You win.

 

I lot of good advice here. I just went through this with my 76. I tried going the budget route, but never got them "right". I finally got fed up and replaced everything . . . brake lines, calipers, rotors, master cylinder with all new. Then set the runout and now the car brakes better than it probably did from the factory.

My advice as several mentioned would be to bleed the brakes first. There is a lot of info on techniques and tips right here on the forum. Use the advanced search feature and plan to spend at least a couple of hours reading. Getting the air out of the rears can be pretty tricky, depending on how you are doing it. I found that if I got someone (other than my wife ) to aggressively pump/stomp on the brake pedal while I open/closed the bleeder screw, that it would force the air out. The key is to pump that pedal as fast and hard as you can. That was half of my battle. I tried rebuilding my calipers, but I think they were too worn to seal good; had leaking issues a year later.

Be sure to check the runout too. You can buy an inexpensive dial indicator from Harbor Freight. Again, do a lot of readiing on this. I made my shims from aluminum cans and they worked great.

 

Just curious, how bad was the runout?

 

Dont anyone here know what a brake lathe is? A hint, its to true up rotors...shimming is a joke fabricated by back alley mechanics....Brake shops would never use such a procedure. Its both ineffective and a waste of time,,,

 

I'm the owner of the 71vette. Rear rotor question is moot, the rivets were cut and all rotors machined off the vehicle back around 1982 or 83 before I knew any better. At that time replaced original calipers with rebuilt ones from Stainless Steel Brake Company because old pistons were always leaking. Car always stopped great, hard pedal, no problems, no uneven wear.

If we had any runout I never noticed any symptoms. Current situation is everything is covered with a nice coat of rust (cosmetic, no structural problems), and pedal goes almost to the floor with no resistance. Car has not leaked one drop of break fluid in 18 years of storage. We'll start by a better visual inspection and flushing the old fuild and re-bleeding. We'll get a pic or two posted as well. Very much appreciate the help and spirited discussion!
-pak

 

Hey Walt! Met you a couple times at Sears Lincoln Park. Have you ever measured runout after cutting the rotors? BTW doesyour shop still do this kind of stuff?

 

If they are centered correctly on the lathe there isn`t any runout. If there is, a small surface cut of a couple of thousands will true them up....helps prevent a pulsating pedal

Yes, we can.

I can still be reached in the warehouse behind the parts store thats on the corner. {where the toys are} I might have to re-open the store at least for some labor as I doubt if anyone still cuts rotors anymore besides the brake shops.....

 

How do you accommodate the runout on the spindle face? This frequently is the source of the runout, not the rotor

 

When I installed new rotors is used http://www.brakealign.com/index.htm. The only issue I had was altering the rear alignment plates to allow access for parking brake adjustment. Other than that, they were easy to use and did the job.

If you decide to go this route, measure your runout before you order the correction plates. That way you'll know which plates to order. The folks at Brake Align are helpful and freindly, so give them a call if you have any questions.

On a related note...my factory rear rotors were shimmed. Must have been a back alley around the St. Louis plant.

 

Hi Wally
I think we agree on most things except for turning the rear rotors. Front hub/rotor assemblies can certainly be turned on a brake lathe by an experienced operator. Rears, well most times they are not going to be inline with spindle center line. Add into that operator experience. I'm not saying you are not doing them correct as I know you're been around a while and are experienced. I fully expect you to disagree with me and that's ok. My aim is to help the car owner who may not know about these cars all that much and usually will not get a good response from their local garage or dealership. There are plenty of stories on just that subject on just about every forum, car show,car club meeting and at swap meets to fill a LA telephone book.

If we look at the history of typical corvette brake systems from 65-82 the one common complaint posted over and over and over again, year after year, is how bad the system is.
Some take it to a new level of installing aftermarket systems thinking they have solved the problem. If i tlooks good in a magazine hten it must be better then OEM, right? In fact the aftermarket systems are fine but may not really be needed for most owners of street cars. Slotted rotors, drilled rotors, SM pads all have their place but most are not needed for driving a vette on the street. Road racing , auto cross, hard braking applications well that's different.

