Brake question

Suspension, including wheel, tire and brake.
vetteguy22
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Re: Brake question

Post by vetteguy22 » 26 Jul 2018 23:07

Thanks for the ideas guys.
I think at this point I’m going to reclean and scuff the rotors and install new pads front and rear just to make sure.
They’re cheap and I want to make the car safe.
I did bench bleed the MC before installing.
I remember that when we were two person bleeding the rear brakes that the pedal would go to the floor easily when the bleeders were opened so don’t believe there’s an obstruction in the line anywhere.
I’ll do this stuff this weekend and report back.
Thanks again,
Rob

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Re: Brake question

Post by Three B's Racing » 27 Jul 2018 04:36

Byron510 wrote:
26 Jul 2018 06:38
Three B's Racing wrote:
26 Jul 2018 05:28
Is the master cylinder setup for rear disk brakes or drums? Because that will make a big difference.
Eh Lou, good of you to chime in.
Curious, what design change is there that makes a BMC a disc or drum BMC? To me a BMC is simply a piston pushing fluid through a bore. The only design feature in addition to this that I’m aware of is residual pressure valves often found on drum brake systems that are designed to keep the pistons expanded keeping the shoes closer to the drums. But I don’t believe any of the Datsuns used this feature that was more common on North American drum brake systems.

Just currious, that’s all. Thanks.

Byron
Well, Datsun/Nissan speaking, I was told that if your master cylinder was from a vehicle with front disk and rear drums going on a 4 wheel disk setup (4wd) that you need to either make sure the master is from a 4 wheel disk setup or you change out the rear brake bias valve in the master. In the 15/16" and 7/8" masters (and probably others) underneath the master there are two bolts, one for the front one for the rears (I know you know what I mean) The one for the rear you remove and the little valve in there gets replaced with the one from the 15/16",,,I don't know maybe? All I know is I did exactly this in my 4wd setup and wow!!
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vetteguy22
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Re: Brake question

Post by vetteguy22 » 27 Jul 2018 09:32

So I had a few minutes and the talk about the difference between MC for 4 wheel disc to disc / drum made me think. I still had the original 3/4” MC from the car that was a disc drum set up so I took it apart to check for anything different between the front and back.
There was a a difference between the front brakes and rears in that there was a removable oriface that one was smaller than then the other. To my surprise the front brake oriface was smaller than the rear. I would have thought it would have been the other way around. And yes I know the front reservoir is for the rear brakes.
I don’t know about the set up of the MC I am using yet but thought I’d let you guys know what found.
Also checked the surface contact on the rotors and the fronts are definitely not making full contact so will be changing out those pads after recleaning and scuffing the rotors.
The rears still don’t look like they are really making any real contact marks so sound like they aren’t getting enough brake pressure to the rears.
Rob

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bertvorgon
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Re: Brake question

Post by bertvorgon » 27 Jul 2018 09:42

Obviously having SQUARE contact of pads to rotors is beyond paramount. Things will try to move/bend and this also creates a bad pedal, both in travel and feel.

You would be amazed at what might seem like very little movement at the caliper/pad interface, that translates to both poor pedal travel and braking.

I had some calipers that flexed quite a bit many years ago, the pedal feel was so crappy it was amazing.

Andy at Specialty made a truing device for the brakes pads, basically a pad holding device and then a belt sander the "surfaces" the pad square again. I do that periodically and it makes a foot feel difference.

Over time and amount of hard braking, TAPER WEAR comes into play, where the leading edge at the bottom of the pad gets thinner before the top section. That creates a "bend" where the top of the pad contacts first, then because of the different thickness at the bottom, hydraulic pressure tries to then squeeze the bottom to the rotor, this translates to more travel and a crappy feel of the brakes itself.

While I think, of it as an FYI for anyone reading this thread, the type of seal in the caliper can come into play, whether it is round or square. This dictates how far the piston is pulled back into the bore and away from the rotor. That translates as to how much TRAVEL , which is FLUID DISPLACEMENT, it takes to get the pads back out. This can make for a "double pumper" on the brake pedal, to get everything out there. I specified the square seals on my Brakeman as I know everything is truly square on the pad/rotor interface, so wanted as minimal travel as possible to maintain my brake pedal to gas pedal height for heel and toeing.

There is also "PAD KNOCK BACK" which can be the sum of loose wheel bearings, hub flex, and g-loading, ( plus seal retraction)which pushes the pads back in further than normal. This of course does create the need for the confidence double pump when heading into the braking zone, be it on the street or race.

Just some thoughts at any rate.

Keith
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Re: Brake question

Post by duke » 27 Jul 2018 13:16

I just browsed through this thread and I saw that bedding the pads was mentioned early on, but vetteguy22 never confirmed that the pads had been properly bedded in (unless I missed it). The importance of performing a proper bedding process when changing either pads or rotors is paramount to proper braking system performance.
Duke Schimmer

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Byron510
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Re: Brake question

Post by Byron510 » 27 Jul 2018 16:48

bertvorgon wrote:
27 Jul 2018 09:42

While I think, of it as an FYI for anyone reading this thread, the type of seal in the caliper can come into play, whether it is round or square. This dictates how far the piston is pulled back into the bore and away from the rotor.
Curious, is there such thing as a round seal on brake calipers? If so, I've not seen such a design.

