Brake line question

[dbo_texas]

I just happened to be reading through TTimmy's build thread and saw a comment (https://thefactoryfiveforum.com/showthread.php?49785-TTimmy%92s-MK3-Basket-Case-Build-Thread-SEAT-HEATERS&p=566569&viewfull=1#post566569) from the one and only Jeff Kleiner about the brake line routing to the master cylinder. He mentions that the front port on the master cylinder should route to the rear brakes and the rear port should route to the front brakes. The explanation that follows seems to make sense to me. In all my years on this forum I had never seen that comment or discussion before....so it got me wondering how I routed my brake lines. Sure enough, I did the same thing. Only difference is I've got a hydroboost in my setup.

https://thefactoryfiveforum.com/attachment.php?attachmentid=174581&d=1667787319

So now I'm wondering if I have a problem and need to drain my brakes and redo those sections of brake line. God I hope not....but looking for feedback from the collective. Is this a safety issue I need to correct?

[CraigS]

I have always heard the 'front to the rear and the rear to the front' but I have never come across a reason why. I will be following this thread.

[Norm B]

That set up is backwards to all the brakes that I have seen. Front port should go to the rear brakes and rear port to the front calipers.

Norm

[dbo_texas]

Jeff's explanation from the other thread (linked in my first comment) gives good reasoning behind this. Sounds like I need to seriously consider swapping my brake lines going into the master cylinder coming off the hydroboost. Uhg....I thought I was done with brakes with the fiasco with the banjo fittings that I had. Maybe I can drain the lines and cut them just below the master cylinder port and put an adapter on them and criss-cross them. Would require adding two F-F adapters and re-flaring 4 lines. Not the end of the world but more time wasted (lesson learned).


Ambitious project Timmy. I haven't been following along and just now checked your thread out---it's looking good! I've done complete builds on two roadsters that were started by others (one was really a disaster!) and I'd much rather start fresh!

In looking at your brake lines I see that you have the rear port plumbed to the rear and the front to the front. This is actually backwards. What difference does it make you may ask... The rear port is the primary chamber and the front is secondary. If you disassembled the master and looked at the cylinder pistons you'd see that the spacing of the seals on primary side result in a larger chamber which means that more fluid is moved for the same stroke. Additionally there is a spring between the primary and secondary chambers and the piston in the secondary chamber doesn't move until the primary has traveled enough to compress the spring; i.e. the brakes connected to the primary will be applied slightly before the secondary when you initially stab the pedal to energize the brakes. I'm afraid that with it plumbed as it is you're going to see premature rear lockup both due of the larger volume of fluid acting on the smaller rear caliper piston area as well as because of the rear being pressurized slightly before the front.

Jeff

[Jeff Kleiner]

Jeff's explanation from the other thread (linked in my first comment) gives good reasoning behind this. Sounds like I need to seriously consider swapping my brake lines going into the master cylinder coming off the hydroboost. Uhg....I thought I was done with brakes with the fiasco with the banjo fittings that I had. Maybe I can drain the lines and cut them just below the master cylinder port and put an adapter on them and criss-cross them. Would require adding two F-F adapters and re-flaring 4 lines. Not the end of the world but more time wasted (lesson learned).


Originally Posted by Jeff Kleiner
Ambitious project Timmy. I haven't been following along and just now checked your thread out---it's looking good! I've done complete builds on two roadsters that were started by others (one was really a disaster!) and I'd much rather start fresh!

In looking at your brake lines I see that you have the rear port plumbed to the rear and the front to the front. This is actually backwards. What difference does it make you may ask... The rear port is the primary chamber and the front is secondary. If you disassembled the master and looked at the cylinder pistons you'd see that the spacing of the seals on primary side result in a larger chamber which means that more fluid is moved for the same stroke. Additionally there is a spring between the primary and secondary chambers and the piston in the secondary chamber doesn't move until the primary has traveled enough to compress the spring; i.e. the brakes connected to the primary will be applied slightly before the secondary when you initially stab the pedal to energize the brakes. I'm afraid that with it plumbed as it is you're going to see premature rear lockup both due of the larger volume of fluid acting on the smaller rear caliper piston area as well as because of the rear being pressurized slightly before the front.

Jeff

Yep, that's why!

Jeff

[Avalanche325]

Because front to front and rear to rear makes sense, so the right way is the opposite. It just physics.

[TTimmy]

Daryll,
I got lucky and was able to "Stretch" one of my lines to the alternate port. For the second one I did have to make up a new line. Not a big deal because it was a short run to the bias adjuster. Plus my system was dry. I was bummed because everything had gone very smoothly with the brake lines up to that point.

It's hard to tell from your photo, but it looks like you might be able to massage the lines into their new homes. Removing the "P" bracket may give you enough slack.

Good luck with the fix - and I guess we should be very happy that we found out before everything was buttoned up!

Timmy!

[dbo_texas]

Daryll,
I got lucky and was able to "Stretch" one of my lines to the alternate port. For the second one I did have to make up a new line. Not a big deal because it was a short run to the bias adjuster. Plus my system was dry. I was bummed because everything had gone very smoothly with the brake lines up to that point.

It's hard to tell from your photo, but it looks like you might be able to massage the lines into their new homes. Removing the "P" bracket may give you enough slack.

Good luck with the fix - and I guess we should be very happy that we found out before everything was buttoned up!

Timmy!

Yeah that’s exactly what I’m going to attempt. I was looking at it last night and I have some strain relief bends that I might be able to unbend a little and get some length back which might allow me to not have to make new lines. But yeah I’ll have to drain and re-bleed which sucks.

[dbo_texas]

I was able to cross the hard lines going into the master cylinder banjo connections without too much trouble. Detailed the process in my build thread but it only took about 20 min. I still need to re-bleed the brakes but I'll take care of that later.

https://thefactoryfiveforum.com/attachment.php?attachmentid=209046&d=1736729724