Mark Williams Billet Caps for 8 3/4

I am wondering if a set of Mark Williams billet caps and spanners would be overkill or not.
I am going to be going through a 8 3/4 rear to put in my 69 Bee. I am going from a 4.56 behind my low 13 second at altitude 383 4 spd car, to a 3.91 and a 500 stroker by spring. I have everthing to do it ( new Detroit Tru Track, bearings, ordering a Dr. Diff yoke) and was wondering if these caps and spanners might be in my best interest while its apart ? I don't have the money to go Dana and would like this to hold up. In all honesty it will see may ten to fifteen passes a year.

Wouldn't it be close to the same money as a Dana after you buy all that stuff and have the case machined. If that big B-body hooks with a 500" something will break and believe me you really need to build a stroked B-body from the rear forward
Gus

I would be in this less than $1000 with the caps and machine work included. I would love a Dana and I am not ruling one out, just can't swing it now. Sounds like anything would help.

these old cars FROM THE FACTORY had D-60 rears with the performance big block/4spd combos. If that doesn't make you rethink..... good luck. Going from a 4.56/383 to a 3.9 gear 500 cid.... increasing the torque AND making it more work to move the weight. Save your money boy!

Jump on Craigslist and find a Dana 60 out of a pickup [I paid 80 dollars for one complete] You should be able to put one together for around 1200.00 dollars.

Heck NO!!

I wouldn't spend any money on a 8 3/4, save it for a Dana or even better a 9".

Mark Williams would shake there head(and laugh) and take your money if you asked them to do that. Real bad investment IMO.

If you hook it good at the track with slicks, it will break someday but it will take a while.
The ring gear (or pinion, or both) will develop cracks and eventually break. If you don't hook it hard, and mostly street drive it then it's not as bad....after saying all that I agree the Dana 60 is the best and really should be what you use. I use one in my duster and I would not use anything else personally.
Brian

I run a BB MT stroker in a handling application with 8.75. In perfect conditions it will "hook" in 2'nd gear with 200 TW road track tires. Full power 1'st gear would blow off the tires and I have never even tried it. Launch means feather the clutch and throttle in 1'st and if the track is warm maybe full power in 2'nd. I believe the 8.75 will live with full power in 2'nd and higher gears.

If I got to the point I thought it might hook in 1'st the 8.75 would be gone. D60 or well beefed 9". Major parts breakage is expensive. The 8.75 worked on high speed circle track behind hot Hemis... not so much for drag race.

I think this issue has been well covered , but there are differences of opinion.
The cap is a band aid.
If you brace the housing and add the cap , there isn't much more to do.

Making sure it is well set up and using quality parts goes without saying.
With a stick and a lot of weight ( 3000 or more ) I don't like their odds.
With an auto , a light car and foot braking , it may last forever.
I believe that weight is a big issue for them , but a stick and the shock they impose on the driveline just compounds that.
If it hooks hard , I really don't like their odds.
I am in the 9" camp , but the Dana is also a decent choice.

Speaking from experience, I broke multiple 8 3/4 rearends with a mild 440 and a 4 speed in my old '68 Charger R/T. Axles, yoke, a pinion in half, etc. If you launch it hard at all, you're going to break parts. Sell what you have and use part of the proceeds to finance a Dana or 9".

The only other option is to never put drag radials or slicks on it, and slip the clutch on launches.

the problem with the stock 9" is that it breaks the cap too. you have to buy a Strange nodular housing or similar. i modded my 8 3/4 years ago before Mark Williams had their fix for the problem. stuck behind a 650hp bb with a brake this held up well.

My 8 3/4 broke the teeth off the ring and pinion gear, the cap was fine. I put a new r&p in it and sold the whole rear end and put the money on a new Strange S-60.

I'm a guy that generally believes 8-3/4's can live if you prep them right, but @ 500 cubes with a 4-speed and B-Body weight, my sense is that you're way past the limit of an 8-3/4. I'm running MW steel maincaps in my 742 8-3/4; along with a Detroit Locker differential, Dr. Diff axles, and a Moser Backbrace. A couple of years in, it seems fine and has held up to my abuse, but that's in an automatic car with 452 cubes, and my 67 probably weighs a bit less than a 69 Dodge. Frankly, I'm surprised Cass sold you the TruTrac (Assuming you talked with him and he knew where it was going??). I would think your only chances for survival involve a Spool, a hefty backbrace, and the steel caps. At that point, the gearset itself becomes the weak link.

