- Moderator
- #61
- Joined
- Nov 9, 2000
- Messages
- 7,501
- Location
- Edgerton, Ohio, United States
- Corvette
- 1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Good idea but it's too pretty to hide.
Tom
Tom
Tell me it is a good thing to have gray metal fake in your rear end oil
- Thread starter jackfit
- Start date
- Thread starter
- #62
jackfit
Well-known member
Posi Unit Update Ring bolts
We are reworking a 78 Corvette Rear from 3:70 to 3:36 , plus tuning it.
Gary is doing the rebuild and here is a quote from him on bolts that attach the Ring gear.
"Here I countersunk the posi case ring gear holes. You see in picture#1 that the holes are square edged and the stock bolts work with that but not the ARP's. The ARP's have a larger radius under the head for more strength and have the shoulder on them like the old GM bolts did. Somewhere around 1977 they changed to the bolts that were in here before, shorter, no shoulder, and not loctited in place. Not good, many backed out in use sometimes within the factory warranty period. QC with the late 70's vettes wasn't as good as the earlier cars but that is probably the case with most lines of the period."
Stock bolts vs ARP's Stock on right
Before milling notice flat surface
Counter sink
Cut
Polish
Perfect fit
We are reworking a 78 Corvette Rear from 3:70 to 3:36 , plus tuning it.
Gary is doing the rebuild and here is a quote from him on bolts that attach the Ring gear.
"Here I countersunk the posi case ring gear holes. You see in picture#1 that the holes are square edged and the stock bolts work with that but not the ARP's. The ARP's have a larger radius under the head for more strength and have the shoulder on them like the old GM bolts did. Somewhere around 1977 they changed to the bolts that were in here before, shorter, no shoulder, and not loctited in place. Not good, many backed out in use sometimes within the factory warranty period. QC with the late 70's vettes wasn't as good as the earlier cars but that is probably the case with most lines of the period."
Stock bolts vs ARP's Stock on right
Before milling notice flat surface
Counter sink
Cut
Polish
Perfect fit
- Thread starter
- #63
jackfit
Well-known member
Posi Unit Update assembly of Unit
Gary is now assembling the posi unit after polishing.
Here is his commentary on the process.
Here I radiused the spider teeth to prepare to tune them. I used new solid steel clutches, new cross shaft, retainers, and washers. Next up the tuning process starts. Unlike a stock posi, where the spider lash is set between 002-008" and then the plates and springs are stuffed in there, I will set the posi up to a balanced, much more precise unit then any stock or rebuilt vette posi. where it is now I could just use the springs but it really works better to put the time and machine work in to tune them.
Pictures Parts laid out
Cross shaft and steel clutches
Radius Spider Teeth
Ready to Tune
Next series will be the tuning
Jack
Gary is now assembling the posi unit after polishing.
Here is his commentary on the process.
Here I radiused the spider teeth to prepare to tune them. I used new solid steel clutches, new cross shaft, retainers, and washers. Next up the tuning process starts. Unlike a stock posi, where the spider lash is set between 002-008" and then the plates and springs are stuffed in there, I will set the posi up to a balanced, much more precise unit then any stock or rebuilt vette posi. where it is now I could just use the springs but it really works better to put the time and machine work in to tune them.
Pictures Parts laid out
Cross shaft and steel clutches
Radius Spider Teeth
Ready to Tune
Next series will be the tuning
Jack
- Thread starter
- #64
jackfit
Well-known member
Tuning the Posi Unit
Gary is now ready to tune the posi unit. Here is his explanation of the process.
"Here I started to tune the posi. While some think you just remove the springs and plates and bolt it together, there is much more to it. The process requires running in the new clutches to "seat" them. This will change the lash after about 50 rev's but I go at least 300 per side, CW & CCW. Then check it on the bench fixture and re-shim. The shims come in 005 increments so I grind them to within 001" to dial in the tune. The end result is a balance setup between both the Left & Right sides. The naysayers will tell you it will not work, yet Tom's has been building them like this for over 40 years for street, strip, and road race cars. You will have full posi action yet there won't be any hammering in the corners and there is less load on the clutches. All my vettes are setup like this and work great."
