Steel caps for 8.75" Mopars???
 

I have a bracket car that has a Vortech-blown 360 Magnum, and I am wanting to build a third member for its 8.75" rear end that will have a reasonable life-span.

I have no transbrake, nor high stall converter (it stalls about 2,500 rpm) and the ring and pinon are 4.10:1 ratio.

The tires will be 9"-wide M-T bias-ply slicks (no d.o.t. tires or drag radials) and will be 28"-tall.

I plan on leaving at about 2,000 rpm, if the brakes will hold it still. (Less, if they won't/can't.)

The engine was tested on a chassis dyno @ 477 ft. pounds of rear wheel torque (445 rear wheel hp) at 10 pounds of boost. Abundant low-end torque....

It will hopefully, be capable of some low 1.70 60-foot times, maybe better, but not counting on it.

I have a NEWLY BUILT 489-case center-section (with a crush sleeve eliminator kit installed) that has a cone-type limited-slip unit (this is a street/strip car), with the larger, (7290) u-joint yoke.

I am wondering if I might need to install a steel carrier-bearing back support (CAP) in place of the cast iron one that it comes with (OEM.)

I don't want to have to do this if it's overkill. The car weighs 3,600 pounds and should run mid-11's if it hooks (118 mph.)

I'd appreciate some advice on this from people who have experience with the 8.75" in a moderately powerful 3,600-pound car like mine. {That's 3,600 pounds with me in it, ready-to-race weight.)

Like I said, this is not something I want to do unless it's actually necessary. Do these 8.75" units break that bearing cap in the kind of useage I described? I will only race it occasionally.

Thanks for any information... it will be much appreciated.


Bill

Re: Steel caps for 8.75" Mopars???
 

Mark Williams sells the caps you want. I would think they are only neccessary if you have a t-brake or stick. I've known guys that run an 8 3/4 with these caps with both a stick and t-brake and they hold up very well. For your application it's probably overkill. If you get one or both caps you will need to align hone the case. At the very least I would get the billet spanners. They move less and maintain the side-play clearance.

Re: Steel caps for 8.75" Mopars???
 

Get in touch with Jim Bailey, his suggestions will $ave you time & $$$$$

Re: Steel caps for 8.75" Mopars???
 

Thatks for the good advice!!! Both of you.

Bill

Re: Steel caps for 8.75" Mopars???
 

I have a 8.75 in my Duster 3200lbs with me in it Braced housing 35 spline spool and Moser axles Everything else stock stuff.Its a 440 runs 7.0,s 1/8 @93 MPH So about 475HP ? Foot brake sometimes t/brake I have broke a couple of stock axles before I went to the Mosers and 1 R&P but thats it.
I think the housing brace is very important to keep everything in line.

Re: Steel caps for 8.75" Mopars???
 

my car weighs 3665 we me in it,i have two center sections 4:86 & 4:57 with 35 spline axles the 4:57 is a yukon 489 case with the stock caps i have 80 or so passes on it and and no troubles,pulled it and swaped to the 4:86 witch has the mark willams caps,this 60's around 1.60 but we had 1.589's this weekend ,like mentiomed the most important thing is to get rid of the stock spanners,the threads are to loose and somtimes will give way from the side load,the billet ones have more threads and are by far a tighter fit,also check your bolt lenght you might want to put in longer allen head bolts to get all of the threads , gmonde

Re: Steel caps for 8.75" Mopars???
 

Well, it looks like speed costs money, but I'm afraid I'm already going about as fast as I can afford to,,,... LOL!

All that expensive stuff is wonderful to have, and surely works to provide a trouble-free drivetrain (which, of course, I'd LOVE to have), but I think this business with housing braces and billet spanners just might be overkill for my junk. I dunno; my car weighs 3,600 pounds with me in it and runs 93+ in the eighth-mile, but doesn't run anywhere CLOSE to 7-flat. More like 7.50's....

With bite like that, perhaps I won't break anything, after all.

I will take everything you guys have suggested under advisement and as funds become available (and, hopefully, they will), I'll add what I can, when I can.

Thanks a bunch for all the great information!!! I appreciate it a lot!

Bill

Re: Steel caps for 8.75" Mopars???
 

i've seen braces on ebay for less than 100, spanners for around 25....
the caps will be the most expensive cuz of some maching work....

try finding an "A" body housing.....$$$....
i'm gonna narrow one...

Re: Steel caps for 8.75" Mopars???
 

Bill -

Race it till you break it. Then fix it. Analysis paralysis. Guys have abused those 8 3/4 MoPar rears for years and the percentage of breakage is low.

Re: Steel caps for 8.75" Mopars???
 

My 66 Belvedere with a 3500 converter, 440, slicks and 4.30 gears running low 7's never broke the 8 3/4. Who knows how old the center section was. I bought it used and was on stock axles for 3 years. So if its not your daily driver and you can't afford to beef up, just enjoy it until it needs it.:cool:

Re: Steel caps for 8.75" Mopars???
 

Thanks again for all the good advice, guys!

This setup has new, Moser, hi-strength axles, a new cone-type Sure Grip, a crush sleeve eliminator, a new driveshaft with 7290 u-joints and 11/16" axle/wheel studs.... You're right; I'm probably not gonna hurt it footbraking it, with this ol' 360, boost, or no.

I really do appreciate all the good advice!!! :)


Bill

Re: Steel caps for 8.75" Mopars???
 

Never enough money to do it right the first time, and than we do it right the second time.

