Corvette Interface Adapter Kit - Installation Instructions

(A hard-copy of these Instructions is included in every Adapter Kit)

So you've decided to install a C5 Corvette IRS in your project vehicle. Great – and Thank You for selecting Dobbertin Performance as a big part of the upgrade!

 

Just to make sure everything goes smoothly, remember to check out and understand, the sections leading up to these instructions - especially Section 13, which deals with the rear frame rails.

 

Some of the information compiled here is available in other sections on our website in even more detail if required, and we're always happy to hear from customers who might have a question – or a suggestion to improve our products, website or instructions.

Assembling the Suspension Module
At this point, in the conversion, the frame rails are already tacked in place, but not permanently welded. 

The adapters need to be mounted on the cradle to take an accurate measurement between their mounting surfaces before the frames are permanently welded in. It's also a good idea to install a 2” x 4” between the frame rails to keep the correct distance between them, until everything has been permanently welded.

 

Ideally, the adapters' mounting surfaces should be a total of 1/8” wider than the frame rails. This allows for a snug fit with the 1/16” rubber pads installed on each side.

         Frames positioned with tack welds                 The Adapters mounted on the Cradle

The Corvette Interface Adapters can be installed on a bare cradle, such as the one pictured above right – or on a completely assembled cradle, such as the one in the photo below.

 

A lot of this will be determined by which method you will be using to install the unit onto the frame rails.  This is discussed in detail within the next Section – Installing the Suspension Module.

Open up the parts bag and remove the four Cradle mounting hardware assemblies.

Each assembly includes – top to bottom:

1 – 1/2”-13 x 2-1/4” Stainless Steel (SS) Hex Head Bolt

1 – 12mm SS Flat Washer – We selected metric flat washers because of their fit.

1 – 1/2” x 2”OD SS Fender Washer – To be used to align the Adapter to the frame.

1 – 1/2” x 2”OD Neoprene Fender Washer – As a cushion for the Cradle and Adapter.

1 – 1/2” x 3/4”OD x 1/2” Aluminum Bushings – For 3/4” Cradle mounting holes.

1 – 1/2” USS SS Flat Washers – Bottom washer, with larger OD than 12mm washer.

1 – 1/2”-13 SS Elastic Stop Nut (ESN) – To keep it all together

- STOP AND READ -
PLEASE NOTE - A QUALITY ANTI-SEIZE COMPOUND MUST BE APPLIED TO THE THREADS BEFORE ANY STAINLESS STEEL HARDWARE IS ASSEMBLED.  NOT DOING SO WILL RESULT IN PARTS THAT WILL SEIZE UP AND GALL, WHICH WILL REALLY PISS YOU OFF! 
TRUST ME ON THIS ONE... BEEN THERE – DONE THAT!

As you'll notice, the mounting holes in the factory Corvette cradles are 3/4” in diameter, whereas the holes in the adapters are 1/2” in diameter.  The back of the adapter also has a locating pin on each side for making sure that the cradle lines up squarely with the stock Corvette frame – as well as with our Corvette Interface Adapters.

Back             (Left side of a stock C5 Corvette Cradle)             Front

To make up the difference in the sizes of the holes, we have supplied four 1/2” x 3/4” ID bushings for the job.

 

Also in the kit are four neoprene fender washers that should be placed over the mounting holes – between the cradle and the adapters. This will take up any differences in the two machined areas, (usually .005” or less.)

Place one neoprene washer over each one of the cradle's four mounting holes.

  • Line up one of the adapters over a pair of the cradle's holes.  (There is only one way these can fit properly – and it's pretty obvious.)

  • Starting with one side, put a 12mm washer on each of the 1/2”-13 x 2-1/4” bolts and drop them through the adapter and cradle.

  • Slide the bushings up the bolts from the bottom, and into the cradle's 3/4” holes.

  • Slide a USS washer onto the bolt and follow it with the nut.  (REMEMBER THE ANTI-SEIZE.) 

  • If you have four standard 1/2”-13 nuts, you can use them temporarily, because it's not necessary to use the ESNs at this time.

  • Tighten only enough to bring all of the parts into alignment – so the adapters don't rock back and forth.  (Please Note: The cradle in the photo below is equipped with a differential and axles, which are not necessary, nor recommended at this point in time.)

Now the upper control arms can be mounted. The easiest way to do this is to jack up the lower arm,  under the spindle, then raise the control arms over the adapters and drop them in from the top.

 

Select a 12mm x 1.75 x 100mm hex bolt and a 12mm flat washer for the rear control arm bushing.

