68 corvette MC for CJ7

[RkCrlr]

First the required: I DID search and read for hours. There is alot out there on this. Unfortunately, there is contradictory postings and alot of other MC swap info mixed in. I lurk alot and post rarely. Hopefully, I can consolatate this info for at least the manual setup. Once I get it working I will post easy instructions/ requirements (for noobs even).

I am trying to debug my brakes and and wanting help from thos out there with working brakes using the manual 68 corvette MC. I don't want power brakes and I can't afford hydro right now, so please don't suggest them. BTW, the bug is they are grabbing in the front and I mean HARD. Only after I get up some speed tho.

the setup: 68 corvette MC, stock proportioning valve (unmodified as of yet), stock brake rod, dana 44 front disc brakes, rear exploder disc brakes.

A few things I have yet to positively determine:
Brake rod length- modified or not? (Does not seem you have to right now.)
Brake rod need to be attatched to MC as in stock CJ or just float inside bore?
Routing- front bowl to rear line, rear bowl to front lines? Adapters then are needed? Fairly, certain this needs to be done.
modified prop valve? Some do, some don't.

Things that are definate:
brake light switch has to be adjusted or lights will be constantly on.
MC must be bench bled (I did, some people are not)
MC fits with no mods, very close to hydro clutch MC tho.

[Meyer]

Front bowl to rear, Rear bowl to front

Ditch the prop valve

[BMB]

I'm going to be doing pretty much the same swap soon on a CJ (44 Front calipers/ Lincoln rear calipers) manual master. I'm thinking a Caddy four wheel disk prop valve to replace the stock one should work pretty well, might want to look into it.

BMB

[RkCrlr]

BMB, letme know how it turns out.

Meyer, I have heard some very good safty reason NOT to ditch prop valve. I want to see if it can be done with it.....if not I'll obviously ditch it.

[LilRocky]

You need a disc/disc combo valve.

[SPEEDCRAVIN]

David I am in the same boat as you. I read a lot of stuff that was contradicting as well. I am in the process of wraping up things with my YJ build and got a lot of smart assed replies because I "need to sharpen my search skills".

I know you have a cj but from what I have found out and may not be always true, but the 1969 or 1968 vette MC will bolt up with some hole grinding and grinding a lot around the mount flange.

I spoke to some guys at WMS, and they are running a lot of 1tons and 2.5 tons with still running the stock booster and the vette MC.

I have done all the grinding and got it mounted and I did not have to mod. the push rod. I would take your stock cj MC to the parts store with you and make sure the MC piston has about the same lenght inside for the push rod.

Goodluck, JOSH

[XJJack]

I just put in a corvett master (ovcourse with hydroboost) and the way I was told is that this and other chevy masters are front front rear rear. Not sure if it is the same or will help you but if the prop vavle is a comination valve it is suposed to delay the presure to the rear until the front activates so if it is reversed this may be causing it to staret to stop then the presure equlizese then it tries to send to the rear but goes to the front causeing it to grab.

Just a shot in the dark.

[RkCrlr]

Speed, I hear you about all the info. Sounds like you are doing power brakes...I am trying to stay away from them since you loose some your brakes if you stall. Could be nasty if you are in a nasty spot and really need your brakes. With hydro you don't (reverts to manual) but I have too many other things I have got to spend $ on that I can't afford it right now. (shocks, driveshafts, better springs, etc).

Xjjack, you just pointed out an example of contratitory info, but you are also pointing out one of the reasons to keep the prop valve. That and the safety feature if you break a line.

Would really love it if some people with working corvette brakes would chime in here. I know Wheelingpiazza has em w/o prop valve and Vanco has been a good source of info.
Keep the info coming....

[Meyer]

It's not that hard. I am running the same thing, no boost, no prop valve. Wheelingpiazza has a writeup too on how to determine pushrod length. I would not take it to the parts store for that, most of those people are idiots. Also, the bowl/line setup is what I listed above, not what XJJack listed. I did all this 2.5 years ago and have replied on this type of stuff since then. You can try it with the prop valve.

By grabbing do you mean locking up? Just starting to drag? If it is dragging, you most likely have a pushrod problem. How much pedal swing do you have before?

You have determinations listed above, how is it hooked up now though?

I would hookup like I/Wheeling did and recheck the results.

