Chevy 1973-1988 Straight Axle Trucks. Crew Cab / Suburban through 1991

Posted by Diesel Conversion on Oct 15th 2020

Chevrolet Conversion Overview

KEY POINTS TO CONSIDER

  • 4x4 trucks have taller tunnels than a 2WD truck 
  • 2WD trucks will need a body lift or tunnel modification (depending on transmission)
  • Requires firewall modification to allow removal of #6 valve cover
  • Need to bend the pinch weld where the tunnel meets the firewall for bell housing & exhaust clearance
  • Crossmember under oil pan needs to be dropped 2 inches
  • 5 and 6 speed manual transmissions don’t fit without additional modifications

AUTOMATIC TRANSMISSIONS

Automatic transmissions in this era of truck do not make good conversion transmissions due to lack of overdrive and lock-up torque converter. Now is the time to upgrade. A 4L80 is a great option.

4L60/80

  • 4 speed overdrive. Final ratio is .75
  • Lock-up torque converter
  • Requires an aftermarket transmission controller, such as US Shift, Quick 4
  • Transmission Control modules add multi-use functionality and are very reliable

“Turbo” 350 / 400

  • Not a good choice for fuel economy or power transfer
  • Does not have an overdrive gear
  • No Lock-up torque converter
  • Non electronic
  • Requires vacuum modulator or modulator delete plug

 

If you insist on using this transmission we recommend speaking with a reputable transmission shop who assist you with setting up these transmissions based on your conversion specifications.

700R4

  • Same information as above but the 700R4 does have an overdrive
  • Requires a custom kick-down linkage
  • Small input shaft not designed for low RPM torque

MANUAL TRANSMISSIONS

Manual transmissions in this era of truck do not make a good conversion transmission due to lack of overdrive. Now is the time to upgrade.

NV 4500

  • GM uses a small 12” clutch (not 13” like Ford or Dodge)
  • 95+ GM NV4500 can swap to a Dodge bellhousing, input shaft, bearing, race & seal.
  • 95 and earlier have a different bolt pattern where the bellhousing bolts to the case of the transmission

PARTS INFORMATION

Engine Mounts-  These bolt-in replacement engine mounts use the factory GM perches.  Brand new polyurethane isolators do a great job of dampening the vibration and handle the additional weight of the Cummins engine.  Custom fabrication is necessary. The cross-member under the oil pan needs to be lowered about two inches to make room for the Cummins engine which is taller than a V8.  You will also need to notch the front cross-member under the core support making room for the harmonic damper and A/C compressor.

ALTERNATOR REGULATOR KIT

When using the 12 Valve Dodge alternator, an external voltage regulator is needed to replace the Dodge’s PCM regulating function. The kit also includes a wire pigtail connector. 99-02 Cummins swaps may use the Dodge PCM to regulate the alternator. Most GM alternators have a single wire connection to the battery and can be desirable but we have concluded that no custom pulleys or belt lengths is much better for routine maintenance reasons.

TACH KIT

The tach kit consists of three parts; A sensor, mounting bracket and Tone ring. These parts are necessary to make your factory tachometer work.

It is not necessary to buy a diesel instrument cluster for your truck.

A/C MANIFOLD

This manifold bolts to the back of a ’94 and newer Dodge a/c pump, making the a/c plumbing less of a challenge. All you will need to do is have some new hoses crimped between our manifold and your Chevy pieces at the drier and condenser.

The 94 and newer pump works fine in these trucks, but you may have to move the power steering lines on the engine cross member and cut a hole in the cross member to allow access to the manifold mounting bolt.

SOME OTHER PARTS TO SOURCE ON YOUR OWN

If you have ever done a custom conversion before you are no stranger to the fact there are lots of small details that need to be worked through. Because the way we have done the conversion may differ completely from your build this can be a challenge to provide a detail specific list of each and every part. We’ll do our best to summarize.

Intercooler - We used air-to-air cooler.  DCS Part #1035.  You’ll have to make brackets for mounting.  

Intercooler Tubes – Your local exhaust shop can be a big help with these and your exhaust too.  An online resource is frozenboost.com

Exhaust work - DCS Part #1808 or a stock Dodge downpipe can provide for a good start.

Throttle Cable - Dodge stock throttle cable. We used a Chevy gas pedal and they work great together.

Extra Battery- Not completely necessary but you may want to consider depending where you live

Transmission Mount- There are numerous transmission options and you should expect to modify your driveshafts (front & back).  You may also need to make a transmission mount

!