Video of process
Just click on picture for video
Gary is now ready to tune the posi unit. Here is his explanation of the process.
"Here I started to tune the posi. While some think you just remove the springs and plates and bolt it together, there is much more to it. The process requires running in the new clutches to "seat" them. This will change the lash after about 50 rev's but I go at least 300 per side, CW & CCW. Then check it on the bench fixture and re-shim. The shims come in 005 increments so I grind them to within 001" to dial in the tune. The end result is a balance setup between both the Left & Right sides. The naysayers will tell you it will not work, yet Tom's has been building them like this for over 40 years for street, strip, and road race cars. You will have full posi action yet there won't be any hammering in the corners and there is less load on the clutches. All my vettes are setup like this and work great."
Video of process
Just click on picture for video
- Thread starter
- #65
jackfit
Well-known member
Preparing the Case
Continuing the rebuild, we are now preparing the case . It must be cleaned both inside and out. Here are comments from Gary on this procedure.
"Here I worked on the housing, cover and pinion yoke. I finished blasting them to bare iron. Now most places will just shoot a cheap top coat of paint and call it done. I never liked that since once the car is in use that paint isn't going to last as long as it should. So I blast the parts to bare iron. Then Etch them for 30 minutes, rinse, blow dry, flame dry, cool, POR15 and then when just right shoot the top coat to mix with the POR15 and harden together. I'm waiting for the POR15 to setup now to shoot the top coat. Then I'm going home to fire up my 72 vette for a weekend ride!
"
Blasting first
Etching
Flame Dry
POR 15 Base coat
Final Coat
Interior Case Prep Next
Continuing the rebuild, we are now preparing the case . It must be cleaned both inside and out. Here are comments from Gary on this procedure.
"Here I worked on the housing, cover and pinion yoke. I finished blasting them to bare iron. Now most places will just shoot a cheap top coat of paint and call it done. I never liked that since once the car is in use that paint isn't going to last as long as it should. So I blast the parts to bare iron. Then Etch them for 30 minutes, rinse, blow dry, flame dry, cool, POR15 and then when just right shoot the top coat to mix with the POR15 and harden together. I'm waiting for the POR15 to setup now to shoot the top coat. Then I'm going home to fire up my 72 vette for a weekend ride!
"
Blasting first
Etching
Flame Dry
POR 15 Base coat
Final Coat
Interior Case Prep Next
- Thread starter
- #66
jackfit
Well-known member
Installing the 3:36 Gears
We are now installing the gears after countersinking bolt holes and using new bolts. Gary's comments:
"Once I had the posi were I wanted it, I stoned the back of the new USA 336 ring gear and the posi flange. Then I cleaned the new ARP's in Acetone, same with the RG holes. I use alignment studs to keep the ring gear in place since it is a press fit on the case OD. I use #271 red on the ARP bolts, torque them and then check for full seating of the bolt and the ring gear. I'll let the Loctite set up at least 24 hours before applying any load to them."
Clean Bolts in Acetone
Tom's US Gear 3:36 to replace 3:70
Stone surfaces
Alignment Bolts
Torque Bolts
Check Fit
All Set Up
We are now installing the gears after countersinking bolt holes and using new bolts. Gary's comments:
"Once I had the posi were I wanted it, I stoned the back of the new USA 336 ring gear and the posi flange. Then I cleaned the new ARP's in Acetone, same with the RG holes. I use alignment studs to keep the ring gear in place since it is a press fit on the case OD. I use #271 red on the ARP bolts, torque them and then check for full seating of the bolt and the ring gear. I'll let the Loctite set up at least 24 hours before applying any load to them."
Clean Bolts in Acetone
Tom's US Gear 3:36 to replace 3:70
Stone surfaces
Alignment Bolts
Torque Bolts
Check Fit
All Set Up
- Thread starter
- #67
jackfit
Well-known member
Preparing the Interior of Case
We are now working the inside of the case prior to installing gears and posi unit. Gary's comments:
"Hi Jack
Here I final prepped the housing. You can see there in the ready pictures the inside didn't look so good after etching and rinsing. It was really only minor surface rust but I cleaned it up good with a wire wheel.
