wasp

i have a gm 7.5 10 bolt, with upgraded auburn posi and 3.73 precision gears, i bought the aluminum cover with bearing cap supports from summit, it says to tourque the support studs to 10 ftlb max....................should i go the full 10 or less? and how exactly does this help?

Don 79 TA

i am putting that cover on too
yes do what they say, it helps to put support on the bearings

depending how hard you plan on launching, i've been told to use black rtv inplace of the gasket, this assures less flexing

but since we arent going that hardcore, we will use the gasket with black rtv since it's so thin anyway.

looks sweet too huh?

wasp

the gasket isnt good enough? 10 ftlb or less? it says 10 max it doesnt specify................

TKOPerformance

First, yes, the preload bolt itself is torqued to 10 lbs/ft or 60 inch/lbs. Then you hold it still and snug down the lock nut. Don't go overboard or you can break the bolt and/or strip the cover. You don't want to hear about how I know that.

Second, a gasket by itself as a rear cover seal doesn't usually work that well. I know that seems odd, but trust me I've tried to do them without RTV and they leak. I skin the rear end housing and the cover with a little Permatex Ultra Black and use a standard gasket. I've never had one leak with this technique.

Third, the purpose of the cover is to support the bearing caps to prevent housing flex. This is the single biggest reason for gearset failure. You should also be using studs in the caps instead of bolts. This way the caps are tied in to the housing in three places per cap. It's very strong. I haven't seen a rear with a cover girdle fail yet.

Also, take the preload bolts all the way out and use a little RTV or liquid Teflon on the threads. This will prevent leaks from around the bolts. Use some on the drain plugs too. Another important point about the girdle covers. Pull the factory fill plug when you go to fill the rear with oil. Use the fill hole in the cover. When oil just starts to trickle out of the factory fill port seal it all up. Don't use the fill hole in the cover as a gauge. It's over the axel centerline, so you'd have to fill the tubes with oil before it came out the cover. There's another story there that you also don't want to hear...

wasp

yes it says 10 ft lbs for the lock nuts as well, ok ill do 10 on each, thanx for the help..........

88 350 tpi formula

iTrader: (9)

I see you are a very smart person being that we learn from our mistakes. thats how I leard my most usefull information


but, the last one. did you use a pump on an oil drum to do that?

Don 79 TA

he's not the only one that experienced that, i have heard similar from others, so sources like this are great to make sure you don't do.

i too agree on the black rtv, or ultra black.

the jeepers use just rtv to seal their diff's.
if you read the online instructions, says dont use the gasket, if you read the box instructions, says to use it.

also great point about the studs instead of bolts.
either way, adding the cover is not going to make the entire rear strong like a 12 bolt or 9", but it should help nonetheless.

is there any swaybar interference?
just glimpsing under the car, it doesn't appear that it would, since the bar is lower then the girdle.

Zepher

iTrader: (1)

I don't understand the part about the studs. Do you have any pictures or maybe describe it some more?

TKOPerformance

When I fill a rear with oil I just use the bottle and nip the top off the fill spout, turn it upside down, jam it in the filler hole and squeeze. Low tech for sure, but it works. You don't get 100% of the oil out of the bottle like this, so I take the bottles when I'm done and drain them into an empty bottle so I get every penny's worth of oil out of them. A 7.625" 10-bolt will take a little over 2 bottles of gear oil usually.

The preload bolts and girdle work like this: The factory bolts for the carrier caps, or studs if you choose to use them instead, anchor the caps into the housing. The problem is that the entire backside of the housing is open. Under load the housing can flex, which allows the carrier to move around relative to the pinion. When the gears move out of the proper alignment you have the potential for breakage, because the teeth are designed to handle loading only in the proper alignment. Loading the teeth on parts of the tooth that aren't meant for it results in gear failure.

The girdle cover reinforces the housing by bridging the open space at the back. This makes the housing less prone to flex. The next weak link is that the bolts holding the caps in must keep the carrier from moving backwards under load (kind of like rod bolts). When power is applied to the gearset the natural tendancy is for the gears to try and seperate because the teeth are cut with a helix (swirling angle instead of straight cut, look at the pinion and you'll see what I mean). The carrier tries to move backwards away from the pinion. If the bolts aren't up to the task the gears can come out of alignment, and we're back to breaking the gearset again.

The preload bolts offer additional support for the caps. Effectively the preload bolts are tied into the housing now, since the girdle cover when tightened down is effectively part of the housing. The preload bolts put a small amount of pressure on the backside of the cap, so that when it is loaded it can't move backwards. You don't want to overtighten the preload bolts, or you could oblong the bearings and cause them to fail prematurely. The preload bolts provide additional support to keep the caps from moving around.

