Me and wanda are having brake issues. Could use some advise.

So last year i started having some issues with my brakes. Shortly after installing my new engine.They work fine but if you drive slow with a foot on the brakes say in a parking situation problems start. It feels like my vacum disappers. First push of the brake pedal is fine next is ok and then if you push third time it feels like vacum is going away and you have too push harder to get any bite?

I replaced the mastercylinder and booster with no improvement. Tried another still nothing.
Then i replaced the little brake thingy on the frame along with some Lines, still no improvement. I bleed all 4 corners and have a Nice pedal. I changed the vacum hose and put it directly on the manifold. Still the same. Ok brakes with ok bite. as long as you dont use the brakes repeatedly.

I was wondering if i maybe have a leaking intake, but the engine runs Nice and i have 17-18 inch of mercury on the gauge. I have although had some problems with getting a Nice idle in gear. But it seems to be ok right now. I feel like im missing something. Would it help to identify the problem if i put a vacum reservoir in?

I drove a bodys 77 elcamino Yesterday and it had alot better brakes with good bite to them. Mine feels nowhere near as good.

Any advise or help would be welcome. I sure could use it, cause im Lost here. I will try and answer as fast as i can but i dont have alot of time weekdays. Hope someone have an idea. Regards from Copenhagen Henrik.

First question I would ask is about the vacuum hose from the booster to the manifold. Is your "vacuum" hose actually vacuum hose? It should be 11/32" vacuum hose. Not fuel hose. All vacuum hoses are listed by 32nds. Here is some info about it. https://techtalk.mpbrakes.com/how-to-series/picking-the-proper-vacuum-hose-for-your-brake-system.

Next, make sure your vacuum hose is connected to the base plate of the carb OR a port on the manifold. You need full vacuum, not ported vacuum.

Next, can you borrow a vacuum gauge and confirm your vacuum reading of the engine? Depends on the engine but usually 16-18 inches of vacuum is the least you want to be. Some cars work fine with a bit less. Can you raise your idle a bit to grab some more vacuum?

Those are the first things I would be looking at.

Hi Joe. I hoped i would hear from you. You have been alot of help over the past Many years, so for that i Thank you.
Yes i have tried to change the hose too. And moved it from the base of the carb to the manifold port in almost the same location. I have a vacum gauge i use to tune my carb. And it reads between 15 and 18 depending on idle speed and how i turn the air screws on the carb. It fluctuates a little bit in idle. The brake problem persist even with the car cold and running higher idle due to choke on.

Im pretty baffled as to why this is going on. I installed a brand new gm performence 350 engine. And Shortly after th brake issue started. I first thought it was due to th master leaking though the back. But still after replacing almost everything brake related i have this issue.

That is why i started thinking May the idle in gear issue i had, the fluctuating vacum gauge and the brakes maybe all to do with my install of the manifold on th new engine. It runs strong but has had a problem with lumpy idle in gear, it would not stall but try to Creek forward and be very lumpy. I have played around with a brand new edelbrock and it seemed like its ok now though

But still. I was thinking that if i put a vacum reservoir in and the brakes work better, that would point to a dodgy manifold install with a leak somewhere. I was my first attempt in manifold install, and i belive i followed instruktions. However i could have done something Wrong.

Im am sure the booster is ok cause i have a hard pedal til the engine starts, then the pedal drops. And the first push feels ok and it feels ok if you keep the foot on the brake. Its only when you push the brakepedal repeatedly it feels like vacum goes away. I feel it most trying to park in my garage, cause i have to turn a couple of times to get the angel right.

Im sure it has to do with my vacum source Being dodgy somehow. I also tried different check walves. I put a 11 inch booster from a camaro in an used the upper hole in the brakepedal after modifying the firewall a little. So it should have super sensitive brakes with alot of bite. But it dos not come close to the original elco i drove a couple of days ago. It felt almost like new car brakes with alot f bite with very little effort.

Just tomme sure i will replace the hose and look close at the fitting to make sure nothing is blocking and put the vacum gauge on to see what it says now.

If it produces less than 15 Inc vacum, would that be a sign of a vacum leak in the manifold? Its nothing with a Big cam. Only a 290 horse L82 350. It should not have vacum issues right?

Thank you all for helping

That engine shouldnt be lumpy, so it shouldnt be a "too big of a cam" issue.

Booster hose at the throttle plate of the carb is just as good as directly on the manifold.

Is the hose definitely a "vacuum" hose? Not a fuel hose. See the link I posted explaining the types of hoses.