The holes were all chased. The pad holes were bottom tapped and countersunk, this means a bottom tap was used to cut new threads to the bottom of the holes. The factory used a starter or plug tap and the bottom threads don't always get a full tap. The bolt may not fully engage the threads so I know now the hole is fully threaded beyond the length of the bolt. The reason to countersink the holes is to cut the lead- in thread to prevent it from pulling when the bolt is torqued. The same process used on head bolt holes. All the oil passage were brush, washed, and blown clean with compressed air."
Rusting Before picture
Wire Bush
Chase holes
Radius Edges
Cleaning bores
Cleaned and ready to go
We are now working the inside of the case prior to installing gears and posi unit. Gary's comments:
"Hi Jack
Here I final prepped the housing. You can see there in the ready pictures the inside didn't look so good after etching and rinsing. It was really only minor surface rust but I cleaned it up good with a wire wheel.
The holes were all chased. The pad holes were bottom tapped and countersunk, this means a bottom tap was used to cut new threads to the bottom of the holes. The factory used a starter or plug tap and the bottom threads don't always get a full tap. The bolt may not fully engage the threads so I know now the hole is fully threaded beyond the length of the bolt. The reason to countersink the holes is to cut the lead- in thread to prevent it from pulling when the bolt is torqued. The same process used on head bolt holes. All the oil passage were brush, washed, and blown clean with compressed air."
Rusting Before picture
Wire Bush
Chase holes
Radius Edges
Cleaning bores
Cleaned and ready to go
- Thread starter
- #68
jackfit
Well-known member
Putting in a drain plug !
We are putting in a drain plug which will make changing oil a 5 minute job. Gary's comments:
"Here I tapped the drain plug hole and fit the plug. With new gears you will have to heat cycle them the first 10 drives you make. Drive 25-30 minutes, no racing, get the diff hot. Stop and let it cool at least 1 hour. At 500 miles you drain the oil and add fresh. With this drain plug it will be a 10 minute job, just jack up the RR of the car , pull the wheel off, put your drain pan under the plug, remove the fill plug with a long extension and 5/8" 8 pt socket and drain the oil. Clean off the fines on the plug, put a little #2 permatex on the plug and snug it up. Add posi additive and pump in Lucas 85-140 gear oil, should take just under 2 qts. Seal plug and install- done."
Tap hole
Fit Magnetic Plug
Installed
We are putting in a drain plug which will make changing oil a 5 minute job. Gary's comments:
"Here I tapped the drain plug hole and fit the plug. With new gears you will have to heat cycle them the first 10 drives you make. Drive 25-30 minutes, no racing, get the diff hot. Stop and let it cool at least 1 hour. At 500 miles you drain the oil and add fresh. With this drain plug it will be a 10 minute job, just jack up the RR of the car , pull the wheel off, put your drain pan under the plug, remove the fill plug with a long extension and 5/8" 8 pt socket and drain the oil. Clean off the fines on the plug, put a little #2 permatex on the plug and snug it up. Add posi additive and pump in Lucas 85-140 gear oil, should take just under 2 qts. Seal plug and install- done."
Tap hole
Fit Magnetic Plug
Installed
- Thread starter
- #69
- Joined
- Feb 13, 2003
- Messages
- 5,475
- Location
- Ottawa, Canuckistan
- Corvette
- 1973 coupe L82 (gone as casualty of divorce)
Thank you for posting the progress pics, Jack. 
Mac
Mac
- Moderator
- #71
- Joined
- Nov 9, 2000
- Messages
- 7,501
- Location
- Edgerton, Ohio, United States
- Corvette
- 1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
It fun to watch a real pro set one of these up.
Tom
Tom
- Thread starter
- #72
jackfit
Well-known member
Too pretty to put in car!
I think it will look better in the living room on a display table........
Jack
I think it will look better in the living room on a display table........
Jack
- Thread starter
- #73
jackfit
Well-known member
Tail shaft bearing can be removed in car
I had removed the transmission last week to both adjust the linkage and to replace the rear seal and bearing. I did not want to take the case apart and in one of the recent posts, John Z mention a tool that would allow you to change the seal and rear bearing while the tranny was still in the car. I located the tool on E-bay and although my tranny is out of the car, I left the shift on to show it can be done .
