Which caliper would be better suited to my combo and why?

1970 Chevelle;
Front; b-body spindles & LE1 rotors.
Rear; 81 TA rotors & mid 80's front caliper.
Wilwood adjustable prop valve.

I have seen the larger suburban caliper (JD7?)mentioned in several posts but never got a clear understanding, I know its a larger piston which translates into more available clamping force but which would provide a better overall BALANCE for MY set-up?
And, which master cylinder would be most appropriate for each?

Thanks as always - it has been the advice and wealth of knowledge available on this site which has got me this far on my low buck yet proven approach to a four wheel disc set-up.

What are your intentions? The JD7 caliper is HEAVY. It indeed has virtually no deflection and clamping force is the best but at the expense of unsprung weight and do you need that much clamping force? As soon as the brakes can lock the wheels under all conditions you have enough caliper. I think the C4 setup is the way to go, calipers are plentiful and light weight. They stop a vette, should work good on a velle.

I think that the JD7 (for 12" HD Suburban brakes) is for a 1.25" thick rotor as well. The 1LE 12" and most 11" rotors are 1" thick, as I understand it.
Also, IIRC, to use the G-body front caliper on the rear, you need the 76-78 Caddy/Big Buick brackets, or the custom brackets from eBay or wherever. The neat thing with this setup is you can use the same pads on back as front. graemlins/thumbsup.gif

Originally posted by 70OldsSportsCoupe:
I think that the JD7 (for 12" HD Suburban brakes) is for a 1.25" thick rotor as well. The 1LE 12" and most 11" rotors are 1" thick, as I understand it.
Also, IIRC, to use the G-body front caliper on the rear, you need the 76-78 Caddy/Big Buick brackets, or the custom brackets from eBay or wherever. The neat thing with this setup is you can use the same pads on back as front. graemlins/thumbsup.gif Ahem, I did not recall correctly. graemlins/clonk.gif The 80s front and rear calipers have the same spacing on the sliding pins, according to FO_FDYFO's website. Whoops. Must be the earlier A/B-body calipers that fit on the 76-78 brackets. I do know that there are "big" and "small" rear calipers, with pre-79 being "big", and 79-up being "small". I know that the throat is the same size, but the pistons are bigger on the "big" calipers. See this page. (http://www.geocities.com/diels12000/RearDiscBrakes.html) Good stuff all over that site, BTW.

Originally posted by 70OldsSportsCoupe:
</font><blockquote>quote:</font><hr />Originally posted by 70OldsSportsCoupe:
I think that the JD7 (for 12" HD Suburban brakes) is for a 1.25" thick rotor as well. The 1LE 12" and most 11" rotors are 1" thick, as I understand it.
Also, IIRC, to use the G-body front caliper on the rear, you need the 76-78 Caddy/Big Buick brackets, or the custom brackets from eBay or wherever. The neat thing with this setup is you can use the same pads on back as front. graemlins/thumbsup.gif Ahem, I did not recall correctly. graemlins/clonk.gif The 80s front and rear calipers have the same spacing on the sliding pins, according to FO_FDYFO's website. Whoops. Must be the earlier A/B-body calipers that fit on the 76-78 brackets. I do know that there are "big" and "small" rear calipers, with pre-79 being "big", and 79-up being "small". I know that the throat is the same size, but the pistons are bigger on the "big" calipers. See this page. (http://www.geocities.com/diels12000/RearDiscBrakes.html) Good stuff all over that site, BTW. </font>[/QUOTE]i dont think thats what i am saying. i dont know if The 80s front and rear calipers have the same spacing on the sliding pins. i do know that i used 82-88 camaro front calipers on my rear disc brackets. which happen to have the same mounting pattern as the ford calipers. also i know that the 90 caprice from calipers mount the same as 70 chevelle front calipers but with different hose locations. i am pretty sure the suburbam calipers have the same mounting patterns as the chevelle front calipers only with a wider throat for a wider rotor. and i also am pretty sure that he piston on the suburban front calipers is larger then the chevelle calipers. ahhh clear as mud now right graemlins/thumbsup.gif

Wally, ;)

I'll try and clear up a few things and possibly throw in a bit of my own opinion also...