 

Also select a 12mm x 1.75 x 110mm double-end stud, a 12mm x1.75 ESN and a 12mm flat washer for the front control arm bushing.

The rear 12mm hex head bolt
The front 12mm stud with two nuts

Push the 12mm hex bolt all the way through the rear control arm bushing, then tighten it 4-5 turns, which is plenty to keep the control arm in its place. (No need to use any thread coatings on the bolts or studs at this time.)

 

For the front 12mm stud, push it past the access hole on the second upright and all the way through the front control arm bushing. Then spin on the plated 12mm x 1.75 standard nut (only one of these in the parts bag) so about three of the stud's threads stick out of the end of the nut.

 

Next, spin on the 12mm x 1.75 ESN, and snug them together with two wrenches. Once the threads in the adapter have been reached by the stud, use a wrench on the ESN to turn the stud in about 4-5 turns.

 

(When it's time to remove the stud, use the wrench on the 12mm standard nut to back it out. Remember, whether installing or removing the stud, you want to turn the 'following' nut to keep positive pressure on the union of the two nuts.)

The shock absorbers can be added next, which will raise the control arms up a bit, and make the suspension module a little easier to handle. (If you use the ESNs, remember to also use the Anti-seize.)

 

The upper shock absorber mount
The shock added to the suspension
The Suspension Module is now complete!
Installing the Suspension Module

For this portion of the instructions, we'll be using photos from our Chevy S-10 project to show the installation of the Corvette Suspension Module. This is a very simple operation on a pickup truck, with the bed removed.

 

Before the final positioning of the axle can be determined, make sure that the alignment is about right. There are several Internet sites that explain how to do a 'quickie' alignment that should get you pretty close.

 

It's important to try and semi-align an independent suspension before positioning it in a vehicle, as sometimes the final alignment can actually change the axle centerline – up to a half an inch in either direction. This is because the spindles usually turn slightly during the alignment process, unlike a vehicle with a solid axle.

 

Once the alignment is completed, it's time to install the entire suspension as one complete unit. This is one big advantage that the Corvette Interface Adapter Kits have over conventional suspension installations.

 

Method OneIf you have access to a transmission jack or similar type dolly, you can assemble the entire suspension module together as a unit before you roll it under the vehicle – then jack it up to the frame rails.

 

Method TwoJack up the back of the vehicle quite a bit and roll the complete assembly under the rails, then lower the frame rails onto the adapters.

 

Method ThreeIf it looks like it might be too much of a hassle to install the complete unit, or it's a one-person installation, the adapters can be mounted to a bare cradle, then rolled under the frame, jacked up and C-clamped to the frame temporarily. Then the remainder of the suspension components can be assembled.

Using Method Two, jack up the frame and set up a couple jack stands with adequate height to roll the entire suspension module under the frame rails. Make sure to place the stands far enough forward as to not interfere with the suspension.

 

Note the Type I suspension module in the background, complete with the differential and the driveshaft adapter.  (The stock transverse spring is only retained to give the display a bit more stability.)

 

The suspension module includes all of the components that are related to the C5 Corvette IRS as well as adapters to mount it to the frame.

Next, roll the entire unit under the frame to its approximate final position. Then install the tires and remove the dolly from under the Corvette cradle.

 

Then lower the frame onto the adapters – just to the point that the adapters are barely touching the frame rails. Don't add the long neoprene pads this time, but keep in mind they are 1/16” thick and very useful in taking up some minor imperfections.

Now it's time to take a quick inspection of the adapter's fit.

If you find that the adapters are too close together to fit the frame between them, or have a gap between the adapters and the frame, there is a quick fix if the gap is 1/8-inch or less, either way.

 

On the left adapter, the cradle's locating pin hole is round, however on right adapter, the locating pin hole has been slotted, (1/8” right and 1/8” left) to make up for minor frame discrepancies.

 

(This is the same way the Corvette factory frames are made for a smooth installation in the assembly plant.)

Left Adapter with the Round Hole
Right Adapter with the Slotted Hole

If it becomes necessary to adjust the adapters width, then the two aluminum bushings must be removed from the right side of the cradle to allow for the adapter to be shifted wider or narrower. This will not effect the location of the assembly, as the left side will retain the bushings, which will square the suspension.  This is the Horizontal Adjustment.

 

Now take a look at where the adapter's lower mounting surfaces meet the frame on both sides. Make sure that one side of the adapter is tight against the underside of the frame rail – from front to back.

