Raising the Rear Differential up 1" ? Or More? From Chevy Power
01-01-2005, 12:02 AM
#1
Drifting
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St. Jude Donor '05
Raising the Rear Differential up 1" ? Or More? From Chevy Power
Raising the Rear Differential up 1" ? Or More? From the Chevy Power, C-3 Corvette Frame/Chassis section.
I was talking to my friend that builds stock car chassis today. He is going to weld and box my frame and gusset everything that can be. He will fab a new transmission cross member for the TKO and the rear six link upper mount cross member for me this spring.
I was telling him about the idea of raising the rear end up in the frame an inch from the Chevy Power Book. Has anyone done this? Is it something that will assist with the re-alignment of the rear components from the lowering of the cars rear suspension ?
It's easy to raise the '80 differential mount up in the frame. I would then add a 1" spacer in front to level it.
I was reading a post here about using longer bolts to lower the rear ride height, but is it a good way to lower without changing the position of the rear differential to regain proper joint relationships? The raising of the mount will raise the spring position instead of just using spring compression to alter the ride height.
I have located a shop close by to powder coat the frame after we get all of the preparations completed.
I am also planning on re-positioning the gas tank to where the spare tire was located using a fuel cell to lower the CG.
Am I on the right track? Comments? jim
I was talking to my friend that builds stock car chassis today. He is going to weld and box my frame and gusset everything that can be. He will fab a new transmission cross member for the TKO and the rear six link upper mount cross member for me this spring.
I was telling him about the idea of raising the rear end up in the frame an inch from the Chevy Power Book. Has anyone done this? Is it something that will assist with the re-alignment of the rear components from the lowering of the cars rear suspension ?
It's easy to raise the '80 differential mount up in the frame. I would then add a 1" spacer in front to level it.
I was reading a post here about using longer bolts to lower the rear ride height, but is it a good way to lower without changing the position of the rear differential to regain proper joint relationships? The raising of the mount will raise the spring position instead of just using spring compression to alter the ride height.
I have located a shop close by to powder coat the frame after we get all of the preparations completed.
I am also planning on re-positioning the gas tank to where the spare tire was located using a fuel cell to lower the CG.
Am I on the right track? Comments? jim
01-01-2005, 01:19 AM
#3
Drifting
Moving the differential in relation to the frame would decrease upward wheel travel (joust) and make the suspension bottom out sooner. Of course lowering the suspension in any fassion will do the same.
I think lowering is very over rated and really not necessary. But that's just me.
BigBlockk
Later.....
I think lowering is very over rated and really not necessary. But that's just me.
BigBlockk
Later.....
01-01-2005, 04:35 AM
#4
Melting Slicks
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I've got a tubular crossmember in the rear and the highest part of my differential is half an inch from the fiberglass. The front mount is bolted in with no bushings/shims flat to the frame mount. A washer was welded in the large frame hole to give it the right offset. Pinion angle is ~2 degrees. Half shafts sit about parallel with the ground with the coilovers.
01-01-2005, 06:58 AM
#5
Originally Posted by PROSOUTH
Raising the Rear Differential up 1" ? Or More? From the Chevy Power, C-3 Corvette Frame/Chassis section.
I was talking to my friend that builds stock car chassis today. He is going to weld and box my frame and gusset everything that can be. He will fab a new transmission cross member for the TKO and the rear six link upper mount cross member for me this spring.
I was telling him about the idea of raising the rear end up in the frame an inch from the Chevy Power Book. Has anyone done this? Is it something that will assist with the re-alignment of the rear components from the lowering of the cars rear suspension ?
It's easy to raise the '80 differential mount up in the frame. I would then add a 1" spacer in front to level it.
I was reading a post here about using longer bolts to lower the rear ride height, but is it a good way to lower without changing the position of the rear differential to regain proper joint relationships? The raising of the mount will raise the spring position instead of just using spring compression to alter the ride height.
I have located a shop close by to powder coat the frame after we get all of the preparations completed.
I am also planning on re-positioning the gas tank to where the spare tire was located using a fuel cell to lower the CG.
Am I on the right track? Comments? jim
I was talking to my friend that builds stock car chassis today. He is going to weld and box my frame and gusset everything that can be. He will fab a new transmission cross member for the TKO and the rear six link upper mount cross member for me this spring.
I was telling him about the idea of raising the rear end up in the frame an inch from the Chevy Power Book. Has anyone done this? Is it something that will assist with the re-alignment of the rear components from the lowering of the cars rear suspension ?
