5 speed trans. problem

[victormotorsports]

Ok I'm victor and I have a brain buster of a problem need some help with. My 90 nissan 240 single cam is stick shift and I have a transmission problem the car won't pass 75mph. it goes in to neutral on its own at that speed no mater what gear I'm in. Even if I hold the gear in it doesn't pop out but it goes in neutral still and it has new clutch and flywheel, and this is the 2nd. transmission. can some one help?
Modified by victormotorsports at 7:30 PM 6/12/2007

[90nissan240sx]

Is there a check engine light on...?

[victormotorsports]

there is no check engine light in that car.

[90nissan240sx]

maybe like a fuel cut off from the ECU or spark... is it like redlining like a limiter would? or is itdose the rpms drop like u pushed in your clutch?

[LayNLow240]

does it do it at a certain rpm? like 2500 or 4000?

[victormotorsports]

yea when attempting to red line the car drops like i pushed in the clutch yes.

[victormotorsports]

no only when i floor it even sitting still redlining it won't even float at the red line.

[LayNLow240]

i was thinking that it could be your syncros are shot, or your 4th and 5th gear sensors are dead, but seeing your last post makes me wonder.so check your MAF, make sure it is plugged up and make sure it is clean. go buy some MAF cleaner and clean it to be sure.if your problem presists get a known working MAF and try it on your car. if the problem is still there, check to make sure none of the MAF harness wires are cut/split/frayed and make sure they are properly shielded.