 

Now look at the other adapter.  If it is off by .040” or more, either at the front or at the rear, it should be corrected. Again, the fix is an easy one.  Simply remove the bolt at the adapter base with the gap and slide in the proper amount of stainless steel fender washers necessary to make up the difference.  This is the Vertical Adjustment.

 

This discrepancy is usually caused by a slight twist in the cradle or the possibility that the new frame rails are not running perfectly parallel.

 

The kits are supplied with four fender washers.  If you need more than this, it would be wise to find a different cradle - or look into adjusting your frame rails.

Before the final positioning of the suspension can be determined, the bed has to be temporarily installed, to see exactly where the wheels are in relation to the wheel wells.

With the bed installed and the wheels/tires on, it's time to take a few steps back and look over the entire profile of the project.

 

Even if the axle placement looks perfect, take a few minutes to move the suspension forward and backward, just a little, to make sure you're satisfied with its final position.

 

It's always a good idea to have a couple friends help you decide on the exact axle placement. (Then you can blame it on them, if you don't like it later on.)

 

Now the bed can be removed and the frame must be accurately marked for the precise placement of the adapters.

We recommend using a center-punch to mark the front two holes in each adapter. However, running a strip of masking tape on the frame against the front and rear edges of the adapters will also work just fine.

 

Once marked, the suspension module can be removed and the frame rails welded in permanently, if it hasn't been done already.

 

Now that the frame is secure, unbolt the two adapters from the suspension module, as well as the upper control arms.  (Make sure to write down where the fender washers go.) Then mount the bare adapters back on the frame with C-clamps, using your earlier markings to locate them.

With the upper control arms removed, there is easy access to all six mounting holes on each adapter. Again, using a center-punch, make sure that all of the holes are clearly marked, then drill them all.

 

Make sure that the holes are drilled straight through frame.

 

It's also a good idea to drill them a bit larger and weld in tubes through the frame, so the frame won't be crushed when the hardware is tightened.

 

An aluminum plate that extends past all six holes is another way to reinforce the frame, but we like the through-frame tubes.

The Adapter C-clamped and marked with tape and a punch

Please Note: Although the placement of the adapter's mounting holes may seem somewhat inconvenient, their horizontal locations were specifically designed for maximum strength due to their close proximity to the control arm mounts.  Their vertical positioning was then determined using the centerline of the adapter's mounting surfaces, including the width of the cover plates.

Just as any project, the final assembly takes much longer because everything is now painted and/or powder-coated. Since the suspension module has already been assembled, the basic step-by-step instructions may seem unnecessary – but there are a few important additions, so here's everything again:

 

  • Place one neoprene washer over each one of the cradle's four mounting holes.

  • If it was necessary to add any fender washers to the cradle, for the vertical adjustment, do so at this time – making sure to place them on the proper mounting hole.

  • Line up one of the adapters over a pair of the cradle's holes and put two 12mm washers on two 1/2”-13 x 2-1/4” bolts and drop them through the adapter and cradle, (AFTER COATING THE THREADS WITH ANTI-SEIZE.)

  • Slide the bushings up the bolts from the bottom, and into the cradle's 3/4” holes. (Remember to add the aluminum bushings in all four holes on the cradle, or only in the two on the right, if a horizontal adjustment was necessary.)

  • Then add the USS washers and ESNs to each bolt and thread them together.

  • Leave the four adapter to cradle bolts loose enough to allow the adapter to sway back and forth about 1/4-inch each way.

 

Now it's time to install the upper control arms, (without tightening them.) The arms are being loosely attached only to keep everything together until the suspension module is in place.  (They will be removed again to access the adapter's mounting holes.)

 

Push the 12mm hex bolt all the way through the rear control arm bushing, then tighten it 4-5 turns, which is plenty to keep the control arm in its place.  (No need to use any thread coatings on the bolts or studs at this time either.)

 

For the front 12mm stud, push it past the access hole on the second upright and all the way through the front control arm bushing.  Then spin on the plated 12mm x 1.75 standard nut so about three of the stud's threads stick out of the end of the nut.

 

Next, spin on the 12mm x 1.75 ESN, and snug them together with two wrenches.  Once the bottom of the threads in the adapter have been reached by the stud, use a wrench on the ESN to turn the stud in about 4-5 turns.

 

(When it's time to remove the stud, use the wrench on the 12mm standard nut to back it out.  Remember, whether installing or removing the stud, you want to turn the 'following' nut to keep positive pressure on the union of the two nuts.)

