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Old 03-28-2005, 09:39 AM
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Bel Air AWD conversion

Hey everyone!!!
I would like to turn a 1957 Bel Air into a awd daily driver. Has this ever been done? My idea is to take a Gmc typhoon complete rolling chassis (with the turbo engine) and fit it to the Bel Air body..... Is there a better awd chassis to use (one that fits better so I don't have to mod as much)? any input/guidance?

**** P.S. I do have all necessary Tools to work and can do pretty extensive modification just would like some guidance before stepping into this one! THANK YOU VERY VERY MUCH for you help in advance!!

***** Lastly does anyone know the dimentions of the bel air chassis?? This would help a ton!

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Old 03-28-2005, 10:12 AM
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There are a couple of threads out there on this. Do a search for "AWD" to find them.

The problem with converting any Rwd vehicle to AWD using the Typhoon (and Astro Van AWD) running gear is that those vehicles (the Typhoon and Astro AWD) locate the engine on top of the front differential. Not a problem for 4wd trucks, which have bodies raised up above the frame, or a van which has plenty of vertical space, but trying to do this with a normal car will necessitate making the engine much higher than it is now. This causes all sorts of problems, including finding vertical space under the hood and raising the center of gravity. You could probably raise up the body above the frame, like GM does with its 4wd trucks, but that might look awful...

The only vehicle that I've seen successfully converted is Summit's QuadraDeuce, but you'll notice that the front axle is ahead of the engine on that vehicle, while the front axle would go right through the engine of any other car. Other vehicles of that era (30's) that had straight axles ahead of the engine would be great AWD candidates. Even if you can locate the differential in front of the engine, you still have to have the engine high enough to clear the front driveshaft, or offset enough - not as huge a problem as the differential, but something to plan around, nonetheless.

I suppose if you really wanted to do it, in some vehicles it might be possible to push the engine far enough back to clear the front differential, but you also have to keep in mind that the transfer case has to be accomodated behind the transmission. That starts seriously encroaching on the interior.
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Old 03-28-2005, 11:48 AM
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If i where to use the typhoon's turbo engine i still would have this problem?? that thing is pretty low down to the ground
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Old 03-28-2005, 01:24 PM
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Hmmm.

Using a shorter engine might help. You'd have to take measurements. I suspect you'd still have to sink it into the firewall, but it all depends on how much room you have in there.

The front axle is going to have to be mounted essentially in a straight line connecting the front wheel centers. Typically, the engine sits right there on a huge crossbrace where the suspension is mounted. Assuming the BelAir is that way, you'd have to then fab up engine mounts further back in the frame, and either hack out the cross brace, or graft the typhoon front frame clip onto the frame. Also, the typhoon, like most GM 4wd vehicles, uses torsion bars rather than springs to provide for the clearance for the front drive shafts. The torsion bars have to be mounted somewhere aft on the frame - not a huge deal, but something to keep in mind.

Anything is doable with enough money and time. If you want to do it with largely off-the-shelf parts, its not going to be easy. The first step, IMHO, is to get some measurements of all the parts required. The older cars had a lot of room under the hood, maybe you can make it work.

OTOH, the fact that no one seems to have done this (at least to my knowledge) might indicate that the problems getting to work are difficult to surmount. On previous posts, one member suggesting taking a look at the AMC Eagle, which was a 2wd vehicle made into a 4wd in the late 70's early 80's. They had to raise the body 3" to make it work, but it might give you some ideas. I haven't been able to find a junkyard with one to check it out.
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Old 03-29-2005, 04:40 PM
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Here's a thought...don't know if it would work.

FWD GM's in the 70's and 80's used a longitudinal engine with a transaxle that was driven by a chain and ran next to the engine. The major models were the TH425 and TH325.

Info's a little more scarce on the TH325, but the TH425 was essentially a TH400, which is pretty bullet-proof. On the TH425, the differential sat on the LH side of the engine with the right axle going through the oilpan, just clearing the main bearing on Cadillac engines.

The transmission itself actually ran in the reverse rotation, because it was pointing backwards and was connected with a chain drive to the engine. Supposedly, however, the differential can be flipped (with some work - check the Fiero-based kit car guys) which effectively reverses the direction (if that were required, which it may not be since the transfer case also uses a chain drive).

Now what might, and I stress might, work, would be to take the guts out of the transaxle and modify it to fit a clutch where the torque converter and chain used to be (no small feat), then run that into a manual transmission (for space reasons - I guess you could somehow tack an automatic back there...), then to a transfer case. From the transfer case, one driveshaft would go straight back to the rear differential, and the other would go into the gutted transaxle case to the front differential.

