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Need more legroom in your Avanti?


James T
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I did. I'm about 6' 2" and the seat simply did not go back far enough for me to get comfortable. Following Mr. Loewy's advice to never leave well enough alone, I decided to engineer a solution. Here's what I came up with.

I went to Home Depot and bought a flat bar of weldable steel about 1/4" thick and 2" wide by 24" long. I cut four sections out of it, each one 3" long. I drilled two holes 1/4 inch from each end large enough for a 5/16" bolt to go though. I removed the driver's seat, which is an easy job of removing four bolts from their captive nuts in the frame. Once the seat was out of the car, flip it over and see that the seat attaches to individual slider frames, one with a lock and one with a spring. Each one was held on by two bolts, which I removed. I then mounted the seat track to one end of the flat bar and mounted the other end to the seat itself, resulting in the seat being 2.5" further back relative to the track. I had to drill a hold in the seat track to clear the head of the inner bolt (one per side) but it didn't affect the track at all. To remount the seat in the car, I replace the two rear mounting bolts with studs so I could just mount a nut on them. Moving the seat back results in not being able to access the rear mounts easily, and takes some time to get the nuts on.

The end result is the 2.5" of additional legroom makes all the difference. I can now stretch out my right leg on the accelerator in comfort and leave the steering wheel in the lowered position. As a bonus, I now have more headroom as when the seat slides further back it is on an angle that increases.

If anyone is interested in doing this, contact me directly and I can give you more details.

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  • 4 weeks later...
I did. I'm about 6' 2" and the seat simply did not go back far enough for me to get comfortable. Following Mr. Loewy's advice to never leave well enough alone, I decided to engineer a solution. Here's what I came up with.

I went to Home Depot and bought a flat bar of weldable steel about 1/4" thick and 2" wide by 24" long. I cut four sections out of it, each one 3" long. I drilled two holes 1/4 inch from each end large enough for a 5/16" bolt to go though. I removed the driver's seat, which is an easy job of removing four bolts from their captive nuts in the frame. Once the seat was out of the car, flip it over and see that the seat attaches to individual slider frames, one with a lock and one with a spring. Each one was held on by two bolts, which I removed. I then mounted the seat track to one end of the flat bar and mounted the other end to the seat itself, resulting in the seat being 2.5" further back relative to the track. I had to drill a hold in the seat track to clear the head of the inner bolt (one per side) but it didn't affect the track at all. To remount the seat in the car, I replace the two rear mounting bolts with studs so I could just mount a nut on them. Moving the seat back results in not being able to access the rear mounts easily, and takes some time to get the nuts on.

The end result is the 2.5" of additional legroom makes all the difference. I can now stretch out my right leg on the accelerator in comfort and leave the steering wheel in the lowered position. As a bonus, I now have more headroom as when the seat slides further back it is on an angle that increases.

If anyone is interested in doing this, contact me directly and I can give you more details.

I did. I'm about 6' 2" and the seat simply did not go back far enough for me to get comfortable. Following Mr. Loewy's advice to never leave well enough alone, I decided to engineer a solution. Here's what I came up with.

I went to Home Depot and bought a flat bar of weldable steel about 1/4" thick and 2" wide by 24" long. I cut four sections out of it, each one 3" long. I drilled two holes 1/4 inch from each end large enough for a 5/16" bolt to go though. I removed the driver's seat, which is an easy job of removing four bolts from their captive nuts in the frame. Once the seat was out of the car, flip it over and see that the seat attaches to individual slider frames, one with a lock and one with a spring. Each one was held on by two bolts, which I removed. I then mounted the seat track to one end of the flat bar and mounted the other end to the seat itself, resulting in the seat being 2.5" further back relative to the track. I had to drill a hold in the seat track to clear the head of the inner bolt (one per side) but it didn't affect the track at all. To remount the seat in the car, I replace the two rear mounting bolts with studs so I could just mount a nut on them. Moving the seat back results in not being able to access the rear mounts easily, and takes some time to get the nuts on.

The end result is the 2.5" of additional legroom makes all the difference. I can now stretch out my right leg on the accelerator in comfort and leave the steering wheel in the lowered position. As a bonus, I now have more headroom as when the seat slides further back it is on an angle that increases.

If anyone is interested in doing this, contact me directly and I can give you more details.