In my work life as a machinist, I have seen many hydraulic seals, and all are square. In industrial hydraulics, back up rings and other parts are often used in conjunction with various designs of seals, but never a round seal. It doesn't seem like a round seal could even work. Maybe someone can point me in the right direction?

Byron
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bertvorgon
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Re: Brake question

Post by bertvorgon » 27 Jul 2018 18:07

Maybe it is only on performance/racing calipers. I know I had the choice of either on my F3 BRAKE MAN calipers,

I have attached link to their site: https://www.tbmbrakes.com/product/f3-calipers/

You can see that you can option which type of seal. It sounds like "SQUARE CUT" is more the norm now, Tracey said my early JFZ's had round seals, maybe into the Wilwoods you have Byron, cannot remember.

It is possible the terminology maybe says round, but, is it truly a round o-ring or.....

Would be interesting to phone Brake man and find out.
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Byron510
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Re: Brake question

Post by Byron510 » 27 Jul 2018 19:32

The old Wilwoods I have do have the square seals - got very close to them last week as I renewed them all during overhaul.

Byron
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bertvorgon
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Re: Brake question

Post by bertvorgon » 27 Jul 2018 19:34

Ok, Tracey wasn't sure when they transitioned. I even phoned after your post as I do not trust my memory at times, that was some 40 years ago.

I have been thinking of going through my rear calipers in the next few winters.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
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vetteguy22
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Re: Brake question

Post by vetteguy22 » 28 Jul 2018 07:23

All 4 of my calipers have square seals. I do know that I have seen rebuild kits for Vette calipers that offer round seals though I’ve never used them.

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Re: Brake question

Post by bertvorgon » 28 Jul 2018 07:54

It just points out how old I am getting....that round seals were back in the 60's -70's for some cars...YIKES.

I feel your pain, as I went through all sorts of stuff before I finally got good brakes that would last a 20 minute session at our local race track, do street duty and of course my hillclimb years.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

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1968 Vintage 3HP Mini Bike
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vetteguy22
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Re: Brake question

Post by vetteguy22 » 29 Jul 2018 21:04

I worked on the brakes today.
Cleaned the front rotors and scuffed them with 80 grit sand paper. Went to put on the new pads but they got me the wrong ones so I’ll have to try to get the correct ones tomorrow.
Cleaned and scuffed the rear rotors and put on the new pads.
It really doesn’t look like the rears are applying much pressure.
Very little contact marks are visible. It’s not uneven but just very negligible.
Having to start wondering if it’s the master cylinder not being set up for 4 wheel disc? Don’t know if it is or not.
Also the comment about the brake line block on the firewall restricting flow?
Hopefully I’ll be able to get the correct pads tomorrow and take it on another test drive.
Rob

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Re: Brake question

Post by Byron510 » 30 Jul 2018 16:03

vetteguy22 wrote:
29 Jul 2018 21:04
Having to start wondering if it’s the master cylinder not being set up for 4 wheel disc? Don’t know if it is or not.
I can’t see the stock BMC being an issue, if the brakes were sticking on, then the 2 lb residual valve may be the issue (the bit under the fitting like you found on the one you took apart). But that doesn’t impede application pressure.

vetteguy22 wrote:
29 Jul 2018 21:04
Also the comment about the brake line block on the firewall restricting flow?
If you can blead the brakes and see flow when you crack the bleeder, then the restriction isn’t doing you any hard. The actual ‘fluid movement’ is minimal when applying the brakes.

Interesting that you are not getting pressure on both front and rear. It’s almost like you’re not pushing hard enough on the brake pedal! But you say you are, and that the pedal is firm.

Again, when you bleed the brakes, tell me that you have good fluid flow out of the bleeder? When using a clear piece of vinyl tubing, you see a good shot of fluid moving though, correct?

Byron.
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Re: Brake question

Post by vetteguy22 » 30 Jul 2018 19:31

So got the new front pads installed today and took it for a test drive and bedded them in. The brakes are greatly improved and the fronts are very acceptable. I believe they would have locked up if I really stood on it.
The backs still don’t feel like they are fully applying.
I checked the temps of the fronts compared to the backs when I got back to the shop and the fronts were 80 degrees hotter than the backs.
Not sure if that’s an indicator of an issue or not.
I was able to find out that the MC i have is a disc/drum set up. I’m thinking maybe I should change to a 7/8” MC but not sure what one to get. Any suggestions as to year and model to look for that came with 4 wheel disc.
Also should I remove/bypass the block on the firewall to a straight through coupling?
Again, thanks for the help.
Rob

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Re: Brake question

Post by Three B's Racing » 01 Aug 2018 05:38

vetteguy22 wrote:
30 Jul 2018 19:31
So got the new front pads installed today and took it for a test drive and bedded them in. The brakes are greatly improved and the fronts are very acceptable. I believe they would have locked up if I really stood on it.
The backs still don’t feel like they are fully applying.
I checked the temps of the fronts compared to the backs when I got back to the shop and the fronts were 80 degrees hotter than the backs.
Not sure if that’s an indicator of an issue or not.
I was able to find out that the MC i have is a disc/drum set up. I’m thinking maybe I should change to a 7/8” MC but not sure what one to get. Any suggestions as to year and model to look for that came with 4 wheel disc.
Also should I remove/bypass the block on the firewall to a straight through coupling?
Again, thanks for the help.
Rob
Troy Ermish has the proper 7/8"MC for 4 wheel disk. Juts let him know it's for a 4 wheel disk.
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