Studs instead of bolts for the caps offer an additional measure of protection. A stud grips the housing better than a bolt, and since it is theoretically never removed it doesn't damage the threads in the housing from being put in and taken out repeatedly, which you will typically do several times setting up the gears. This ensures that the caps are secured as well as possible. Then the girdle cover with the preload bolts makes for a very tough assembly that can survive a lot more power than it ever could from the factory. It won't magically make a 7.625" 10-bolt into a 9", but it will get you close. Rear end strength is tied to ring gear size, axel spline count, pinion spline count, the metallurgy of the parts used, and housing rigidity. You can improve the housing rigidity, axel spine count up to 28 (early rears only have 26), and parts strength by using aftermarket parts made from better materials. You can't get around the ring gear size, pinion spline count, or increase axel spline count beyond 28. Even so, a properly built 7.625" 10-bolt is a lot stronger than most people think. It will work fine in the majority of street drive cars, even those with high power. The strip on slicks is where it will eventually fail.

No swap bar interference on my car, and I've got an IROC Z28 with the biggest factory swaybars, except for maybe the 1LE cars.

BTW, most of my knowledge is hard won. I know a lot of stuff because I've set things up wrong before, and broken a lot of parts over the years. It's not the cheapest way to learn, but it may be the best. You rarely ever make the same mistake twice when you pay for it the first time. A great person once said that "Stupidity is doing the same thing repeatedly and expecting different results."

Zepher

iTrader: (1)

ok, I understand now. I didn't know that you were talking about changing the maincaps bolt to studs.
If you already have the rear set up with bolts, can you just replace each bolt with a stud one at a time? Is there any chance of having to re-shim the carrier?
Where would I get these studs, and what would they be called? Rear end main cap studs?

I am getting a pair of axles from a friend with longer wheel studs and will put on my T/A cover at the same time, I'd like to change to studs at the same time.

TKOPerformance

Putting the studs in won't affect anything. Just pull the bolts and install the studs. Do one cap at a time, but don't do one bolt at a time, or you risk cocking the cap because one side is torqued and the other isn't. Just pull the bolts, install the studs, torque th studs to spec, and then install the nuts and washer and torque those to spec.

TA Performance has the stud kit, they are about $20. Just tell then you need cap studs for a 7.625" 10-bolt GM Corporate rear.

Zepher

iTrader: (1)

Cool, thanks a bunch.

wasp

was pretty easy, used rtv on outside edges of bolts holes on cover and case, gasket inbetween, it only took a little under 2 quarts tho , the bottle of modifier included............i did have the cars rear axle setting on jackstands, maybe the pitch made it a little off? it did run out of both holes at the same time........

TKOPerformance

If oil was running out of the filler hole int eh cover something was not right.

A little under 2-quarts with a bottle of modifier is about right though.

You really need to fill the rear in the car, while it is sitting level.

I will actually level the car at the rocker panel and make sure that it is as close to level as possible before I fill a rear or a trans. It seems like overkill, I know, but when you are dealing with 2 quarts of oil every drop counts I figure.

cwalsh

iTrader: (9)

Does anyone have ARP's P/N for main cap studs??
Chris

TheMysticWizard

iTrader: (1)

How about replacing the carrier bearings... i would need to re-shim it then correct? I was thinking of install studs, and since I have the caps off, installing new bearings, but I don't want to throw anything off... so is that a bad idea?

TKOPerformance

If you just replace the bearings you shouldn't need to alter the shims, but if you remove the factory shims you will have to install new shims of equal thickness (stacked shims from the aftermarket). You won't get the factory shims back in without a case spreader.

BTW, if the bearings need to be replaced I'd take a look at the backlash of the gearset. Mostly I find that if the bearings are shot so is the gearset, and probably the axels too.

TheMysticWizard

iTrader: (1)

Well that's the thing, The bearings probably don't need to be replaced, but I was thinking since I had the caps off I'd do them... but It sounds like it would be a pain.

TKOPerformance

Don't bother. It's more trouble than it's worth. I'd check the backlash on the gears. If it's within spec (0.005-0.010) then toss the studs in, reinstall the caps, and install the cover.

If the backlash isn't within spec seriously consider a complete rebuild. Otherwise the rear's a ticking time bomb.

TheMysticWizard

iTrader: (1)

:repairing to be flamed::

How do I check the backlash? Do I need special tools?

TKOPerformance

Yes, unless you've done a lot of rears and can do it by feel (I can tell if the gears have too much by feel, but I know a mechanic who sets rears up by feel alone, but then he's done a couple hundred). You need a dial indicator with a magnetic base. The whole deal is like $40 from Harbor Freight. You'll use it for a lot of other stuff too like crank/cam/shaft endplay, degreeing in a cam, etc. It's a useful tool to have.