As for the lumpy idle. I say a vacuum leak is the source of your problem. Grab either a small bottle of propane with nozzle, a can of ether or FLAMMABLE carb/brake cleaner. With the engine running, spray or let the propane GAS (not lit) get into areas where there are gaskets. Places like the base of the carb, hose connections, along the hoses themselves even where the manifold meets the heads. Everywhere. When you see the engine change rpm, that would be source of the lead. Even if you find a leak, keep checking, there might be more than one.

Also spray the booster hose and fitting base its connected too. Anywhere there is vacuum. The engine fan while running doesnt make this easy but give it your best shot.

If you have a true vacuum hose on the booster, then I think your problem lies with a vacuum leak.

Im going to try your advise and see what happens. I will use a can of brake clean and spray around everywhere there could be a leak. I have a closed airfilter so i should be able to get an increase in Rpm if i hit a leak.

Im leaning Towards this Being to only thing left as all brake components are new and checked repeatedly to no awail.

I have to wait until next weekend to work on it but i will let you know what i find. Im happy for your help so far.

Just to clarify, this engine should produce more than 15 inch mercury at idle or is between 15-18 enough?

I was told by a friend that my old carb was the culprit amd reason for the dodgy lumpy idle, so i replaced it with a new edelbrock 600 but still had hell of a time in getting this thing to sit still and idle right in gear. It seems to work now, but i still feel it could be smoother. So maybe all of this could be a vacum leak? I havent thought of looking for.

Ill let you know what i find next week. But Thank you again for your help. Regards Henrik.

I cant remember exactly how i put the edelbrock intake on. I used of course the right gaskets to the heads. And im pretty sure i did some homework in how they should sit. I know i used silikone gasket material in the ends as in the instruktions Said. Also tourqued it Down as instruktions Said. However come to Think about it i have noticed a little Oli recidue around a couple of bolts. Should there be Sealent on the treads? Or somewhere Else i could have forgotten? Or did not know about. Thank you Henrik.

Oil around the manifold bolts should not be. I doubt it in your case but I have seen when people mill cylinder heads too much, the manifold doesnt sit correctly.

Spray everything really well. Even the carburetor. Although it could be dangerous, I like to use propane for finding a leak. Carb and brake cleaner sometimes effects the painted surfaces.

I will use propane then. It will increase Rpm if there is a leak in the manifold yes? But what about around the booster? If the hose or similar has a leak, will it increase Rpm or just change how to engine sounds?

I am a body man by Trade and can make things pretty, however im still learning engine stuff. Because here there is a shortage of people that know how to fix USA cars. You can find plenty that says they know, but they lack ability to perform in everything exept taking your money.

So im guessing i need to study Real hard how to get the manifold on right. There is not alot of oil around every bolt, but a small recidue around a couple in front. It leaves a little grease spot on a cloth. Do i lack Sealent on the bolts? Or do they need some form of bigger washer? Im sorry if i seem to talk alot and ask to Many questions. It is just that i know how much work a manifold can be, and i want to know exactly what i missed last time. And again Thank you.

Im sure it is nothing Big as it runs quite Well, but just needs the last 10 procent and brakes of course.

Its getting to be bed time here, so ill sign of for now and be back next week with my findings. Thank you for your always helpful Nature. Regards Henrik

I would spray or use propane around the brake booster hose, check valve and port threads on the manifold as well. Check everywhere, there may be more than one.

As for the manifold, get the correct gaskets, remove yours, clean everything real good, lay the head gaskets in place then the manifold. You should have equal distances on the front and back of the manifold because you left those gaskets out. If everything looks to line up good, I would grab some Permatex Ultra Black and put a very thin coat with your finger around each port including the water jacket ports on both ends. I do this even if its a fel pro perma gasket with the blue rings around each port. Lay the gaskets in place, then put a nice even bead on the front and rear of the engine block and overlap a bit onto the intake head gaskets. Let it set up for how long it says on the Permatex package. If its cold out, give it extra time. Get your head bolts clean and ready to go in. They should have some sealant on them since a few of them enter a water jacket in the head. Once the Ultra Black is tacked up sufficiently, lay the intake on and install the bolts and torque in three (3) steps in the correct pattern. I would let the manifold set overnight before I do anything else. Come back and trim the front gasket if it squeezed out to far.

I think you have a vacuum leak somewhere which is causing your weak brakes and lumpy idle.

