Opinions on Master/Booster combo

[LeighP]

Ok, so I'm asking for some opinions on which way to go with my mastercylinder/booster combo.

Car is a 71 Firebird. I'm currently running 12" front 1LE rotors with Wilwood GMIII alloy single piston calipers (basically the same as the stock GM caliper, but alloy). Rear is 11" finned "B" Body police pack drums. Everything is new, including lines and hoses, all correctly bled.

My current mastercylinder is a Jegs branded chromed generic 1 & 1/8" GM style unit, with a replacement Delco style factory booster - not genuine GM.

Issue - the vehicle stops "OK"....I would have imagined the 12" rotors and large drums would stop a little better, but the thing I least like is the feel of the pedal and the fact it seems to have more travel than I think it should.

I've been researching options -

1. Hydratech's hydraboost kit, coupled with the correct GM replacement mastercylinder (I already have this in stock). This was my initial thought as the feedback on these systems is great.

https://static1.pt-content.com/images/pt/2013/05/3022-1.jpg

2. Emailed DSE's tech people and they say that their twin diaphram/latemodel matercylinder combo for 2nd gen F-bodies should work great for my application.
The DSE kit is approximately half the cost of the hydroboost kit.

https://static1.pt-content.com/images/noimg.gif

So, for people who know brakes....what are your thoughts?

[andrewb70]

Leigh,

Before throwing cubic dollars at the problem, have you done some trouble shooting to make sure that your current system is working properly? If your pedal seems to have "excessive" travel, perhaps you have air in the system? I would make sure that the system is fully bled. Often times, if the system was new and completely dry, it will take a while before you get all the air out.

The next step would be to look at your MC. What size bore does it have?

Andrew

[Ron Sutton]

I agree with Andrew to make sure your system is not the issue. What size are the pistons in the front calipers?

[Skip Fix]

What size pistons are the front calipers? Some of the Wilwoods have smaller pistons than the factory 2 15/16"?

The factory used a 1 1/8 for power disc drum and disc/disc. The disc disc on 79-81 got the smaller dual diaphragm booster that look like the DSE-81s used a similar aluminum MC. Do you have a proprotioning valve?

My 78 with disc drum could easily lock up the rears in a turn from the factory.

[LeighP]

Thanks, guys.
Yep, system bled a few times, all clean.
Master is a 1 & 1/8". Clearance between the booster operating rod and the master piston is checked and correct, so I'm not talking about free-play.
No proportioning valve, the balance feels fine....you can just lock the rears under heavy "panic" style stops.
The Wilwood pistons are slightly smaller at 2.750" dia....but I'd think smaller pistons would not cause issues with insufficient mastercylinder volume on a pressure stroke.

This is one of those annoying deals where everything works, but it just doesn't "feel" like you think it should........I hate that....

[andrewb70]

Thanks, guys.
Yep, system bled a few times, all clean.
Master is a 1 & 1/8". Clearance between the booster operating rod and the master piston is checked and correct, so I'm not talking about free-play.
No proportioning valve, the balance feels fine....you can just lock the rears under heavy "panic" style stops.
The Wilwood pistons are slightly smaller at 2.750" dia....but I'd think smaller pistons would not cause issues with insufficient mastercylinder volume on a pressure stroke.

This is one of those annoying deals where everything works, but it just doesn't "feel" like you think it should........I hate that....

Leigh,

I suggest getting a pressure gauge and seeing what kind of pressure you are getting to the front brakes. This will help greatly in determining if you have a problem with your current set-up. If your present system generates ample pressure, then adding a hydra-boost or another booster will do little to help.

A 1 1/8" bore MC is fairly big and you should ample pressure and relatively short pedal travel. You might also try running manual brakes with a smaller MC and see if you like the feel.

Andrew

[Skip Fix]

The rear drums need a residual pressure valve if you do not have one in the MC or prop valve. GM put them in the old iron MC and then on the prop valves for disc/drum cars. Be sure the Jegs MC has one or that could be a big factor.

[andrewb70]

The rear drums need a residual pressure valve if you do not have one in the MC or prop valve. GM put them in the old iron MC and then on the prop valves for disc/drum cars. Be sure the Jegs MC has one or that could be a big factor.

Good call. Not having a residual valve can certainly cause longer pedal travel.

Andrew

[LeighP]

you know, you may be onto something there.......I'll have to check that the existing combination valve incorporates a residual pressure valve.
The master cylinder is what looks to be a copy of the older style master used on 1st gen F-bodies. What I may need is the stand alone residual pressure valve used on 70 and earlier cars.
Good call, guys....thats good thinking. :)

[andrewb70]

Let us know how it works out...