My old slip yoke had 300,000 miles on it and it shows it.
My new slip yoke and balanced drive shaft
The tool to extract the rear bearing , with seal removed
Close up of tool
Rear Bearing , the tool slides in just like a yoke
I use a hose clamp to compress flanges of tool , edges grab bearing
Use wrench to extract bearing , bolt pushes on tail shaft , pulling bearing
Bearing pulled out
Can be done with tranny in car and not taken apart
I had removed the transmission last week to both adjust the linkage and to replace the rear seal and bearing. I did not want to take the case apart and in one of the recent posts, John Z mention a tool that would allow you to change the seal and rear bearing while the tranny was still in the car. I located the tool on E-bay and although my tranny is out of the car, I left the shift on to show it can be done .
My old slip yoke had 300,000 miles on it and it shows it.
My new slip yoke and balanced drive shaft
The tool to extract the rear bearing , with seal removed
Close up of tool
Rear Bearing , the tool slides in just like a yoke
I use a hose clamp to compress flanges of tool , edges grab bearing
Use wrench to extract bearing , bolt pushes on tail shaft , pulling bearing
Bearing pulled out
Can be done with tranny in car and not taken apart
- Joined
- Feb 13, 2003
- Messages
- 5,475
- Location
- Ottawa, Canuckistan
- Corvette
- 1973 coupe L82 (gone as casualty of divorce)
Easier to take pictures with the tranny out tho... 
Mac
Mac
- Thread starter
- #75
jackfit
Well-known member
Run out in Posi Unit - Setting Lash
Gary Ramadei is putting the final touches on the rear end he is building for me. He discovered excess run out in the posi unit. Here are his comments and process to reduce run out to his specs.
Hi Jack,
So as I mentioned yesterday there was a wide range of lash in the setup. I wanted to see if it was in the gears or the posi case. I removed the ring gear from the posi and checked the bare posi in the housing. I checked a few places; the posi flange where the RG mounts, the case OD where the RG ID is press fit, and the flange OD. I found the case OD was good with only 001" or less runout in it but the flange had 006" runout and the flange OD had 008". The flange OD doesn't matter but the case OD & face do. I set the posi up in the lathe using a small 4 jaw chuck to dial in case OD as my reference. I dialed the case OD to less then 001" and rechecked the flange run out in the lathe and it was out 006". I faced the flange 005 in small passes and turned the flange OD. In the lathe they were both 0 but I knew it would open up in the housing because it will be referenced off the case bearings.
"I found the caps were loose on the bearing races and set them up to 001" gap. Then I installed the bare case and found the flange runout 002 which is good. The case OD is still 001 and the Flange OD is under 001". I was able to keep the case bearings installed without issue. The lash is now within 002-003 compared to 006 before. I couldn't do a pattern test because I have to let the Loctite setup on the RG bolts again. Next up I will check the pattern to see how it looks. I did radius the edges of the teeth on the RG, this is an old blueprinting trick.
I will see how the pattern looks on Monday."
This video is an example of what he did to my unit. Just click on it
1963 Chevrolet Biscayne Positraction Differential Overhaul - Part 3.1 - Repaired - YouTube
Pictures
On milling machine
Caps
Gary Ramadei is putting the final touches on the rear end he is building for me. He discovered excess run out in the posi unit. Here are his comments and process to reduce run out to his specs.
Hi Jack,
So as I mentioned yesterday there was a wide range of lash in the setup. I wanted to see if it was in the gears or the posi case. I removed the ring gear from the posi and checked the bare posi in the housing. I checked a few places; the posi flange where the RG mounts, the case OD where the RG ID is press fit, and the flange OD. I found the case OD was good with only 001" or less runout in it but the flange had 006" runout and the flange OD had 008". The flange OD doesn't matter but the case OD & face do. I set the posi up in the lathe using a small 4 jaw chuck to dial in case OD as my reference. I dialed the case OD to less then 001" and rechecked the flange run out in the lathe and it was out 006". I faced the flange 005 in small passes and turned the flange OD. In the lathe they were both 0 but I knew it would open up in the housing because it will be referenced off the case bearings.
