Something holding back acceleration
Thread Starter
Instructor
Joined: Jan 2006
Posts: 153
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Something holding back acceleration
Hey guys, Ive been experiencing an issue for a while now where it seems as though something is holding back acceleration on my 78. As best as I can describe it, it feels like Im towing something when driving around. When accelerating the car feels very heavy and the second you let off the gas its almost as though the brakes were being applied (it slows down very quickly).
To give some background of possibly related factors and rule out others here are some things to consider:
1-diff whines due to a bit of gear lash after having upgraded to 3.73 some years ago
2-all filters are new
3-all hoses are new
4-pressure builds up in gas tank with new vented cap installed
5-running sanden a/c compressor (issue persists whether or not a/c is on-someone told me these compressors add more load to the accessory drive)
6-tranny is fresh rebuilt 200-4r
7-no brake components are sticking
Has anyone else experience something like this in their vette?
Engine has stage 1 cam, edelbrock intake, holley carb, headers, aftermarket heads, hei distributer, new spark plugs and wires
To give some background of possibly related factors and rule out others here are some things to consider:
1-diff whines due to a bit of gear lash after having upgraded to 3.73 some years ago
2-all filters are new
3-all hoses are new
4-pressure builds up in gas tank with new vented cap installed
5-running sanden a/c compressor (issue persists whether or not a/c is on-someone told me these compressors add more load to the accessory drive)
6-tranny is fresh rebuilt 200-4r
7-no brake components are sticking
Has anyone else experience something like this in their vette?
Engine has stage 1 cam, edelbrock intake, holley carb, headers, aftermarket heads, hei distributer, new spark plugs and wires
Last edited by jsera; Sep 26, 2014 at 11:31 AM.
Thread Starter
Instructor
Joined: Jan 2006
Posts: 153
Likes: 4
It definitely shifts properly, i couldnt tell you specifically rpms because im away from home for college (hoping to do some tinkering next chance i get to go home), but its been through a couple of different tranny shops and all agree that its properly adjusted
Race Director
Joined: May 2006
Posts: 18,729
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you have felt the brake calipers after a short drive and no excessive heat? still curious about those RPM numbers, cannt guess at any of them?
You should have a non-vented cap, and if you have pressure build up I would look at the charcoal EVAP canister and it's associated hoses.
You should have a non-vented cap, and if you have pressure build up I would look at the charcoal EVAP canister and it's associated hoses.
Thread Starter
Instructor
Joined: Jan 2006
Posts: 153
Likes: 4
Brakes are all good visually, there is clearance between rotors and pads and temp gun measurements check out on all four corners.
I could tell you that at 80 its in the neighborhood of 3000 and around town it generally stays under 2k but i couldnt recall with any certainty rpms for other speeds
I could tell you that at 80 its in the neighborhood of 3000 and around town it generally stays under 2k but i couldnt recall with any certainty rpms for other speeds
Race Director
Joined: May 2006
Posts: 18,729
Likes: 2,579
not that it's related to your issue but at 3,000 rpm with a 3.73 rear and 27" diameter tires you would be doing about 65 mph. When you changed the rear end ratio did you change the driven gear in the transmission?
Thread Starter
Instructor
Joined: Jan 2006
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I don't recall but do remember that its an overdrive trans with a lock up converter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
200R4 has .67 overdrive so locked up in 4th gear engine RPM would be 2000 at 65 MPH with 3.70 diff ratio.
You say there is clearance between the brake pads and the discs, if your brakes are standard the pads should be just touching the disc surface at all times.
Try getting up to say 40mph on a clear flat road, shift into neutral and see if the car will coast freely or drags to a stop quickly.
Park brake dragging? - unlikely as you would most likely have toasted it by now if it was
Just throwing ideas out there!
You say there is clearance between the brake pads and the discs, if your brakes are standard the pads should be just touching the disc surface at all times.
Try getting up to say 40mph on a clear flat road, shift into neutral and see if the car will coast freely or drags to a stop quickly.
Park brake dragging? - unlikely as you would most likely have toasted it by now if it was
Just throwing ideas out there!
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Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
200R4 has .67 overdrive so locked up in 4th gear engine RPM would be 2000 at 65 MPH with 3.70 diff ratio.
You say there is clearance between the brake pads and the discs, if your brakes are standard the pads should be just touching the disc surface at all times.
Try getting up to say 40mph on a clear flat road, shift into neutral and see if the car will coast freely or drags to a stop quickly.
Park brake dragging? - unlikely as you would most likely have toasted it by now if it was
Just throwing ideas out there!
You say there is clearance between the brake pads and the discs, if your brakes are standard the pads should be just touching the disc surface at all times.
Try getting up to say 40mph on a clear flat road, shift into neutral and see if the car will coast freely or drags to a stop quickly.
Park brake dragging? - unlikely as you would most likely have toasted it by now if it was
Just throwing ideas out there!
Thread Starter
Instructor
Joined: Jan 2006
Posts: 153
Likes: 4
to address some of the suspects:
Catalytics: they dont exist (hush hush)
Rear end: gear lash is bad it howls at certain rpms (reverting back to oe gears as current are likely beyond salvation
parking brake: though i havent inspected it myself, a vette specialty shop did me the favor of adjusting it since it was previously completely defunct
wheel bearings: fresh grease on new bearings
timing: no idea
Catalytics: they dont exist (hush hush)
Rear end: gear lash is bad it howls at certain rpms (reverting back to oe gears as current are likely beyond salvation
parking brake: though i havent inspected it myself, a vette specialty shop did me the favor of adjusting it since it was previously completely defunct
wheel bearings: fresh grease on new bearings
timing: no idea
Thread Starter
Instructor
Joined: Jan 2006
Posts: 153
Likes: 4
