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Using coilovers w/ torsion bars + clutch replacement - help

 
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Dynamite76  



Joined: 13 Mar 2007
Posts: 21
Location: Richmond, Virginia

PostPosted: Sun Apr 08, 2007 12:44 am    Post subject: Using coilovers w/ torsion bars + clutch replacement - help Reply with quote

I have an '88 924S. The clutch is shot as best as I can tell; thrashing in rear end as I apply and remove throttle inputs. So, I have the task of replacing the clutch coming up.

I would also like to work on the rear suspension at the same time. Initially I wanted to prep the car as a spec racer, but am now considering saving some time and money by adding coil overs and leaving the torsion bars alone.

I am thinking, that I am about 1 1/2 years away from driving in the more advanced groups on the track, possibly at some point either becoming an instructor or racing the car, or both. But, I am a good number of track sessions away from that.

The car is a track only car for the most part, unless my daily driver needs major work like rebuilding the front right brake caliper . There is always things that I need to spend time and money on with the 924S, like a roll bar, AC delete, stripping interior, tires, engine maintenance, all the good stuff to turn the car into a better track machine.

So, I was thinking, mostly concerning the savings in time, of adding coil-overs to the rear and leaving the torsion bars alone. Will this even work, or will the geometry of coil-overs and torsion bars together cause the rear end to be all funky? If they will compliment each other, what spring rates should I be looking for? Torsion bars are stock, 23.5 mm and I imagine, worn below the factory 126 lbs spring rate.

I will index and lower the rear, and already have lowering springs and camber plates for the front. Need to replace the front inserts though. My goal is a better handling car than what I currently have. Another thing that limits what I can do is that I have to do the work in the parking lot and it is against local regulations to leave a car jacked on stands. 4 tires have to be on the vehicle and supporting it if unattended.

Sorry for the long post and thanks for any feedback.

Paul C.
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Dynamite76  



Joined: 13 Mar 2007
Posts: 21
Location: Richmond, Virginia

PostPosted: Sun Apr 08, 2007 2:14 am    Post subject: Reply with quote

Update:

I "discovered" Koni 30 series mono dampers. Anyone else using them? For the cost and ease of installation, I cannot see a reason not to use them, especially since I am not bound by class rules as a DE driver.
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John Brown  



Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA

PostPosted: Sun Apr 08, 2007 3:36 am    Post subject: Re: Using coilovers w/ torsion bars + clutch replacement - h Reply with quote

Dynamite76 wrote:
I have an '88 924S. The clutch is shot as best as I can tell; thrashing in rear end as I apply and remove throttle inputs. So, I have the task of replacing the clutch coming up.

I would also like to work on the rear suspension at the same time. Initially I wanted to prep the car as a spec racer, but am now considering saving some time and money by adding coil overs and leaving the torsion bars alone.

I am thinking, that I am about 1 1/2 years away from driving in the more advanced groups on the track, possibly at some point either becoming an instructor or racing the car, or both. But, I am a good number of track sessions away from that.

The car is a track only car for the most part, unless my daily driver needs major work like rebuilding the front right brake caliper . There is always things that I need to spend time and money on with the 924S, like a roll bar, AC delete, stripping interior, tires, engine maintenance, all the good stuff to turn the car into a better track machine.

So, I was thinking, mostly concerning the savings in time, of adding coil-overs to the rear and leaving the torsion bars alone. Will this even work, or will the geometry of coil-overs and torsion bars together cause the rear end to be all funky? If they will compliment each other, what spring rates should I be looking for? Torsion bars are stock, 23.5 mm and I imagine, worn below the factory 126 lbs spring rate.

I will index and lower the rear, and already have lowering springs and camber plates for the front. Need to replace the front inserts though. My goal is a better handling car than what I currently have. Another thing that limits what I can do is that I have to do the work in the parking lot and it is against local regulations to leave a car jacked on stands. 4 tires have to be on the vehicle and supporting it if unattended.

Sorry for the long post and thanks for any feedback.

Paul C.


Hi Paul:

I see you're in Richmond. By any chance have you run with NASA or PCA at either VIR or Summit Point?

