Whose broken an 8 3/4" pinion?

[drag-n-cuda]

What hp level, how, what, where, conditions, car weight etc. If I go ahead with purchasing Moser axles & spool, I've been told that the pinion is the next weakest link. As ratios get numerically higher the pionion gets weaker due to it's reduced size. Trying to decide between the cheaper, existing 8 3/4" and a more expensive and more work of putting a dana 60 in my car.

Thanks,
drag-n

[Mills]

While there is no doubt that the Dana 60 is stronger, I would say unless we are talking about UNREAL amounts of HP, you would be fine with either the 742 or 489 8-3/4".

Jimmy Addision's Silver Bullet used the 742 casing for years w/o problems. He had power (mid 10's in the 1/4), and he had traction (lift the front end). His '67 GTX weighed in a 3200 lbs or so.

He had a Dana 60, but due to added weight and simplicity of gear swaps w/ the 8-3/4, decided to keep the 742 8-3/4.

Maybe not the answer you were looking for, but I'd sleep OK at night.

Mills

[Kevin Garceau]

I broke several. I broke one last season with my little 440. I believe it had about 450hp and only ran in the 10.60s in the qtr mile but eventually broke the ring and pinion after about 5 seasons. It makes a big difference how you leave the line. A transbrake is very hard on them since there is slack in the drive train upon launch. Footbraking isnt so bad as all the slack is taken up.

First pass this year with the new motor, and new ring and pinion I disintentagrated them.

Put a 9 inch or dana in it and forget about it.

[Mister Fiberglass]

The car weight is the major consideration - IMO.

HELL....they used these in TF carz for years...and still use them in some real fast/quick Comp Elim cars.

If you have a heavy, GOOD hooking stick-shift car.....FORGET using an 8 3/4.

[littlecampbell]

This is off the topic but have you had any head work done? I see your best time is in the 12s. That seems very fast for your setup. I have a Dart that has similar engine specs, except 355s. I would be thrilled to be in the low 13s with mine...Thanks

[dwc43]

Never broke one in anything I raced.Whether it was drags, road courses, or dirt. Main thing you need to do if you are worried the least little bit is to install the back brace. It eliminates flexing, which is one of the 3/4's major probs. That's why the 1/4 replaced it since it's case has no flex problems.

[bwlizard]

Originally posted by dwc43
It eliminates flexing, which is one of the 3/4's major probs. That's why the 1/4 replaced it since it's case has no flex problems.

Just asking, are you saying the 8 1/4 is stronger than a 8 3/4 ? Maybe I misread your post.

[drag-n-cuda]

littlecampbell,
Yes, I had head work done. But my porter says I should be in the high 11's, not 12's. He told me when I changed my heads over from my bowl ported "j's" to my complete ported "j's" and didn't really go any quicker/faster that I had a built in governor in the car. I hope I found it in my fuel system, but I broke another sure-grip at the last test-n-tune on the first pass and didn't get to see if my fuel pressure was dropping off or not. This is the reasons for all my rearend questions lately. When I'm at the track I drive it like I stole it, no babying it.

drag-n

[dwc43]

Originally posted by bwlizard

Just asking, are you saying the 8 1/4 is stronger than a 8 3/4 ? Maybe I misread your post.

It's not better it is equal though. The 3/4's biggest problem is flex of the axle houding. The biggrst prob for the 1/4 is the c clip design, but that's easily taken care of by a c clip eliminator kit from moser. The 1/4 has no flex. Other than slower gear changes they are pretty equal. The main reason the 3/4 was replaced with the 1/4 was cost to build.

[drag-n-cuda]

dwc43,
What is the weights of you race cars and transmission used. I know circle track cars can get so awesome bite, but I'm failing due to shock loading a heavy car.

drag-n

[littlecampbell]

Thanks for the info drag-n-cuda.....I have a stick car also that has not seen the track. Thats the main reason it hasnt. I'm currently running an old 657 and it sure seems these 4 speeds are very tough on rear ends. I dont have a replacement laying around or the money for one at the moment. When you crash your rear where is the damage done? Anyone actually have pinion shaft break?

[1972roadrunner]

just be sure everything is setup correctly inside.

in my manual transmissions/transaxles and driveline class at college, a guy brought in a ford 9 inch that was making noises and not moving the truck...

turns out, he read somthing in a magazine that said he could get better towing results or sumthin by adjusting the backlash... ended up completely stripping the pinion nearly flat, and the ring was very bad in several spots where the pinion spun on it...

wonder if he filed that lawsuit yet?? i dunno, he got a set of 4.11's (i think) for the 9" for more towing torque for his horse trailer and camper.

oh, my professor has a slant 6 wagon (or sumthin) with a 8 3/4 and 5.##? in it. i think it runs 12's or 13's i can't remember, but he said the same thing about flex being a weak thing in the 3/4, but gear swaps and setting backlash/brg pre-load was much easier. i had a hard time setting backlash in my 1/4! had to build my own tool!

[dwc43]

Originally posted by drag-n-cuda
dwc43,
What is the weights of you race cars and transmission used. I know circle track cars can get so awesome bite, but I'm failing due to shock loading a heavy car.

drag-n

3490 loaded on dirt and around 3600 asphault. Trannies are 3 spds or A 833's. And dirt is by far more harder on a rear gear and really the whole car compared to any other form of racing.

[Marc]

My brother had a 1963 S22 Comet with a Ford 9", and he broke the pinion in half with the STOCK 260 ci engine.
Strange?

[Sterling]

I have not broke a ring and pinion racing yet, just lucky. I have put hairline cracks in pinions, I guess because the pinion is so small with 5.38 and 5.57 gears. I think the weak link with 8 3/4 rears is the small pinion and the caps that hold the carrier to the housing. I have seen at least 2 break there. My last 742 rear I put the Mark Williams caps on it.

[dwc43]

Actually it's not the caps at fault. It's the flex from the axle housing. It stress's the the caps to the point of bearing wear or failure. Moser sells a weld on back brace to eliminate the flex problem.