Now, all of this is assuming the car hooks at the racetrack, and you're stepping fully into it. on the street with the hardware you've described, you'll likely never see enough traction to break it. If you're going to the track, my advice is: Have a trailer ready for the ride home.

Waste of time IMO. I've seen way to many 8 3/4's break. Save your money do it right once with a Dana 60.

Trust me, the 8 3/4 will fail.

Let see, 500 C.I. stroker with a 4 speed with a 8 3/4 in a 1969 B body, what is wrong with this picture Don't do that

There is an alternative to going with a Dana. About as strong. A lot less $. Bone yards are full of them.

I'd sell your 8.75 and build a Dana 60 starting w/ a junkyard truck rear. My dad did exactly that w/ his 440-6 4 speed '69 road runner. After selling his 3.55 suregrip 8.75, he was only a couple hundred bucks short of breaking even on a 35 spline, 3.54 gear Powerlock diff. Dana 60.

I'm soon to be in the same boat.
Just curious, what's the best donor vehicle to get a 60 housing from?
Looked at Moser's website & a complete 60 starts at about $2200.
I've got more time than money so building one myself may be the way to go.

Mine came from mid '70s dodge and ford trucks I believe. They came in lots of different vehicles over a wide range of year models. Got lucky w/ the one from the dodge truck...it had 3.54 gears and the stronger powerlock differential. Install new bearings, cut the housing and weld on the pass. car ends, new 35 spline axles and 35 spline side gears from Dr. Diff, and put it in the car.

The new rears have definitely gotten more expensive. Back in 2003 or 2004, I paid $1750 for the Moser 60 that's in my cuda. No brakes, 35 spline spool and axles w/ long studs, 4.10 street gear, billet 1350 yoke, chrome cover. Been beating the snout out of it ever since and only took the cover off one time to change the fluid after 10 years.

I was wondering what differential is best for a street/strip car.
A complete 60 with a Truetrac or Detroit Loocker will cost me $2890 from Moser ... i think i could do one myself for less.

Thanks for the input. My quest for a Dana begins

A spool. Many will disagree , but I've done it for years and never had a problem.
Regarding the " wet road ' stories that this post is sure to generate , I don't drive my car when it is raining.
There are certainly things you need to be aware of , but for a toy car , it is an easy choice.

I agree.........

I had a spool in my 8 3/4 for one summer on the street. 3900#car + manual steering + spool = a b**** going around corners.

I was hesitant to have a spool installed in my S-60 when I ordered it. The only time I can tell it's in there is turning tight into a parking spot which I try to avoid. On the street it shows no ill handling characteristics, even the few times I've been caught out and it rained.

spools are only a prob when you're trying to parallel park or push the car by yourself.

Nothing wrong w/ a spool on the street...even in the rain.

Don't listen to these guys....The weakest part of an 8.75 rear is the stupid adjusters which is a bolt in the center of the cap.
The billet caps from MW will make your 8.75 a much better piece and it's more the Enough strength for 90% of the mopars out there.

really not even close to being the real problem with an 8- 3/4

Not sure exactly what "bolt" you're talking about? The adjusters, which are threaded discs on either side of the carrier don't change a bit moving to steel maincaps, and they certainly are not the weak link in an 8-3/4. The steel maincap (really needed on the driver side only) certainly do make the 8-3/4 a better piece, but still not applicable to a 500-cube, 4-speed, B-Body (IMO).

How about a 3200 lb 700 horse 470 BB w/stock caps and w/60 ft`s in 1.36`s.......?

Me think you mean the stupid boss for the retainer bolt for the adjuster, yes? The left(driver side) cap usually breaks at that boss first which destroy a bunch of other parts, been there, done that The last 8 3/4 I built and raced ended up bending the housing bad enough on the passenger side to rip the ladder bar mounts off it during a run at the starting line, NOT GOOD OP, if you do decide, or anyone else who wants to drag race a 8 3/4, do what ThumperDart did, add a backbrace before starting to race it

four speed car deserves a D60.

