I am about to pull my rear end to replace the front seal and since I am going to have it out from under the car what else should I replace? I am a little bored waiting on my short block to come back from the machine shop so I have a little time to kill. I have a set of HR upper and lower control arms that I am going too install a the same time but is there a common failure mode with these things or are they pretty bullet proof? Ring and pinion, new rear cover? Axles are a little much at this point after spending so much on my new motor but I also don't want to find the next "week link" either. The new motor should be putting out anywhere from 750-850 HP, are these rear ends ready for that?
Rear end upgrade?
- Thread starter Nero328
- Start date
if you're going to really make the power you're quoting than everything has to be replaced.. larger billet pinion, different carrier with larger axles and the rear girdle.. it all has to be done. I don't know if any of these original parts, especially the factor posi, has lived reliably past low 10's.
Depending on how it breaks, it can really mess up some stuff. Rear end to Transmission all the way to engine thrust. Hate to scare you, but it's a concern.
If you're asking this question, what about all the supporting drivetrain and fuel system?
By the way, if the pinion seal is leaking, likely your pinion bearings are suspect.
Depending on how it breaks, it can really mess up some stuff. Rear end to Transmission all the way to engine thrust. Hate to scare you, but it's a concern.
If you're asking this question, what about all the supporting drivetrain and fuel system?
By the way, if the pinion seal is leaking, likely your pinion bearings are suspect.
Yeah, I suspect the pinion bearings for sure and was thinking that all bearings should be replaced while I am in there. I have already replaced the trans with an Art Carr built 200R4 and 9" NL converter. The driveshaft has been replaced as we'll with an aluminum set up from Kirban. I believe I am going to need a second fuel pump but have already replaced the first one and a Hotwire kit was already on this car. I am running 80# injectors with Alcohol so I am fairly certain I will need another pump...any thoughts on that too?
So...it sounds like this rear end is nowhere near ready for this kind of power. Would it be better to just go with a Ford 9" or something? I would rather keep the stock rear end housing to at least make it appear to be stock. This is in a very clean 87 GN so I don't want to do anything that I can't undo later. If I ever decided to go back to stock.
My motor is a stock block 4.1 (obviously not original to this car) 4" bore with all forged internals, Champion Aluminum heads with double springs and Scorpion Roller Rockers, Champion Aluminum intake . 9:1 compression with billet main caps and a high output oil pump. 3/8 push rods and roller cam that is custom ground but pretty tame with a gross lift of .562 intake and .547 exhaust and 110 degree lobe center separation. I am sure I am forgetting something on the motor but you get the picture I think. I am certain that this motor will make 650-700HP but I have been told by others on this board that I am looking at somewhere between 750-850. Oh...I am running an old school TE 66 and plan to run around 23-25 PSI boost levels.
So...it sounds like this rear end is nowhere near ready for this kind of power. Would it be better to just go with a Ford 9" or something? I would rather keep the stock rear end housing to at least make it appear to be stock. This is in a very clean 87 GN so I don't want to do anything that I can't undo later. If I ever decided to go back to stock.
My motor is a stock block 4.1 (obviously not original to this car) 4" bore with all forged internals, Champion Aluminum heads with double springs and Scorpion Roller Rockers, Champion Aluminum intake . 9:1 compression with billet main caps and a high output oil pump. 3/8 push rods and roller cam that is custom ground but pretty tame with a gross lift of .562 intake and .547 exhaust and 110 degree lobe center separation. I am sure I am forgetting something on the motor but you get the picture I think. I am certain that this motor will make 650-700HP but I have been told by others on this board that I am looking at somewhere between 750-850. Oh...I am running an old school TE 66 and plan to run around 23-25 PSI boost levels.
A property built 8.5" rear end will hold up to all of the power that your engine can make. That is limited by your turbo and what your engine can absorb. Your weakest link will likely be the engine itself with the limit being the supporting parts. It's a money and "want" thing at your proposed power levels. If you want a 9", then it'll handle the power we all know and will be trouble free. If you don't want a 9", an 8.5" can be done with proven parts and levels of reliability depending on what mode you do to it: what type of carrier, what sized axles, welding bracing axle tubes, etc. Either way this is going to cost you.
I don't "want a 9" but I also don't want to spend 4X as much to make an 8.5" work. I ,now I can go buy a 9" with new 31 spline axles and a new ring and pinion for around $1600 but I would rather build the 8.5" and make it bullet proof for around $900...am I in the ball park here?
I will upgrade this turbo one day so I do want to make the rear end solid but I can take it easy on this thing until I figure out what I want to do too. It seems finding an 8.5" is not too hard to do so I may even find a donor rear end and build a bullet proof system and keep this one stock after rebuilding it of course. My guess is that the ring and pinion are ok...it just needs a refresh after many hard miles.
Ha, no...not yet but there will be one day soon. Several people have asked me that now...is there that much of a concern about the stability of these cars?
- Joined
- Jan 3, 2012
The axles are probably the weak link in the stock rear. I have a similar build to yours that is close to completion except it's a stroker. My rear has a rebuilt stock posi and carrier, stock ring and pinion, 1350 yoke, Moser 28 spline axles, and a TA girdle. For the power levels your talking about I think every piece except maybe the gear set will need to be upgraded.
If your build is similar to mine what do you think about the quoted HP numbers? I am really just going off of what others have told me this thing will make. This is my first GN and of course the first GN motor I have built so I don't have anything to go off of.
- Joined
- Jan 3, 2012
I assume we're talking about rwhp. I think 750+ is unrealistic. At that point the 4.1 block's integrity is questionable. 550-600 or so is more likely. My old 4.1 combo made 430whp on 20psi and alky with low timing. There are some 4.1 builds on this board making 600-700whp without issue.
Ok, I was really thinking around 600-650 was most likely where it would get comfortably but I would really be happy if it was 500-550 RWHP. I don't really want to be pushing this thing to the max...I want it to be reliable! So with those numbers is this rear end still questionable or will it be to go back together stock? I think it's cheap insurance to just replace the axles with some modern ones, do you think I am safe to stop there or are we still talking a full upgrade?
- Joined
- Jan 3, 2012
With a couple upgrades the rear should be reliable at that level.
Thats what I figured you were referring to. I don't think this car is going to get there. Now, I have been bitten by the GN bug so it's not completely out of the question to reach that HP level but this car is just too nice to start installing a roll cage. I did find a car last night that might be the one to make into a track queen....now I just have to convince the finance committee!
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