1988-99 GMT400 has been nicknamed OBS for Old Body Style after the Chevy Silverado 1st generation (GMT800 1999-2006) was released and they nicknamed them New Body Style (NBS). GMT400 is the GM platform itself. It is similar to the A Body, B body, etc. platform name but it is also year specific. The platform name changes slightly depending on the vehicle. Take a 1995-2000 Tahoe for example, it is technically a GMT420. Most parts will be posted online by the generic "88-98" Chevy truck and it will generally cover the entire GMT400 platform. You will need to know some subtle differences for your specific application.

The motor mount and motor mount bracket in the following photo goes by a lot of names. A and B make up the Clamshell Style engine mount. GM refers to A as engine mount and B as a bracket. Nowadays, A is most commonly referred to as engine mount while B is most commonly reffered to as the clamshell. Engine mount is a loose term however and in order to not confuse the style of motor mount you have with the Early Style you can refer to them as the clamshell mount. A can also be referred to as: rubber isolator, rubber mount, SBC/V8 engine/motor mount, "mounting, engine". B can also be referred to as: buckets, elephant ears, cups, motor/engine mount bracket, "bracket, engine mount", "bracket, engine mt".

In the following photo, A is the "Clamshell" with a rubber isolator and "B" is the metal motor mount bracket that bolts to a SBC/BBC GEN 1. "B" is no longer available from GM and there were many different types throughout the years. OER and other companies  make reproduction brackets but you have to understand that they are not a one size fits all. 2WD and 4WD 1973-1991 C10 "B"s will not interchange for instance. The Clam Shell Style started to phase out the Early Style Short and Wide/Tall and Narrow's in 1972.

All OBS Trucks with a V8 or Diesel used the Clam Shell Style. 2WD frames and 4WD frames used a different Clam Shell Mount.

A- Clamshell Mount; B- Clamshell

The clamshell itself (B) is no longer available from the dealership but the clamshell mount is still available at local parts stores. OER and other companies make reproduction 2WD clamshells but you have to understand that they are not a one size fits all. 2WD and 4WD clamshells will not interchange for instance. Some clamshells are passenger/driver oriented as well. It is good practice to label them if you are removing them to install newer clamshell mounts to avoid any confusion later. You do not need to worry about acquiring the correct clamshell when using our EZ Mount conversion mounts. 

If your GMT400 originally had a 4.3 V6 you will have to remove the V6 frame perches circled in red in the following photo. Once removed, you are able to install the V8 clamshell mount in its place. 2WD and 4WD frames used a different clamshell mount, the 2WD clamshell mount is mounted on a flat surface all the way around while the 4WD clamshell mount has one mounting side higher than the other like a step. The clamshell mount is not side specific and generally are not sold in pairs. You can use the same polyurethane insert from Energy Suspension for both. 

V8 Clamshell Motor Mounts

2WD Clamshell Mounts (rubber): GM GENUINE 15529450, WESTAR EM2621, PIONEER 602621,  ANCHOR 2621, DEA / MARMON RIDE CONTROL A2621

4WD Clamshell Mounts (rubber): WESTAR EM2637, PIONEER 602637, ANCHOR 2637, DEA / MARMON RIDE CONTROL A2637

Polyurethane insert for 2WD mounts: ENERGY SUSPENSION 3.1121G Black

Polyurethane insert for 4WD Mounts: 3.1152G

Which Motor Mount is best?

It's all preference. GM Genuine's are much higher quality and last longer than any aftermarket mount found at a local parts store, but they are also more expensive. Aftermarket clamshell mounts are cheap, you get what you pay for in this instance. The aftermarket clamshell mounts rubber isolator itself may become unseated from the middle of the clamshell housing allowing your engine to sag.

The ultimate motor mount in my opinion is using the OEM clamshell mount (as its thicker and more quality metal than aftermarket) along with some black poly inserts from Energy Suspension. Rubber dries out fairly quickly in the dry heat of Arizona, so I prefer poly inserts. Why black over red? Their black poly material is self lubricating while the red ones need to be lubricated every so often otherwise they squeek. 