"I found the caps were loose on the bearing races and set them up to 001" gap. Then I installed the bare case and found the flange runout 002 which is good. The case OD is still 001 and the Flange OD is under 001". I was able to keep the case bearings installed without issue. The lash is now within 002-003 compared to 006 before. I couldn't do a pattern test because I have to let the Loctite setup on the RG bolts again. Next up I will check the pattern to see how it looks. I did radius the edges of the teeth on the RG, this is an old blueprinting trick.
I will see how the pattern looks on Monday."
This video is an example of what he did to my unit. Just click on it
1963 Chevrolet Biscayne Positraction Differential Overhaul - Part 3.1 - Repaired - YouTube
Pictures
On milling machine
Caps
- Thread starter
- #76
jackfit
Well-known member
Rear end update
Here are more photos of the build of my rear end by Gary Ramadie and his comments on Pattern.
Hi Jack
Here is the pattern. Now what you will see is the pattern is center to toe, which is how these gears typically set up, unlike "textbook" patterns which are perfectly center on the tooth. What I go by is the pattern being equal in length and somewhat uniform. Attached you will see the Drive & Coast sides of the teeth plus the lapping pattern that is on the gear out of the box- which I call "new pattern". Some gears do not have this but US Gear always does and I like to reference it since it may show how the gear set was lapped. In this case you can see the pattern is center to toe as well only a little high. Setting up this gear set it followed "suit" and the Coast side is center to toe. You will se in my pictures the lengths are equal. Now even though these are final lapped they are never uniform from one tooth to the next. Some may show a full pattern, the next one may be center to toe. I have seen them with one tooth tapering high and the next tapering low. This is where a lot of guys get caught, it is a time consuming process because each pattern change requires break down, cleaning, reshimming, reassembly, then testing. Many cycles to dial them in. Different ratios setup differently but it call comes down to how they were machined and lapped to start. Some new patterns are center on the coast and center to toe on the drive. The rotation is smooth with no binding or noise using a handwheel setup.
Here are more photos of the build of my rear end by Gary Ramadie and his comments on Pattern.
Hi Jack
Here is the pattern. Now what you will see is the pattern is center to toe, which is how these gears typically set up, unlike "textbook" patterns which are perfectly center on the tooth. What I go by is the pattern being equal in length and somewhat uniform. Attached you will see the Drive & Coast sides of the teeth plus the lapping pattern that is on the gear out of the box- which I call "new pattern". Some gears do not have this but US Gear always does and I like to reference it since it may show how the gear set was lapped. In this case you can see the pattern is center to toe as well only a little high. Setting up this gear set it followed "suit" and the Coast side is center to toe. You will se in my pictures the lengths are equal. Now even though these are final lapped they are never uniform from one tooth to the next. Some may show a full pattern, the next one may be center to toe. I have seen them with one tooth tapering high and the next tapering low. This is where a lot of guys get caught, it is a time consuming process because each pattern change requires break down, cleaning, reshimming, reassembly, then testing. Many cycles to dial them in. Different ratios setup differently but it call comes down to how they were machined and lapped to start. Some new patterns are center on the coast and center to toe on the drive. The rotation is smooth with no binding or noise using a handwheel setup.
- Thread starter
- #77
jackfit
Well-known member
Rear end update
Almost done, more comments from Gary.
Hi Jack
Here I fit the new ( rebuilt) Lone Star standard axles. With a common built posi with the springs and plates you would just pop these in with the snap ring and that's it. I have seen rebuilt diff's with axle endplay over .100"!
The tuned posi requires the axles to be fit most of the time, the last diff I did they fit perfect but just about all tuned posi's will have -0- endplay or you might not even get the snap ring on. So I set them up in the surface grinder and grind off 005-010" from the hardened face and set the end play to 005-008". This varies because the spiders are not a fine machined gear so they might be a little different through 360*.
Going back to the posi tuning, this is important to get right otherwise you will issue with the axle gap in addition to the posi not working correctly.
So here it is, all I have to do is fit the cover, shoot a touch coat of paint and crate it up for you. Tomorrow I am off so I will be at it on Friday and have it on the dock for pick up on Monday, you will have it on Tuesday.
Any questions?
Thanks
Gary
Almost done, more comments from Gary.