What catches my eye is your statement that 'I am a good number of track days away from that'. If you just want to 'do stuff' to the car it's fine; but if you are seriously looking for frugal optimization congruent with your skill level ... then my personal suggestions change.

You probably have already seen that any of the coilovers with rubber bushing are NOT recommended with significant spring rates. I think the Koni you mentioned fall into that category. Coilovers are something you should either do or not do, in my opinion. And frankly, because after you do do them it paints you into a corner I'd suggest you wait. Also, only the very lightest spring rates can be added without re-indexing the torsion bars there's little point. Once you get into re-indexing the torsion bars you could have also replaced them with the requisite 30mm. The limitations on working on the car would seem to preclude doing it at your home as at BEST its an all day job. And the last torsion bar changeover I attended once again proved that 'stuff can happen' to screw up even basic jobs.

Lowering springs for the front. Must be either the 200 or 250s? 200 works OK. 250 with stock rear torsion bar tends to cause understeer. The 200 can be had that does not advertise lowering. They really do lower just a bit and so work very well for a car that's driven to the track.

If I didn't address it above, yes, the geometry is almost impossible to keep correct if you add springs and don't re-index the torsion bars.

Two suggestions. First, check out the www.44cup.com forum Good place for track info specific to your car.

Second, wait a bit to decide where you want to run before mods. Some racing venues may not allow coil overs. Visit the 44cup race group some to see how those cars are setup.
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dgz924s  



Joined: 03 Nov 2002
Posts: 592
Location: Kansas

PostPosted: Sun Apr 08, 2007 9:32 pm    Post subject: Reply with quote

Most often the T bars are removed and coilovers are used in their place. The CO will allow easier adjustment vs a T bar. Having said that most series for stock prod cars do not allow CO's. Also do not confuse real coilovers for rear helper springs that look like CO's but are not, but only a booster to the T bar.

Adding CO's to a T bar is added weight and 2 things to adjust vs 1, the T bars and the CO's. T bars also keep the weight lower than a CO will even if the CO are lighter....nick picking here but relevant.
Cost of a CO is much higher too.

Dal
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Dynamite76  



Joined: 13 Mar 2007
Posts: 21
Location: Richmond, Virginia

PostPosted: Mon Apr 09, 2007 9:26 am    Post subject: Reply with quote

My desire for frugal optimization congruent with my skill level means that I will be reverting back to a more stock front suspension. Maybe after I tackle the seemly daunting task of replacing the clutch I will have the confidence to start considering the rear suspension. I just knew the front was too easy for a reason and was searching for a way to do the same in the rear

I was considering assisting springs as a temporary fix, between stock and 30 mm torsion bars. However, since adding them is half of the process of upgrading the t-bars themselves, there seems to be no point. When the time comes, I'd rather be the only spec racer than the only frugal non-spec racer.

Aside: getting there for me means getting a garage with a house attached. HPDE 3 or 4 is the contingency plan. Another HPDE 1 is the next step in the process though.

I was at VIR with NASA last week. I had so much fun and gained so much experience, breaking some nasty Honda habits to boot. Like downshifting into the turns and keeping the RPM's pegged just below red. It took the rear end of my car trying to pass me in 11 in the rain to learn this lesson . Not sure because I didn't test it, but I think they meant 2 feet in... only if you have ABS. Brakes in a spin = snakes on a plane, or that is the association my brain cannot get over.

The next and last session was by far the most rewarding. I got more positive feedback from my instructor, was easier on the equipment, and I suspect, turned faster laps times. One of my instructor's last comments was "Wasn't that more fun? You did much better when you were not worried about going fast, like most of the times before."
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Paul  



Joined: 02 Nov 2002
Posts: 9414
Location: Southeast Wisconsin

PostPosted: Mon Apr 09, 2007 10:19 am    Post subject: Reply with quote

The rear suspension is a cake walk compared to a clutch job!!!

I suggest you find someone who has done this before to at least watch (drinking your beer on a lawn chair) while you do this. (BTW how far away are you?)

And of course read all about it at:

http://www.clarks-garage.com/shop-manual/clutch-01.htm
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