15” should be fine.  But it should be constant.  You are definitely describing a vacuum condition if it stops once and then the pedal gets hard. And yes the manifold bolts should should be sealed. I may be mixing big and small block heads but some go into coolant and some are in oil.

Joe73 wrote:As for the lumpy idle.  I say a vacuum leak is the source of your problem.  Grab either a small bottle of propane with nozzle, a can of ether or FLAMMABLE carb/brake cleaner.  With the engine running, spray or let the propane GAS (not lit) get into areas where there are gaskets.  Places like the base of the carb, hose connections, along the hoses themselves even where the manifold meets the heads.  Everywhere.  When you see the engine change rpm, that would be source of the lead.  Even if you find a leak, keep checking, there might be more than one.

I agree with Joe73. I would like to add that if the vacuum leak is underneath, in other words on the valley side of the intake manifold, the propane trick will not work. The photo illustrates this scenario happening to me…



However, consider that if there's a leak where the intake manifold meets the cylinder heat at one (or more) of the intake ports, that (those) cylinders will not have a proper air/fuel charge and thus not burn well, if at all. An easy way to test that is using a handheld contactless thermometer with a laser sight. This works much better if you have headers but may still work to some degree if you have cast iron exhaust manifolds. Measure the temperature of each header tube about 1.5-2.5cm from where it meets exhaust port at the cylinder head. The temperature should  be ~370°C. Mind you, some fluctuation is to be expected but if you see a drop of around 100°C, that's something to be investigated.

Good luck.

Now im pretty sure there is a manifold leak. I doubt is Big but never the less there. The engine runs Nice and has no loss of or leaks of coolant or oil. Exept i have noticed a little recidue around some of the manifold bolts.
I will spray around everything to see if i can find a leak or more. If it is only at a couple of bolts, can i safely remove one or more and seal them? Or should i remove the manifold and start over?

I dont Think i used Sealent on the bolts. I cant remember if i did, But it is only a around one or 2 in the front i have noticed a little oil around the washer. So if i spray and its only there. It seems like a lot of work to do it all over, if i could get away with resealing the bolts themselves.

I will of course remove the manifold and start over if it is impossible to just do the bolts?

And Thank you Joe for the instruktions it will make it a bit easier if need be. Thank you all for your input. I will return with Update. Regards Henrik.

Joe73 wrote:As for the manifold, get the correct gaskets, remove yours, clean everything real good, lay the head gaskets in place then the manifold.  You should have equal distances on the front and back of the manifold because you left those gaskets out.  If everything looks to line up good, I would grab some Permatex Ultra Black and put a very thin coat with your finger around each port including the water jacket ports on both ends.  I do this even if its a fel pro perma gasket with the blue rings around each port.  Lay the gaskets in place, then put a nice even bead on the front and rear of the engine block and overlap a bit onto the intake head gaskets.  Let it set up for how long it says on the Permatex package.  If its cold out, give it extra time.  Get your head bolts clean and ready to go in.  They should have some sealant on them since a few of them enter a water jacket in the head.   Once the Ultra Black is tacked up sufficiently, lay the intake on and install the bolts and torque in three (3) steps in the correct pattern.  I would let the manifold set overnight before I do anything else.  Come back and trim the front gasket if it squeezed out to far.

Different folks will give you different opinions regarding the "best" way to seal things on engines so, here goes mine. I really hate leaks. My process for installing an intake manifold starts with what Joe73 said; correct gaskets. After the gasket failure I had in my previous post (the engine builder installed those gaskets and the intake; another example of "should've done it myself from the beginning"), I went with Fel-pro steel core gaskets which are far less likely to deform and trimmed them to exact fit. I used Gasgacinch on the cylinder head/intake manifold mating surface mainly to hold the gaskets in place. While that dried, I applied Permatex 22071 Water Pump and Thermostat RTV Silicone Gasket Maker (specifically formulated to be impervious to antifreeze) around the water ports and Permatex 29132 MotoSeal (specifically formulated to be impervious to gasoline) around the intake ports on the cylinder head side then set the gaskets in place; I left the intake manifold side dry for the next step. I installed the intake manifold and tightened the bolts to maybe 10 ft/lb and let it set twice as long as recommended for curing. I then took off the intake manifold and applied a continuous bead of Permatex black RTV in place of the end seals, a thin film of the water pump sealer around the water ports, and a thin film of MotoSeal around the intake ports. I pretreated the intake manifold bolt threads with Gasgacinch to prevent oil from seeping up the threads. The intake manifold is carefully set in place then properly torqued down. I let that sit twice as long as recommended to ensure everything has properly cured before I move on with reassembly.

