Brakes very soft after engine swap

[Terroth 5]

After a recent engine swap from an M20B20 to an M20B25, without touching the braking system at all my brakes have become extremely soft. So soft that they don't engage until the pedal is literally at the floor. At first i thought somehow there must be air in the system, but after having a good look at the different intakes on the motors it appears i may have found the issue, but I'm still unsure and have no way of currently testing it.

Basically

The original rubber intake boot from my M20B20 connected to the lines running into the master cylinder or break servo or whatever via a junction in the rubber boot. Like this (Note, this rubber boot doesn't fit over the throttle body so i cant just use it instead)

Yet... On the new rubber boot that came with the M20B25 the brake vacuum line is blanked off with a bolt and some crappy gasket around it, and has not junction to that hose like the M20B20 one does.

Like so

Is this likely my issue? The brakes are perhaps not getting air pressure from the intake?

Any help would be appreciated, as these brakes are far too soft and spongy to even consider driving around normally with.

[_ethrty-Andy_ 2122]

here are three pictures of my car that should help.

My car is a Motronic (aka Facelift) M20B25 E30.

there are different size boots for the 2L and 2.5L engine, the correct 2.5L one i would expect to be delivered with the engine you have brought, but if not, they are approx $60-$80 new from memory from the likes of Gavin at EuroItalian, Brent @ BM World (if he has them) etc.

if you need the car running asap, probably possible to fit the 2L throttle body onto the 2.5L manifold so you can use the 2L boot, but not the correct way to do it.

Edited January 14, 2016 by _Ethrty-Andy_

[Terroth 5]

Cheers Andy, the Rubber boot that was supplied with the engine seems to be off of a pre-facelift m20 Engine, and has the same fitting as yours for the ICV, but not the junction to go into the brake booster line.

I was informed on another forum that potentially the one way valve is broken on the brake booster hose fitted to the M20B25 engine. I'm suspecting this might be the case too as when i bought the engine the brake booster hoses were disconnected from the throttle body and I had to use a gasket sealer to reconnect them.

It was my first drive of the car today, so i'm not desperate to use the old boot, as it would need a bucketload of curse words to get on (Its the same size as the throttle body, not larger like it should be like the B25 specific one, so it'd take a lot of convincing to get on haha). But I may give it a shot tomorrow arvo.

I was also told that the blanking plug should be of no issue if it was sealed properly, but i'd like to rule it out and try the correct boot anyway, so I'll see if i can source one locally before hitting up the guys in Auckland.

Seeing as my brakes were perfectly fine on the car beforehand, and i still have access to my old brake booster lines, ill think about trying to pull them from the B20 throttle body and seal them into the B25 throttle body and hook it up to the brake booster again and try that.

Edited January 14, 2016 by Terroth

[Terroth 5]

Unfortunately replacing the boot and the one way valve didn't change anything. Obviously the next step would be to bleed the brakes and flush the fluid and check the lines for bulging or leaking, which i will try and do when i can get the time again.

What i cant seem to find online is the tell-tale signs of either a bad master cylinder or Break booster? I'm assuming if the brake booster is bad, the pedal would instead be super f**king difficult to press down, and when i pump the brakes with the car off they firm up and the pedal then softens / goes down a bit when the car is started, which i believe is normal for the booster? But what about the master?

Are there any tests that could be done to eliminate these as issues as i go along?

Cheers

Edited January 16, 2016 by Terroth

[_ethrty-Andy_ 2122]

brake booster or master is highly unlikely to fail coincidentally to your engine swap. something is still not hooked up correctly i would say.

does yours look like the pictures i posted above now?

[Terroth 5]

Yes exactly the same except using the L shaped ICV instead of the T shaped one. I even swapped out the hoses leading into the Throttle body and resealed them back in. The system is receiving air pressure from the intake as when i removed the old one way valve to replace it I got a nice woosh of air blasted out at me.

The only reason i'd be thinking the brake booster / servo or the Master Cylinder is due to the storage time that the car had. It was taken off the road in August and has been on jack stands since November till last Thursday.

So the brakes haven't been used for a long time and perhaps air or moisture has gotten into the system.

Edited January 16, 2016 by Terroth

[_ethrty-Andy_ 2122]

prehaps the booster has failed from when it was hooked up incorrectly? or would the brakes be hard not soft if the booster failed (from no assistance)

or maybe the booster over pressurised the master cylinder and blew that up?

i dont know enough about how the system works though, someone else will now more. E30 brakes arent that flash, but are very reliable, in the 15 odd E30s i have had, never had brake problems so havent needed to learn.

Edited January 16, 2016 by _Ethrty-Andy_

[Terroth 5]

I think if the booster fails it means a lot more leg muscle work, so the pedal would be firm, IE when you switch the car off and press the brakes a few times they firm up because the booster is no longer there to aid it.

There may be the chance that i pressed the brakes when moving in and out the car during the swap and over pressurised the system, but I too don't know the braking system that well as i've never previously had issues.

I'll start with the simple solutions and have to move my way up perhaps.

Thanks for the help though Andy.

If anyone else has more information and can chime in that would be greatly appreciated .