Brake Problem 70 Coupe

[Dennis Voiro]

This is a continuation of a prior posting. My thanks to the individuals who previously responded.

I have a leaking front passenger caliper on my 70 coupe. This car was a frame off about 10 years ago and I was told that all the calipers are stainless lined.

The casting numbers off the calipers are: (Not positive about the first digits, could be 5 or 6. Both are 4 piston units.

Passenger front 6473798 Delco-Moraine
Driver front 5473798 Delco-Moraine

Can someone tell me if I should have these units rebuilt of just replace them. Where is the best place to have them rebuilt or what vendors have the best quality product.

I also want to replace the brake hoses and am not sure if I should go with rubber or stainless. Do stainless require replacement like the rubber hoses?

I also heard that these units are harder to bleed. I saw in a prior posting discussion about using a bleeder system (Motive)? Any suggestions?

I really appreciate the assistance with this. My first Corvette.

Thanks, Dennis

[Jim T.]

Re: Brake Problem 70 Coupe

Original owner of 70 and I replaced my hoses with rubber, excellent braking abilities with the rubber hoses. If in fact you calipers are stainless, I would just do a rebuild of new seals and dust covers. It is really pretty easy to install new seals, just have to install the seals correctly on the pistons. Seals do fail/leak from wear. Flush the whole system with new fluid. Brake fluid is hydroscopic, absorbs water, and although most don't your brake system needs a complete flushing about every two years by installing new fluid.

[Joe L.]

Re: Brake Problem 70 Coupe

Dennis----

As Jim said, all you probably need to do is to replace the piston seals. As a matter of fact, most firms that install stainless steel sleeves will not accept previously sleeved calipers as cores. So, that adds about $200 to the price of a car-set if you just go and buy a set of completely rebuilt and sleeved calipers. Some of these firms will rebuild your existing calipers for you with new seals, boot, etc.---they just won't accept the calipers as cores.

There's a very good reason why they won't accept the calipers as cores, too. You see, all stainless steel sleeved calipers are not equal. Some use low quality, DECORATIVE stainless for the sleeves. Some don't install the sleeves properly and these can be forced out of the bore by the high hydraulic pressure in the brake system.

If you rebuild the calipers yourself, you can purchase kits which include all the parts you need from many Corvette parts vendors. You want to carefully inspect the caliper bores for any problems. If you note any CORROSION (actual corrosion, not just staining which can be cleaned up with crocus cloth), then you have calipers with low quality stainless steel sleeves. In that case, get rid of them---just bite the bullet and purchase a set of HIGH QUALITY sleeved calipers outright.

Also, you need to inspect the pistons. If any of the gold anodize is worn off the pistons on the sealing ring (the part of the piston with the greatest OD), then the piston should be replaced. You can get these from the Corvette vendors, too.

I always recommend the use of new rubber brake lines. Most of these are DOT-approved. Most of the stainless braided lines are NOT DOT-approved. There's a reason why they are not DOT-approved, so you don't want them. Use rubber lines. They will last between major brake overhaul jobs. That's as long as you need for them to last.

All 65-82 Corvette brake systems are difficult to bleed. The Motive Products pressure bleeder may ease the process. I don't know yet, but I soon will. I am about to bleed the brakes for the first time with a Motive Products unit.

By the way, your caliper castings are not the original casting numbers used on your car. These castings were used for 1973+ Corvettes. They are 100% functional and interchangeable for your application, though.

[Dennis Voiro]

Re: Brake Problem 70 Coupe

Just wanted to thank Jim and Joe for their assistance with this. I will be using rubber brake hoses and have a starting point for the repair. Joe please share your experience with the Motive Product when you can. Do you have their web site?

When you mention replacing the brake fluid every 2 years. Do you flush the system by performing the bleeding process starting with the farthest wheel and continue while purging the system of the old fluid and adding new? Prefer any specific brand of Dot 3?

Thanks

[John H.]

Re: Brake Problem 70 Coupe

Dennis -

The Motive Products pressure bleeder takes all the grief (and time) out of bleeding the Corvette brake system; terrific tool, and I think Joe will agree once he tries his. Their website is www.motiveproducts.com .

