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View Full Version : 8.75 Main Caps


JANDJ
02-21-2001, 07:17 PM
WILL THE MARK WILLIAMS 8.75 MAIN CAPS PREVENT THIS?
http://albums.photopoint.com/j/View?u=1490930&a=11694878&p=41638058&Sequence=0

http://albums.photopoint.com/j/View?u=1490930&a=11694878&p=41638056&Sequence=0

JERICOGTX
02-21-2001, 07:38 PM
As long as you replace both sides you should be OK. Since I changed mine I've had zero problems. What does your car 60 ft in?

JANDJ
02-21-2001, 07:41 PM
1.55 BUT I AM CHANGING THE MOTOR COMBO RIGHT NOW. HOPEFULLY IT WILL BE BETTER

JERICOGTX
02-21-2001, 07:48 PM
Been told that the 8 3/4 can only take about a 1.40 60'. No matter how well you beef it up. Don't know for sure, just what I've heard.

DartGT66
02-22-2001, 05:57 AM
I tried a different route to that but has yet to see wether it works or not. In the other style rearaxles they use a lot of rear covers with cap preloaders, so I figured why couldn't they be used in a 8 3/4"? I took mine apart, tied the backand front portion around the chunk together, installed a back brace and cap preloading nuts through the housing and the brace. Also straightened the housing. I have not had problems with the rear whatsoever, but my car has only run a best of 1.46 and is usually in the low 1.5's. Hope for better though.

Beeracuda
02-22-2001, 12:34 PM
Originally posted by JERICOGTX
Been told that the 8 3/4 can only take about a 1.40 60'. No matter how well you beef it up. Don't know for sure, just what I've heard.

We typically 60' in the 1.39-1.41 range and haven't had any problems with the main caps.....gears are another story. Until we went with the 4.86 pro gears, they only lasted about 100 passes. The pro gears have 155 passes on them and still look great. That's with a powerglide, transbrake and 5200 rpm stall.

Monty

JERICOGTX
02-22-2001, 12:50 PM
Monty, what does your car weigh? After I install ladder bars my car will weigh 3380# and should hook in the high 1.30's low 1.40's. I am hoping that it holds up though, if not time for a pro gear or Dana 60.

Beeracuda
02-22-2001, 01:09 PM
Our car weighs 2800 lbs. We just replace the factory disks with Aerospace discs and dropped 50 lbs. I would be willing to bet that the 8 3/4 won't hold up very well at 3380 lbs. with that kind of 60'.

If it does fail, it can get pretty expensive. The time before last, when we broke the (street) gears, it also took out the yoke, driveshaft, trans case and the planetaries. We were able to save the case with an UltraBell, but it was still pricey.

Monty

Christopher
02-22-2001, 10:18 PM
I finally had enough of using them and didn't learn my lesson the first time.... In the Road Runner with a factory bottom end 383 and a 4-speed,we blew the main caps right off the case.So we went to a Dana after talking with Larry Shepard at Chrysler.When we built the Demon,we went with a 8 3/4 and Strange axles,this time with a mild 440 and a 727.Blew that one up as well.So we put in the Mopar 52" Dana and it's been in for 20 years with zero problems.My Demon weighs in at 3300#.

JANDJ
02-22-2001, 10:24 PM
YOU GUYS ARE DEPRESSING ME. THERE IS NO MONEY LEFT FOR A DANA AT THIS POINT IN TIME

PRO
02-22-2001, 11:02 PM
Look guys I cant relate,all these broken parts/stories,what are the real causes?Consider this,I had a 3650lb car for 4 yrs,I left the line at 6000 rpms,(4spd)with the n2o on,turned consistent 1.45-1.50 60 fts with a "741" carrier(1.375 pinion),I ran this car on the street mostly but it saw the strip at least once a month,and I beat it hard,I just dared it to blow up..all the time.Of course I set up my own diffs,and Im a mopar guy with the right tools and proper knowledge,I own a High Performance shop and have for 13 yrs,if any of you walked in the doors Id tell you the "742" would be plenty and stand behind it,Heres what Ive found to be problematic in 8.75's,people are too lazy to press the front pinion bearing off if the depth is off and add shims until its perfect,also switching the main brg caps!!!!!!Ive seen it several times,setting up used gears causes several probs,or older fatigued gears too,running it with Bad front pinion brgs,reusing ring gear bolts!!!,reusing pinion nuts and not torquing them,reusing crush sleeves,remeber if it howls its wrong!!(could set up right if gears are used but then its not really right)I like to use studs instead of main cap bolts it adds alot of strength for cheap.Some failures are due to poor castings although Ive only seen one,weigh your main caps if one is light its a bad casting,unfortunately youll need a different center section as caps are NOT interchangeable,I guess what Im really saying is Id suspect something other than the 8.75 and its design and strength...................PRO.................

JANDJ
02-22-2001, 11:06 PM
PRO WHAT STUDS DO YOU USE?

