Engine timing and braking problem

Alright, this seems crazy but I'm gonna ask the question anyways. I know that this is a lot to read but when you get to end you will understand why I have given all of this information. Please bear with me.

I recently bought a 1970 Cutlass Flat-Top Wagon. In 2012 it had a front disc brake conversion, new master cylinder and power booster.

I noticed the following problem when I test drove the car but I figured I could fix it so I bought it anyways. When I step on the brake pedal the pedal feels like it should and the brakes work like they should until the pedal reaches about half of what should be it's normal travel. After pushing the pedal about half way down the pedal feels like it hits a brick wall and you can't push it any further. At that point the brakes have not achieved full effectiveness. So, the pedal feels like it hits a wall when you step on it and the car will not brake hard. This makes for some uncomfortable moments when trying to stop the car because you start to panic when the pedal stops and the car doesn't. Actually, the car stops but more like a rolling stop. Not good if you need to make an abrupt stop.

So, I took the car to the mechanic that I have been taking all of my cars to for the last five years. He owns a reputable local auto repair shop and works on just about every kind of car. I know him by name and he knows me by name. My kids sale fundraising candy bars at his shop and he lives in my neighborhood. I say all of that just to let you know that I trust this guy. He's a good dude.

The mechanic discovered that the rear cylinders and drums needed to be replaced so I had him do it. The brake shoes were okay though. He also adjusted the emergency brake. The vacuum suction going to to the power booster was great, the master cylinder checked out okay and the linkage to the pedal from the master cylinder/ power booster was fine. The proportioning valve was stuck when he took it off and inspected but was able free up the valve and get it in good working order (I guess there's a little valve inside that moves. I've never actually seen what one looks like other than when it's mounted on the car).

At that time brake fluid pressure at each wheel checked out good.

After all that I still had the same brake pedal/ brakes not achieving full effectiveness problem. All of that fixed nothing.

The mechanic had my car for about three weeks (he's not charging me for any of his trouble shooting or anything past the cost of the rear brake cylinders and drums). He spent time over the last three weeks trying to find out why the problem still persisted.

Good news! He called me yesterday and said that he fixed my brakes. The pedal feels good now like it should and the brakes stop like they should. Sounds great right? Well, it is great but the cause of the problem has me scratchin' my head. When the mechanic called me he said "you're gonna think that I'm crazy but it was an engine timing issue". He said that he called an old timer that has worked on many of Cutlass' and the old timer told him to check the engine timing. The old timer said that engine timing being off can cause that problem. He thought that the old timer was crazy but figured he would give it a shot. Well, the timing was off a little bit. So, he adjusted the timing and sure enough it fixed my brake issue.

That sounds crazy to me so here's my question;

Has anyone heard of brake problems being cause by the engine timing being off a little in an old Cutlass?

 

Don't know if it applies to your situation but timing effects the overall vacuum your engine produces. Vacuum gauges are used for checking carb tuning and timing by alot of people.

 

Werd. And if it has the original Delco point-condenser ignition, engine vacuum is further affected by a change in dwell caused by the weardown of the points (A change in dwell changes timing, so that's why you check/set dwell before you check/set timing on points ignition).

 

just in case you find the problem still isnt fixed check the length of the pushrod from the brake pedal to the brake booster sometimes in the conversion kits they are too short and are adjustable

 

Thanks for everyone's input. I hadn't thought about the points wearing down and affecting timing.

Does anyone know how I can tell if the push rod connected to the pedal is the correct/ wrong length?

 

Thanks. Interesting but I have nothing to add except the rod from the pedal to the booster does need to be a certain length and angle to fully go into the vacuum booster.
When changing from manual brakes to power the end at the pedal often needs to be moved.
Sadly I forgot up or down on the pedal arm!

 

Check the master power brakes website I think they have a tech section

 

Even with low vacuum from improper(late) timing the booster ought to hold enough reserve for a single well assisted stop.
There is, or ought to be, a one way check valve where the hose enters the booster. If you remove that valve from it's grommet there should be a vacuum behind it, if not check the valve for flow in one direction only, the grommet for a tight seal and finally the booster may have a leak.

 

I will check that this weekend.

 

Report back. This is interesting and I'm confused about why timing affects the brakes.
Actually I was already confused!

No rain in the forcast. Just had a gulley washer and didn't know if this message went.

 

But that's what he said--he'd get one application, then the loss of boost.

 

The scariest thing on any vehicle is loss of brakes. Even bad steering is not as bad as no brakes.

 

I got the car back today. The pedal does feel better. It still doesn't feel totally right but I have full braking power now. So if I have to stop in a hurry I can. The pedal still travels a long ways until the brakes really engage. Once the brakes engage there is very little pedal travel between easing into a stop and throwing you forward into your seat belt.

Advancing the timing did fix the "pedal hitting a brick wall" feel but I still think that something more could be done to change the pedal feel. The timing was at 12 and now it's at 16. When the engine was rebuilt it had a bigger cam put in it. I didn't know that until today. So, adjusting the timing helped.

However, since I have never had a Cutlass before, the pedal feel might be perfectly normal and I just don't know it because I am judging it based on my experience driving other older cars years ago.

I'm gonna try some of the things suggested in this thread this weekend. I'll report back.

Worst case scenario I can live with it the way it is and just get used to it.

 

The bigger cam can affect the booster, if the maximum vacuum is less than 18-22" that a stock engine in good trim produces. If you are thinking of restomodding it, either a hydroboost or a stand-alone hydraulic boost system.

 

I would not think the problem would be with a oversized cam that he didn't realize was in the engine. It would have to be a pretty big cam that would have a noticeable idle to need a canister. I understand timing has a effect on vacuum but I would think it would have to be so far out to create that problem that the car wouldn't even start. I think the problem is somewhere else. Just my