Black RTV is a good general all-purpose sealer and though it's somewhat resistant to coolant and gasoline, it's not formulated to be impervious to those fluids. If I was building a race engine, I would use black RTV on everything out of convenience. In a racing application, engine components frequently get removed and swapped before the engine runs for 50 hours. My application is as a daily driver so I do whatever I can to make a build or repair a "once-and-done" affair, hence the different sealers I use. Of course, your mileage may vary.

I like Zucchi's write up as well. I would just use the Motoseal around all the ports since Permatex water pump and thermostat rtv is not impervious to gas and oil. The bottom of the manifold is going to be in contact with oil during its life, if a small amount gets by the gasket it will eat the permatex.

Thanks for the Nice instruktions. Im leaning Towards removing the intake and start over, mainly because i want to make sure everything is ok. Even if it runs ok right now, im unsure if i did it correct the first time. I remember Reading the instruktions that Came with the manifold.  so im proberly going to go ahead and rip into it.

By the Way, is it ok to use a little Sealent on the carb gasket or is that a no no?

I will make sure i get the right Sealent materials it makes good sense to use different ones to oil / coolent and gasoline.

No sealant on the carb gasket.

Why dont you try with some propane or spray before you do anything. You might luck out and find and issue or two and save yourself some work.

No sealant on carb.

I encourage you to do the all the diagnostics (a serviceable thermometer would be something like https://www.ebay.com/itm/125173911750?epid=1022611956&hash=item1d24f250c6:g:xZIAAOSw-k5iHIRj) before expending labor on a job that may not be necessary. Re-doing the intake is a hassle. For all you know, your intermittent rough idle could be a weak sparkplug wire.

So if i find a leak around a bolt or 2, it will be ok just to seal those up or is it a no no to remove intake bolts. Im thinking one at a time seal and re torque. That if im luckey and find a leak around a bolt or something small.

I know its a larger job to remove and redo the intake. So i will do the leak spray first and see what im going to find.
Im sure some vacum leak is present somewhere, cause the rest of my fuel and ignition system is new with less than 500 miles on it. And nothing i have tried so far has had any effect on the brake issue. The lumpy idle seemed to be better after the new carb and some seriusly fine tuning of both carb and timing. Which also gave me some more umpf by the Way.
Im slowly learning to do things myself, cause it seems i have never had any luck with guys claming to know what they where doing.

So your writing about why pay for someone to break stuff when you can dont yourself, is wery true.

Here in Copenhagen there is not alot of Pro us car mechanics, and the few there is are only Breaking, scratching or not abel to perform the task in wich they overcharge you for..

So to sum up. I will come saturday perform a leak test. And see what it will tell me. And hopefully it will show me something. Ill give you and Update. Thanks guys.
This is how she sits today by the Way.

By the Way i ask about Sealent on carb base , cause im using a heat insulator between carb and intake. Its made of some sort of hard paper like material. And i use a normal gasket on both sides of that. And im unsure if the 3 combined is ok. The last guy i had work on it used Black rtv on the gaskets. But im guessing thats not right then.
And here she is in all her glory for those that dosent know wanda.

You shouldnt need any sealant on the carb base or insulators. If the guy put some one and its not leaking, leave it alone. I run a hard plastic insulator as well, it has a gasket on either side of it and no sealant. Also, dont overtighten the carb bolts, its easy to warp the carb baseplate and cause a leak.

Thanks Joe. Im Aware of the carb bolts. And i will be careful. I will Update when i have leak testet. Ill let you know what i find. Its diner time so see you all later. And again Thank you.

Hs1973 wrote:So if i find a leak around a bolt or 2, it will be ok just to seal those up

Yes.

Hs1973 wrote:Im thinking one at a time seal and re torque.

That works.

I see you have the Mickey/Thompson valve covers; I do too.

I also see you have the cast-iron exhaust manifolds with the A.I.R. injector holes capped off. If you still have the A.I.R. injector manifolds and you never intend to reinstall the A.I.R. system, you could use those injector manifolds to help diagnose your rough idle problem.

By the way, do you still have the gas tank vapor recovery carbon canister? It should look something like this…



The hoses going to and from that thing could also cause a vacuum leak, plus, that thing has a filter on the bottom which should be replaced every 30,000 miles.

By the way, I suppose you replaced the check-valve on the booster where the vacuum hose attaches to it?

Hs1973 wrote:The last guy i had work on it used Black rtv on the gaskets.

@$&%*#! monkeys.