brake booster rebuilt, now brakes are WAY TOO sensitive!

[darth_linux]

So I just got my brake booster back from Power Booster Exchange in San Jose (took two months!). Got everything installed, brakes bled, etc.

Brakes are now EXTREMEMLY touchy. Dangerously so. It's basically nothing and then full lockup.

Is this a booster pushrod issue? The push rod looked to be in the same place when comparing my before and after photos, so I didn't adjust it.

The pedal definitely FEELS different. Also, pedal is not returning ALL the back up, leaving the brake light switch engaged. I know how to fix the switch, but why would the rebuilt brake booster have this effect in the first place?

Thanks in advance for your tips.

BTW I put the vacuum hose on to the check valve after taking these pix, so it's NOT that.

 

[MoPar~Man]

Do you have all drums or do you have disks up front?

I know about the brake pedal thing - I have a bungy cord that pulls my brake pedal back up the extra 1/2 inch. I'll have to check the service manual but I know that other mopars had brake pedal return springs - my '73 Satellite had one.

 

[darth_linux]

Do you have all drums or do you have disks up front?

I know about the brake pedal thing - I have a bungy cord that pulls my brake pedal back up the extra 1/2 inch. I'll have to check the service manual but I know that other mopars had brake pedal return springs - my '73 Satellite had one.

It’s Drums all around and I didn’t have any problems with the pedal returning correctly before the booster got rebuilt.

 

[Lefty71]

and I didn’t have any problems with the pedal returning correctly before the booster got rebuilt

In your shoes, i wouldnt mess with too much before you make a phone call to the rebuilder and just get their two cents.

 

[MoPar~Man]

Did you confirm with the rebuilder at some point if your booster was for a disk/drum combo or was a 4-wheel drum booster? I think your master cylinder might be for a disk/drum combo, I think it's possible to see and measure the diameter of the piston on the back side but you'd have to take it off to check it which is a pain at this point. but a disk-brake booster will have more of an effect here as far as stopping force.

 

[darth_linux]

Did you confirm with the rebuilder at some point if your booster was for a disk/drum combo or was a 4-wheel drum booster? I think your master cylinder might be for a disk/drum combo, I think it's possible to see and measure the diameter of the piston on the back side but you'd have to take it off to check it which is a pain at this point. but a disk-brake booster will have more of an effect here as far as stopping force.

No. I have the proper master cylinder, and I sent the original brake booster from this car off to be rebuilt. There are no wrong parts, it's all the same exact parts. Only the booster has been rebuilt.

 

[CBODY67]

By observation, ALL power drum brakes from the 1960s-1970s ARE more sensitive than power disc/drum systems. Period. Especially GM and then Chrysler in order of touchiness.

When all we had was power drum brakes, this was a known issue so we all acted accordingly. Conceptually, when somebody who had a car with manual drum brakes gotr "a better car" with power drum brakes, the advisory was "Use your big toe rather than your foot on the brake pedal".

It could well be that the booster was getting weak, which it is now not after the rebuild.

Some people sought to decrease the vac level by sticking a restrictor into the vac supply line to the booster. That might delay the replacement of the vacuum, but not the vac level after it took longer for the vac to be replenished.

In the world of Turbo Dodge Shelby fwd cars, one of the tricks is to get a vac bleed from Grainger to keep the wastegate on the turbo closed longer. Perhaps something of that nature might be orf benefit? From what I remember, that vac bleed plus some travel limiters on the rear suspension to keep the car more level was a sure way to get high 13second quarter mile times. With a basically stock car. Back in the later 1980s, seems like it cost under $2.00 USD?

Just some thoughts,
CBODY67

 

[darth_linux]

By observation, ALL power drum brakes from the 1960s-1970s ARE more sensitive than power disc/drum systems. Period. Especially GM and then Chrysler in order of touchiness.

When all we had was power drum brakes, this was a known issue so we all acted accordingly. Conceptually, when somebody who had a car with manual drum brakes gotr "a better car" with power drum brakes, the advisory was "Use your big toe rather than your foot on the brake pedal".

It could well be that the booster was getting weak, which it is now not after the rebuild.

Some people sought to decrease the vac level by sticking a restrictor into the vac supply line to the booster. That might delay the replacement of the vacuum, but not the vac level after it took longer for the vac to be replenished.