Your just as well off to take that billet cap money and light it on fire..........does about as much good. The cap is NOT the weak link

You will NEVER fix what is wrong with an 8.75. It flexes the case, which causes ring gear to move away from the pinion and shells teeth.......THEN, when all that carnage gets going in there running over itself, it breaks the cap. When it is trying to turn with gear teeth piled up on top of itself, SOMETHING has to give........it's usually the cap. So yeah, you can put a cap on it, and when it DOES shell the teeth, which it WILL, you still have a bunch of broken parts, in a rear with some really pretty, expensive caps

To fix something, you have to know what is actually happening..........seems a few, actually many, have no clue.......LOL!!!

700 HP are those CAB 700HP?

cost was a factor for me. i just bought a strange driveshaft, trans and pinion yoke to replace in my '74 challenger. when i got my clutch issues straightened out, first pass, this happened. i didn't even have the driveshaft and yokes in the car yet either. the car hooked like it never hooked before. i couldn't just toss the stuff i just bought and switch to a dana so i went with the MW caps, crush sleeve eliminator, and all new parts and case. it wasn't hard to machine the caps to fit the housing.

Yes, we share the same dyno and I drive to Oregon every sunday to dyno my stuff.

First, let me say that the car in question would be better suited with a dana.
I don't agree with the forensic explanation by Monte though, and here's why.
I was breaking ringgear side caps on mine(3 times), and also seeing chipped teeth. Had I stopped there, I would have agreed with Monte's explanation.
I went with a heavily gusseted housing, and added cap support load bolts. Still using the factory caps. I no longer broke caps, or chipped teeth. The failure at that point was pinion shaft shear. After 2 episodes of that, I went with a strange ultra case 9 with 35 spline pinion. Never even had to think about the rear end again.
8 3/4 has its place. But it's not under the car in question.

Housing flex is hard on the caps. There are also diffrent thickness housings, some are heavy duty and some are flimsy. But at the end of the day after you make it as strong as you can. You will shuck pinion teeth.

I would think long and hard on a Dana.

thats what I thought . 700 CAB HP is around 600 real HP. to give you an example my challenger at 3100#s made 468hp to the wheels and ran 10.40 @ 130mph and thats with a tight converter and 16x32 steam rollers. car would run easy 10.20s range with those corrected. if you think you are making 700hp you are only fooling yourself.

8.75s break teeth because the ring gear moves away from the pinion, because of flex. This has been pretty well proven and also that you CAN'T fix it. Yep, you can brace the housing, install better caps and anything else you can think of, but it will STILL flex the case itself and shear teeth. That, you can NOT stop.

A Dana does not do that simply because of sheer mass and heaviness of the case. A Ford does not do it because the pinion is supported on both ends. Other rears, 12 bolts, 10 bolts, 8.8s, Olds, etc, break for the same reason the 8.75s do........CASE FLEX. Look at it from a logical and engineering standpoint. The ring gear wants to roll, NOT go back. The REASON it tries to move back is you stack teeth and close the gap. At this point the teeth are trying to roll over themselves and the ring gear is trying to make space between itself and the pinion. It tries to push back at THIS point and breaks the cap. Yes, you can put a better cap on it, but I have also seen rears with good caps push the whole web out of the case. Something, somewhere, HAS to give unless it just knocks the teeth off clean and puts them in the bottom of the case

exactly, what Monte said is spot on. there is nothing you can do to an 8-3/4 to prevent it. you can prolong it a little but it will spit out teeth at some point.

this should be put in the archives/best of forever

Thought that was your new signature Slo-twig!

What Monte said is the real engineering answer. WHENEVER torque is applied through gears, there is a component of the force that is trying to separate the gears. It is impossible to design a gear tooth that does not do that.

The more rigid the housing, the more torque the gearset can transmit. Most pinions are cantilevered, only supported on one end. When the gears start to push apart, the pinion is moving away but also bending away a little. The Ford 9" and other differentials that use a pinion support bearing on the inside are stiffer because it's harder for that bending to occur. Check out big truck differentials, many of them have the pinion support.

