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74 vette brakes go to floor - car dangerous to drive

13K views 20 replies 9 participants last post by  big2bird 
#1 ·
just got a 74 vette

Runs and drives good

BRakes have a problem - pedal goes to the floor

Supposedly, new master cylinder - it doens't look to old, brake fluid in it is clean , supposedly had a new caliper on the rear too. Don't know for sure what is new since I just got the car last night.

He told me that the brakes needed bleeding. I tried to bleed them - and had no luck. Are these hard to bleed and is there a special trick to them?

Why would the brakes go to the floor? Don't see a leak, the master cylinder seems to stay full and the brake light does not come on.

Help please
 
#8 ·
Make sure you bleed the calipers in the write order
Also are the calipers the original caliper if so the old seals might be bad

On my 71 the o ring calipers solved the soft pedal problem
 
#13 ·
The books say furthest from the master, working toward the closest.
The GM books from the 30's say to do the closest, then work towards the furthest:crazy:
I imagine it just doesn't matter.:thumbsup:
GM manuals of the day recommend power bleeding. I would bet that is more about saving shop time more than anything. It IS the fastest, and most thorough, since you expell and change the fluid.:D
Being hydroscopic, it's best to do it anyways every other year.
 
#11 ·
I am to understand that the original calipers came with lip seals
If the car sets for long periods of time the brake pedal will get soft
You can buy oring caliper from most of the corvette venders

Get that motive brake bleeder
 
#14 ·
I agree that the Motive Bleeder is a GREAT investment. For $90 it's well worth it. (http://store.summitracing.com/partdetail.asp?autofilter=1&part=MVP-0250&N=700+115&autoview=sku)


One tip when using it: get a 4" or 6" C-clamp and use that to hold the plate on top of the master cylinder. The chains and hooks never worked too well for me.

Can you ask the guy when the problem started and if it got worse or better after he replaced the MC? It's tough to narrow down the source without more info.

Do you notice any fluid around dripping on your wheels or splashed on the underside of your fenders? If your lip seals are bad (they get flat spots from sitting for extended periods) then you should see evidence of leaks. Especially if you have no pedal pressure.

Then I'd bleed the MC. Just do a google search and you should find some decent instructions with pics. It will involve disconnecting the hard lines from the MC, so be careful not to spill that brake fluid all over your engine compartment and fenders! Once the MC is bled, move on to the rest of the system. Go in this order: right rear, left rear, right front, left front. Furthest to shortest distance to MC.

Give that a shot and let us know how it works out for you :thumbsup:

Oh yeah, and congrats on the new car! We like pics :D
 
#15 ·
Since you don't who worked on the car in the past or what was really done to it I suggest you start from the beginning.
First be sure you have the correct M/C. The bores are different between manual and PB cars. Take off the cover and look at the BF, is it clear or muddy? If muddy then you have moisture in your system and it hasn't been worked on in a while.

Remove the M/C and bench bleed it. The best way is to go to NAPA with it and get the metric steel line conversions. The tapped hole are 2 different sizes. Once you the line with the correct flared nut, cut the other end off and bend them up into the chambers so you can bleed the M/C with a plunger,screwdriver,punch etc.


Lip seal calipers are fine to use and once the system is setup correctly will work for years. Be sure the calipers are in good shape, just because they may be SS lines doesn't mean they won't lock up with bad BF. You may want to get a seal kit and open them up and clean them out with CLEAN dot3 BF. You don't need DOT 4 or 5, 3 will work you just need to bleed the system if you store the car for a few months.

Now check your rubber hoses, if they are older then 5 years or you don't know, replace them.

Look at the rotors, mic them. They should be in the 1.215- 1.250 range. I toss them if they are under 1.225" Do they have the rivets in them? If so that's good no one was in there. If they're gone then who know what hack laid his hands on them.Check the rotor runout and bearing endpay both should be under 003" If you need rotors you do NOT need slotted and drilled rotors, send me your cash if you want to throw it away. I use both USA and imported rotors with the rivet holes,not all have them. I hate imports but the ones I used are good and sad to say as good as the USA rotors. Do not expect new rotors to dial in without help. Some may but most will be out. I've found both import and USA out as much as 012. This is where someplaces will tell you the spindle is bent and you need a new one.:nuts:

Then assemble with organic pads. You don't need metallics for the street, if you're going to be road racing and laying on the brakes then use the metallics.

If you follow all the above and use the Motive you should have brakes that stop on a dime- just like they did 40 years ago before the hacks started working on them.

Good luck
 
#17 ·
what method are you using to bleed it? Do you have someone pushing the pedal down while you open and close the valve? If so, put a 2x4 or something behind the pedal to make sure it doesn't go past its usual range of travel. That can push the piston in the MC far enough that the seals can actually be damaged. Ask me how I know :rolleyes:
 
#18 ·
No one has mentioned the idiosyncrasy of these cars actually pumping air into the rear calipers if the rear disc "wobbles" by more that a few thousands. Guys may chime in here giving you specs. I have found that some are more susceptible to the problem than others. Ask the guy you bought it from if he has had any rear spindle work done recently or if the rotors in the back have been replaced.

Congrats on your ride brother! :thumbsup: Don't let this get you down, you are just in a high learning/dues mode right now, but you will catch on. Very simple machines! :cheers:

BTW, the '74 is my all time favorite year of the C3 production! Nice choice! :D

Good luck! :cheers:
 
#19 ·
Here's my take on your problem. I'll start with a bit of history on my '73 and it's brake problems, and what the cure turned out to be. when i bought my 73, the brakes were terrible, leaking and worn, so I bought a full brake replacement kit from SSBC. Bench bled the MC first, then Put them on and used a pressure bleeder to bleed them through. Hard, solid brake pedal. take it for a drive. 5 miles later, brakes are near the floor and ti barely stops. The new calipers were like stock seals, not the o-ring type. Re-bled, air in the rears. changed the rears to O-rings. now does not fail. Grinding noise was coming from the rear at speed at this point. Rear wheel bearing was shot. Original problem turned out to be, bad wheel bearing causing back wheel the move out of spec, putting air into the rear brakes, the O-ring calipers solved the symptom, but the underlying problem remained, until i had the rear trailing arms rebuilt at the dealer, and had all the rotors turned on the car at the same time, with a 'bolt to hub' machine. Now brakes are perfect. Moral- i would put worn rear wheel bearing high on the list of things to check. Also, I think that a pressure bleeder is the only way to bleed the brakes on these 'Vettes, successfully. I will run a quart of fluid through each caliper, for a total of 1 gallon of fluid when i bleed them, from experience. Tap on the calipers when they are running out and you should be good, but use a pressure bleeder witha C-clamp with piece of flat, strong wood over the plate. C.
 
#20 ·
I think I got them fixed seemd to be good for the last couple of days.

Bought a new master cylinder - that wasn't the problem

In the instructions there was a paragraph about adjusting the pushrod. I have never heard of this. I turned the adjusting screw out about A LOT and brought the pedel up to where it should be. Brakes wrok fine now.

Thanks to everyone for input on the situation.
 
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