First off, to give a good recommendation of MC and calipers and such, one really needs to look at the whole cars setup... especially the suspension. My first question would be why do you want the rear disk brakes? Rear disk brakes CAN provide more rear braking, but most cars I've seen them on cannot use any of the additional force because the car is not set up correctly for it. We all know that the front brakes do most of the braking, but often we do not look at WHY that is so. Well, it is so because the good people at the factory have made it so you cannot kill yourself easily when braking hard! Under hard braking, the car's weight will tranfer mostly to the front, thereby unloading the rear and causing the front end to 'dive'. In doing this, the rear wheels do not have much weight on them and will therefor lock up really easily. We do not want the rear brakes to lock up easily, so we limit the rear braking force to be minimal so we can't lock them. In doing so, we have now cut there usefulness down to a minimum. Adding rear disk brakes to that situation gains you nothing! You can already provide plenty of force to lock the rear wheels using drum brakes, only it is limited by the prop valve to not provide that much force. So, in order to have a safe vehicle that will not lock the rear brakes easily, we most limit the rear pressure, even on disk brake rears.

So, what can we do? In a nutshell, the whole car needs to be tailored around the front a rear disks working together. This means trying to get as much rear braking bias as possible without creating a hazard. Tuning the suspension and many other mods will help cut down on the amount of weight transfer that occurs when braking hard. THis in turn will allow you to bias the rears more and help you get better stopping. The amount of rear braking will be a guess and you will probably have to tune it quite a bit to get it where you like it, so I highly suggest the adjustable prop valve in the rear line if you do rear disk brakes.

As far as the Suburban calipers go, I don't think I would use them on the 1LE rotors. As already been said, the 1LE rotors and stock 11" rotors are 1.1" thick. The calipers for them have a 1/4" narrower throat than the thicker 1.25" truck and suburban rotors. This could cause major problems as the pads wear and the caliper can not slide on the pins enough to make up for the wear. The stock Chevelle caliper and stock front hoses work quite well for the 1LE rotors on the B-body spindles! As for the weight difference... there really is none. In fact, I'd bet that the suburban calipers are actually lighter than the stock calipers because more of the metal on the inside has been machined out! I have compared the two calipers several times and they are exactly the same in all dimensions and such save for the suburban calipers being 1/4" wider in the throat area.

You never said what rear backing plates you are using, but if they are for the 'small' rear calipers, then the mid '80's calipers should fit fine. GM was not too stupid when they made the rear disk brakes as they basically just took a front caliper and modified it to use a different piston and added the crappy racheting ebrake mechanism into the piston, then just stuck them on the rears. Not a bad idea, the ebrake just sucks on them.

Anyway, hope that helps clear the fog a little. If you can provide some more info, it might make suggestions easier.

Good luck,
Bill C.

or put a truck arm rear suspension on it and actually gain the use of the rear brakes as the weight transfer is not nearly as bad as the stock half-a$$ 4-link. Can you tell I'm a HUGE fan of the truck-arm rear set up.

Thanks for the replys guys.
Bill; you caught me - I must admit that my reasoning for adding rear discs is just as much for the look as for the function. With a larger wheel upgrade on the way I want to prepare some discs to see throuh the spokes. Plus adding the rear discs (with all GM parts w/ the exception of an e-bay bracket) while already doing the fronts, the cost is really quite reasonable. I've got the adjustable prop valve and look forward to the fun of setting these up and dialing them in.
I see that the suburban calipers use a wider rotor - which one gives me 1.25 thick with a 5 on 4.75 bolt pattern??? I also see that the suburban caliper has a larger pistion diameter which (if used with the correct rotor) would give more clamping force but possibly at the expense of a high unsprung weight and that bigger rotor must add more rotational mass also.
I must say that although both seem as though they would work just fine, I fail to see an advantage of one over the other unless ... the stock caliper uses a stock rotor which is therfore cheaper and easier, while the suburban caliper provides more clamping force but with a custom and therfore more expensive rotor. I think that I may have just answered my own question.

Well, you got me too... I like the looks as well, but wanted to give you something to at least think about!

The only rotor I know of that is 1.25" thick and the same 5x4.75 bolt pattern is a corvette one. They are usually 12" also, but they don't have hubs, so you have to make some. That's the setup I had on my car and really liked the stopping power, but yes, they did weigh a little more, but it was not bad.

The suburban caliper will give you more clamping force per increment of force on the brake pedal. This is mainly useful if you are doing manual brakes like I had. If you stick to power brakes, I'd stick to the stock calipers as the suburban ones might be too touchy.

Hope that helps,
Bill C.

Something I was just thinking about. Could you use the older B-body spindles (pre 77) that use the A2 outer bearing and then use an old drum brake hub to hold the Corvette rotor?

Peter

Peter,
you could do this, but it will take some measuring, etc... I think BC, RJ and others use later style B-body spindles (larger bearings) and use an old rotor as a hub for the Corvette (65-82) rotors. I think it was the 3rd gen F-body (mid-80s Camaro) rotor that was used for a hub (although there are probably other applications that will work...