This would take huge amounts of fabrication, if it could even be done at all. There might be a couple of benefits; the front differential would be effectively mounted to the engine, which would simplify mounting via the engine mounts rather than separate ones for the differential, and its already set up for front wheel independent suspension, so fabbing up axle shafts would be easier. Also, depending on the engine, this setup mounts the front differential pretty much as close as possible to the bottom of the engine (although it might not work with anything but a Cadillac/Olds depending on where the shaft runs under the crank). The trans case and the few parts utilized should definitely hold a decent amount of torque, especially since they'd only get 40% or so via the transfer case, so you wouldn't have to worry about breaking anything, like you might trying to fit other front differentials up there.

If you used an independent rear axle, like that of a Corvette (or others), then the entire drivetrain could be mostly fixed in place, with only the drive axles moving with the suspension. This might simplify hooking up the driveshaft from the transfer case to the front differential, since its unlikely they'd line up perfectly - you might be able to rotate the transfer case so at least it would be on the same horizontal plane as the front differential. Also, you would need less space for the driveshafts, since they wouldn't move with the suspension.

Downsides include plenty of extra weight, a pretty darn complicated setup, and lots (and lots) of fabricating. It also doesn't solve all the space that the transfer case is going to take up, along with that of the front driveshaft. Maybe you could alleviate this by going to a torque tube from the engine to the trans and mounting the trans/transfer case closer to the rear differential, with a long driveshaft up to the front differential, but that leads to even more fabrication and some serious engineering, or just mount the transfer case back by the rear diff - that might be easier for fitting it under the passenger compartment. Also would need to match the front and rear differential ratios, which might be problemmatic.

Maybe if all that worked, you could consider a dry-sump system to keep the oil pan off the ground, but that would be the least of your worries.

Since only 40% or so of the total torque goes to the front axle, you might be able to get by with the lower-capacity TH325. Don't know enough about them, but they probably weigh less than a TH425, and might be cheaper since they're pretty much useless for anything else and didn't last very long in what they came in. The TH425 was used in FWD GM motorhomes, along with Eldorados and Toronados. The TH325 was used in FWD Eldorados, Toronados, and Rivieras in the 80's before transverse-mounted engines became the norm.

Its an idea I had...thought I'd throw it out there. It is certainly not a bolt-in solution - solves some problems, while creating others.
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Old 03-30-2005, 05:26 PM
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After thinking more about the TH325/TH425, I'm not sure that's the best way to go. Its a lot of extra weight for minimal gain.

I think it might make sense to utilize the TH425 differential, which is pretty compact compared to, say a Corvette rear IRS diff and plenty stout since Cadillacs were putting out around 500 ftlbs of torque in the early 70s.

Routing the RH driveshaft through the oilpan under one of the main bearings is probably a good solution compared to trying to fit a differential under the engine. I would probably try to mount the front differential directly to a fabricated bracket assembly attached to the engine.

With the differential no longer attached to a transaxle, you then would have the flexibility to use any standard transmission and then either mount the transfer case aft of the transmission or ahead of the rear differential.

I'd be inclined to go with a manual, because they tend to take up less space than an automatic, not only in overall width, but also in length (with some exceptions)

A lot would depend on the spacing between the input shaft and the front output shaft on the transaxle - it would be best if the shaft spacing was far enough apart to allow the front differential to be mounted beside the engine and go straight back to the transfer case, although a slightly-offset arrangement is probably possible. Engine would likely need to be offset to the right a bit, because you need to mount the other end of the RH driveshaft somewhere on the other side of the engine. If I understand correctly, the closer you can get to having equal-length front axles, the less likelihood of torque steer.

That would also keep both driveshafts closer to the center of the floor, which makes packaging easier.

Its difficult to find good info on the TH325/425, but I believe one of the final drive ratios was 2.73, which is also available on Corvette (and other) rear differentials.

Personally, I'd be inclined to go with an IRS so you can keep the drivetrain mounted in one spot - a lot of the driveshaft tunnel is taken up by the need for the rear driveshaft to move up and down with a standard rear axle. With an IFS and IRS, the driveshafts would stay in place, minimizing some of the floor clearance issues.

If it was me, I'd probably try to mount the transfer case in front of the rear diff. With an IRS, you may even be able to fit it under there without major floor modifications - it would end up being somewhere around the back seat.

Another thought is that a fuel-injected setup is probably going to take up less space on top of the engine than a carb and air cleaner. FI is getting easier and easier to implement. Since your lower limit for the engine is the main bearing on top of the front axle, you may not have clearance under the hood without a low intake. Scoops and bumps are possible, but there are so many benefits to FI, that it would be a good choice.

It also occurs to me that this thread might be better placed in the suspension category...
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