67 Shelby Brake Problem

[texas swede]

A Swedish former NHL player bought a grey early 4-speed 67 GT350 (#0153) and his brakes acted up.
When he stopped at a red light and held the foot on the brake pedal the car started shaking and finally die.
I sold him an extra Midland Ross booster I had which was repaired by a company in Dallas.
Roland, my Swedish friend installed it. Now almost a year later (almost no miles driven) the brakes act up again.
Roland took the booster apart but couldn't find any fault with it. He followed the 67 shop manual
and created a tool to measure the adjustment on the rod. It should be almost an inch from the edge of the
spacer to the middle inside of the tool. He then realized that the distance between the opening of the backside of
the master cylinder to the end of the piston was more than one inch. Shouldn't the tip of the adjustable rod
just touch the end of the master cylinder piston? Does he have the wrong master cylinder and can this cause the
problem in question. Roland tested the booster and it doesn't leak. Vacuum at idle is 13-14 inches of mercury.
car is euipped with a Paxton.
Any help would be appreciated
Texas Swede

[1967 eight barrel]

13-14 inches is way too low for proper function. I used the guy in Dallas to do mine the first time. It leaked internally. He refused to fix it. I spoke to Steve at Power Booster Exchange. He stated that about 18" of vacuum is required for proper operation. The Ford sevice manual lines out the procedure for booster to piston rod adjustment. -Keith

[texas swede]

Thanks Keith,
These are 289 HiPo engines and the vacuum is normally 15 inches of mercury.
My 67 Shelby has 15-16 and the power brakes works fine.
I will tell Roland and the owner to adjust the engine to achieve the 15-16 required.
Texas Swede

[JWH]

From what you tell us, the car starts shaking and then dies AFTER it is completely stopped and at rest. This would indicate the problem is in the idle of the engine and not in the brake system. If the problem were in the brake system, Roland would have issues getting the car stopped smoothly. If it seems the shaking/dying is related to applying the brakes while at a dead stop, I would check for a vacuum leak causing the engine to run poorly and die. This leak would occur somewhere between the brass fitting on the back of the intake manifold and the brake booster. Check that there is no leakage around the brass fitting that is threaded into the rear of the intake manifold (stripped threads? Are there rubber caps on any of the fittings coming out of the brass fitting to plug them? If so, are the rubber caps cracked, loose or leaking?), check the lines that attach to the brass fitting and run to the booster itself, check that you have a rubber hose designed for power brakes and not a fuel line that will collapse under vacuum, check the rubber check-valve grommet on the booster and that the check valve is tightly sealed. If you think it could be the brake booster itself, perform this simple test - with the car off, press down firmly on the brake pedal, start the car, and you should feel the brake pedal drop a small but noticeable distance. If the pedal does not drop, then the driver is not getting any help from the booster to apply the brakes and the booster may require repair.
        As for the adjustment of the push rod going into the back of the master cylinder, this would not cause the car to shake/die. If the push rod is adjusted too short, when the driver applies the brake he/she will notice the brake pedal moving a fair distance before the brake system begins to respond and slow the car. If the push rod is too long, when the driver applies the brake the pedal most likely stick to the floor and will not "release" and return to the normal position when the driver takes his/her foot off the pedal. The brakes will remain locked. If Roland is getting immediate response from the brake system when he first presses on the brake pedal, and if the brake pedal is releasing after a full stop, the push rod adjustment should be fine.
         I hope this helps and please let us know what solves the problem if you get it figured out. 
Jeff
PS- my engine vacuum reading is quite a bit lower than Roland's and the power brake booster still operates as I would expect and the car stops fine. I would double-check the engine timing though with the vacuum reading that low. If the engine timing is way off, it may both raise the vacuum reading and smooth out the idle when the car is at a stop.

[texas swede]

Thanks, I will forward your suggestions to Roland and the owner of the car.
Spoke to Roland this morning and he is putting the booster back as he found no fault with it and every part
looked completely new. However, I believe the master cylinder is not correct as the adjustable rod length must be increased to
just barely touch the piston in the cylinder.
Again thanks,
Texas Swede

[1967 eight barrel]

If the pedal doesn't seem to feel right I'd suspect the rebuild. I used the guy in dallas per Dallas Mustang. I can't say anything positive about his work or him standing behind it. At Bob Gains suggestion I sent it to power brake exchange. Excellent customer service and very responsive time-wise.

[texas swede]

Keith,
I bought a rebuilt Midland Ross booster from American Power Brake and Clutch about 10 years ago.
Ended up to have the original rebuilt by a guy in South East Dallas who was closing his business. He also
rebuilt another one I had. Both while Roland and I were waiting. This is 8 years ago. Still have the rebuilt
original in my car and the extra on the shelf.

Texas Swede

[Bigblock]

Just went through this with a friends 289 hipo. Shake and stall at idle. Intake manifold gaskets were crumbly and the carb spacer was warped. Went from 12/13 to 16 on the vacuum.

[JD]

Just went through this with a friends 289 hipo. Shake and stall at idle. Intake manifold gaskets were crumbly and the carb spacer was warped. Went from 12/13 to 16 on the vacuum.

'67 GT350's don't have a carb spacer when delivered new, must have been added later.

[1967 eight barrel]

Just went through this with a friends 289 hipo. Shake and stall at idle. Intake manifold gaskets were crumbly and the carb spacer was warped. Went from 12/13 to 16 on the vacuum.

'67 GT350's don't have a carb spacer when delivered new, must have been added later.

Nor do 1967 GT 500s have spacers from Ford. 

[texas swede]

When you measure the vacuum, shall the booster be connected or not? Roland put back the booster
and with booster connected the vacuum was 8 Inches of Mercury at idle and with it disconnected and plugged it was 13.
Daniel (the owner) drove the car home from Roland and the brakes worked perfectly but when parking it in
his garage it acted up and the engine died.
Well, Roland has given up. Will see if I can help Daniel next summer.
Thanks for all help.
Texas Swede

[Jimbc123]

I had a similar problem on my 1968 GT350. The idle got very unstable when the engine got warmed up and it would die when I applied the brakes. Everything seemed fine on start up but the problem occurred as everything warmed up. I was sure it was a vacuum problem but could not find anything obvious. It drove me crazy for several months until I found the same problem and a possible resolution in a posting on the Vintage Mustang Forum. The problem turned out to be the intake manifold sealing. The intake had been off to replace lifters about 6 months earlier, and even though the intake had been carefully torqued when it was reinstalled, all of the bolts had loosened to about half the torque spec on the drivers side of the engine. I retorqued all of the bolts and the problem was resolved.

This is worth checking and easy to fix.

Good luck, Jim

[texas swede]

Thanks Jim,
I will tell Daniel.
Texas Swede

[greekz]

If they have not already tried this, disconnect all vacuum users and measure the vacuum.  Adjust timing and carburetor to achieve desired vacuum. Systematically add back the vacuum users as you measure vacuum.  When it drops, you have found your culprit.  That is what I did to find my booster was the problem.   If you cannot get the desired vacuum with everything isolated perhaps it is an engine related problem.  Long process, but saves a lot of frustration.

Greek