Assembling Jag rear in ERA subframe

Carnut427 · #1 (**permalink**) 02-03-2005, 12:07 AM

Bob, I've got a '95 XJS rear with outboard brakes. You folks shortened my lower control arms, but my halfshafts are a bit longer than the standard XJ units, so I had to shorten them on my own per dimensions you furnished. I made them a bit short so I could adjust the camber. I'm finally assembling the unit in one of your subframes. I've got the top housing mounting bolts loose and the unit upside down on the bench. I installed the inner fulcrum shaft through the subframe and differential bracket on the right side and the bracket is tight against the differential. I installed the left fulcrum shaft through the subframe and differential bracket and it's going to need .087 of shims. The differential housing will not move side to side to change this (everything has been powdercoated, so the bolts holding the housing to the subframe are snug in their holes). I'll have trouble getting my camber correct with this discrepency. My thought is to elongate the housing mounting holes in the subframe to center the housing in the subframe. Is this the best cure?
THANKS,
Dan

RICK LAKE · #2 (**permalink**) 02-03-2005, 04:21 AM

Dan The cradle is made in a jig. I have inboard brakes and had the same problem. I oblonged the holes where the lower rod goes through. This is not right but worked for me. Doug checked it out and said I was 1/2" off in toe but I checked it on the alignment rack and with my 220lb in the car it comes up fine. I would like the small blocks at the bottom just tac welded, this way you could but the rear in, adjust plates, remove have welded and coated and reassembled. Rap it in paper before you put the rear in the car, it saves the paint.

Rick Lake

ERA Chas · #3 (**permalink**) 02-03-2005, 07:39 AM

Dan,
I had CWI replace my center section with a modified unit as core - exchange. When the new unit arrived, I had the same problem as you. Bob's advice at the time was to slot holes as you describe. Worked perfectly. Be sure to drill/safety wire the bolts.

strictlypersonl · #4 (**permalink**) 02-03-2005, 10:13 AM

Dan,

Grind out the uppper differential mounting holes so that you can center the lower brackets. We never have to mickey-mouse the differential into the subframe, but we do clean the powdercoating out of the holes. Also, make sure that the mounting surface of the top plate doesn't have any powdercoating "runs".

Maybe the later ('95) casting was a little different.

Carnut427 · #5 (**permalink**) 02-03-2005, 12:59 PM

Bob, I obviously cleaned the powdercoating out of the fulcrum shaft holes, but not the top housing mount holes. There are no runs in the powdercoat on the subframe, and I taped off the mounting areas on the housing, fulcrum shaft brackets, etc. before I had them powdercoated.
You're the engineer, so I'll do as you suggest; however, Rick Lake's suggestion to modify the fulcrum shaft holes in the subframe makes more sense, as having the fulcrum pivot point over .040 away from it's original position is going to affect camber as well as wheel position. I could weld the hole back to the correct "round" size and shape so the pivot point would be solid.
Make sense?
Also, the bolts weren't safety wired on this unit as they are on my original. I beleive Jaguar uses loctite now.
Dan

strictlypersonl · #6 (**permalink**) 02-03-2005, 02:27 PM

I do not recommend making the the shaft holes bigger. They are what determine the toe-in of the LCAs. They are quite accurate. The bracket that bolts to the differential is not meant to take much side loading - it's there to integrate the stiffness of the differential casting into the subframe's.

Carnut427 · #7 (**permalink**) 02-03-2005, 09:02 PM

OK, you da boss...I'll remove the diff housing first & double-check it's mounting.
THANKS,
Dan

Mike Bontoft · #8 (**permalink**) 02-04-2005, 09:05 PM

Dan
Are the top bolts tapered, if not I would elongate these top holes, On the stock jag setup there are shims behind the side brackets to make everything line up. First center the diff then shim behind the side brackets as equally as you can so the shafts slide thru without much binding.
Mike
CWI

Carnut427 · #9 (**permalink**) 02-05-2005, 10:39 AM

The original top bolts are tapered, but I purchased standard grade 8 bolts as replacements. I've already got an inboard rear in the car, and rebuilt & assembled it when I first built #338 about 10 years ago, so I'm aware of how to assemble them, thanks to XKs Unlimited's excellent parts catalog and the Hanes Jaguar XJ6 manual. The Jaglovers website is also an excellent resource.
Thanks,
Dan

Carnut427 · #10 (**permalink**) 02-21-2006, 01:19 PM

Bob, I finally got around to comparing the original & outboard brake rears; I measured the threaded portion of the inboard pivot shafts outside of one shaft to outside of the other, as my original unit is still assembled. I also measured the outboard-brake rear from the outside of one shaft to the other (not over threads):

Cobra Rears:
Old, over threads: Front: 9.645
Old, over threads: Rear: 9.639 =.006 narrower in rear

New, over threads: Front: 9.637
New, over threads: Rear: 9.657=.020 wider in rear

New rear:
Front, over shaft, not threads: 9.766
Rear, over shaft, not threads: 9.783= .017 wider in rear

The gear case measurements are the same as the old, so the new inner pivot shaft bracket is evidently thinner.

My question is, are the measurements of my outboard brake pivot shafts within spec, as being wider in the rear will lesson the toe-out? It appears the toe-out is built into the lower control arm, correct? I've got around 600 flywheel hp, which I understand wants more toe-out?
THANKS for your help,

Dan

strictlypersonl · #11 (**permalink**) 02-21-2006, 01:31 PM

CN,

It's not ideal for accelleration, but for transitional stability, I'd keep some toe-in at the rear. When you have toe-out, you get slight oversteer when you start into a turn. When the effect is exaggerated, it's not a good feeling.

As far as the difference in bracket thickness, just shim as necessary.