If you think your alright than leave it alone, but remember this when it does break, now you also need a transmission fix and possibly a case too, the sprag doesn't like to be hit like that.

Re: Steel caps for 8.75" Mopars???
 

Your point is well-taken... I did put a crush-sleeve eliminator in it... :)

Re: Steel caps for 8.75" Mopars???
 

My suggestion is too find a 742 case. I broke a 489 with my stocker.

Re: Steel caps for 8.75" Mopars???
 

John is right, find a 742 case. My 3500 lb. stocker has gone low 1.40 sixty foot with a 340. Last time I broke a rear end it was costly, it took out the trans and also damaged the thrust bearing in the motor. Contact Jim Bailey and have him process your gears and housing, it will help it last much longer.

Re: Steel caps for 8.75" Mopars???
 

John and Chuck are right. Use a 742 case from the get go. Every gear I ever broke in the SS car was in a 489 case. Jim

Re: Steel caps for 8.75" Mopars???
 

dittto......my 67 Satellite is set up almost identicle to this and i have had no problem with my stock 8 3/4. I'm running low 7's leaving off a trans brake ..i'm only running 4.10 gear though. http://[IMG]http://i228.photobucket....007/16-140.jpg[/IMG]...well i tried for a half hr. trying to post a pic of my heap...lol..ive posted pics of it all over the net but for some reason i can't do it on this site...no biggie you get the idea. run that rear-end till it breaks...imo

Re: Steel caps for 8.75" Mopars???
 

Gotcha...
I have a 742 case on the floor in the garage. Got a 2.73 in it.... Bonneville, here I come!!!

No, I'll start buying parts for it as soon as there's some loose change around here; just spent each dime I could afford on a new driveshaft and that crush sleeve eliminator for the 489.

Now, lets see if this ol' 360 can do any damage to this much-maligned 489... LOL! New tires comin'... :)

Thanks, everyone, for all the good advice!!!

Bill
PS Al, mine's a 4.10, too...

Re: Steel caps for 8.75" Mopars???
 

I've found the tapered pinion is ok, as long as the crush sleeve is replaced with the spacer. The last time I checked, the only pro gears for the 8-3/4" were for the 1-3/4" 'stepped' pinion gears (4.44 and 4.86:1 ratios). That's the only reason I went away from the tapered pinion.

I think the weak link is the differential. I've had both late and early Suregrips ('68 & '69 340-S Barracudas) and burned up both. As the late style wears out, it deposits trash in your gear oil. The ring & pinion don't like that.

The early type (that uses clutches) lasts longer. Another advantage is that you can just throw a new clutch pack at it, and be on your way. A machinist friend (L.D. 'Dennis' Smythe) has rebuilt the late 'cone' style but it involves milling some material off the small end of the cones and installing taller springs.

Early style Suregrips are hard to find, and expensive when you find one. On the other hand, spools are easy to find, and VERY hard to break!

Bryan (aka By-Run)
"Be a good sport at the drags...
help your competitor O-U-T!"

Re: Steel caps for 8.75" Mopars???
 

Who still makes pro gears for the 8-3/4"? Is my recollection correct that the above mentioned 1-3/4" stepped pinion is for 742 case?

Thanks,

Re: Steel caps for 8.75" Mopars???
 

No one makes pro gears anymore for an 8 3/4. Well thats atleast what i ran into.

Re: Steel caps for 8.75" Mopars???
 

Yes, the 2070742 case is for the 1¾" stepped pinion. The only current source of pro gears (that I'm aware of) for the 8¾" uses this pinion...

Mfr: Strange
PN: RP03987486E
Ratio: 4.86:1
Alloy: 9310

By-Run

Re: Steel caps for 8.75" Mopars???
 

So, it looks like the "smart money": is on the 742 case and a mini-spool???

I hate to break down this 2.73 setup in my 742, because it's dead quiet, but money being what it is these days (scarce!) and 742 cases being what THEY are these days (scarce!), I might as well do just that...but, it's going to be a 3.90...This engine combination doesn't LIKE rpms...
That's okay; it's a street car, basically....
Thanks again for all the good information, guys...

Bill

Re: Steel caps for 8.75" Mopars???
 

Gettin' too OLD for this *****...

Those third members are getting heavier every year; I ain't gettin' any younger, so I built a "labor-saving device" to aid me in my time of need (old age!!!)

Here are some pictures of my creation; built from a Harbor Freight tranny jack and some 3/16" steel plate, it will roll right up to the rear axle housing and adjust to the proper height and angle so you can just shove the third member right into place without having to lift the %#@*&$%#@!!! thing!!!

I also built a "cradle" to pick it up off the floor and hold it elevated so it's easily attached to the "labor saving device."

Now, I can change a third member without lifting anything heavier than a half-inch ratchet (used to elevate the jack.) Guess I could use an impact tool for that...

Anyway, here are the pictures, direct for my Photobucket account.

I THINK if you click on the "thumbnails" they will enlarge, somewwhat, for better viewing...

Bill

Re: Steel caps for 8.75" Mopars???
 

Maybe I'kll finally get some pictures posted this time...
We'll see...

Sorry for the delay!

Bill

Re: Steel caps for 8.75" Mopars???
 

i like the cheapo tranny jack thing and i've got one, too.

btw, i bought a 742 empty case off ebay for 51 bucks + shipping....

Re: Steel caps for 8.75" Mopars???
 

That's a really good price ($51.00) I think!!!

I'll keep my eyes open.... thanks.

Bill