[ROCKEATR]

My understanding of the prop valve is
1) prop between front and rear (obviously)
2) IF a brake line fails, the little ball will be pushed to the failed side and you retain the other end of the brakes. WITHOUT a prop valve, if you loose a line, you loose ALL your brake fluid, front and rear.

.02

JB

[LAME]

I got a chopped up CJ brake pedal set up, 68 vette master. No mods to mounting, no prop valve. D44 front, Monte Carlo calipers on the rear axle. Pedal feel is typical shitty Chevy feel, but I can lock up my 38.5's on tar without a problem.

[WheelingPiazza]

sounds like you have your lines mixed. On the Master, the front port is the for the rear and the rear port is the front.
Ditch the Porp valve, Your stock one will not work with discs in the rear. Get an adjustable one for the rear. or get 5lb residual valves for the the discs.

Its been a while since I did the write up on teh proper rod length. I think its still in the search stuff. If not ping me outside of this and I will review or look for it.

The stock poportioning valve is setup for disc/drum combo, which is 5lbs residual front, 10lbs residual back. Remove it, use either residual valves rated at 5lbs

Check your lines, Front port is for the rear and rear port is for the front.

Thats all I can think of off the top of my head.

[Meyer]

FWIW, Wheeling's and mine are pre76 CJ's, not sure but I think the pedals and MC's were different in those middle years. This means the measurements for our rods might be different from what you need.

[DieselCj]

I have a 68 vett MC, manual brakes, no booster of any kind. I have stock CJ-7 calipers/roters on the front, and 87' maxima calipers on the rear. I have don't have a proportioning valve. I'm not sure which way I hooked up the lines. However my pedel is stiff, but it won't lock up anything, and doens't stop real fast. All together I'm not real happy with it, but I don't have the time or money to fix it.

I think my calipers in the back are just too small to work well.

[CrustyJeep]

Originally Posted by ROCKEATR

2) IF a brake line fails, the little ball will be pushed to the failed side and you retain the other end of the brakes. WITHOUT a prop valve, if you loose a line, you loose ALL your brake fluid, front and rear.

WRONG.
The front and rear circuits are seperate. Fluid is *never* exchanged between the two. Modern M/C's are designed to operate on only one circuit in an emergency.

I cut the rear brake line on my heep a few weeks ago on the trail, with an adjustable prop valve and no combo valve, front brakes still work *just fine*. Pedal goes almost to the floor before they hit, but they grab just as hard as they ever did up front. I had to drive it 20 miles home, no problem.

I'm running a mid/late 70's 3/4 ton chev truck M/C with 1.25" bore, BTW. Bolted right on to the stock CJ booster with no adjustments needed.

[WheelingPiazza]

Originally Posted by DieselCj

I have a 68 vett MC, manual brakes, no booster of any kind. I have stock CJ-7 calipers/roters on the front, and 87' maxima calipers on the rear. I have don't have a proportioning valve. I'm not sure which way I hooked up the lines. However my pedel is stiff, but it won't lock up anything, and doens't stop real fast. All together I'm not real happy with it, but I don't have the time or money to fix it.

I think my calipers in the back are just too small to work well.

Depending on what tires you have, I would say you dont have enough brakes to stop your rig. With any manual brakes the pedal will be stiff, but with an 1 5/8 bore it should move plenty of fluid. I am not sure why you would use Maxima calipers considering there rated for a 195/205 tire rating. not a 31 on up tire. I say change your rear calipers, or get a set of 205 stockers and try your brakes then.

[WheelingPiazza]

Originally Posted by CrustyJeep

WRONG.
The front and rear circuits are seperate. Fluid is *never* exchanged between the two. Modern M/C's are designed to operate on only one circuit in an emergency.

I cut the rear brake line on my heep a few weeks ago on the trail, with an adjustable prop valve and no combo valve, front brakes still work *just fine*. Pedal goes almost to the floor before they hit, but they grab just as hard as they ever did up front. I had to drive it 20 miles home, no problem.

I'm running a mid/late 70's 3/4 ton chev truck M/C with 1.25" bore, BTW. Bolted right on to the stock CJ booster with no adjustments needed.

A Poportioning valve does nothing but poportion that amount of fluid that is directed to the front set or the rear set and keeps pressure where needed. Drum brakes require 10lbs of constant pressure, Disc require 5lbs of constant pressure. So think of the Poportioning valve as a one way valve.