It's easy to raise the '80 differential mount up in the frame. I would then add a 1" spacer in front to level it.
I was reading a post here about using longer bolts to lower the rear ride height, but is it a good way to lower without changing the position of the rear differential to regain proper joint relationships? The raising of the mount will raise the spring position instead of just using spring compression to alter the ride height.
I have located a shop close by to powder coat the frame after we get all of the preparations completed.
I am also planning on re-positioning the gas tank to where the spare tire was located using a fuel cell to lower the CG.
Am I on the right track? Comments? jim
01-01-2005, 08:48 AM
#6
Melting Slicks
This what John Greenwood has to say in a series of articles,Vette Improvement Program, he did for Corvette Fever back in 1985.
"...take the rubber biscuits out of the differential crossmember and raise the rear crossmember up into the frame 3/4". This does not change the geometry but lowers the CG back to it's proper point and mounts the differential solid - a performance change."
Is this the method that the Chevy Power Manual recommends? By the way, where can you purchase the manual? I have been wanting one for quite some time.
"...take the rubber biscuits out of the differential crossmember and raise the rear crossmember up into the frame 3/4". This does not change the geometry but lowers the CG back to it's proper point and mounts the differential solid - a performance change."
Is this the method that the Chevy Power Manual recommends? By the way, where can you purchase the manual? I have been wanting one for quite some time.
01-01-2005, 10:30 AM
#7
Drifting
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Location: Manchester, Dead Center in the Middle of TN 25 miles to Jack Daniels,10 miles to Geo Dickle, and .8 mile from the Liquor Store at I-24 Exit 114
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St. Jude Donor '05
This is from the old 5th Edition Chevy Power Manual 1984 that I bought 20 years ago. It's still good book. I believe this chapter is also posted at over at Corvette FAQ.
1984 Chevy Power;This is not the complete section, but relevant information to topic.
From the frame section,
The rear suspension differential mounting crossmember should have the rubber mounts removed and replaced with steel plates.There is some freedom to adjust the height of the carrier further up into the frame. If this is done the corresponding adjustment should be made in the front differential case attachment.
From the rear suspension section,
The differential mount crossmember may also be replaced by a fabricated tube to raise the differential approximately 1 inch higher. The rear frame rails must be also trimmed to raise the bump travel and the shock absorber brackets are relocated upward 1 inch.
The rear differential carrier mounting crossbar rework was discussed in the frame preparation section (above) The rubber differential mounting insulators should be replaced by solid steel plates. The pinion nose front bushing should be also replaced by a solid metal bushing, preferably an aluminum block. care should be given to maintain the correct differential case attitude. If the plates have been moved up in the crossmember, this should be duplicated by adjusting the height of the aluminum block the same amount.
The use of longer spring bolts allows the adjustment of weight from side to side to equalize corner loads. Trim the rear jounce bumpers to approx. .60" thickness which provides maximum suspension travel while preventing the universal joints from bottoming out during full bump. The production jounce bumpers may be completely removed if the shock absorbers are equipped with rubber bumpers.
If the Axel has been moved up in the frame, it may be possible to remove the jounce bumpers entirely. Before this is done, a static check should be made in full jounce position to determine if the universal joints are grounding out. Rebound control should also be checked to make sure universal joints do not ground out in full rebound.
Production rebound control is maintained by shock absorber length. If replacement shock absorbers are used, a check should be made at full rebound to assure universal joints are not grounding out. If the shock cannot do this, a strap or cable should be provided between the control arm and the frame to prevent excessive rebound travel.
The production type rear stabilizer bar is satisfactory if the links from the control arm to the stabilizer bar are replaced with are replaced with rod end joints and threaded shafts to allow adjustment. When installing the bar make sure the linkage is such that the stabilizer bar will not travel to an "over center" condition in full rebound. It may be necessary to lower the axis of the bar to prevent this.
The F-41 rear spring and the recommended 1 1/8" front bar should be used with a 3/4" rear bar.
======================================== ==========
So if I want to lower my center of gravity it looks like it would be best to raise the mounting of the rear differential up an inch to allow me to maintain drive-line relationships in the u-joints etc without just pulling down on the rear to obtain a height setting. jim
1984 Chevy Power;This is not the complete section, but relevant information to topic.
From the frame section,
The rear suspension differential mounting crossmember should have the rubber mounts removed and replaced with steel plates.There is some freedom to adjust the height of the carrier further up into the frame. If this is done the corresponding adjustment should be made in the front differential case attachment.
