[Bman]

I built an 01 suburban for a guy. It's a 4btaa, NV4500, chevyauto 4X4 T case with an exhaust brake. In the bown shift when using the brake, some times after it holds back for 20 secounds something that sounds like metal on metal lets loose and it starts to freewheel. It is a mechenical noise in the area of the bellhousing. When he pushes in the clutch it will grab again when it is released. The clutch never slips under lots of torgue. He took the trans out to replace the sincros and could not find any other problems. So he opened the T case to check it and it is all in order. So we thought it was the auto 4X4 contols so he disconnected the shift motor to keep it in the two wheel mode but it is still giving the same thing. We have come to a conclution that it is in the clutch. But to me it is stange. Please help me think strait, what are we overlooking.

 

[Bman]

Thanks Jimmy that is a good suggestion. It is a BD vaccuum controled brake,and maybe the vaccuum has a problem and allows the butterfly to fluter under pressure. I didnt test it myself becuase it is a freind that lives 6 hours away. Im just taking his word for it. But I will defenetly have him check his backpressure to see if it fluters.

 

[Bman]

I've spent some time on the phone with my friend and learned of some changes he has made with his exhaust brake. We had put in the 60psi valve springs but the backpresser was higher than that so he placed a presser regulator in the manifold to let presser into the vacuum line to deffet the brake and control backpresser. This I believe is the reason for the noise.

 

[Bman]

It was for the 6bt and we use 6bt 60psi valve springs