Unfortunately for the street, the pinion support takes up room that could otherwise have been used for a beefier limited slip unit. For the track, a spool is a better choice as it is shaped to not run into the pinion support.

There is no magic inside a race rear end. The billet caps can help as they are 2x stiffer and also stronger than the cast iron caps, but that is not going to prevent the pinion from moving away and the pinion shaft from bending away from the ring gear. As that happens, the tooth loading point moves farther away from the root of the tooth, and the tooth breaks. Just as simple as that. No magic involved.

The only solution is bigger/stiffer or a design more appropriate to the use, which in the Ford 9" is the pinion support.

R.

Weight KILLS... also a stick car doesnt have any
cushion like a conv does.. I've been happy with
my 8 3/4... I ran a stock one for 600 passes and
used a trans brake all the time... it finally broke
a cap.. that was with a back brace.. I swapped over
to a alum housing that has the threw bolts... its
been in there for years now... the car is light..
but if I had a heavy car I wouldnt use a 8 3/4...
my Rampage has a 9".. thats what I had when I built it
and that has a back brace also
EDIT
the 60' has been 1.19 with this rear end.. never
slower than a 1.26

Aftermarket ring and pinions are ALL made from exactly the same stuff. Yet some rears shell teeth off like chiclets and some hardly ever break. What, you think 8.75 gears are made weaker than Danas, or that slight increase in ring gear size "fixes" the issue...........hell no. It's ALL about stuff moving that is not supposed to move. It's been pointed out several times, that 8.75s and Danas, as well as Fords have roughly the same diameter pinion shaft and there is little difference in ring gear diameters..............so, if you look at it from something resembling a rational thought process, that leaves only the CASE as the inherent problem. Most all cast rears have cast caps. Why don't the rest of them spit caps off?

The problem I have with the answer given, Is the fact that I DID stop mine from breaking teeth. The problem was after doing that, I started shearing off the pinion shafts. No broken teeth, just clean breaks at the yolk.
I am not advocating the use of an 8 3/4.
I will say, that using the gearing I did compared to most others, combined with the car weight and trans brake, would put much more strain on the pinion shaft, and with more(numerical) gear, would have most likely run back into the tooth failure zone. However, that is not the "case" (pun intended)
I mean no disrespect. Healthy debate. I just go by my experience. Yours may vary...

Not sure why, if nobody uses the search function.

For example, 6? years ago:

https://board.moparts.org/ubbthreads/ubbt...html#Post565526

And the MP Alum 742 case is supposed to be stiffer, and I also suspect a spool supports the ring gear better, all in harmony of keeping the gears properly meshed. OP should just get a dana and move on.

Ding Ding Ding - winner winner chicken dinner - that's what happens exactly - you can try the elusive POS aluminum mo-par 742 case - and guess what - pretty much the same thing happens with shelling the teeth on the gear - only it looks real pretty under the car.............

My alum has been doing great for years now.....
DING DING

No chicken for you!

only real difference is the heat treat of that same material, as for the 8.75 they are a good diff for their intended purpose, but I changed to a D-60 after grenadeing my 8.75 and never looked back.

I have seen quite a few 9" launch the pinion right out the front when guys tried to get away with just a stock non-nodular case. Even with a 9" you can't cut corners and expect long life.

Mike, just how does your car relate to the OP's B body? Other than the fact they both came from Ma Mopar, nothing. Hell a 7 1/4 would probably live in your car.

simple... mine is much lighter... I know a 7 1/4 wont work...
I tried one in my old car(used it for a mock up but tried
it).. didnt live 2 easy passes
Why do you think they use to run 8 3/4 in the old dragsters
they worked because they were light... they had dana back
then... why didnt they run the dana... didnt need
it because it was light... if any of them ran a big
diff it was the Oldsmobile

How many hits on the P-body in the last five years?

about 75... I pretty much quit racing after I
got my license pulled.. I just didnt feel like
running 10.0... before that it had about 750 hits

It's NOT because of the case though.....it's the pinion support. The stock pinion supports are very weak, unless it is the Daytona support like came under some Mustangs, Torinos, etc. A factory Ford case, nodular or not, is still better than a factory 8.75 case. Just needs a decent support.

