AMC20 Advice

I'm about to embark on putting an AMC20 rear end together to go in my Gremlin. The primary purpose of this car is to go drag racing with slicks and maybe a little bit of tarmac rally/motorkhana stuff, probably won't see any normal road use. Will initially run a fairly stock 360 and 727 and would aim to eventually see it run low 11s with future upgrades.

At this stage I have an AMC20 housing out of a Hornet, new Truetrac centre, new 4.10 gears and an install kit. I also have a pair of Moser axles that I originally bought for my 69 Javelin, so I'm hoping to use those with a bit of a Dr Diff style trim if necessary to make them fit.

I will probably get someone to install the centre and setup the gears to make sure it's done right. AMC20 rear ends aren't exactly commone here, so just need to know if there any traps I should look out for with the installation side of things to watch out for? I'm thinking a crush sleeve eliminator would be a good idea, I think they use the same one as a 9", so hoping I can source one locally.

Is there anything I should be doing with the housing, I see some people reinforce the spring perches and weld the axle tubes in?

Should I run the bigger 10" x 2" rear drum brakes on it or leave the original narrower ones on there?

Cool, I didn't check the drum width, just know I have fat and skinny ones available to me.

Somewhere I read an article, I wanna say it was in the Tough Americans newsletter from NAMDRA, about a fella in the Illinois area who rebuilt his AM20 for road racing.It may be on here too just can't remember.

From memory,

Reason for staying with a 20 instead of Ford 9 inch is because 20 is lighter yet retains the same or very close to strength of the nine inch (8-7/8 ring gear on a 20)
Used larger three inch Ford 9inch axle tubes, had center section machined to fit larger tubes.
welded tubes to center section.
Used Ford 9 inch axle flanges so he could install better aftermarket brakes made for Fords (more common)
I don't think he was using a full floating axle, I wanna say he used one piece axles, the reason for the 9 inch axles and flanges is because the axle bearing is larger as well as the axle shaft.

He said he ran the stock 20 until it broke an axle. He tried I wanna say Moser one piece axles but they broke too, so he went with the above mentioned setup. No more failures.

This guy did really well in whatever series he raced in, winning much of the time. I think he retired from racing because of old age. He raced a Humpster Javelin


Edited by White70JavelinSST - Mar/01/2017 at 11:32am

The stock axle uses tapered roller bearings, and those must have the right endplay, set by shims. The differential has a spacer in the middle that the axles butt with to transfer end loads, so the length of the axles is critical to endplay. You need to have the right length axles to a pretty accurate level to have the right endplay, so be very careful of swapping them.

WesternRed wrote: That sounds like a lot of work went into it, I think at that stage I would just run a 9" and be done with it. I know the left side axle is the same between Hornet and early Javelin because I originally bought the Hornet diff and used this axle to replace the one in my Javelin which spun a hub. Pretty sure the other side is a little different in length. If there is not enough spline, I will just install the axles in my Javelin and take my chances with the two piece axles in my Gremlin. I'm wary or doing any welding one the housing unless it is absolutely necessary as there is always the risk of heat distortion from the welding and the potential of putting something out of alignment. If people are routinely ripping the spring perches off for example then I will address it, if it's just a precaution for the sake of it, then I will probably leave it alone. Fairly light car with not a lot of power at the moment even accounting for the slicks, so it's not going to be too stressed hopefully. I can only run down to 11.00 under the local regs before I have to install a cage and that is not in the current plans, so low 11s is the current goal.

Factory AMC20, with a fresh torque of the axle nuts oughta handle an under-powered light drag car with no issues....why even worry then??