Front suspension spring rate

[Guest Mustfire]

Does anyone know or know how to find out what the spring (torsion bar) rate is for an 85 Riv? I am thinking of going with coilovers.

Thanks for your help,

Mustfire

[NTX5467]

One beauty of torsion bars is that they can be adjusted. The more preload, the stiffer the spring rate (and the higher the ride height, typically). IF you're wanting "coil overs" on the front, you might get the same effect with a little more preload on the bars without the expense.

Typically, coil over shocks (i.e., LoadLeveler) are more about increasing load carrying capacity and not about added stiffness in the spring. Many have a variable rate coil spring that adds little stiffness until the more closely-wound center coils are compressed and the outer coils (wider apart) come into play with suspension compression.

Many racing applications have "universal" coil-over shock setups. In these cases, the spring is adjusted on the shock housing to achieve the desired "ride rate" and at a particular "ride height". If one spring does not work, you get another one to try.

In the case of that generation of GM E-car chassis, there were no real "performance" suspension options per se. There will be different springs to deal with different vehicle weights (on each axle, front and rear) due to differing equipment levels and engine weights. The Oldsmobile Toronado bars might be a little stiffer than those on the Riv or Eldo, possibly, but I don't know of a way to prove that. I also suspect that each one might have their own OEM shock applications to further fine-tune the ride to the market demographics of the respective carline's customers, but applications which would be (very possibly) consolidated in the aftermarket replacement lines.

In that general time frame, a "performance suspension option" would include different (firmer) shocks, probably Goodyear Eagle GT tires (stiffer sidewalls and tread), and larger front/rear sway bars. Spring rates might have been increased some too, but I suspect the tire difference and sway bar differences would be the most significant items to give a more sporty feel to things.

There might be some specs filed with the SAE that would include the suspension "ride rate" of the "springs". Finding that might be a little in-depth.

What sort of situation are you trying to fix? Just curious. Please advise.

Enjoy!

NTX5467

[Guest Mustfire]

Thanks for the info and perspective. For this application (more later), it is more about not having the frame mounts to deal with. I am (or I am in the process of) using the front frame, engine, transmission, and driveline frome the 85 Riv that was wrecked, in a 84 Chevy S-10. Before you go "What the hell is he talking about", let me explain further. I have grafted the above structures to the S-10 frame just behind the cab and made a rear-engined, rear-drive vehicle. I'd never seen one, couldn't find anything about one on the 'net, so I said "Why not?' So, now that has been done and I have already shortened the torsion bars. But that still leaves the frame rails extending back to rear bumper area (no bumper now). Because the rails run more or less on the same horizontal line as the bottom of the lower a-arm, they just sort of hang out in space, uncovered by any body panel. Ugly. So I would like to get rid of the whole assembly, along with the frame rails past the transmission support brackets. That is where the coilovers would come in. The weight at the rear wheels is now about 400lbs. lighter than in a stock application, so if I could just duplicate the stock spring rate, it would be plenty taut enough for my needs as an auto-crosser.

Just to prove how nuts I am about this project, I am also trying to find a source to replace the stock 2.08 (or whatever it is) differental with the highest number I can get.

Any thoughts?

Mike

[NTX5467]

Sounds like an interesting project . . . but not really that much more involved than a friend that put an earlier Toronado "assembly" in the back of a '68 Camaro, if I recall correctly.

In the transaxle ratio situation, there were a few different "final drive" ratios available on the Toronado/Riviera/Eldorado cars of that era. I think there might be one for "trailering" somewhere, but they aren't going to be in the "low" gear territory you might need.

On the current production GM fwd transaxles (i.e., 4T65E), they use sprockets to run the chain. There are different ratio combinations for the sprockets they use (as mentioned in the GMPowertrain website on that transmission family). You might investigate such a situation on your transaxle family, but you'd probably need a really sharp transmission person to get those answers, I suspect. Of course, the 4T60-65E transmission family will (or should be) a good deal stronger than your existing transaxle AND aftermarket sources have beefed-up assemblies ready for sale of them too. As in a towing situation, the electronic GM automatic transmissions have a temperature override system that'll let them do some unusual things (like freewheel!) when the atf fluid temp gets above a certain level. Therefore, you'll need the biggest atf cooler you can find (to replace the stock cooler) to keep the temps down so the "failsafe" system does not kick in.

The other side of the deal is that you'll most probably be running a shorter sidewall tire than the Riv had on it. The shorter tire (more revs/mile) will effectively lower the gear ratio and result in more rpm per mph to drive down the road.

Enjoy!

NTX5467

[83RivConv]

Mustfire, how's about posting a pix of this Rivolet beast!! Sure sounds interesting...

[tim63riv]

Mustfire,

Sounds like an interesting project, though not a unique one! There were quite a few cars and trucks back in the day that got a first generation Toro or Eldo driveline swapped into them, both FWD and a RWD application! There is even a 46-48 Olds Sedanette that comes to Back to the 50's in Minnesota that has a FWD Toro under the front, neat car and nicely done too!

As far as your coil-overs go, pull off a regular front (rear?)shock and measure the extended length and fully compressed length, that will give you your "travel" limits. Weigh the total vehicle and then just the rear half. Get this information to your local race car shop or Carrera supplier and they should be able to come up with something that works. You will probably have to modify your shock mounts for spring clearence and reinforce them so they can carry the full vehicle weight. If you have got your project this far, you probably have the skills to finish this last portion of it!

As far as axle ratio goes, you are going to be very limited with the 79-85 "E" body selection. Most of these cars are products of the gas crisis of the 1970's, so fuel economy was the big concern, not performance! The 84-85 Riviera T Types have a low 3 to 1 ratio, but I don't have that information here with me now. If I do come across the final drive ratio of the T Types, I get it posted here!

Good Luck,

Tim McCluskey

[Guest Mustfire]

I'll try and get some pics up soon. Thanks for all the info. Does anyone have a source for the 3:36 or even the 3:15 gears found in the T-Types? I'd also take a used "pumpkin" with those gears if its available.

[Guest acboxer]

My Olds shop manual 1984 lists list : 3.36 ratio as code 4MN Stamped code N trunk code FW4

Code Stamped on cover side of case on 3.15 Ratio as code 4MM Stamped code M trunk code F57

left side viewed from front. 2.93 ratio as code 4ML Stamped code L trunk code F45

2.73 ratio as code 4MK Stamped code K trunk code F47

The trunk code is Service Parts idenification sticker Gm installed on inside of trunk lid easy way to check factory istelled equipment whe looking in self ser U pick parts JUNK YARDS . Ive used this to get rear end parts (lower gears for my Olds 98. Hope this helps.

[Guest Mustfire]

Thanks, that'll help. You wouldn't know of any aftermarket suppliers would you?