Flushing is simply a fresh bleed that fills the whole system with fresh fluid after expelling the old fluid. I use DOT4 Castrol GT LMA (Low Moisture Absorption) fluid in all my cars - allegedly is less hygroscopic than other brands; have never had an issue with it, and every auto parts store has it.




Motive Products

[Warren L.]

Re: Brake Problem 70 Coupe

for my 70 I bought new stainless sleeved calipers. Looked at them years later and not yet on the car the seals were toast.

We took them apart and rebuilt them with GM seal kits. Sure the rebuild guys are using better quality seal kits than the one that did mine at the time.

Warren

[Gary R.]

Re: Brake Problem 70 Coupe

Good info, the Motive is great found it better then any other setup for home use. I use a c clamp instead of the J hooks it comes with and I had to use a hose clamp where they crimped the hose on the cover,otherwise it works great.
One thing I didn't see mentioned is rotor runout and bearing endplay. You can have the best calipers in the world but if your runout is over .002" and the endplay also over .002" you'll have brake problems. You may get by with up to .005 on the runout but shoot for under .002. Endplay I wouldn't use over .002" This could lead to other issues such as settig up rear bearings but check yours first to see what you have.
Good luck
Gary

[Gary Schisler]

Re: Brake Problem 70 Coupe

Can I assume that the model you use is the one labeled CLASSIC CAR POWER BLEEDER Model 0102?

Gary

[Dennis Voiro]

Re: Brake Problem 70 Coupe

Gary, thanks for the response. I was looking at the Motive Web site and am also wondering which model you use. Which model come with the correct connectors?

The car only has about 3k miles since it was restored. Rotors still have the cross hatch on the surface. I plan to repack the bearings while eveything is apart. Just not sure if I should rebuild the calipers or buy another set. I don't hav a way to pressure test the calipers after the rebuild.

My thanks to everyone else who has responded also.

Dennis

[Mark H.]

Re: Brake Problem 70 Coupe

I've been looking at getting one of the Motive Products bleeders as well. Please let us know what you think of it.

[John H.]

Re: Brake Problem 70 Coupe

Mark -

Best sixty bucks I ever spent - bleeds Corvette disc brakes in ten minutes, high, solid pedal. Puts all the MityVacs, Phoenix Injectors, etc. to shame - wish I had one years ago.

[Joe L.]

Re: Brake Problem 70 Coupe

John------

Your photo reminds me of something I noted right after I opened the box: I wish they'd come up with a better and more convenient retention system for the master cylinder adapter. I realize that the reason they have the design they have is to make the the adapter more "generic" and fit a wide range of master cylinders. I'd like to see a specific adapter for the 67-82 Corvette (and, many other GM) master cylinder.

I wonder if it would be possible to purchase such an adapter from a firm that supplies professional bleeder equipment to the automotive service industry and adapt it to the Motive Products kit?

[George D.]

Re: Brake Problem 70 Coupe

I worked for Wagner Brakes. They had an adapter that fit perfectly on the tandem master cylinder, but I don't remember the part number. It had a quick disconnect fitting for the fluid inlet and pressure. There was also a chain type set up to hold the adapter in place on top of the master cylinder assy.

[John H.]

Re: Brake Problem 70 Coupe

Joe -

I didn't care for the chain arrangement either, so I developed the one in the photo in my previous post - it's a 7"-long piece of 1-1/2" aluminum square tubing (left over from my Grand Sport project), with a 6" C-clamp; spreads the load nicely on the adapter so it seals completely. One of these days I'll add two pieces of tubing that protrude about 3/8" from the fill holes in the "wet" side of the adapter, to draw off the excess fluid to proper depth before removing the adapter.

This thing makes "duck soup" of the job of bleeding any Corvette brake system; no such thing as "I can't get my brakes to bleed".

They also make a handy vented bleed bottle with a wire lanyard on it so you don't have to fumble with jars, cans, etc.

[Joe L.]

Re: Brake Problem 70 Coupe

John-----

Yes, I purchased those bottles, too. I got 4 of them, so if I ever wanted to gravity bleed, I could put one at each wheel. I may never need to, though, if the bleeder works for me as well as it has for you.