::Andy::

Hi all,

I recently purchased someone else project, I think ill health was the main reason for selling, also possibly they were some what disappointed in the cars 1/4 mile performance for the amount of work put into it.

Anyway, I've been going through it and making it legal for my drag racing series over here. I run a very slow bracket racing series, (12 seconds and slower) but you still have to have basic safety equipment, the flop forward seats and non-inertia reel belts don't cut it.

The first thing I noticed about the car when giving it some large from a standing start is the ferocious axle tramp that starts. The car is pretty built, it's running a Edelbrock 350 RPM Performer crate engine, fully built 700R4 into a Moser 9" Ford crate axle. Having gone over the suspension on my other car, the first point I noticed is that the LCA to the axle were pointing downwards at the front body mount, a tell tale sign of poor suspension geometry. So sure enough, ordered myseld some Tubular adjustable LCAs, LCA relocation brackets and got that all fitted.

First thing I noticed when I went to fit them, at first I though the shocks were dead, unbolted them and they didn't move, then realised they were hydraulic shocks, as opposed to what I believe should be on there, gas? Is this correct? Could this be the cause of my axle tramp?

Any help appreciated.

Andy

AlkyIROC

Even gas shocks have oil in them. Suspension springs hold the car up. You just need enough spring rate so that the suspension can move without bottoming out. The shocks do all the work of controlling the springs. Too stiff of a spring and the shocks do very little work. Geometry controls how the diff reacts under power. With the third gen torque arm suspension, there's not a whole lot of adjustment available.

The LCA should be level with the ground. relocation brackets on the diff allow you to readjust the LCA if the suspension has been lowered. You can have the back end of the LCA slightly lower than the front but higher in the front isn't good. Adjustable LCA just allow you to fine tune the wheel base. Same thing with an adjustable panhard bar. It allows to you center the diff under the car if the ride height has been modified.

An adjustable torque arm allows you to adjust the pinion angle. The angle of the pinion in the diff should be at the same angle as the crankshaft. Doesn't matter if the diff is pointed up or down and it has no relation to the driveshaft or the ground. Measure the angle of the crankshaft and set the pinion to the same angle.

Change the shocks. Springs hold the car up, suspension determines how the car will hook but the shocks control everything. In a drag car, a double adjustable is the best way to go but they're not cheap. If the suspension is set up properly, the diff should be driven down into the ground planting the tires. The shocks should allow for a quick extension to allow this then a slow compression to allow the diff to come back up after launch. The best inexpensive alternative is some 50/50 shocks. I ran factory rear shocks on my car for years until I finally did a back half and went with coil overs and adjustable shocks.

If you don't have it, install a rear sway bar or anti roll bar. It will help get traction to both wheels easier and reduce a lot of body twist.

::Andy::

Hi AlkyIROC,

Thanks for the detailed reply!

I had been through all this with my other car, I run a 1991 Camaro with a bog standard 305 TBI setup, but this was running high 15s / low 16s damn consistently. This car (with the axle tramp) came up at half the price it would've cost to build the thing so I thought two cars were better than one.

The LCA arms pointing down at the front was one of the first things I noticed as being something I wanted to rectify. I was told the springs were aftermarket, but NOT lowering springs. They have a beehive appearance as opposed to the standard cylindrical style I normally see fitted in the rear. I shall have to go through the box of receipts and find what they actually are.

I have ordered some 5 way adjustable gas shocks in an attempt to cure the tramping and have some adjustability in the rear, I was more curious as to whether gas shocks were maybe designed to work with this suspension setup as opposed to hydraulic shocks?

Now you mention it, I didn't see any sway (or as we call it over here, anti-roll bar) on the axle. Could this cause the tramping too?

AlkyIROC

No, but not having an anti roll bar will allow the right rear tire to easily lift off the ground or at least have less downforce (one wheel burnout). The anti roll bar also keeps the left front tire down which is caused by the twisting of the car.

When I first installed my back half and 4-link system, I didn't have an anti roll bar. If I was in the left lane, launching felt like I was going to take out the tree. After install the anti roll bar, both front wheels come up equally and the car goes straight.

