Need power booster, can't find...24' MH, 1977

[Elisa]

Our 24 foot MH needs a power booster. The other half has put in 3 replacements, and each of them locks up the brakes immediately. He is a good mechanic but clueless on a computer, so I am asking for him - where can we purchase the CORRECT power booster for a 1977 24' Argosy motorhome? This is a Chevy 454 on a P-30 chassis.

I did a search on here but got so many hits that I am just starting a new thread. Thank you in advance.

[bkahler]

Originally Posted by Elisa

Our 24 foot MH needs a power booster. The other half has put in 3 replacements, and each of them locks up the brakes immediately. He is a good mechanic but clueless on a computer, so I am asking for him - where can we purchase the CORRECT power booster for a 1977 24' Argosy motorhome? This is a Chevy 454 on a P-30 chassis.

I did a search on here but got so many hits that I am just starting a new thread. Thank you in advance.

When replacing the power booster the mechanic needs to make sure he uses the original push rod that is used between the booster and the brake master cylinder. If an incorrect rod is used that could easily be the cause of brakes locking up.

I experienced this exact same problem on a 1984 310 after we had a shop replace the booster and mc. The shop didn't use the original push rod and spent 4 weeks trying to figure out how to fix the problem.

Brad

[Elisa]

Originally Posted by Elisa

Our 24 foot MH needs a power booster. The other half has put in 3 replacements, and each of them locks up the brakes immediately. He is a good mechanic but clueless on a computer, so I am asking for him - where can we purchase the CORRECT power booster for a 1977 24' Argosy motorhome? This is a Chevy 454 on a P-30 chassis.

I did a search on here but got so many hits that I am just starting a new thread. Thank you in advance.

Brad, thanks - tell me more. My info/clues: The original pushrod is gone. The original is three-quarter inches shorter than the later model ones. We are on power booster #3 from various sources. So he cut down the newer push rod and it still doesn’t work. It has new brake lines, master cylinder, brakes were bled and a separator used in order to make sure they were bled correctly - I had the privilege of helping with this. The vehicle can be moved as long as the engine isn't on. It locks up as soon as it is started.

[bkahler]

Originally Posted by Elisa

Brad, thanks - tell me more. My info/clues: The original pushrod is gone. The original is three-quarter inches shorter than the later model ones. We are on power booster #3 from various sources. So he cut down the newer push rod and it still doesn’t work. It has new brake lines, master cylinder, brakes were bled and a separator used in order to make sure they were bled correctly - I had the privilege of helping with this. The vehicle can be moved as long as the engine isn't on. It locks up as soon as it is started.

The original "what" is 3/4" shorter? Where did he get the number to know what size to make the new push rod?

From the description you've given it sounds like he needs to keep shortening the push rod until the brakes don't activate. It would seem your problem is once the pump is running and pressurizing the hydroboost, the hydroboost is pushing the rod towards the master cylinder just enough to activate the brakes.

When the pump isn't running there's no pressure on the push rod so the brakes are released.

[Elisa]

Firstly, I should have said hydrobooster, not powerbooster.



Secondly, the pushrod had to be cut back 3/4". Some other mechanic told him that the old pushrods were 4" long. Ours was 4 3/4", so he cut it to 4". It is still locking up.


How much more should he shorten it from the 4" length it is now?

[bkahler]

Originally Posted by Elisa

Firstly, I should have said hydrobooster, not powerbooster.

Secondly, the pushrod had to be cut back 3/4". Some other mechanic told him that the old pushrods were 4" long. Ours was 4 3/4", so he cut it to 4". It is still locking up.

How much more should he shorten it from the 4" length it is now?

Just to be clear, we're talking about the push rod (aka output rod) shown on the left side of this picture, correct?



Unfortunately that's a question I can't answer. As painful as this may sound you might just have to shorten it by something like 1/16" at a time until it works.

I know it's a pain to unbolt the master cylinder just to get the rod out but I don't know of any other option. I've been doing some searching but having found anything that might described the required length.

[bkahler]

There's some interesting info in this hydroboost thread. Apparently a push rod could be a short as 3.45" on some vehicles.

One thing of not that I read is apparently there is supposed to be a little bit of pre-load on the master cylinder piston, but not a lot. One way to determine how much to remove from your push rod would be to start loosening the bolts that hold the mc to the hydroboost and see if you can figure out at what point the brakes release.

[GCinSC2]

Might be a long shot might pay off. No clue but try contacting these folks direct.

http://m.cardone.com/

[Elisa]

Thank you all - our next day to try will be Thursday. I will push the brake pedal while he is underneath figuring out the push rod/master cylinder/brakes as y'all stated.


Yes, Brad, that rod in the center of the cylinder in your photo is what I am calling the push rod.


Cardone didn't have what we needed, as I recall. The chassis is a P-30 Chevy from 1977.



We have been fooling with this for quite a few months. Other than this brake system update, the motorhome is fabulous - now.

[GREEN ARGOSY]

Here's an output rod which was removed from my Argosy's hydroboost.
My Argosy is 1977 20' model with Chevy 454 motor.
I don't know it's the OE hydroboost but it had worked well (At least never locked) a long time ago.
(Because my argosy is sleeping for about ten years..)

A vernier caliper says "4.8 inch "


And the rod is sticking out about 29 to 30mm from their mounting surface.
Sorry, I'm not familiar with SAE. I should have said "about 1.1 inch".
Moreover I can't say that with imperial measurement.
That's too difficult for me..


This is a remanufactured hydroboost that I'm going to use for the Argosy in the near future.
Yes, I know it. That is not same shape as the original one.
But the manufacturer said "it would work for 1977 P30 even if the shape is different." I'm doubting it, but should believe them..
I don't have any options..

Fortunately, the vernier caliper says the similar value as the old one.
However I can't say that the new hydroboost would work well on the Argosy. Because I haven't installed it yet.

Thank you, Yuki

[bkahler]

Originally Posted by GREEN ARGOSY

Attachment 336658
Here's an output rod which was removed from my Argosy's hydroboost.
My Argosy is 1977 20' model with Chevy 454 motor.
I don't know it's the OE hydroboost but it had worked well (At least never locked) a long time ago.
(Because my argosy is sleeping for about ten years..)

A vernier caliper says "4.8 inch "

Yuki, your information should be just what Elisa is looking for. Elisa's Argosy is a 78 and to the best of my knowledge there should be no difference between a 77 and 78. I do know there were differences between 74 and 76, but after 76 the system pretty much stayed the same until the larger coaches were built. Even then I believe the parts were probably interchangeable.

If it was me I'd cut down the 5" rod to 4.8" and give it a try.

Brad

[GREEN ARGOSY]

Originally Posted by bkahler

Yuki, your information should be just what Elisa is looking for. Elisa's Argosy is a 78 and to the best of my knowledge there should be no difference between a 77 and 78. I do know there were differences between 74 and 76, but after 76 the system pretty much stayed the same until the larger coaches were built. Even then I believe the parts were probably interchangeable.

If it was me I'd cut down the 5" rod to 4.8" and give it a try.

Brad

Brad,
I am glad if my post would help them.