Andrew

[LeighP]

So, a little more reading and some investigation......

The master cylinder data on the Jegs website shows it as usable for "drum/drum" or "disc/drum" or "disc/disc".....which, now that I understand whats going on would seem to indicate that the master cylinder does not have built in residual pressure valve/s.
I've ordered a Wilwood (red) 10lb residual valve and will plumb it into the rear brake pressure line.

Job for next week when I'm off.

[andrewb70]

Please keep us posted.

Andrew

[Zee]

Leigh, I have the 1LE set up with stock hydraulics, booster and aluminum drums and it stops on a dime so I would hang in there to get this sorted out. That being said, I am itchin' to get at my 13" C4 ZR1 fronts. I only need brake lines for the fronts and well everything for the rears. I think I will be going with the Blazer set up out back. Probably would help if I had the motor back in the car first though

[LeighP]

To Skip Fix and Andrew....thanks guys! The residual pressure valve suggestion worked out to be the issue.
Just one of those things that you don't think about but come back to bite you when you're using aftermarket parts. we plumbed a Wilwood 10lb valve into the rear line between the master and the combination valve, and the pedal feels much more like I think it should.
Another thing that doesn't help on the way it feels under my foot is that I'm running a Claytons Machine Works alloy brake and throttle pedal arrangement, and the brake pedal height is set down to match the height of the throttle pedal....that in itself feels a little odd when you're used to the brake pedal sitting up higher with the factory pedal....lol.
Thanks again, guys.....saved me some money that wouldn't have fixed the problem. I've always been a believer in sitting down and thinking through stuff like this before going off half cocked. Sure helps to get a few others thinking about the issue as well.

[andrewb70]

To Skip Fix and Andrew....thanks guys! The residual pressure valve suggestion worked out to be the issue.
Just one of those things that you don't think about but come back to bite you when you're using aftermarket parts. we plumbed a Wilwood 10lb valve into the rear line between the master and the combination valve, and the pedal feels much more like I think it should.
Another thing that doesn't help on the way it feels under my foot is that I'm running a Claytons Machine Works alloy brake and throttle pedal arrangement, and the brake pedal height is set down to match the height of the throttle pedal....that in itself feels a little odd when you're used to the brake pedal sitting up higher with the factory pedal....lol.
Thanks again, guys.....saved me some money that wouldn't have fixed the problem. I've always been a believer in sitting down and thinking through stuff like this before going off half cocked. Sure helps to get a few others thinking about the issue as well.

Thank Skip Fix! I was just along for the ride. Glad you got it worked out.

Andrew

[ROBS6T8]

So, a little more reading and some investigation......

The master cylinder data on the Jegs website shows it as usable for "drum/drum" or "disc/drum" or "disc/disc".....which, now that I understand whats going on would seem to indicate that the master cylinder does not have built in residual pressure valve/s.
I've ordered a Wilwood (red) 10lb residual valve and will plumb it into the rear brake pressure line.

Job for next week when I'm off.

Confused? Based on the info wouldn't or should I say, shouldn't it work? Residual valve built in to the M/C? So it wasn't built in. But why say it would work with all of the above?
I have the DSE set up with Wilwood disc up front and stock drums in the rear. I have plumbed a proportioning valve in in the rear. Am I going to run into the same issue? Call DSE? I still have the Currie 9 inch with the Wilwood disc waiting to be installed! Suggestions or thoughts?
Thank you.

[ROBS6T8]

I think I just found the answer reading "canyonkiller's" thread. Unless this DSE cylinder has the valves built in, I'll have to install 2# valves front and rear. Correct? After I install the 9 inch of course. Otherwise 10# valves in the rear for the drums.
Then again, according to the info, they've only needed if the MC is mounted lower and there is drain back from the lines. Help!

[LeighP]

The 10lb rear residual valve is need for drum brakes regardless of the position of the master cylinder. The 2lb residual valves for the discs are, from my understanding, only needed where the disc caliper is higher than the master cylinder.

[ROBS6T8]

Thanks Leigh. I just got done installing the DSE set up. I had an issue at first with air in the M/C. I bench bled it but obviously didn't work. After some research, I found another way to bleed it and did it again. I went for a drive yesterday and I have to say it stops! No residual valves. I'll be replacing the rear drums for disc in a few months. Love the DSE set up.