*Budget Tips:

*The 3 bolt clamshell mount (#2395) for BBC and Diesel equipped Square Bodies use the same exact bolt pattern as the 88-98 OBS GMT400 2WD trucks clamshell mount (#2621), however the rubber isolator is flipped upside down. You could technically interchange them if you drill out the rivets to separate the top and bottom metal housing and flip the rubber isolator around. 2395’s are cheaper than 2621’s due to supply and demand. It’s the same exact part number for the poly insert from Energy Suspension, you just have to pay attention to which way you install the isolator with the tabs sticking out the sides. 2395's are about 1/3 of the price of 2621's normally. 

*As seen on Hot Rod Garage (Season 4, Episode 37, at 9 minutes), you can use 3M 08609 Window Weld in a caulking gun to fill in the gaps between the rubber isolator and the metal clamshell mount housing to ensure that rubber isolator does not move around on you. This is NOT needed with poly inserts.

Remove 4.3 Frame Mounts

The three-bolt clamshell is mounted with the single centered bolt on the outter sides of the engine crossmember. 

Same story for the 4.3 mounts on a 4WD frame. Remove 4.3 brackets on engine crossmember and install V8 stepped Clamshell Mounts. 

V8 Clamshells (2WD in grey and 4WD in black)

Poly inserts still require the metal housing of the clamshell mount

Conversion Motor Mounts

Dirty Dingo Truck Mounts are designed to bolt to the engine and the CNC cold rolled steel tabs will wrap around your stock clamshells. These mounts will allow you to move the engine from the original bell housing position up to 2 1/2 inches forward, and up to 1/2 inch rearward. Low mount AC will fit but you will require you to mount the engine forward 2-1/2" from the original bellhousing position for the compressor to clear the frame perch/engine crossmember. 

Engine Accessories

Stock LS low mount AC compressors and our low mount Sanden Mini compressors require notching the frame. Drivers' side low mount alternator setups will limit you on your engine placement. Basically everything else fits! 

Notch for Low Mount AC

This is our Corvette Style brackets in Truck spacing. Don't forget to add a ground strap to your alternator and compressor when painting the brackets!

89-95 OBS trucks used an R4 Pancake Compressor. If it was in good running condition, you can still run it on your LS engine. We make the R4 bracket in Camaro and Truck spacing. Don't worry, if you decide you no longer want to deal with the R4 Pancake, you can change out to a Sanden 508 setup using the same exact bracket, just differnt mounting bolts for the compressor! 

DD-LS-R4-AC-CM     DD-LS-SANDEN-AC-CM

DD-LS-R4-AC-TR     DD-LS-SANDEN-AC-TR
 

If you have a VVT water pump such as a 2010-15 Camaro water pump, then you need the VVT specific AC bracket. We do not make a VVT R4 bracket at this time. 

DD-LS-SANDEN-AC-VVT

SANDEN 508 AC COMPRESSOR:

DD-508

Billet compressor head for using R4 lines with our 7 piston Sanden compressor

 DD-SANDEN-B-R4 

When installing a Sanden 508 Compressor with our billet 7 piston compressor R4 head on 88-95 OBS trucks you can use v6 AC lines by Murray 56164 and they will bolt on.

Exhaust

2WD Frames: 

DD-72-1302LS1-C

Schoenfeld Long Tube 1 3/4" with 5/16 flanges, 16ga primaries, 02 Seconor bungs installed in collector, and excellent spark plug access. Ceramic Coated.

Fits 2WD frames. 

 

 

 

 

Speed Engineering Shorty Swap Headers

25-101

4WD Frames:

Pacesetter 72c2265 (Recommended)

Additional Helpful Links:

AZ Pro Performance GMT400 LS Swap Guide

Auto Metal Direct Catalog

     Everything body relates from hoods, grilles, windows, truck beds, all the way to the rubber grommets in the firewall.