Thunderace Rear End Transplant

This mod 'kills several birds with one stone'. Okay, so what do you get for your money? There's a chunky new alloy swingarm, an underslung caliper unit and a 5.5" rim sporting a 170/60x17 rear tyre. It is possible to fit a 180/55x17, but more of that later.

In short this mod is an excellent way of getting a modern rim, so that you have better tyre options than the standard FJ doughnut or lorry tyre, as it's commonly called.

It gives a firm, taunt feel to the rear and does seem to 'turn in' quicker, probably due to the slightly shorter wheelbase. The mod is largely cosmetic, but even at this early stage I do feel there is a positive gain in rigidity and handling. In fact the more I ride it the more I like it!

Acquiring the rear end shouldn't be a problem and needn't be expensive. The rear end seldom gets damaged in an accident, so the breakers are full of Aces with good rears. You'll need the whole rear section, but not the shock absorber or suspension linkage, as the OEM one's are used.

Note:- I have carried this this mod out on my 1990 FJ. Suspension linkages vary from model to model, so please read and satisfy yourself whether the same mod is possible to earlier and later models. (Go on, you're a clever bunch, you can do it!)

PLEASE NOTE - AS WITH ALL MODIFICATION WORK MENTIONED IN THIS SITE, IT IS ENTIRELY THE RESPONSIBILITY OF THE PERSON CARRYING OUT THE WORK TO SATISFY THEMSELVES THAT THE WORK IS CARRIED OUT SAFELY AND TO A SATISFACTORY STANDARD. ALL DETAILS CONTAINED WITHIN THIS SITE ARE GIVEN PURELY AS INFORMATION ON WORK I HAVE CARRIED OUT ON MY OWN BIKE. I ACCEPT NO RESPONSIBILITY FOR ANY DAMAGE, INJURY OR LOSS, BE IT FINANCIAL , PHYSICAL OR OTHERWISE TO ANYONE CARRYING OUT SIMILAR WORKS. Sorry, but you knew that already. Right?

1. First step is to reduce the width of the swingarm across the bearing tube at the front of the arm. The Ace arm is 8mm wider at this point.

Don't panic ! This is nowhere near as difficult as it sounds. First , using your original FJ rear wheel spindle and suitable packing pieces, press the existing Ace swingarm bearings, 4mm further into the bearing tube, on each side. Using some insulation tape, or similar, put a ring around the 4mm mark. Also mask the bearings up to prevent contamination with swarf. Now with a DECENT hacksaw, not some cheap and cheerful 'go where it wants to' piece of crap, remove the 4mm. Try not to remove too much and try above all to keep it square.

At this point I must say, that as always you must have at least some competance as far as hand tools are concerned. Sure it would be better if you took the lot down to the machine shop, had it all jigged for squareness and the 4mm milled off. But we're not talking critical clearances here. By taking some care and checking with a square afterwards, the whole thing can be accomplished to completely satisfactory standards. Once done the OEM FJ dust seals/end caps locate on the ends to form the contact surface with the frame itself. The original FJ swingarm bearing inner sleeve, through which the swingarm spindle passes, is used instead of the Ace one.

2. Unlike the Exup wheel conversion, the wheel is already centralised. This time it's the chain alignment that has to be addressed. This is done in two stages. First the studs in the sprocket carried (cushdrive hub) need to be removed. I found this easiest done by locking two nuts on the stud, then heating in a domestic oven to about 250C. You may need to reheat between extracting each stud. Once done get the carrier down to your friendly engineer and have 5mm removed from the sprocket mating surface, so that the sprocket sits further onto the carrier. If you've got a lathe and can do this yourself (you flash b*stard :>).

The OEM Ace sprocket rear sprocket is 46T and needs to be changed. I'm using a 40T Renthal alloy item. The jury is currently out on whether this will last the trip, as I've heard mixed feelings about these alloy sprockets. I'm using an 18T front sprocket (steel of course!), but I suspect I may want to go down to a 38T on the rear later. Once you get your sprocket, you will notice it has one side that is recessed but about 2mm. By reversing the sprocket's normal mounting a further 2mm is gained.

Left View

Right View

Home Made Links

Duly Modified

3. Finally a new pair of suspension links 'dog-bones' have to be made. This is to 'adjust' the ride height back to normal levels, as the Ace linkage geometery differs from the FJ's a little. Again, don't panic, this is basic stuff. I used 1 1/2"x 3/16" bright mild steel plate. I made mine 3 5/8" between centres. (shorter will raise the back end further, but the shock then starts to foul the swingarm; a cut and shut job on the central swingarm brace would then be necssary). Basically cut to length, mark the centreline and drill the holes at each end. As seen from the picture, mine are substantially more robust than OEM, simply to ensure they are up to the job. The things to remember when drilling the holes are one; use a pillar drill or similar, to ensure the holes are completely square with the plate and two; drill both plates together (one on top of the other) to ensure the holes are exactly the same distance apart. Shape 'em up, make 'em pretty. Job done!

 

ASSEMBLY:- Assemble the swingarm bearings using the FJ inner sleeve and end caps. Use the FJ swingarm spindle. The linkage bearing sleeve (inner) in the Ace swingarm is about 5mm shorter than the FJ's. Either use this with appropriate spacers (as I did), or use the FJ one with rubber sleeving to prevent corrosion of the exposed part of the sleeve. It will all become apparent when you see it.

There is a clearance issue between the swingarm and rear silencers. I have a 4 into 1 fitted and merely loosened all the clamps and found there was sufficient 'give' in the system to move the silencer out about 3/4". This is enough. I can't say however, what the situation would be with OEM silencers at this stage.

180/55x17 TYRE - Initially I contemplated fitting the big 180, however several factors stopped me. Firstly it involves packing out the front sprocket or buying an offset one (which are expensive), to make sure of suffient clearance between the tyre and chain. Secondly, I felt it would only serve to slow the rear end down further and being lower still in profile would reduce ground clearance slightly. Lastly the difference between the 180 and 170 when measured was in fact very little. My D207 170/60 actually measured 175mm, whilst the BT57 180/55 was only just 180mm. So very little actual width difference existed.

 

That's probably the last Mod I'll be doing to the FJ for some time now. Domestic chores beckon and a move of house planned, with much needed workshop facilities.

My next project will be a ground up rebuild and to start looking at what I can do with the lump !

Since 'paving the way' with this particular modification, it has grown very popular. Check out these other FJ's with Ace swingarms :-

Marc Rittner's FJ

Dave Carter's FJ

Dave Dean's FJ

 

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