In the world of Turbo Dodge Shelby fwd cars, one of the tricks is to get a vac bleed from Grainger to keep the wastegate on the turbo closed longer. Perhaps something of that nature might be orf benefit? From what I remember, that vac bleed plus some travel limiters on the rear suspension to keep the car more level was a sure way to get high 13second quarter mile times. With a basically stock car. Back in the later 1980s, seems like it cost under $2.00 USD?

Just some thoughts,
CBODY67

I've been reading that if the "reaction disc" was mistakenly left out of the rebuild, one would experience the exact symptoms I'm experiencing. I'm going to double check that the pushrod is not too long, and that the pedal assembly is correctly tightened, etc., but an overly sensitive pedal that doesn't return all the way after application is looking like a missing reaction disc or other problem with the rebuilder.

I know Chrysler brakes are sensitive, but this is different. The pedal feels different than before and it goes from very little braking to instant lock up. Not safe!

 

[MoPar~Man]

I'm flipping through the 1965 Chrysler / Imperial service technical manual. I know you have a 1966 Chrysler.

What I find interesting - they show the Imperial using the tandem-diaphram Bendix unit - but do not show or say that the Imperial is using front disk brakes. Unless I missed it, I don't see any mention of disk brakes in this manual. The use of a dual-diaphram bendix unit on a 4-wheel drum car goes against what thought was accepted knowledge - that the bendix dual-diaphram unit was introduced for or designed for disk brakes.

The manual goes on to show the Kelsy Hayes and Midland Ross boosters. The manual doesn't say why there are 3 different boosters. It seems that the Bendix was only used on the Imperial. All 3 were used on single reserviour master cylinder units.

Your booster is not any of these 3 as far as I can tell. I believe in 1966 your Chrysler would still have the single-cylinder MBC, not the dual-cylinder unit you have now.

I'm looking into what year / make / model MoPar would have had you particular booster.

What were the symptoms or behavior that led you to getting the booster refurbished?

 

[darth_linux]

I'm flipping through the 1965 Chrysler / Imperial service technical manual. I know you have a 1966 Chrysler.

What I find interesting - they show the Imperial using the tandem-diaphram Bendix unit - but do not show or say that the Imperial is using front disk brakes. Unless I missed it, I don't see any mention of disk brakes in this manual. The use of a dual-diaphram bendix unit on a 4-wheel drum car goes against what thought was accepted knowledge - that the bendix dual-diaphram unit was introduced for or designed for disk brakes.

The manual goes on to show the Kelsy Hayes and Midland Ross boosters. The manual doesn't say why there are 3 different boosters. It seems that the Bendix was only used on the Imperial. All 3 were used on single reserviour master cylinder units.

Your booster is not any of these 3 as far as I can tell. I believe in 1966 your Chrysler would still have the single-cylinder MBC, not the dual-cylinder unit you have now.

I'm looking into what year / make / model MoPar would have had you particular booster.

What were the symptoms or behavior that led you to getting the booster refurbished?

I've seen my booster on several '66s, and in most all cases, they were cars assembled in Delaware (as mine is). It's possible that it was a "field replacement" for a failed original booster, but there's no way for me to know that. It's a Bendix 9" single diaphragm designed for 4 wheel drum brakes. It's listed as an option on Rock Auto brake booster parts list, unavailable of course, like all the other options.

[EDIT: the Bendix 9" single diaphragm booster is shown as an option for 67-70. My car is a Late 66 model, so perhaps they were phasing in the new boosters at the Delaware plant where mine was built.]

I replaced my original single pot style MC 2 years ago with the '67 and later dual pot MC you see in the photos and have never had a problem with it.

The symptoms that lead to me sending the booster off to get rebuilt was a hissing sound that went away when the brake pedal was depressed. No change in idle quality with pedal depressed or not depressed. Over about 18 months time of driving it this way, the hissing got louder and louder until finally it didn't go away completely when I pressed the brake pedal. I decided the booster was on borrowed time, and sent it off to San Jose to be rebuilt, after reading several good reviews of that business, and reading several reviews saying that "Booster Dewey" in Lynnwood WA had excessive wait times and higher prices.

 

[CBODY67]

EARLIER, like 1955 Imperials had a different form of "disc brakes", but the normal power disc/drum brakes did not appear until 1966. NO Imperials had disc brakes back then, just 40wheel power drum brakes.

The dual-diaphram booster would be due to the possible combined weight of an Imperial AND a big Airstream travel trailer behind it. AT 70mph or in a hilly area of the country. NOT a power disc brake option.