Buying someone elses race car has advantages and disadvantages. It's probably cheaper than building the same thing but may also need work or isn't exactly what you wanted. I can honestly say my race car is "my race car" It was a street car when I bought it and I made it into a race car. People can't look at it and say "That's what's his names old car". If I was going to do it all again, I'd build or buy a tube chassis car right from the beginning. Would have been a lot cheaper in the long run.

::Andy::

Finally got around to putting this on a track, and it wasn't great.

Some other stuff since the last post though. Having two car that are similar makes it easy to swap parts across. I changed over the rear tyres, and that dramatically made an improvement, or so I thought, only once I got home did I realise that I had just the previous day filled the car up, so I think the combination of rear weight and tyres made an improvement.

The previous day to putting it on a track I managed to get the thing on a four post lift so I could check all the drivetrain angles out. The gearbox tailshaft angle is pointing up by 2.6*, driveshaft pointing down by 2* and the diff was pointing up by 2*.

I set about adjusting, first problem I could see was there was no way I could decrease the gearbox angle unless I shimmed the crossmember downwards. Looking at it, the whole lot has new looking bushes in it, I'm just wondering if they're the right size. Anyway, not getting too distracted with that, I went as far as I felt comfortable with the pinion angle and got it to pointing down by 2*. The finished numbers were Gearbox 2.6* up, driveshaft 2.5* down, diff 2* down.

The thing I really notice with this car is how much the body rises just loading up the torque convertor, it lifts about 1" - 2" in the rear. Not sure if this is good or not. The settings on the LCA were to the middle hole of the UMI brackets, this gives a slight angle going down towards the axle from the front chassis location.

Anyway, at the track, wasn't the best day, the track wasn't brilliantly prepped. I got the car off the line and instantly got wheel spin all through first, as I started coming off of it, it violently started hopping.

I had a few friends watching, they said it was a very prominent up and down movement not front to back as though it's trying to drive out of the wheel well.

Currently a bit lost for where to go with it all and what to try. The rear springs seem incredibly soft and when pushing down on the rear quarter the car sinks very quickly and then comes up very quickly. A friend said he would be looking at springs and shocks combo.

For a complete low down here is the spec:

Engine, Edelbrock 350 RPM Performer 435hp
Gearbox, Built 700R4 w/ 2500 TCI stall convertor.
Axle, Moser 9" crate axle w/ 3.50 gears and Detroit Locker. No sway bar. Moser Adjustanle Torque Arm with Poly bush,
KYB 8 way adjustable shocks, Moog CC635 rear springs variable rate, UMI Performance LCA Relocation Brackets, UMI Adjustable arms, UMI Adjustanle panhard bar.

Any advice or ideas appreciated, I'm not contemplating fitting the rear springs off my other car, they're lowering springs, but a lot stiffer.

no green

What tires? psi?

I'd move the LCA's to the lower hole.

read this: http://www.spohn.net/support/questio...inion+angle%3F

if i understand your post right, in relation to that artical, your driveshaft is +2.5, your pinion angle is -2, so you have a .5 true angle, and spohn (and I) recommend 2.

If I understand your post right, you said it hooked then started spinning and wheel hopping, or did it almost instantly?

That's your shock setting, I weigh 350#, and cant get the back of my car to move down, but i can push it up an inch or so... With factory springs.

no green

If a person is trying to hook a torque arm car, this is not correct information.

::Andy::

Hi No Green, thanks for the reply!

I initially tried them in the lowest hole but was told that would possibly be making the situation worse further down the track if the car unloads after the initial hit. I've got to be honest, it's all a bit of a dark art to me and I'm trying to understand it, but from what I do know, any LCA which is lower on the body than it is on the axle will induce wheel hop, whereas the lower you mount the arm on the axle compared to the body, will make it hook up stronger, I hope I got that right?

As I was making the adjustments I was getting worried about if I was putting any undue stress on components as it seemed like quite a large adjustment going from +2* to -2*, I had my dad with me and he was sure that adjusting the torque arm wasn't right and I should be doing something with the LCAs, but I'm pretty sure I was right in what I was doing.