Everyone wants to generalize.........that being stock Fords are junk. No, they are NOT. A center that came under a Cobra-Jet Mustang was VERY good. One from a 6 cylinder Torino was not. Same with an 8.75. One under an early 6 cylinder A-body was weak as water. The hi-po units were much better. Danas are good because they are massive, not because of some superior engineering design.

Also talking about 8.75s in flyweight tube frame cars, roadsters and front engine dragsters has no bearing on 3000+lb door cars.

I lost count of the number of 8.75s my dad or me broke over the years and have tried every band aid there is. You will NEVER "fix" it...........that simple

Same deal with Thumpers car..... once in a great while the car sees a track, yet every discussion on this topic the same two chime in on how it doesn't not happen to them. Mike you constantly chime in on this.... are you telling the OP to use the 8.75 over the D60??? Heavy big block stroker with a 4 speed. Your chit, as noted above, is apples to oranges. What a coincidence the factory put the D60 behind performance big block 4 speed cars..... guess they ran low on the mighty 8.75 and figured the D60 would do in a pinch.

Same with an 8.75. One under an early 6 cylinder A-body was weak as water. The hi-po units were much better.


So which 8 3/4 was the better one? 489,741,742?

You must not read... I said... heavy car or a 4
speed will break a 8 3/4.. they work great in LIGHT
cars

If anyone doesn't believe that 8 3/4 cases don't flex because of the lack of pinion support, look at the housing & the damage to it from the ring gear shearing teeth. This was done prior to the brace being welded to the housing. Dry hops, on & off the throttle at 20-30mph in 1st on the street showing off in my younger years claimed the ring gear that did this. The brace covers the worst part, not sure why the cap didn't break.
I am still running the 8 3/4 because i still have quite a few spare cases & only get to the track 1-2 times a year. As mentioned previously, billet caps & braces are just band-aids ... especially on heavy BB cars.
A 60 is in the future for my car, because it's stronger/more dependable.

Early /6 a-body's? 99% had 7 1/4 rears. My 3 speed /6 Twister has the 489. 741 weakest, 742 then 489 but of those two each has their good and bad points but neither will not hold up behind a 4 speed unless he has 675-14s, they where made with grease I think.

YOU`RE kidding right? Screw the "math" equations this and that bs. My old solid cammed 906 headed motor on Pettis`s dyno made 615 hp and 580+ tq. and went 10.40`s at around 3250 lbs. all day. So you`re telling me that a bigger better fully ported e-head and a 680-660 lift w/276-281 @ .050 solid roller and low drag back cut rings is making LESS hp.... Ya right. Put your motor in a street weight car like mine and get back w/me............

you are a silly man,Dyno's don't go down the track. your numbers don't add up to 700hp any way you look at it. you are 100 pounds heavier than my challenger I ran 130mph with a stock stroke 360 don't you think I would gain more than 5mph with 200 extra HP?

Stop it your hurting my feelings...........NOT! Some of you guys act like I`ve only made 50 passes or something. I have a stack of time slips from the 90`s up till now and use to T&T at L.A.C.R. almost monthly w/a warmed 360 then my BB and even showed Al Alguire my stack of slips when he was here. Back to building carbs and at the end of the year I`ll hit Bakersfield for my 9.60 or better and HOPEFULLY my lowly 8 3/4 lives but if it breaks which according to some it will, then I`ll put it back together and move on.......

If you we're making any real power you'd have broke that rear gear by now! (come on! thats funny no matter who ya are!)

The 742 is the best stock 8 3/4, the 741 will live very well in a medium weight, medium power BB A body My 440 powered 1969 Dart GTS weighed 3300 lbs with me in it and had many, many runs on the OEM 741 case and posi with the OEM 3.91 gears. That car went 11.17 at 122 MPH in Las Vageas in November many times the last time I raced it here The stock 489 case with the crush sleeve is the weakest of the three, the 489 and 741 have the same size pinion gear diameter size at the front bearing If you put a pinon gear spacer in place of the crush sleeve then it is as good as the 741 The 742 and Dana 60 pinion gear shafts are bigger diameter at the front bearing

It IS funny cos everyone I know drives a 9-second car on the street and ALL of make around 599 hp.............just crazy and don`t know how they do it.......

