Something interesting after lowering my '85 GMC

[d stroud]

So, I lowered my ’85 GMC slightly over the weekend.   I cut exactly one coil from the bottom of the front coils which resulted in exactly 1-1/2” drop.  I used the DMJ 2” shackles in the rear, which lowered the rear just a little less than 1-1/2”???

Anyway, now that the truck is lower, it seems to run much, much better.  Rolling off in 1st gear, at about 20 MPH, I nail it and when the q-Jet kicks in the secondaries, the tires bark…then when going to second gear, it barks again (bone stock 350C tranny – no shift kit or anything done to it.)  It never could do that before.

I assume that what has actually happened is that I’ve lost a little traction, but it sure is more fun this way!

Anybody else experience anything like that?

The engine is a fresh Vortec headed 355 with Comp Cams XE262 cam and flat tops.  So, it should definately have the power to turn em over, but, it never has before I lowered it.

[Blazin]

How fresh? It might just be getting broke in is all.

[d stroud]

Its got about 1200 miles on it now.  Put it in during New Years holiday.

It really is pretty peppy, but with teh weight of the truck and the 3.08 gears, she was never able to chirp the tires like that before.

Plus, I have never heard of a bone stock tranny chirping the tires going in to second gear like mine does now.

Not that I'm complaining 

[Fordeatinz71]

d stroud, i LOVE your "Family Muscle Site".  ya'll do some gorgeous work...

[Blazin]

The TH 400 in 55 is bone stock, It will scratch 2nd pretty good.

[Dragon]

Lowering a bit causes less drag, which allows for better airflow(More over the top, and lesser underneath), which can result in better performance....  Ever notice why most Sports Cars sit so low, or even Race Cars/Trucks... 

One of the things I will never understand about raising a Truck(or even a car for that matter) Higher than what it can realistically be used for... Sure I understand Lifting it for Optimal Off Road/Crawling/Etc. Characteristics, but beyond that it seems excessive...  What's the point of a 16+ inch Suspension lift, Whatever size Body Lift, and Huge Mudders, if the truck never is taken Off Road, or actually put to proper use other than "Look" aspect... (Must Be Nice to be able to put that on Credit, Pay for the GPM's, and not have to worry about it)

[Captkaos]

Lifting or lowering the truck doesn't affect the power, only the handling...

[d stroud]

d stroud, i LOVE your "Family Muscle Site".  ya'll do some gorgeous work...

Thanks!

[SUX2BU99]

It could affect how the power is being put to the ground though. Stock height, your suspension could be putting more leverage and weight transfer on the tires when the truck is pushed forward, improving traction. With the lowering, center of gravity is affected and so is suspension compliance and weight transfer so now there is less traction or energy absorption into the suspension. It now goes directly to the tires, which break them loose easier.

My brother bought a stock, low-mileage 84 Z28 back in 1989 with the 165 HP 305, 700R4 trans and 3.23 gears. As far as we knew, it had a stock tranny but I've never felt a stock tranny shift so hard. It would bark 2nd all the time. And then the torque arm bushing wore out and the 1-2 shift felt like someone was kicking as hard as they could under the center console with a steel toe boot   lol

[Stewart G Griffin]

The other thing is that i suspect what happened was the pinion angle of the rear diff may have changed in relation to the frame and driveshaft when you lowered it. Similar to what SUX pointed out. i'll try to dig up some articles about pinion angle, but it does affect traction.

 
Like Dragon, i'm anti-raising/lowering a truck.  i will, however, admit that lowering helps mpg, while raising is nessesary for serious off-roading.  And, if you really like it, then more power to you.

[Stewart G Griffin]

Actually i see that there is a whole other post on pinion angles in this section which i briefly had a chance to skim over.

Here are some interesting articles i found on web.  i don't have time to read them right now as i may be out-of-town the next few days.  One of them asserts that pinion angle has nothing to do with traction.

http://www.carcraft.com/howto/91758/index.html

http://buickperformance.com/Pinion.htm

http://www.2quicknovas.com/happypinions.html

[HAULIN IT]

I have posted my opinion on the pinion angle deal in the other post. My take on it is this: The pinion angle itself can't, doesn't & won't have an effect on traction. Here is where things get a little gray. Methods of moving the pinion angle at the rear suspension change other things (as mentioned in the link that Stewart posted)  & that can & will effect traction. Look at it this way, If you raise or lower the transmission tailshaft 1", you have drasticly changed the angles or if you built a rearend with flanges inboard on the axle tubes & matching ones on the center section (so you could "clock" the pinion angle) with holes to move the center, say 5* increments. You have moved the pinion angle in either case, but traction will be the same, the "wrap-up" of the suspension hasn't changed,instant center,squat,lift, ect. have not changed. Now when you shim, pre-load, adjust upper arms, lower arms, ect. This also changes the pinion angle as measured on the angle finder, but you obtained that by moving suspension parts that can & will effect traction. Can everyone relate? Lorne     

[Stewart G Griffin]

Yes, and there was a pretty heated debate also on who is "professor automotive."  i'm just glad that they both have lots of knowledge...........

i was reading somewhere that pinion angle can affect traction in that depending on the angle, it could help "press" the tire(s) onto the pavement.  i think stock and superstock drag racers really know about this. i will try to locate the article.

Also, i think i may have seen somewhere, possibly in a salvage yard, but the exact place and time escapes me, a Mack truck with one or both of the rears with pinions pointing straight up!  i thought this was pretty bizarre and wondered what was the rationale behind the engineering.  If time permits, i may try to further research this.

 

[eventhorizon66]

SUX2BU99 hit the nail on the head.  Lowering the truck simply reduced traction a bit, giving the illusion of more power.  But hey if it makes the truck "feel" faster and you aren't serious about racing it, then it was a positive change, just don't get to silly in the rain.