I want to replace the power brake booster on the ‘73 Delta 88 with 350/2-bbl I recently (about a month ago) acquired. There is nothing wrong with the booster on the car, but I need to replace the master cylinder because it is leaking, and I thought why not replace the power booster as well. It is the original, I believe.

I have found that there are two different boosters for these cars, depending, apparently, on whether the system is made by Bendix or Delco (and probably depending on the engine/carburetor combination?). The Delco booster is 11-inches in diameter while the Bendix, the one on my car, is about 9-inches. They’re not interchangeable (not that I want to), at least on my car, because the larger booster cannot be put up tight to the firewall without making contacting with the steering column. It cannot be made to fit.

I have also found that the 9-inch booster is far more difficult to come by than the 11-inch, and I’m guessing that’s because the 9-inch came on the most basic of engine/carb combinations (350/2-bbl as noted) versus the 350/4-bbl and 455/4-bbl options that were available and were apparently far more commonly ordered. I could find only one vendor, Autozone, that had the 9-inch booster available. Everyone else, from Rockauto to O’Reilly to Summit to Joe’s Garage next door shows it as not available. Not just out of stock or backordered, but simply not available. I was ready to clean up my old one and reusue it (which I might still end up doing for reasons explained below), but then I found a new one at AZ and ordered it. It came the next day (today).

Below is a side-by-side photo of the old (on the right) and the new (on the left). Everything is identical except for how far out the pushrod extends on the new one. What you see is the pushrod pushed in as far as it will go. The end of it is threaded so it can be screwed in or out to a desired position, but it cannot be screwed in far enough to be as far in as it is on the old one.




Is this a problem? Obviously, the piston in the new master cylinder will be pushed in part way if it is going to be mounted on the booster. But will it be pushed in too far? Will there still be enough pedal travel for the brakes to operate properly? Is it worth me installing this on the car and seeing what happens, or is the situation hopeless before I even start?

I thought about using the pushrod from the old booster on the new one, but I can’t pull it all the way out. Is there a way to do this? Unscrew something somewhere? The pushrod on the new one pulls all the way out easily, which I was a bit surprised to discover.

Thank you for any advice!

 

I believe that the main difference between the two other than size is the 9 inch is a dual diaphragm and the 11 inch is a single. I have seen both on mid 73-77 Cutlasses. I know that doesn't help you just an FYI. Good luck getting it figured out.

 

The pushrod sticking out too far will be the same as you pushing on the brake pedal all the time. That would not be good.
Since the new push rod comes completely out, you may be able to cut it down to the same length as the old one. I dunno if that's the way to go or if there may be other issues with the new booster. I'm sure others will reply with useful information.

edit: I just realized you should check the depth of the piston on the new master cylinder to see if it's the same depth as the old one.

 

This^^^^^

 

I thought this, too, but I was thinking that I would install the booster and master cylinder WITH the MC piston pushed in as far as it needs to be to accommodate the extra-long pushrod AND THEN reconnect the brake lines. Wouldn't this make the new "off" position be the position of the partially pushed-in piston? That's why I wondered if there would be enough piston travel remaining to actually actuate the brakes. I'm not thinking that this is the greatest idea.


I had this thought, too. Seems a bit kludgy, but it might work.


I did, and they are identical in appearance.





Before I do anything to the new booster to make it unreturnable, I found another source of these who claims to have them in stock, and I've ordered one from there.

https://brakeandequipment.com/

I can return the new one I have to any Autozone store for a refund, and I may do that. If the old booster was not working, I'd be resorting to whatever is necessary to make a working one. But the old one does still work so far as I know, so I'm inclined to put that one back in if I can't find a correct new one. I'm hoping that the latest one ordered will be correct.

 

The master cylinder has what is called a compensating port. This is the opening that allows the fluid in the reservoir to flow into the cylinder to "refill" as needed when the pistons move outboard (as is the case when disk brake pads wear). If the pushrod from the booster is too long, this port will not be aligned properly, resulting in incorrect brake performance. Do NOT use the booster with the pushrod longer than on the original.

 

Thanks, Joe.

I decided that discretion is the better part of valor, and I returned the Autozone booster this morning. I thought it wasn’t a good idea to be driving around with a jury-rigged brake system.

