No reverse

[tedforbes]

I have a 99 Sierra Z71 that will not go into reverse. Just sits there. Dash indicator lights up and reverse lights come on but no backup. Forward gears are fine but I just bought this truck for my 16 y/o and dont want him to drive in circles. Any idea what could cause this and what the solution might be? Thanks

 

[Molson02536]

I have a 99 Sierra Z71 that will not go into reverse. Just sits there. Dash indicator lights up and reverse lights come on but no backup. Forward gears are fine but I just bought this truck for my 16 y/o and dont want him to drive in circles. Any idea what could cause this and what the solution might be? Thanks

Sorry for the bad news, Slow, slipping or no reverse: “lo-reverse” clutches are worn out, fluid leak in the reverse apply circuit, or broken sunshell. It is possible to remedy a fluid problem by removing the checkball from its cage in the case in the rear of the trans may help (must remove valvebody), or adding a high-viscosity additive such as Lucas Transmission additive or other seal restorer product. May also have worn boost valve (can replace in the pan).

Put a line pressure gauge ($55 shipped on Ebay, or visit a local trans shop) on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.490" boost valve (easy fix in pan).

Good luck and keep us posted.