Please help with the wrong booster from POL

[derotoreut]

I just received my 8-lug front disc conversion from Performance Online. The conversion was supposed to include a 11" single diaphragm booster, but came with a 8" dual booster. POL is telling me that the 8" dual will work fine and is better then the 11" single. Is this true? The information on page-29 of their catalog says, "not available in dual due to clearance issues" for the 67-72 trucks. I'm confused.

I am also wondering if they sent me the right master cylinder. Once I complete the conversion I will have a disc/drum set up. Is there a way to tell if I have the right master?

Also I have heard that it is better to have the larger 1-1/8" bore versus the 1" bore. How can I tell what I have if the master is already mounted on the booster?

[68gmsee]

POL is correct. It is a better booster and costs more than the single one. Since you've converted to disc brakes it is a better option for you.

Usually disc master cylinders are larger with different size reservoirs. If you research a drum/drum master cylnder vs. a disc m.c. for a newer truck you can see the difference. Not sure how you can tell the bore difference by looking while mounted.

[AusTx68]

The 8" dual my work better but in my opinion it looks like crap compared to the 11" when installed. That's just me and I'm speaking from experience. It pushed my MC way forward and didn't look right. I swapped back to the 11" and it worked great with my disk/drum setup. I was running a stock 72" MC for disk brakes. The difference I found between the manual and disk MCs was the bore depth (where the booster rod meets the MC). The manual MC has a depth of about 1 1/2" while the power had a depth of 1/4". So when you look at the back of MC you will either see a deep hole or shallow hole. The bore depth I'm talking about is different from the bore size(1" vs 1 1/8"). Bore size refers to the internal piston bore size. I'm not sure if there's a way to know the bore size just by looking at the outside.

I've since upgraded to hydroboost and I'm lov'n it!

[jocko]

yep, nothing i like more than a company telling me "here, take this, it's not what you ordered, but WE think it's better"... Don't get me wrong, I DO like POL very much - but this has happened with other vendors in my case. Drove me nuts. Why not just advertise what you're gonna ship - or have the courtesy to call a customer whom you will not be shipping what he or she asked for to ask if theyh are ok with the substitution? These companies aren't THAT big that they can ignore the hobbyist.

Here's the thing - just like AusTx68 said - even if the dual d works better - perhaps it looks like crap to the customer and he wouldn't have bought it if it loked different from the advertised picture...

I do agree the dual diaphragm should perform fine - if not better. To confirm you actually have a disk/drum master - just separate the master from the booster and look at the depth of the hole in the master piston that AusTx mentioned - the difference is very obvious - shallow nub (that happens to match the booster's protruding nub) means it's correct.

I would expect that what you received is correct (if not what was advertised) and will work just fine. Comes down to whether you actually wanted the larger booster which looks a little more like a stock one. If not, send er back or ask for the 11" in return. Frustrating, yes.

[derotoreut]

Originally Posted by jocko

yep, nothing i like more than a company telling me "here, take this, it's not what you ordered, but WE think it's better"... Don't get me wrong, I DO like POL very much - but this has happened with other vendors in my case. Drove me nuts. Why not just advertise what you're gonna ship - or have the courtesy to call a customer whom you will not be shipping what he or she asked for to ask if theyh are ok with the substitution? These companies aren't THAT big that they can ignore the hobbyist.

Here's the thing - just like AusTx68 said - even if the dual d works better - perhaps it looks like crap to the customer and he wouldn't have bought it if it loked different from the advertised picture...

I do agree the dual diaphragm should perform fine - if not better. To confirm you actually have a disk/drum master - just separate the master from the booster and look at the depth of the hole in the master piston that AusTx mentioned - the difference is very obvious - shallow nub (that happens to match the booster's protruding nub) means it's correct.

I would expect that what you received is correct (if not what was advertised) and will work just fine. Comes down to whether you actually wanted the larger booster which looks a little more like a stock one. If not, send er back or ask for the 11" in return. Frustrating, yes.

