway...

soon,

Michael

Thanks Michael!
Any chance that you might sell kits for stock "stock" roadsters? I think they would make lovely mothers day gifts.
I'm pretty confident I can do this, but I really want to see your method, as you have done it more than once. A lot of confidence comes from learning from someone elses mistakes!

Oh, I cant wait to see the conclusion to this thread!!! I (as Micheal and several others know) am rebuilding my brakes with the Spriso 300zxtt kit, and I was hoping to clean up the lines a bit. This thread is just what the doctor ordered! I cant wait to see the continuation of this thread....

so, BUMP!

any updates??? pretty pweez?