So where did the corvette brake system go bad? In the 60's & 70's the system was one of the best around on a production car,the roads didn't change, the pads are still the same. When new theses cars stopped pretty darn good. They continued to do so until the car became a collectible and was pulled from daily use and stored or the brake pads wore down until service was needed. Then the problems began.

Storing with DOT 3 will absorb mositure, turning it into a acidic muddy mess, that will not only eat paint but pit cast iron and clogg rubber lines. This causes the caliper to leak or lock up. Hence a new industry was developed in the mid 70's SS lined calipers, anyone with a Bridgeport was boring a sleeving them, some have survived but a lot are gone now. This solved the caliper issue but not the bearing endplay or rotor runout issue. Guys were still installing new SS calipers and having to pump up their brakes to stop or bleed them every other week. Hell when I was 17 I was doing the same thing!!

Now when the car was brought in for that first brake service, as routine and to make money, the rotors HAD to be removed and turned. Now again, the fronts were no different then any Gm car of the period, tunring them on their races provided a good surface without runout. Turing the rears were, in most cases, causing more runout. I never recalled any mechanic I knew or ones at a dealership in the 70's that checked rotors for runout, most could not use an indicator if they even knew what it was. Again stories abound of cars going back and forth to a garage or dealership,rotors,calipers M/C all replace to solve a problem they didn't understand. Add in rear bearing endplay and you have a $1500 repair bill in 1980 dollars!!! And still many were not done right.

Zoom to the present day. Many shops won't even work on these old cars now because
1- they still don't understand them
2- the guys that did are retired or dead now
3- they still get wacked $$ and the work may not even be good.

So what is the average owner to do? Well most guys with these cars now want to work on them and with some correct information will do a better job then the cars from 30 years ago and save some money, without the fancy catalog brake systems they don't need.

1- Use a quality SS caliper if there are still iron bore calipers on the car
2-replace all the rubber hoses and copper washers when rebuilding the brakes or 7 years.
3- Use DOT3 but bleed the system if the car is stored, untouched, for several month. I like to pump the pedal a couple of times a month if I don't drive it.
4- use organic pads for the street, they stop better in normal use
5- Adjust the front bearings correctly, sorry I'm not writing that up now
6-Check the rear bearings- already wrote way too many threads on those.
7-check the rotors. mic them up, new they are 1.250 (imports are now 1.245) trash size is 1.215 but I wouldn't go that thin. If they are grooved toss them out. You only have 035 to work with on two sides. If they are glazed break it with a 100 grit D/A pad or even a flat block and 100 grit.
8 Check the runout. If under 005 that's ok, I like to get them under 003" If they are not under 005 then the fronts can be kiss cut or shimmed. YES shimmed, it works and works well.
The rears as mentioned leave little to work with. you can bring them to your local brake guy and see where you end up, you can replace the rotors but you'll still have runout, or you can shim them to spec and drive the car. I certainly didn't invent this, look back 35 year to SSBC they used to sell tapered shims for the same purpose, anybody remmeber them?
I just setup brand new 31 spline axles with brand new rotors. I checked the axles and faced the flange to 0005" (That is 5 tens) Installed and set the bearing endplay to 002,still had 006-008 endplay. I shimmed them down to 002. The last T/A did were also 31 spline with new rotors, VB&P in fact, one was out 015 and the other 008 Both were set to 001- 002 by shimming and bolting without removing any material from the rotor.
I've rebuilt a lot of rear bearings and did this on all. Agree or disagree, that's everyone choice as well as their money.
My brakes work, my bearings work.
Have a nice day.

 

I'm thinking the worst was about .015. I got it to .002-.003

As Mike was saying . . . I indexed my rotors and it was within .001" on a new rotor. All the runout was with the spindle face. I shimmed between the spindle and rotor to get the above numbers. THis was the first on only time I have done runout; it was more a learning experience and trying to get as close as I could following the advice here from CF. I can tell you it brakes straight, smooth and on a dime.

 

I have no problem with the analysis as you covered every aspect of a Vette`s brakes and is full of very worthwhile valid material. True the rears would give a back alley do it yourselfer a real headache. But the rears are just cut and serviced as a front wheel drive hub-less rotor. It is a special tool for them {Hubless rotors} and should be part of brake shop equipment. And I do recognize far too many stores and shops stick their most inexperienced employee with the duty to cut rotors, bad mistake but frequently done because its a dirty job and there are some employees that dont like to work with dirty parts. those employees are easily spotted by the wearing several layers of gloves. They also move very slow. Now bent front spindles should be scrapped. Also as you know fronts run on bearings and races and should never be a problem.

