rear jumps down on drive (auto)

[jon79flavette]

I am not that familiar with the the feel of the car, because it was not running when I got it. Just put everything in, and when you put her in drive.... it feels like the rear litterly drops a few inches. (prepare for take-off ha-ha) Maybe not that severe but it sure feels like it!! I have replaced motor and trans mounts with performance suspension poly mounts, I am running (on meter) an idle of 830 rpm, I don't think that is that high, that was my first thought. The A-C is not installed yet. The TH 350 has been totally rebuilt, it has a 2 stage Transgo shift kit, fluids are fine, and the coil spring and shocks are new, . is this normal??

 

[Robin7TFour]

jon, sounds similar to what my 74 does. i am curious to hear some other's opinions on this.

robin

 

[Fishman]

My last 2 C3s did the same. It's normal.

 

[78SilvAnniv]

Relax, this is normal.

Think of it as a tiger preparing to pounce!

When you engage the transmission and put the drivetrain under load, the power traveling from the tranny, through the driveline, the rear end and into the half-shafts...they are preparing for forward power/momentum.
When they 'engage' they cause tension in the moving pieces. This makes the half shafts roll forward with the torque/power applied to them and that causes the rear of the C3 to 'squat'.
Heidi

Did I explain it okay?

 

[clar2001]

830rpm is a little hi 600 is norm for a auto, I have bran new suspension & my 75 does the smae thing some of it is the play in the rear its pretty warn.

 

[JrdnsEdu]

Jon- if you don't mind me asking, approx how much should I expect to be shelling out to get my tranny rebuilt? I have a '69 that keeps slipping out of 2nd and kinda getting sick of driving it that way.

 

[jon79flavette]

heidi: yes your explanation was perfect/and therefore makes perfect sense This is my first vette, I gotta tell you, I (feel) like I have replaced everything, It just feels weird, when you are sitting low. You engage and it drops you lower, I feel that I have some real torque, with my set-up, but it is just gonna take some gettin used to, Clar, as much as I have replaced, you forget the basics, I do need to do the rear end gear oil, any suggestions on simplifing, and or addatives that have helped??

 

[clar2001]

Gear oil & a additave may help with noise or your clutch packs but will not affect the car sitting lower ,

 

[jon79flavette]

jrdns:

I paid $400.00, but it's kinda funny, I was hell bent on a 700 r-4/ 4 speed tranny. The local guy here could not have been more honest, I WANTED to spend more money (not really, but thats what I kept pushin for) but this guy does alot of work for the local Moroso track here in fla. He says you are crazy if you want durability and horsepower to get rid of a 350/400 TH tranny, If you are gonna (DRIVE/RUN) the car.

if you want mileage, and take road trips, then (maybe) go with the retrofit 4 speed, depending on rear , torque-stall converter etc. whitch is what I wanted, but did not need.

Anyhow, I brought him my TH350 cause the motor was out, $400.00 total rebuild, with stage -2 transgo shift kit, hardened sprage, trans steam bath, all new seals, etc, the guy was great, and so is the trans. :cool

 

[bossvette]

jon79flavette
If you are talking about the same engine you posted in the "stroke or not"thread, Just wait till you get it broken in and romp on it and see how much it "squats" :L :L
I idle mine at 850 (with a stick) it smoothes it out a little, if you like a ragged, loppy idle then slow it down some . If you are running an auto you want it low enough so it doesn't creep (you are running a higher then stock stall converter I hope 2200-2500)
Craig sr

 

[jon79flavette]

Clar: Yeah, I did not think read gear oil change would do anything for that, Just got to thinking, I "almost" know it has not been changed since 79, so it would make sense to to so, You replace all the hard stuff, might as well feed them with fresh juices, right,

 

[jon79flavette]

gosh, My fianceee' (how the hell do you spell that word/she always insists I use that termonology for some reason) in georgia, so here I am, and lovin it talkin motor talk cause she always tunes me out----------on a sat. night, god, I love gettin older.

new 2800 TCI stall converter (did not want to get to higher than that) motor is more torque, with an actual lift of 517 with 1.6 rockers. don't plan on going over 70 mph, except for moroso "test & tune runs" still gotta alot to learn with this corvette, but the motor is dialed-in for the most part.

 

[bossvette]

jon
when you get it broken in how about checking your gas milage, you are a little "wilder" then I am but not much I get 10-11 around town (heavy foot) and 15 on the turnpike and was wondering if it was silular to anyone elses?
Craig sr

 

[crause]

I get 18 mpg. highway on my 75 w/auto trans. Have original motor with original trans. 40k on vehicle. As far as the squat down when you put the car in gear, mine does the same thing. It was a little strange at first but I am use to it now.

Andy

 

[Scooter76]

Any car with an independent rear suspension is going to "squat " when dropped into gear or under hard acceleratin. The differintial housing is actually solidly attached to the frame. (unlike a conventional solid axle car). When power is applied, the housing tries to roll over a bit. Since it is attached to the frame it applies this movement to the frame also, resulting in a downward squat in foreward gears & an upward movement in reverse.

 

[jon79flavette]

yes, I realize that, it just seemed excessive. Everyone here says it's OK, so I', OK with that


As I said, this is my first vette, just a chacteristic of the car, I guess, Thanks

 

[aharte]

Mine used to do this. Idle was around 800-900 rpm with an auto. I changed the idle to 600 rpm, and there's no more squat. A little lopey though. I have a 3000 rpm stall too if that's significant.

 

[82ColEd]

Mine runs between 800-900, and when i put it in gear (Auto), it drops the back down. Kinda like it, like Heidi said: Tiger on a pounce.. Though the lower the idle/rpm is set the less it drops you, at some point someone had set it to 1200 and i thought i'd crack the exhaust pipes.. Nice Car, btw !

 

[Fishman]

With the pic now posted, it looks as if the car has been raised up a bit. Coils/shocks indicated changed, but what about the rear spring? With the apparent increase in ride height, I'd guess so.

And... they always appear to look a bit taller without the spare tire underneath. Opinion: put the carrier back on. But... it's your car and it's BEAUTIFUL!!! Nice work.

 

[78SilvAnniv]

Re: Nice pic...

With the pic now posted, it looks as if the car has been raised up a bit.

It does look like it sits high. Could it be that the tires are too small? They don't look tall enough.
Beautiful vette!
Heidi