You can't imagine how mad I am about this. Can't people just do there jobs right these days. Believe me, I will be talking to them about this. All I wanted is what I ordered. Sure the 8" dual may work... Maybe better, but the point is it wasn't what was ordered. They recommended the 11" single, then why would they send me a 8" dual?

[rsavage]

Dan,
The smaller dual diaphragm boosters were normally used on the 3/4 ton trucks and a lot of the 4X4's. Yours probably came with the firewall bracket. There were two brackets used by the factory also - a shallower one for the dual diaphragm and a longer one for the single, so if you change the booster out, make sure you get the right bracket with it.

[Andy4639]

Factory disc brakes and booster.



Notice the front reservoir is bigger that's a factory disc to drum brake master cyclinder.

[derotoreut]

Originally Posted by Andy4639

Factory disc brakes and booster.



Notice the front reservoir is bigger that's a factory disc to drum brake master cyclinder.

Andy,
According to POL, there kits use a master with the same size reservoirs. According to them the proportioning valve is what controls the brake pressure, not the volume (size) of the reservoirs. They told me they use the same master on disc/drum applications as they do on drum/drum applications. It's just the proportioning valve that varies.

[68gmsee]

Originally Posted by derotoreut

Andy,
According to POL, there kits use a master with the same size reservoirs. According to them the proportioning valve is what controls the brake pressure, not the volume (size) of the reservoirs. They told me they use the same master on disc/drum applications as they do on drum/drum applications. It's just the proportioning valve that varies.

Yes, the disc/drum master will work on both disc/drum and drum/drum. But, if you use an original drum/drum master cylinder then the front brake reservoir is not large enough to hold the required fluid for the calipers as the pads wear down and more fluid is required to move them. (read that somewhere)

On my 69 with drum/drum I used the dual booster with the disc/drum master cylinder and never had any problems with my brakes. It does look akward but since it was a work truck I wasn't concerned with how it looked.

[derotoreut]

Originally Posted by rsavage

Dan,
The smaller dual diaphragm boosters were normally used on the 3/4 ton trucks and a lot of the 4X4's. Yours probably came with the firewall bracket. There were two brackets used by the factory also - a shallower one for the dual diaphragm and a longer one for the single, so if you change the booster out, make sure you get the right bracket with it.

Rick,
Thanks for the information. My kit from POL came with the 8" dual booster with master, prop valve, mounting bracket and rod. It was supposed to be a 11" single. I am not using a stock OEM booster, so I don't think this is an issue. Here is some information I found about the brake boosters from a fellow member.
http://outintheshop.com/faq/Brakes/brakeinfo.html
My issue is that I want the best set up for my application. It bothers me that they list the 11" single booster as their standard for my disc/drum conversion and when I ordered it, they sent me something else (dual 8" booster). Which is better? I have searched past threads and the internet for information and I am finding differing opinions. I don't know which is best.

[k2rm]

Funny. I used their kit on my '70 C20 last year. They sent me a single 11" booster with the kit. I am pretty sure at the time their website said that a dual 9" would come with the kit.

I also converted to rear disks and the stopping performance was terrible. I don't know what the problem was, but with the 11" booster, it seemed like I could never build pressure and I could never lock up the wheels.

For the heck of it, I put the original dual 9" booster back on the truck and now it will throw me through the windshield if I stomp on the brakes. The only change was the booster and I am not sure why the 11" didn't work right.

[rsavage]

Dan,
Good info that Livrat put together. I honestly don't know if there is a performance difference. My Blazer is disk/drum and has a single. The Burb is stock drum/drum and has a single. The 70 shortbed 4X4 has stock drum/drum with a dual. All work okay except that the Burb has very grabby brakes - takes a light touch. The other two are more forgiving. If you ordered the single and that's what you want make them make good.
Rick

[68gmsee]

Originally Posted by rsavage

......All work okay except that the Burb has very grabby brakes - takes a light touch. ....Rick

fyi: Had that on my 68 GMC with drum/drum. On quick stops I scared the hell out of everyone around me with the loud squealing. I did a complete brake job and haven't had any more problems.