The rears should be installed on a clean surface which I presume is always done and in reality are the same for all rears regardless of the make and model... car or truck. .oh hell, you know how its done and quite possibly will help those in repairing their brakes, my view was from the other side of the counter.....

btw, backalley is not meant to be offensive, its something I used to describe some of the things customers do and no relation to bubbas as I felt Billie Clinton owned the bubba word.

 

The c3 system was innovative then, but many newer cars and trucks use essentially the same system now and have the same problems.
GM recommends on car lathes, in particular, ProCut PFM900 and Hunter OCL360.
The unclean surface condition Ironcross referred to, is called "Lateral Stackup" by GM, and is also a known condition they address.

Gm has gone further to develop a new system in the following TSB, which in effect is the same shimming the rotors.

Here is part of one of the TSB's, but not the latest one.

TSB

Brake Rotor - Lateral Runout Correction System

Bulletin No.: 01-05-23-001

Date: February, 2001

INFORMATION

Subject:
Brake Align(R) System for Brake Rotor Lateral Runout Correction

Models:
2001 and Prior Passenger Cars

This bulletin is being issued to update General Motors position on correcting brake rotor lateral runout (Refer to Corporate Bulletin Number 00-05-22-002 for additional brake rotor service procedures).

Important : Certain conditions may apply to individual vehicles regarding specific repairs. Refer to those specific repairs in applicable service bulletins. Make sure other possible sources of brake pulsation, such as ABS pedal feedback, have been addressed before checking rotor runout.

Anytime a new or refinished rotor is installed on a vehicle, the rotor must have .050 mm (.002 in) or less of lateral runout. This specification is important to prevent comebacks for brake pulsation. Until now, the only acceptable methods to correct brake rotor runout were to index or replace the rotor or to refinish the rotor using an on-vehicle brake lathe.

GM has approved a new technology for the correction of lateral runout on new or refinished rotors. This new method is called Brake Align(R)*. It will allow the technician to meet the .050 mm (.002 in) or less requirement for lateral runout by installing a specially selected, tapered correction plate between the rotor and the hub. The Brake Align(R) Correction system does NOT require the use of an on-vehicle brake lathe to correct for lateral runout.

 

Interesting on the GM info. I guess we were years ahead! LOL

Wally -no problem here, I'm sure you know these cars well. The concern is most do not, that includes new owners,shops,parts stores,dealerships. I've seen more damage done to boxes, diffs,brakes, and rear bearings from inexperienced people then from the parts actually wearing out. Some by very good new car mechanics as well.It is specialized work but also a very small window of service. How many local shops are going to work on 30-40 year old cars,let alone ones with a unique brake and IRS setup? They concentrate, as you know, on the common, daily-driven cars and they are the ones they are very good at fixing and making money on.

I've talked about brakes for so long now I may just stop, as it's getting old. The info is out there for all to find and these forums are a great resource for that info. I started to shim rotors after an area shop wrecked 2 OEM rotors trying to dress them on a brake lathe. that was back when I could buy new GM rotors/hubs riveted for $99 each(25 years ago). It has worked out great for me, as I said- I find runout to be the norm with new spindles and rotors.

Now if you want a real treat, try the 12 bolt diff or 31 spline axle setup. Just finished a set and that was "fun"!

When I get some time I may play around with various setups but I also want to machine a 30 spline 12 bolt axle setup to fit into the vette 10 bolt posi in time for Carlilse. Not sure I'll get to that on time either.

 

No, please don't stop. This subject, like many other complex technical tasks unique to these cars is bubba's playground. There's always a new generation of inexperienced owners who are tempted to listen to half baked, incorrect or even dangerous information on how to maintain the cars.

 

So after we did our in garage drive, (haha!) we opened up the master cylinder, we were checking to see if we had dot3 or dot5 brake fluid. ye behold there was nothing!!! (may explain why the brake pedal was loose.) So now we will attempt to find where a possible leak may be. (but does hydraulic fluid evaporate?) Then we will blow out the brake lines?