742 case with MW cap, ARP studs and ring gear bolts, back brace
8.93 @ 149 3050lbs with driver. 1.21 60'
I change out the r&pinion every 300 passes.
NEVER broke in 15 yrs of racing. (100 passes/year)

Hmm? 3200# car, 9.79 @ 135.5 ... takes around 590-600rwhp to do that, 700hp seems legit to me.

My ex car weighs 3220 currently. A while back the motor made 705 ish horsepower on a dyno with Best machine.
That motor went 9.62@ 140 on super stock springs.
That almost 5 more mph than the above. Huge difference

When I had the car( little bit different combo) it went 135@ 3350. I figured it made about 640-650 REAL horsepower.
135@ 3250 ISNT 700 horsepower, it's a great elapsed time, but it isn't 700. More like probably 640-645.

Naw, Quick said the "math" doesn`t add up........

it doesn't but keep telling yourself it does and one day you will believe it

whatever the case your car/chassis seems to be working PDG ...

That was my very first pass on new combo and carb was lean up top so there`s more there and now it`s 3050lbs. so a new best is comin soon........

I was running 11.35 with a 489 case in my 64 with the old 446". When we built the Dana I sold the 489. The 3.91 gears looked new yet with no wear. I was always told the 489 case was the good one. Now it goes 10.15 at 132 mph. What is that at a tad over 3600#? About 550 HP?

Nice!

And then some...

Again, first pass off the trailer and definitely a 9.60 based on being lean and other small issues plus a lot of you guys race in really good air back east etc. It was around 800+ ft. corrected iirc and definitely better than the normal 2000-3000+ and higher we see here on the west side. We`ll soon see how it runs w/all of my mods and at 3050 lbs................

Dyno numbers, speculation and all the other stuff doesn't mean squat. Numbers at the track is all that matters. At 3200lbs, it takes roughly 575 rwhp to run 135mph in average weather conditions. If you want to figure 20% driveline loss, that would put the HP number at roughly 690. Can't remember exactly how big his motor is, but that puts HP in at roughly 1.35 per cube or so. Easily attainable with decent parts.

Is there any average/standard loss of HP through the drive train? I know the number will vary on the setup. i was told one time it was in the 15%-18% range.

This is what goes through my mind every time this is discussed.

Here...
Rear End Technical Information
Pro Gears and Street Gears
Pro gears are made from 9310 and then heat treated. Itis a softer alloy than the 8620 Street gears. The softer 9310 alloy allows the gear to absorb higher impact loads that are generated in drag racing without developing cracks. A harder 8620 street gear could shatter under the same loads. As a side effect the "Pro" gears are not the best choice for street use as they will wear faster. Also available in the "Pro" gears is a large pinion with a 35 spline shaft for high powered applications. This requires a bearing change in the pinion support as well as a 35 spline pinion yoke. Gears termed 9-1/2" are also available for the 9" thirdmember. They offer a slight strength advantage over a standard 9" gear.

Another thing with the 8 3/4.. they dont have many
gear choices in the pro gears.. I've always used the
street gear.. mainly due to the lack of pro gear choices
but they have been holding fine due to being a light car..
I have the street gears in my Rampage also because its 90%
street

Good luck finding ANY ratio pro gears for an 8 3/4.

I dont even bother...I have been running the street
gears the whole time

I think everyone knows this........so was there a point to this?

No, not everyone knows. I've never ran or had the need to run pro gears so I didn't know what the difference.

Don't be a dick.

Just pulling back the curtain.

Ruined the teeth on two 489 Third members in one summer, early nineties.
Next winter I ordered a Dana 60 with spole and MW 35 splines axles from Mcandless in New York, problem solved.
440 ported 906 heads and 300hp top gun plate. All steel Road Runner 70. Street car.

Ok just throwing this out there, a lot of old timers swear by it. To soften the street gear so it won't shatter as much, heat in an oven to 425 degrees let cool slowly over a few hours. Poo-poo it or whatever. I didn't bother doing it, I just put the Dana in. 9 is a good rear, but for 1/4 the cost I'll use up my stuff first( maybe in my life time)