CBODY67

 

[James Romano]

I've seen my booster on several '66s, and in most all cases, they were cars assembled in Delaware (as mine is). It's possible that it was a "field replacement" for a failed original booster, but there's no way for me to know that. It's a Bendix 9" single diaphragm designed for 4 wheel drum brakes. It's listed as an option on Rock Auto brake booster parts list, unavailable of course, like all the other options.

[EDIT: the Bendix 9" single diaphragm booster is shown as an option for 67-70. My car is a Late 66 model, so perhaps they were phasing in the new boosters at the Delaware plant where mine was built.]

I replaced my original single pot style MC 2 years ago with the '67 and later dual pot MC you see in the photos and have never had a problem with it.

The symptoms that lead to me sending the booster off to get rebuilt was a hissing sound that went away when the brake pedal was depressed. No change in idle quality with pedal depressed or not depressed. Over about 18 months time of driving it this way, the hissing got louder and louder until finally it didn't go away completely when I pressed the brake pedal. I decided the booster was on borrowed time, and sent it off to San Jose to be rebuilt, after reading several good reviews of that business, and reading several reviews saying that "Booster Dewey" in Lynnwood WA had excessive wait times and higher prices.

I have a '65 Sport Fury with the same MC after I converted from single bucket to dual. It's a '67 Mopar MC from Rockauto (Rayspestos) if I recall properly. I've had it for 6 years.

As for the booster... sounds like something was not done correctly. Sensitivity is one thing... the pedal not coming back to a neutral position is something else. Sounds like the brakes are already engaged by the time you press the pedal. Drive the car down your block slowly, like 5 or 10 mph...then put in into neutral. Let it coast. Does it stop by itself? Or does it slowly roll down the momentum like it should. If it stops by itself, and the pedal is not neutral, you definitely have an issue with either the booster, or a wheel cylinder hanging up. Jack up the car, and spin each wheel. Should have slight resistance, and nothing more. If they're all good.. your issue is either the MC or the booster... and having just had a rebuild... I would be on the same page as you... suspected bad rebuild from the shop.

I do wonder about your booster... should be the same as mine. I don't think they changed until '67, but I could be wrong.

My booster was rebuilt 6 years ago by Booster Dewey... about 1 month turn-over. They accientily sent mine to a guy with a '65 Ford Galaxy 500...and I got his. So the sent shipping tags to both of us, and we swapped back... **** happens.

Jrom

 

[MoPar~Man]

I have a '65 Sport Fury with the same MC after I converted from single bucket to dual. It's a '67 Mopar MC from Rockauto (Rayspestos) if I recall properly. I've had it for 6 years.

As for the booster... sounds like something was not done correctly. Sensitivity is one thing... the pedal not coming back to a neutral position is something else. Sounds like the brakes are already engaged by the time you press the pedal. Drive the car down your block slowly, like 5 or 10 mph...then put in into neutral. Let it coast. Does it stop by itself? Or does it slowly roll down the momentum like it should. If it stops by itself, and the pedal is not neutral, you definitely have an issue with either the booster, or a wheel cylinder hanging up. Jack up the car, and spin each wheel. Should have slight resistance, and nothing more. If they're all good.. your issue is either the MC or the booster... and having just had a rebuild... I would be on the same page as you... suspected bad rebuild from the shop.

I do wonder about your booster... should be the same as mine. I don't think they changed until '67, but I could be wrong.

My booster was rebuilt 6 years ago by Booster Dewey... about 1 month turn-over. They accientily sent mine to a guy with a '65 Ford Galaxy 500...and I got his. So the sent shipping tags to both of us, and we swapped back... **** happens.

Jrom

That is a Midland Ross booster, it's what came on 4-wheel drum cars in 1967. Your MC also looks like a 4-wheel version, not a disk/drum version.

 

[James Romano]

That is a Midland Ross booster, it's what came on 4-wheel drum cars in 1967. Your MC also looks like a 4-wheel version, not a disk/drum version.

Yes, correct. I think mine is a Bendix. I have all drums....same for the MC. It's for all drums so the reservoirs are the same size front and back, no proportion valve needed.

 

[MoPar~Man]

Yes, correct. I think mine is a Bendix. I have all drums....same for the MC. It's for all drums so the reservoirs are the same size front and back, no proportion valve needed.

Bendix is a different type of booster, with a different look. You have a midland ross booster.