From the rear suspension section,
The differential mount crossmember may also be replaced by a fabricated tube to raise the differential approximately 1 inch higher. The rear frame rails must be also trimmed to raise the bump travel and the shock absorber brackets are relocated upward 1 inch.
The rear differential carrier mounting crossbar rework was discussed in the frame preparation section (above) The rubber differential mounting insulators should be replaced by solid steel plates. The pinion nose front bushing should be also replaced by a solid metal bushing, preferably an aluminum block. care should be given to maintain the correct differential case attitude. If the plates have been moved up in the crossmember, this should be duplicated by adjusting the height of the aluminum block the same amount.
The use of longer spring bolts allows the adjustment of weight from side to side to equalize corner loads. Trim the rear jounce bumpers to approx. .60" thickness which provides maximum suspension travel while preventing the universal joints from bottoming out during full bump. The production jounce bumpers may be completely removed if the shock absorbers are equipped with rubber bumpers.
If the Axel has been moved up in the frame, it may be possible to remove the jounce bumpers entirely. Before this is done, a static check should be made in full jounce position to determine if the universal joints are grounding out. Rebound control should also be checked to make sure universal joints do not ground out in full rebound.
Production rebound control is maintained by shock absorber length. If replacement shock absorbers are used, a check should be made at full rebound to assure universal joints are not grounding out. If the shock cannot do this, a strap or cable should be provided between the control arm and the frame to prevent excessive rebound travel.
The production type rear stabilizer bar is satisfactory if the links from the control arm to the stabilizer bar are replaced with are replaced with rod end joints and threaded shafts to allow adjustment. When installing the bar make sure the linkage is such that the stabilizer bar will not travel to an "over center" condition in full rebound. It may be necessary to lower the axis of the bar to prevent this.
The F-41 rear spring and the recommended 1 1/8" front bar should be used with a 3/4" rear bar.
======================================== ==========
So if I want to lower my center of gravity it looks like it would be best to raise the mounting of the rear differential up an inch to allow me to maintain drive-line relationships in the u-joints etc without just pulling down on the rear to obtain a height setting. jim
01-01-2005, 01:45 PM
#8
Race Director
did you miss the part about these mods being for use in SCCA competition?? If you are moving the crossmember up you might have your guy relocate the top shock mount to the inside of the frame.....
...redvetracr
...redvetracr
01-01-2005, 06:57 PM
#9
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I wonder how much travel you take out of the suspension doing this...
My brain is making me think that cutting an inch out or the 4-5 that we have could be bad for bumps...
My brain is making me think that cutting an inch out or the 4-5 that we have could be bad for bumps...
01-01-2005, 07:14 PM
#10
Drifting
Thread Starter
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Location: Manchester, Dead Center in the Middle of TN 25 miles to Jack Daniels,10 miles to Geo Dickle, and .8 mile from the Liquor Store at I-24 Exit 114
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St. Jude Donor '05
Originally Posted by redvetracr
did you miss the part about these mods being for use in SCCA competition?? If you are moving the crossmember up you might have your guy relocate the top shock mount to the inside of the frame.......redvetracr
I will look at the shock mounts and yes I indicated that the mounts must move up 1" also. I will look at them further.
The original question was will this allow a lowered cars rear differential to regain proper joint relationships from lowering? The raising of the mount will raise the spring position instead of just using spring compression to alter the ride height. The spring will not be under constant stress and should provide smoother operation. It should also give better u-joint differential relationships. Thanks for your reply. jim
02-28-2018, 10:22 PM
#12
Team Owner
Yes I have done this on two cars. First since this is C3, make sure if your car does not have rubber body mount bushings and if so, replace those. If it has the aluminum pucks, as long as they aren't deteriorated, it should be good.
If you are running 1330 U-joints on the stock driveshaft, you may or may not be OK on clearance. If you go 1350, then you will probably have to clearance some of the tunnel and body where the driveshaft passes thru.
Just removing the rubber donuts and the sleeve and tabs etc. and then flushing it to the crossmember, and then just a simple weld on the outside, is pretty sufficient. If the welds are done right, the diff won't be moving anymore.
You do lose your shock or drivetrain isolation and cushioning. The front puck on the diff, turns into basically a spacer only to take up the distance, as the diff is now solid.