On older single chamber master that had the poportioning valve (if it had one) was the spliter between front and rear and if you removed it you would have to figure out a way to split the line. IF you lost a line then sure you would loose braking power because you only had a single chamber Master. If you currently have a single chamber master then I recommend you remove it and replace it with a dual chamber master or wilwood dual master set.

[CrustyJeep]

Originally Posted by WheelingPiazza

A Poportioning valve does nothing but poportion that amount of fluid that is directed to the front set or the rear set and keeps pressure where needed. Drum brakes require 10lbs of constant pressure, Disc require 5lbs of constant pressure. So think of the Poportioning valve as a one way valve.

If you're talking about a proportioning valve, then yes, it simply proportions pressure between front and rear, that's it. A one-way valve it most certainly is not. It's more of a pressure regulator.

A combo valve OTOH (as it's name implies) serves several purposes, the main one being proportioning. They also do the idiot light thing (USELESS, IMHO, for offroad vehicles), can block a circuit that has been breached (to keep some firmness to the pedal or make single-circuit systems slightly less deadly), and in disk/drum systems they provide metering for the front circuit so that the rears can begin to grab *just* before the fronts (evens out brake wear and is more stable at high speeds).

Now, residual valves are not inherently required in disk OR drum systems. They should only be needed when the M/C is low enough relative to the calipers or wheel cylinders to cause fluid drain back via gravity. Most rigs don't need them. Usually they seem to be used as a bandaid for other problems, like untrue rotors/drums, or to offset the effect of a M/C that is too small for the job. My position on residuals is to get your system working as well as possible *without* them, then if you cannot solve a mushy pedal, try residuals.

Originally Posted by WheelingPiazza

On older single chamber master that had the poportioning valve (if it had one) was the spliter between front and rear and if you removed it you would have to figure out a way to split the line. IF you lost a line then sure you would loose braking power because you only had a single chamber Master. If you currently have a single chamber master then I recommend you remove it and replace it with a dual chamber master or wilwood dual master set.

Huh? I thought I was clear that I have a modern 2-circuit M/C You're right, if you're running a single circuit M/C, GET RID OF IT!

[DieselCj]

I have the maxima calipers because it was a cheap disc brake system for an AMC 20 axle. I am in college, and don't have a ton of money to swap axles or do much of anything. Some guys claimed to be able to lock up the tires with these calipers, but I've never been able.

[VancoPBS]

I am not going to argue the combo valve anymore (which is what everyone has after the mid 1970s if the have power and front disc). Getting tired of saying the sky is blue and people insist their is no sky.

As for the rod adjustment. You needed a longer rod, about 3/16ths I think. It would be the distance that you need to adjust your stoplight switch. GM used a deeper piston then Ford/Jeep did (Jeep is Ford BTW). It wouldn't be causing this problem though.

GM connect the port closest to the firewall to the rear brakes, closest to the front bumper to the front brakes.

In this case the valve waits till a couple hundred lbs enters the system before allowing the front brakes to activate, so that wouldn't be your problem either.

Really not sure what could cause this on a manual brake system.

[CrustyJeep]

Originally Posted by VancoPBS

I am not going to argue the combo valve anymore (which is what everyone has after the mid 1970s if the have power and front disc). Getting tired of saying the sky is blue and people insist their is no sky.

I knew it'd get ya

I wasn't gonna argue it anymore either, but I ran into a bit of real world data while out wheeling a few weeks ago. Like I said, front brakes still work fine, pedal just feels like hell. Rear line is wide open, resevoir empty, adjustable prop. valve only.

I would suggest that you're thinking of the old single circuit systems, where a combo valve would be the only (hydraulic) safety net if there was a line breach somewhere past the combo valve.

I would also suggest that you open the rear bleeders on a vehicle with a setup like mine and see what kind of stopping power you still have in the front system. You'll see

[will-m]

are the corvette masters split?

[VancoPBS]

You do it for me, remove the brake line on the other end of the vehicle then report back.

[CrustyJeep]

Originally Posted by VancoPBS

You do it for me, remove the brake line on the other end of the vehicle then report back.

On the front? Yuk yuk yuk

Just admit you're wrong, I promise it won't hurt

[VancoPBS]

Go ahead, I can handle it.