QU10331 NV4500 1st and 2nd Gear Downshift Inhibitor Block

QU10331 NV4500 1st and 2nd Gear Downshift Inhibitor Block is a genuine NVG part made for the1-2 Downshift Inhibitor on 1992-1994 GM NV4500 1-2 Synchro Assemblies with 6.34:1 1st gear ratios. Sold individually. Order four blocks per transmission.

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Dan the Gear Man® Tech Notes:
Downshift Inhibitor
Interlock
Matching Parts
Lubricants, Sealants, Threadlockers
NV4500 Tools
Applications

Tech Note 1: Downshift Inhibitor
The downshift inhibitor feature uses centrifugal force to prevent high rpm downshifts from 3rd to 2nd and 2nd to 1st. It was only used on early production transmissions. It is possible to eliminate this feature by removing the 4 synchronizer blocks and 2 springs from the 1-2 synchro assembly. This feature is more important for 1992-1994 wide ratio GM models with 6.34-1 1st gear than it is for Dodge and GM transmissions with 5.61-1 first gear ratios.

Tech Note 2: Interlock
The 1-2 shift interlock feature, which was used on 1992-1994 GM transmissions with 6.34: 1st gear ratio, was designed to prevent high speed downshifting in 1st and 2nd gear. To accomplish this, four sliding blocks and two springs are added to the synchro hub. When the mainshaft is rotating at high speeds, centrifugal force pushes the blocks against the sliding clutch ring and locks it in place. The early synchro hubs were slotted for the four blocks, plus there are four holes in it for the spring hooks. Once the interlock feature was abandoned after 1994/1995, the synchro hub was redesigned to eliminate the hub slots and holes. If you have the early QU10215 Synchronizer with interlock, you can convert it to a non-interlock unit simply by removing the four flyweight blocks and two c-shaped springs. The sliding hub plus the synchro springs and rectangular struts are the same for all years and models.

Tech Note 3: Matching Parts
Matching Parts for QU10331 Shift Interlock Block:
QU10333 Spring, 2nd Gear Downshift Inhibitor
QU10332 Spring, 1st Gear Downshift Inhibitor
QK1085 1-2 Downshift Inhibitor Parts Kit
QU10081 1-2 Synchro Slider
QU10215 1st-2nd Synchro Assembly with Shift Interlock
QU10002 Synchronizer Ring, Center Friction
QU10014 Synchronizer Ring, Inner Steel
QU10015 Synchronizer Ring, Outer Steel
QK1103 Snap Ring Kit, 1-2 Synchro
QU10075 39 Tooth Mainshaft 1st Gear
QU10035 37 Tooth Mainshaft 2nd Gear
QU10052 1-2 Shift Fork
QU90020 NV4500 Manual Transmission Oil
TM1003 NV4500 Shop Manual

Tech Note 4: Lubricants, Sealants, Threadlockers
Early production NV4500 Transmissions used an anaerobic sealant (QU90003) to seal between the main case and input bearing retainer, top cover, and rear housing. Mid-production units used anaerobic sealant just on the input retainer and RTV for everything else. Later production transmissions used black RTV Sealant (QU90006 or QU90005) for everything. Either type of sealant works fine (except the PTO covers ALWAYS should be sealed with RTV), but I prefer RTV for all components. Regardless of which sealant you use, make sure excess sealant does not block the lube access hole at the top of input retainer pilot that fits into the transmission case. Also, the threaded holes in the main case for the four retainer bolts and 12 PTO bolts are open ended, so you must use new bolts with factory applied threadlocker or apply Threadlocker (S24200) to your existing bolts to prevent oil seepage past the bolt threads. See my TM1003 NV4500 Shop Manual or V1003DVD NV4500 Overhaul Video for more information.

Tech Note 5: NV4500 Tools
Need Torque Specs or Rebuild procedures? Order my 116 page, full color illustrated TM1003 NV4500 Rebuild Manual.

You will need some special tools to correctly service your NV4500 Transmission. The chart below lists our current NV4500 Special Tools for popular models.

Applications:
Chevy and GMC:
All with NV4500 5 Speed Manual Transmission: 1992, 1993, 1994