Hi Jack
Here I fit the new ( rebuilt) Lone Star standard axles. With a common built posi with the springs and plates you would just pop these in with the snap ring and that's it. I have seen rebuilt diff's with axle endplay over .100"!
The tuned posi requires the axles to be fit most of the time, the last diff I did they fit perfect but just about all tuned posi's will have -0- endplay or you might not even get the snap ring on. So I set them up in the surface grinder and grind off 005-010" from the hardened face and set the end play to 005-008". This varies because the spiders are not a fine machined gear so they might be a little different through 360*.
Going back to the posi tuning, this is important to get right otherwise you will issue with the axle gap in addition to the posi not working correctly.
So here it is, all I have to do is fit the cover, shoot a touch coat of paint and crate it up for you. Tomorrow I am off so I will be at it on Friday and have it on the dock for pick up on Monday, you will have it on Tuesday.
Any questions?
Thanks
Gary
- Thread starter
- #78
jackfit
Well-known member
Rear end update
Hey Jack,
I installed the cover and shot a touch up coat of paint on tonight. Tomorrow I'll come in and crate it up to ship on Monday FedEx.
I will include 2 bottles of posi additive. You will have to pick up 2 bottles of Lucas 85-140 gear oil and you can reuse your old fill plug which you should have there or you can use the new one I installed. Seal the plug with some tape or thread sealant.
You will have to break in the new gears too, I will have paperwork in with the diff to cover the procedure. This is important, you don't want to burn up the new gears.
You should have it on Tuesday.
Thanks Jack, this was an interesting build to say the least.
Gary
Hey Jack,
I installed the cover and shot a touch up coat of paint on tonight. Tomorrow I'll come in and crate it up to ship on Monday FedEx.
I will include 2 bottles of posi additive. You will have to pick up 2 bottles of Lucas 85-140 gear oil and you can reuse your old fill plug which you should have there or you can use the new one I installed. Seal the plug with some tape or thread sealant.
You will have to break in the new gears too, I will have paperwork in with the diff to cover the procedure. This is important, you don't want to burn up the new gears.
You should have it on Tuesday.
Thanks Jack, this was an interesting build to say the least.
Gary
- Thread starter
- #79
jackfit
Well-known member
Rear End Comes Home
The rear end build is over. I just recieved the box and now I have to start thinking about the instalation of the drive train.
But that can wait for another day.
Here it is , and thanks to Gary Ramadie for creating a work of Art.
Just waiting for the rest of the drive train
Here they are , waiting for me to crawl under the car and install
The rear end build is over. I just recieved the box and now I have to start thinking about the instalation of the drive train.
But that can wait for another day.
Here it is , and thanks to Gary Ramadie for creating a work of Art.
Just waiting for the rest of the drive train
Here they are , waiting for me to crawl under the car and install
- Thread starter
- #80
jackfit
Well-known member
Rear End and Transmission Installation
Well I celebrated Memorial Day Weekend with a little car work. I now have all the parts ready for installation .
The first thing I have to ask is , Why did I think I could do this ?
Next I had to get the transmission back in . Replaced the throw-out bearing, rear bearing and seal. Never easy...I finally resorted to the push the tail over the cross member, roll the tranny on to my chest, and do a push up with it . It went up and in. No problems but a lot of back and blue marks on my arms and body.
Drive shaft hooked up with new slip yoke
Using a jack, I lifted up the rear with cross member and bolted it to frame
Next the haft shafts...using jacks to lift the TA up to level to install HS
Next up the strut rods and spring later in the week, waiting for parts
Well I celebrated Memorial Day Weekend with a little car work. I now have all the parts ready for installation .
The first thing I have to ask is , Why did I think I could do this ?
Next I had to get the transmission back in . Replaced the throw-out bearing, rear bearing and seal. Never easy...I finally resorted to the push the tail over the cross member, roll the tranny on to my chest, and do a push up with it . It went up and in. No problems but a lot of back and blue marks on my arms and body.
Drive shaft hooked up with new slip yoke
Using a jack, I lifted up the rear with cross member and bolted it to frame
Next the haft shafts...using jacks to lift the TA up to level to install HS
Next up the strut rods and spring later in the week, waiting for parts
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