272 Cam causing brake issues?>

[korn]

I brought my car in to have the brakes bled and SS lines put on... I got the call today with them telling me that the work was done....

Except now the car loses power brakes after the first time you depress the brakes at idle... car idles well at 600RPM...

They say it is unrelated to their work: They thought it was a vacuum leak; since the car idles rough. I told them I have a lumpy idle because of the Cam;

so then they said the CAM is causing the braking issue..

Is that possible? I have not heard of it with e30s??

[digger]

measure the vacuum at idle when the engine is hot. the engine should idle faster than 600rpm.

Camshafts with more overlap decrease idle vacuum which reduces the brake booster effectiveness. the 272 is NOT a big enough cam to cause issues of any significance though

[totheredline]

I highly doubt it. I have an M30 with a massive cam with a low LSA (lots of overlap) and when idling at 650 rpm I have no braking issues. Oh and I also have stainless steel brake lines.

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[digger]

I highly doubt it. I have an M30 with a massive cam with a low LSA (lots of overlap) and when idling at 650 rpm I have no braking issues. Oh and I also have stainless steel brake lines.

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what cam?

[korn]

So I drove the car. The brake issue is not noticeable driving. When stopped and idling after three pumps the brakes get hard...

[digger]

So I drove the car. The brake issue is not noticeable driving. When stopped and idling after three pumps the brakes get hard...

SOunds like a big leak somewhere maybe bad booster, connect a vacuum gauge to the booster and manifold and see what the engine pulls it down to at idle . when you drive around and lift off at any sort of rpms the vacuum is higher so you get a normal application of brakes but if the vacuum isnt there at idle under certain conditions in traffic the vacuum is low and brakes dont work properly.

[abit]

I belive that this ''big'' cam is not issue for that. there should be some vacuum leak or smthng else. with 285 cam, and idle @ about 800 I have no issues at all with brakes @ idle.

[digger]

mine is a 298/285 and i notice some loss of vacuum, mainly when engine is cold as i use pretty fast idle, when warm it is lower than stock 12-14" Hg but still functions "ok-ish". i now use a small vacuum pump to take it to 20" and reservoir and its alot better and when cold i can reverse down step hill and actually stop the car.

[totheredline]

what cam?

Custom billet Ireland engineering cam based on their 292 grind. But mine is dual pattern. 298/292 I believe with a good amount of lift and overlap.

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[digger]

Custom billet Ireland engineering cam based on their 292 grind. But mine is dual pattern. 298/292 I believe with a good amount of lift and overlap.

Sent from my XT1585 using Tapatalk

thats not really a massive cam for a 3.5L, and cant have that much overlap if there isnt quite a bit less engine vacuum than stock, thats just physics. it may still work fine and not really be noticebale until you go back to stock but there is a point that brakes drastically reduce their effectiveness when you starting to get to 300 degrees depending on LSA.

All pointless for the OP as hes using a very mild cam that should have essentially the same vacuum characteristcs as stock....