 

[CBODY67]

For clarification, I just downloaded and went through the Brake section, specifically power brake boosters.

THREE boosters in the 1966 Chrysler-Imperial factory service manual.
--Midland-Ross (which is what our 1966 Chrysler Newport Town Sedan came with OEM) has a slanted front section where the vac input is.
--Kelsey-Hayes has a front section that resembles the shape and angularity of a cast iron brake drum, where the vac input hole is
--Bendix is the dual-diaphram Imperial only-application dual-diaphram booster.

++++++++++++

The pictured booster (post #1) is the Kelsey-Hayes booster.

The Mirland-Ross booster is the same booster that is OEM on my '70 Monaco Brougham 383 "N".

I would strongly suspect that the K-H and M-R boosters were also used on Plymouth and Dodge C-body cars, but I'm not going to investigate that at this time. I would rely upon the appropriate FSM and Parts Manuals for that research.

In looking at the listings in RA, I noticed the "field installation" notes, but I also noted in some brands they illustrated the SAME K-H booster in both pictures.

I CONCUR with @James Romano that I would be MORE concerned about the pedal not fully self-returning than not. THAT would indicate, to me, that something internal was not correct. Presuming that the return spring on the pedal assy is still there?

CBODY67

 

[darth_linux]

OMG, the booster pictured in post #1 is a Bendix 9” single diaphragm booster for 4 wheel drum brakes found on C bodies from 67-70, but also many late ‘66s, especially those built in Delaware like mine.

I either have a missing reaction disc assembly or my pushrod is out of adjustment.

Lets reign this thread back on topic please.

 

[MoPar~Man]

For clarification, I just downloaded and went through the Brake section, specifically power brake boosters.

THREE boosters in the 1966 Chrysler-Imperial factory service manual.
--Midland-Ross (which is what our 1966 Chrysler Newport Town Sedan came with OEM) has a slanted front section where the vac input is.
--Kelsey-Hayes has a front section that resembles the shape and angularity of a cast iron brake drum, where the vac input hole is
--Bendix is the dual-diaphram Imperial only-application dual-diaphram booster.

++++++++++++

The pictured booster (post #1) is the Kelsey-Hayes booster.

No, the booster in post 1 is not Kelsey-Hayes. The following photos are the Kelsey-Hayes taken from the 1966 Dodge Polara / Monaco service manual:

 

[MoPar~Man]

OMG, the booster pictured in post #1 is a Bendix 9” single diaphragm booster for 4 wheel drum brakes found on C bodies from 67-70, but also many late ‘66s, especially those built in Delaware like mine.

I doubt that is a bendix booster.

This is a diagram of the Bendix booster from the 1967 Monaco / Polara manual:

Note how it is paired with an MBC with a short (not tall) reservoir. This is described as a single-diaphram booster, used with 4-wheel drum brakes. This might be an actual photo:

This booster is described as follows:

"The Bendix Power Brake Unit can be identified by the twist lock method of attaching the housing and cover together".

The next section of the manual describes the dual-diaphram (tandem-diaphram) bendix, it gives a side-profile internal view, so the external appearance can't be well visualized, it appears to have the same general shape of the single-diaphram bendix. It says:

"The Bendix power brake unit can be identified by the crimped edge method of attaching the housing and cover together."

I believe the photo (above) shows the crimped-housing dual-diaphram Bendix.

 

[detmatt]

I'm flipping through the 1965 Chrysler / Imperial service technical manual. I know you have a 1966 Chrysler.

What I find interesting - they show the Imperial using the tandem-diaphram Bendix unit - but do not show or say that the Imperial is using front disk brakes. Unless I missed it, I don't see any mention of disk brakes in this manual. The use of a dual-diaphram bendix unit on a 4-wheel drum car goes against what thought was accepted knowledge - that the bendix dual-diaphram unit was introduced for or designed for disk brakes.

The manual goes on to show the Kelsy Hayes and Midland Ross boosters. The manual doesn't say why there are 3 different boosters. It seems that the Bendix was only used on the Imperial. All 3 were used on single reserviour master cylinder units.

Your booster is not any of these 3 as far as I can tell. I believe in 1966 your Chrysler would still have the single-cylinder MBC, not the dual-cylinder unit you have now.

I'm looking into what year / make / model MoPar would have had you particular booster.

What were the symptoms or behavior that led you to getting the booster refurbished?

No disc brakes for the 1960s Imperial until 1967.