The tyres weren't anything amazing, but I have had a great experience with them, they are Kuhmo Ecsta street tyres, lots of grip, found them to be great for hooking up at around 28psi on my other car. They were a massive improvement to the Nexens that were fitted on the car. Basically off the line I got wheel spin and as I got close to the 60' mark the axle started hopping bad, probably the worst I'd ever experienced. Once rolling though the car was fine and I put my foot back in and crossed the finish line with a 15.77 @ 96mph.

Hmm, with this car I can lean on the back and it very easily does almost full travel, compared to my other car which has no axle issues its a lot lot stiffer to compress the rear end.

AlkyIROC

Doesn't matter what type of suspension you have. The closer the diff pinion angle is to the engine/trans angle, the easier it is on the driveline. If anything, you want the diff angle slightly down from the trans angle to allow for axle rotation under load. For street use, no more than 1 degree. For street/strip 2-3 is fine. With the old leaf spring suspension 5-7 was normal because the leaf springs would wrap so much.

This is the best video explaining driveline angles and why they should be the same.



As for your diff bouncing, try some new shocks. Original shocks are probably worn out. Springs just hold the car up at ride height. Soft springs just make for a softer ride. Too stiff a spring and the shocks don't do any work.

no green

It might be black magic, but it works. I was weary to try what I said, but when I did, it works 1.3x 60' from a 1.7x 60'... Alkys vid doesn't account for how a torque arm suspension works. Drive train angles for longevity is great, how long you the think u joints will last bouncing around.

Bottom hole, preload torque arm 2* from driveshaft, fix shock settings, go fast.

Try what I said, or don't, its your car. Mine works, and it's not a 4 link. And if it don't work, try something else, what I'm suggesting is free.

::Andy::

Hi AlkyIROC,

I changed the shocks this is where I originally thought the problem was, it had these hydraulic shocks in it, when I first saw that I thought 'Ah! There's my problem!' I ended up fitting some KYB AGX adjustable ones, but I'm still suffering the same problem.

Shocks I fitted: http://www.summitracing.com/int/part...3019/overview/

Springs that are already fitted: http://www.summitracing.com/int/part...c635/overview/

What are both of your opinions on the transmission being +2.6* as opposed to be pointing down towards the rear of the car? Should that be something I sort out? I need to fit a prop loop for competition over here and was thinking that I should really get the UMI kit that relocates the Torque Arm off of the transmission tailshaft, While I'm at it, I could shim the cross member off the bottom of the chassis and get it closer to zero / negative angle.

No Green, I really am open to all options and I appreciate your inputs, I do however need to remember to take a jack to the track next time so I can make said changes while I'm still there (jnr error!)

Thanks guys again, I'm at a loss here so any advice is very much appreciated.

no green

Did you actually make a pass like this, or change it before trying? Because, so far, you haven't had an initial hit, if it's spinning...


That is a good idea. I went fast with an SLP that was attached to the back of the transmission, until it tore the mount and broke the bellhousing. I have a spohn crossmember mount one, now.

I've never put an angle finder on the transmission or engine to find out it's angle, it's in the stock locations. I've only checked the driveshaft to the diff angle.

Those shocks you have might be an issue, they're not a racing shock. I have QA1 double adjustable (way overkill), you probably need something more like this: http://www.summitracing.com/ga/parts/cee-2700

but, try full stiff on the koni's you have & the other settings I stated, and see what that gets you.


Your tires arent the greatest for doing this, either. IDK what kind of track prep you have over there. I run a 28x10.5 slick, and last year they started getting old, i thought it was track prep, until i walked the track. I tried adjusting around it until i could afford new tires, and only successfully beat my head on a wall for 3 weeks until pay day came.

WickedBowtie

are those shocks you recommended for pontiacs only? because when i check application on summit it doesnt list camaro.

redneckjoe

while stock third gens are are a 3-link type suspension, i found this article helpful. best of luck getting rid of that wheel hop. some drag bags might help too?

http://www.how-to-build-hotrods.com/tuning-4-link.html

WickedBowtie

i found this on jEGs website

http://www.jegs.com/247-adjustabledr...plication.html

apparently they do.