JERICOGTX
02-23-2001, 07:28 AM
Pro everything in my 8 3/4 was brand new. 489 case w/ crush sleeve eliminator, new bearings, new gears, bolts, everything but the main caps! They broke in the exact same place as JANDJ's only they broke in 4 places. The gears only broke because the spool, and ring gear were shoved straight out the back of the carrier, and really dented the housing. It did not take any teeth clean off but thats because the guy who sets them up for me, takes all the hard edge off them. This stress relieves the gears. Once I changed to the M-W caps there has been no failure.
I'm not doubting what you had worked, but I would have been money ahead by putting them in right away.
JANDJ the M-W caps come with new bolts and should be fine.

Comp Chassis
02-23-2001, 09:12 AM
The 8 3/4 is hit and miss at best. What people arent saying here is that a 1.35 60' on 9" slicks and a 1.35 on 14" slicks is 2 different things. On a 9" slick, the tires are most likely being spun off the starting line, with a 14" slick, the car is being hooked dead solid. It makes a lot of difference to the rear end.

I personally never broke anything but a ring gear in an 8 3/4, but I have seen plenty of other that have broken them. I narrow and set up rears all the time. Just did an 8 3/4 for a customer that hadnt been having any trouble. But, he just ported the heads and added more rear gear. On the 3rd pass, it blew the main caps apart. It had absolutely nothing to do with installation, just weak main caps.

He asked me about installing the Mark Williams caps, but I told him that there were no gaurantees that it wouldnt happen again. I saw a full Mark Williams 8 3/4 blow apart on its 3rd pass.

I know you may not have the money for a dana, but, it may be time to seriously consider saving to get one. It will only take 1 more blown apart 8 3/4 to pay for the Dana.

Jack Z
02-23-2001, 12:06 PM
I built a fully braced HD 8 3/4" rear axle assembly for my 440 Six Pack, Stock Eliminator car ('71 Challenger, B/SA) to replace the Dana 60 that I had been running just to see if the lighter unsprung weight and lighter rotating would help. The complete Dana weighed about 195 lbs. and the complete 8 3/4" weighed about 165 lbs. The 8 3/4" had a 742 carrier, MW steel caps on both sides, a MW alum. spool, a Tri-City Competition heat treated and coated 4.57 gear set and Strange gun drilled Pro Race axles. My car weighs 3600 lbs. and 60' times are in the high 1.30's or low 1.40's with 9" tires that usually don't spin and I can put the car on the back bumper about anytime I want to (which I never do!). In my car, the 8 3/4" lasted about 90 runs before the gear set (teeth) broke which is what usually happens with the 8 3/4" due to flexing in the carrier. Bracing the housing (like I did) helps but obviously doesn't eliminate the problem. The new MP aluminum carrier may help this flexing problem but I'm not that familiar with it.

I can also say as a fact that I didn't see any noticeable performance gain when I put the 8 3/4" in in place of the Dana (after 30 lbs. of additional ballast was added to make up for the lower weight of the axle assembly) and I didn't see any noticeable loss when I put the Dana back in after the 8 3/4" broke (and the 30 lbs. of ballast was removed).

Christopher
02-23-2001, 07:05 PM
The unit that went south in the Road Runner was a factory Chrysler unit out of the Direct Connection catalog.Everything was brand new.The one in the Demon was actually its second as the first ripped apart the sure grip.We went with a new unit the second time around and then went with the Dana.

PRO
02-23-2001, 09:44 PM
J AND J I use engine main studs,Im sure their for sbc but dont have them here,I ll get the part # when I go to the shop and post it ,Also My car ran 10" slicks and doesnt spin,it does wheelie so I know Im loading the rear hard.This is what I know that when a rear lets go its very hard to determine what went first,Im told by mark Williams that case flexing makes the ring gear pull away from the pinion and then results in destruction.Too much side play greatly contributes to this,its like a plane wreck you can theorize but you could be wrong,I know 2 guys here locally that set up rears also and most of their rears blow up,ask your diff guy for specs,see if he knows right off what torque specs are for main caps,end play,etc.I t might pay to try someone with a good reputation,Randys ring and pinion is great.Also dont forget your launch diff angle,have you ever checked it?I took a piece of hanger and bolted it to my floorboard with it pointing straight down at my centersection,after a pass I looked to see how far up it had bent and determined my 2" of clearance between the snubber and floorboard was way too much,it was allowing my centersection to rise above the ideal driveshaft angle,this in itself can cause a 3rd member great stress and ultimate destruction.I have no doubt several of you guys have too much for the 8.75 but I see too many 500hp cars blowing up 8.75s..........PRO...

JANDJ
02-24-2001, 11:14 PM
IF YOU CHECK THE POSTS ON "1/4 MILE TIMES" THERE IS A LOT OF GUYS RUNNING THE 8.750 EVEN FAST CARS!!MAYBE SOME MARK WILLIAMS CAPS AND GO FOR IT??

JERICOGTX
02-25-2001, 12:49 PM
JANDJ, Is you trans equiped w/ trans brake? If not put em in and go racing! In the mean time save some money for the Dana 60.

JANDJ
02-25-2001, 01:25 PM
JERICO I AM SENDING YOU SOMETHING AT YOU EMAIL