So now I’m waiting on the booster from this latest vendor. Interestingly, when I go to their website now, they show that the booster I ordered is not in stock. It was in stock when I bought it yesterday. The one I bought must have been the only one on the shelf. I hope so. They have charged my credit card.

Anyway, there was a peculiarity in the description of the booster I bought. It didn’t stop me from buying it as there were no sub-options like pushrod length once you chose this booster, and I'm willing to buy and return parts all day long.

But here’s what it says:

THIS UNIT MAY HAVE SEVERAL PEDAL ROD CODES; PEDAL ROD CODE 021 P10 P12

No other vendor, including Autozone, has a comment like this in their description of this part. This sounds somewhat related to the pushrod, but it sounds more like it has to do with the part on the other side that attaches to the brake pedal. That side of the one I got from Autozone is identical to the old one.

Even though they talk about “several” rod codes, they don’t give you an option to choose a pedal rod. We’ll see what I get when it arrives.


Getting back to Autozone for a moment, they were very good. If you add together the ages of the manager and the assistant manager who helped me, you would likely get a number that is still less than my age. It's interesting now how often you ask for a part at one of these stores, and when you say "Oldsmobile," they ask you to repeat it because they've never heard of it. One lady recently said "did you mean Chevrolet," and I said "no...Oldsmobile." She continued to scroll on her screen and then said, "oh yeah, there it is!" It's now been almost 20 years since the last one came off the assembly line, and you rarely see them on the road anymore. If I see one, it's usually being held together with duct tape and has a door or fender that is a different color from the rest of the car. Sad.

All the Autozoners can do is go by what their computerized look-up system says, and they agreed that the part I bought from them is shown as fitting my car. I took the old booster with me when I returned the new one to show them the subtle difference. I pointed out that the pushrod on the new one is removable, and maybe there are different-length pushrods available. But they had no idea on this. I did get my purchase price refunded, and that’s what mattered.

 

If brakeandequipment doesn't require a core return, I'd save the original and send it out for rebuild and restoration. That way you have one you KNOW fits and works properly.

You'd think that as much commonality as GM cars had by 1970s, and as popular as Caprice/Impala are with the donk and Lowrider crowd, it wouldn't be so durned hard to find a brake booster.

 

Interesting thing about their core charge. It's $22.50. If I have to pay for shipping the core back to them, which I probably will have to, it will likely cost at least that much to ship it. So what do I gain by paying $20 to ship it to them to get back $20 in a core charge refund? Nothing that I can see. If I do have to pay for the return shipping, I'll probably do as you suggest and keep the core and perhaps get it rebuilt some time down the road.

 

I was looking at Rockauto to see what brake boosters they have for same year Chevy Caprice, and wouldn't you know it, but they do show the exact same booster, and it shows as also applicable to Buick, Olds, and Pontiac full-sizers from that same era. They also show it in stock. But it has a different manufacturer and part number. Should have thought of this before. Something to keep in mind if the most recent purchase doesn't work out.

 

Update on this.

The search continues. The booster from brakeandequipment.com arrived yesterday, and it has the same issue as the one I received from Autozone. The pushrod protrudes about an inch and a half, and the master cylinder won’t fit. Unlike the Autozone booster, the pushrod on this one cannot be pulled out.

In any event, though, it will have to go back.

I’m now on to my last hope. I ordered the booster from Rockauto I described above. It shows up under the ‘73 Chevy Caprice listing, but it looks just like mine, and, like I said earlier, it is shown (on the partsgeek.com website) as fitting a ‘73 Delta 88. It is Prior part number 7700218. This is a different part number from the booster I received from brakeandequipment, which is also a Prior brand rebuild.

So I’m giving it a try.


Here’s the Rockauto photo of the booster I just ordered. Note, on the left side, that only the two mounting studs protrude. No sign of a pushrod sticking out. This is good. I’m hoping that this is an accurate photo and not just a generic one. It’s supposed to arrive next Tuesday the 11th. We’ll see!

 

We have finally achieved nirvana. The brake booster I ordered from Rockauto that is shown as fitting a '73 Chevy Caprice with a 350 engine arrived today, and the pushrod is where it should be. It's not sticking out!

I only had to order three of them before finally getting one that should work.

 

👍 Fingers crossed it works!🤞