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I installed 2001 Trans Am seats in my '81. The drivers seat is power. I am also 6'2", so I made sure the seat is far enough back. It actually is a little too far back for some, but I like the steering wheel farther away from my body than some.

If mama wants to drive, I'll rig up a block on the gas pedal, I guess.

Worked great. I didn't do quite as good a job as illustrated here, but it is more than adequate, using the Trans Am mounts exclusively.

Paul

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  • 2 weeks later...

How did you get it to fit properly? I found that the power seat assembly

made the seat bottom WAY too high compared to my 63 Avanti seats. I

guess the Avanti II seat bottoms are higher and you sit up higher? Head

room isnt a problem?

Tom

I installed 2001 Trans Am seats in my '81. ..... using the Trans Am mounts exclusively.Paul
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  • 11 years later...

I owned an '84 XJS; when the leather seats got badly worn, I purchased a set that were in very nice condition from an XJS a few years newer than mine, thinking they were a direct fit, but to my dismay, they were not. So, I set about designing a set of simplistic adapters; the adapters would bolt to the old nuts in the floor (bolt heads recessed below the adapter surface) and the newer seats would bolt into the top surface of the adapter such that the seat slider would still work, the only caveat being that the seat would sit slightly higher (the thickness of the adapter, which needed to be about 1/8" thicker than the head height of the floor-mounting bolts). The adapters were rudimentary, simply 2 strips of 3/8" x 1-1/2" steel per seat (overkill, really), with countersunk holes to bolt the adapters to the floor and threaded holes for fastening the new seat's slider bolts; I had a metal shop do the machining for me, and I was overly-obsessed with keeping costs minimal, so simplicity was key,.

If I were doing it now, I'd use aircraft aluminum welded into an "H" design rather than a box, with possibly 2 cross-bars placed forward so as to allow accessible passenger foot space below the rear of the seat; I didn't know where to find aluminum stock back then before computer searches became so easy. These photos should give you an idea of how I determined the dimensions of the adapters:

      

XJS floor.jpg

replacement seat.jpg

brackets3.jpg

 

XJS seat adapter brackets 700x537.jpg

Edited by WayneC
regain some of my image posting allocation
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WayneC thanks for the info! I really appreciate it.

A few points:

1. What you did was in a Jag, correct? I'm not saying it doesn't transfer, but just to be clear.

2. I don't understand the orientation of your drawing.

3. Why countersink the bolt holes?

 

Watching this with interest. Thanks!

 

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It was a long time ago, designed for my Jaguar XJS, and may or may not be applicable in principle to an Avanti... but I'll try to address several of the questions posed:

The material left on the adapter after counter-boring is 0.125", which is thicker than the material that retains the captured nut (in the floor) that the adapter bracket bolts to. In other words, the weak point is not my bracket/adapter, but the vehicle's original mounting points for the seat, so should not compromise safety.

My first job out of high school was as a draftsman, and I later spent time on the drawing board with Chevrolet during and after college... I realize not everyone understands drafting notation. My drawing was a representative sketch, not a real mechanical drawing. The orientation of the sketch/drawing is looking down on (top) of an adapter, with the middle of the adapter shortened (cut away) to fit it on the sheet of paper. Compare the drawing to the photo of the left & right brackets... the difference between left and right brackets is that the counter-bored holes are on opposite sides of the bracket.

The counter-bore is to recess the heads of the adapter-to-floor hold-down bolts so they don't interfere with the seat slider that bolts atop/onto a pair of adapters (left and right). Left and right brackets bolt to the floor, then the seat/slider is bolted to the brackets. Offsetting the bracket hold-down holes from the seat fastening threaded holes (towards the front of the bracket) would provide more space for the drivers legs, at the expense of rear passenger leg room, of course, but offsetting in the opposite direction could bring a shorter driver closer; I wasn't trying to change the driver position, so mine were only offset by 0.5", by necessity because if much closer the bracket hold-down and seat hold-down holes would interfere with each other.

There are many ways the adapters could have been lightened and streamlined, this was my version of quick, simple, and cheap

Edited by WayneC
clarity
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WayneC, Got it! Thanks for the additional post. I really appreciate it. It will be a couple of months till we are ready to tackle the interior but I like your concept. I'll probably PM as we get a bit closer but I do like the design. Rgds, Mike

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