It's now time jack up the rear of the project and roll the suspension module under the frame rails for the final installation!

 

Once in position, jack the entire module up to the frame rails.

 

If all goes well, the holes on the frame should line up perfectly with the mounting holes on the adapters.

 

Now it's time to drop in a long neoprene pad on each side – between the frame rails and the adapters.

12 – 3/8-16 x 3-1/2-inch mounting bolts

With the pads in place, install the two front mounting bolts, (from the adapter side) all the way through the frame rails – on both sides.  Now, remove the control arm bolts and move the arms out of the way for the installation of the remaining four adapter mounting bolts on each side.

 

Once all of the adapter to frame bolts are installed, add anti-seize to the threads, install the washers and ESNs.

Begin drawing the adapter to the frame rail by tightening the upper front and upper rear bolts on each adapter – First. Since everything has already been assembled earlier, there shouldn't be a problem...

 

Scenario OneIf there is no binding and everything lines up, then proceed with all of the other mounting bolts. There is no need to 'torque' these very tight. (To be technical, I'd classify the proper tightness as very-snug.) Remember the neoprene pads will make up for slight differences along the length of the frame rails.

Scenario TwoWhen the adapters and frame rails are drawn together, and the adapters seem to be tilting inward at the TOP – back off the bolts and check to see how far they would need to be pushed apart to make the gap equal from top to bottom.

 

If it's less than 1/8 – inch total and you haven't taken advantage of the alignment pin's slot on the right adapter – you're in luck! Just drop out the bushings on the right side and slide everything into place.

 

But, if the bushings have already removed and there is still an uneven gap, then the best way to repair this is to slide in a couple thin pieces of aluminum as shims, next to the neoprene pads. (One of the neoprene pads can be used as a template.)

Scenario ThreeWhen the adapters and frame rails are drawn together, and the adapters seem to be binding at the BOTTOM – (therefore tilting outward at the top) back off the bolts and check to see how far they would need to be pulled together to make the gap equal from top to bottom.

 

If it's less than 1/8 – inch total and you haven't taken advantage of the alignment pin's slot on the right adapter – again, you're in luck! Just drop out the bushings on the right side and slide everything into place.

 

However, if the bushings are already removed and there is still an uneven gap, the quickest way to repair this is to remove the neoprene pads and see how it fits.

Now it's time to install the upper control arms – for the last time.

 

Put a little Ultra Black silicone on the threads of the bolt as well as on the stud's thread that goes into the adapter. On the nut's side of the stud, apply some anti-seize. Ultra Black is great because once it cures, it won't allow the studs or bolts to back off, yet they will still be easy to remove, unlike using thread lock.

 

To screw in the studs this time, simply install the 12mm washers and the 12mm ESNs, then just use the nut to screw it in. Once the stud hits some resistance, the nut will follow the threads all the way to the adapter.

If you need to remove the stud once you have installed it with the ESN, and the Ultra Black on the threads, the removal procedure is quite different.

Start by spinning on the standard 12mm nut and use two wrenches to snug the nuts together. Then use the wrench on the ESN to back the stud out until it is all the way out of the adapter's threads.

 

You can then separate the two nuts and remove the standard nut. However, to remove the ESN, you'll need to clamp the stud and use a wrench to remove it. Be careful not to damage the stud where the ESN will still need undamaged threads to reinstall it.

When the control arms are in their final position, there is quite a bit of movement back and forth.  This requires that some stainless steel shims be inserted to take up the play.

 

We have included sixteen shims total, in three different widths to accomplish this.

 

It doesn't matter if the arms shift forward or backward or remain in the middle. The goal here is to minimize the free space, so just use any shim combination that works.

 

With the shims in place, tighten the bolt and stud firmly, but don't over-tighten.

Shimming the control arm bushings
The Corvette factory brackets

Please Note: When the control arms are installed in a Corvette at the factory, each bushing is sandwiched between two sides of a metal bracket.

 

Sometimes the tightening process shifts the rubber bushings to the right and sometimes to the left. We've found control arms that the bushing to bushing widths have varied by almost 1/4 – inch, So we designed our adapters with a little extra room and included the shims to make up the difference.

The only thing left to do is bolt on the two cover plates with six bolts per side. Once again, we recommend using a small amount of Ultra Black silicone on the threads –

and don't over tighten them.

Congratulations - That's It!

 

Once again, we at Dobbertin Performance Innovations would like

to thank you for selecting us to be a big part of your project's

Independent Suspension Upgrade.

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