On the suspension, move it up first and then make adjustments to level the halfshafts, and align the car to this height mod that essentially lowers the car. YOu should have long spring bolts, just to help you get to proper geometry! This also helps doing about 1 inch less adjustment on the spring bolts.
If you are retaining stock shocks or softer springs, and stock rear sway bar links and stuff, not adviced, as this is a pure race car mod, and I have done it for my Canyon Racing. My suspension by design is limited in travel.
You also need to gauge where your tires and rims in regards to fender clearance will be.
Essentially this is a very easy mod physically, but serious other things come into play that don't make this an amateur mod.
If you are running 1330 U-joints on the stock driveshaft, you may or may not be OK on clearance. If you go 1350, then you will probably have to clearance some of the tunnel and body where the driveshaft passes thru.
Just removing the rubber donuts and the sleeve and tabs etc. and then flushing it to the crossmember, and then just a simple weld on the outside, is pretty sufficient. If the welds are done right, the diff won't be moving anymore.
You do lose your shock or drivetrain isolation and cushioning. The front puck on the diff, turns into basically a spacer only to take up the distance, as the diff is now solid.
On the suspension, move it up first and then make adjustments to level the halfshafts, and align the car to this height mod that essentially lowers the car. YOu should have long spring bolts, just to help you get to proper geometry! This also helps doing about 1 inch less adjustment on the spring bolts.
If you are retaining stock shocks or softer springs, and stock rear sway bar links and stuff, not adviced, as this is a pure race car mod, and I have done it for my Canyon Racing. My suspension by design is limited in travel.
You also need to gauge where your tires and rims in regards to fender clearance will be.
Essentially this is a very easy mod physically, but serious other things come into play that don't make this an amateur mod.
Last edited by TCracingCA; 02-28-2018 at 10:27 PM.
03-01-2018, 01:27 PM
#13
Melting Slicks
I raised the differential in my car when I did the frame off. Wasn't a big deal to do at all. I used the Greenwood/Powerbook method referenced in an earlier post. I also raised the shock mount location.
Mike
Mike
03-01-2018, 02:40 PM
#14
Burning Brakes
I also raised mine using the powerbook method when I had the body off and have seen no ill effects.
In addition, my rear has been converted to the VanSteel Coil Overs, which use the original shock mount location.
Been fine. No additional vibration from the diff being solid mounted that I can tell.
In addition, my rear has been converted to the VanSteel Coil Overs, which use the original shock mount location.
Been fine. No additional vibration from the diff being solid mounted that I can tell.
03-01-2018, 06:58 PM
#15
Does anyone got pics of their install?
How do you properly center the crossmember with the rubbers out? Then weld it direcly to the frame? Or put a plate on the top and bottom?
Seen they used to make alloy spacers, but not aviable anymore.
How do you properly center the crossmember with the rubbers out? Then weld it direcly to the frame? Or put a plate on the top and bottom?
Seen they used to make alloy spacers, but not aviable anymore.
03-02-2018, 12:10 PM
#16
Team Owner
Measure twice, or thrice! Before welding! But if you make a mistake, it can simple be cut back apart! Centering and squaring should be easy! Actually my eyeballs are so calibrated, I could actually center the bolt holes in the center of where the donuts used to be!
And Vette Brakes still had the donuts to buy, if you are shying away from the idea! But aluminum circles or even squares, octagons, hexagons or anything shape of aluminum could be cut-out and a center hole drilled! So easy, no one should come to a screeching halt if discs are no longer available! Heck, maybe I will one up all of you, and cut out fancy stars and bolt them up!
The hardest part is getting those old donuts out! Next is the metal sleeve! Actually I skimmed the tops flush with a cutting wheel and grinder, welded in sold the remainder and flushed crossmember up and welded! I then put the aluminum donuts on for show only, as camouflage just so other racers would think that was all I had done (not noticing the welding or raised Diff support)!
PS I retired from going out to the garage and jacking up extremely low ground clearance cars or crawling under cars for pictures and dealing with the extreme difficulties of modern picture uploading! A few times I have done that, those pictures still linger here on the forum! This type of mod is so basic!!!!, pictures aren't needed!
The aluminum discs are just a fancy way of saving 2 or 3 pounds! You could cut out steel circles, bolt those up and weld the steel to the crossmember. But you could still have bolt flex!
Last edited by TCracingCA; 03-02-2018 at 12:28 PM.
