Lowering the rear

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Ron Delmendo
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Lowering the rear

#1 Post by Ron Delmendo »

Listers-

I'd like a lower rear end for my ride. Despite what you may be thinking, I'm referring to my Roadster...

For the folks who have commited such blasphamy, how much did you cut off each side of the Transmission hoop? Yes, I have a spare hoop to butcher and leave my current one unadulterated.
Cheers,

Ron

'61 Roadster Outlaw
'69 911E ROW Coupe
'68 911 SWT project
‘18 Macan

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Chris Duerr
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lowering

#2 Post by Chris Duerr »

You can decamber the car and get it very low without altering the hoop. 4 degrees of negative camber is very low. 1.5-2 degrees negative gives good handling without clearance issues.

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Ron Delmendo
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#3 Post by Ron Delmendo »

Chris-

Thanks. Perhaps I should clarify. Hypothetically speaking, if the car is already decambered to -5.0 degrees, how much should be removed from the hoop to get the camber to -1.5?
Cheers,

Ron

'61 Roadster Outlaw
'69 911E ROW Coupe
'68 911 SWT project
‘18 Macan

S.J. Szabo

#4 Post by S.J. Szabo »

Well, since the goal is clearly to slam it, I'll skip the usual advice about drivability, etc. and note this; measure the gap between the bottom of the firewall and the top of the bell housing, subtract a quarter inch and you have your max. allowable distance. Re-set your camber (-5deg is just silly) when you're done.

Of course, if you want to make a real cock-up of it, you could cut a big notch out of the firewall/adjoining floor and really jam it up there.

Here's a thought: if you want to scrape the pans (it would make cool sparks.... for a while), why not run the brakes and wheels off an original Mini.... those ten inchers would really put you down there.


Keep 'em flying...

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Albert Tiedemann
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#5 Post by Albert Tiedemann »

Ron Delmendo wrote:Chris-

Thanks. Perhaps I should clarify. Hypothetically speaking, if the car is already decambered to -5.0 degrees, how much should be removed from the hoop to get the camber to -1.5?
Repeating Chris..."no hoop modification is required" You need to return the spring plate to a more reasonable angle in the unloaded state. If your front torsion bars are set to the factory specification, then the angle of the unloaded spring plate with respect to the horizontal with the entire car set in a level plane is specified. There is a list of these specifications in the little spec book or in the fadtory manual for each car year and model. They are not all the same. Find the specification for your year and model and, if set at this angle, the resulting camber will be in specification if the tire size used is that which was delivered on the car. Shallower plate angles decrease camber. The tolerance about the specification is unstated but the geometry limitation with standard parts is 50 minutes of arc
Albert Tiedemann, C356C
"The Hermit"

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Dirk Heinrich
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#6 Post by Dirk Heinrich »

Anybody ever cut the tranny hoop? Any pics? I cannot imagine it - all sheet metal would be off and the muffler wouldn't fit, how about the shifting linkage and how would you weld the hoop (it comes up in an angle)?

Ron where did you hear about this?

You should post a picture of your roadster here, so we get a get a better idea how low it is - cannot believe you'd want or need to go through any drastic measures with a stock to relative-stock car.

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Vic Skirmants
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#7 Post by Vic Skirmants »

OK, "Lowering car by cutting hoop"
In my SCCA days, we did that to lower the back of the car; 3/4" is about what it takes to put the trans housing against the chassis. If you bolt a 741 nose into an A chassis, that will raise the front of the trans to compensate, keeping it fairly level. If you just cut the hoop, you tilt the trans/engine unit. If you cut the hoop, technically you are raising the trans. This will increase camber in a positive direction! You have to re-set the trailing arms.
When we went to coil-over shocks and no longer needed the torsion bars, we raised the front pivot for the trailing arm to keep the arm more horizontal. The more that the arm is above the horizontal, the more the rear toe-in changes with suspension movement.
Whatever you do back there, be sure the axle tube does not hit the chassis under full deflection. That makes for bad handling!
I will not tell you how we cut the hoop, because I don't think 99% of those wanting to do this will think it through completely. Saw a car where the hoop was lengthened to "lower" the trans. Of course he was "raising" the chassis!

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Mike DeJonge
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lowering

#8 Post by Mike DeJonge »

Instead of cutting the hoop, weld the chasis mounting holes closed and redrill new holes for the chasis bolts, maximum of 3/4 inches. This is the lowest you will be able to go without the transmissio hitting the body. trim the top of the hoop off so it can be bolted back in the chasis mounting recesses. You will have to carfully mark where to drill the new holes, about 1/4 inch outwards to allow for the curvature of the hoop
Mike dejonge
Restoration Design Inc.
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Bruce Baker
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#9 Post by Bruce Baker »

Dirk Heinrich wrote:Anybody ever cut the tranny hoop? Any pics? I cannot imagine it - all sheet metal would be off and the muffler wouldn't fit, how about the shifting linkage and how would you weld the hoop (it comes up in an angle)?....
There may be a picture in Duane Spencer's book(s), but I don't have one here at home.

As Vic said, that was a common trick 'back in the day' for racers to lower the rear part of the center of gravity of a 356 without excessive de-cambering. Without eliminating the main underside of the trans hump (which was done, but disguised by the retained upper 'parcel shelf'), about 5/8" was all that could be had...a lot of effort for a little gain.

I would reject (sorry, Mike) the repositioning of the mounting location of the hoop to the body. That's a strange area in engineering and design, as anyone who has done an autopsy there would agree. You only mess around there if it is included in support by a roll cage design.

The real reason to post about this is safety related. The welding must be first-rate, with added gussets. The geometry and design of the hoop, as Dirk notes, is not conducive to easy modification.

The obvious 'can of worms' was of little concern with racers back then. Engine surround trays could be altered if used at all....remember, when coil-overs were legalized by SCCA, headlight buckets could be removed and turned into air intakes that then joined with ducting that was (usually) crudely cut into the trunk and passed through bulkheads, passing through the cockpit and straight into the fan opening for 'ram-air.' "Extractor exhausts" were the system of choice and those often necessitated modification (or removal) of the rear valence. Pure butchery became accepted so as to 'run with the pack up front.'

I should scan old pictures of 84255 from when I bought it in '88....amazing what damage a 4 pound hammer, a 1/4" drill and a chisel could be done to a nice Speedster by a determined racer in the later '70s.

I would strongly advise against lowering the body by shortening the trans hoop unless professionally done. I'd rather see pick-up points welded to the torsion bar tube for IRS! (Then ya go for the 5-speed, etc, etc....another can of worms!)
 

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