Disc Brake conversion of Live Axle RT104 RA40

**RT104GT** · 10-10-2006, 12:32 PM

Hi guys:
Went to the wreckers yesterday and did a bit of research and matching:
I hope I'm not reinventing the wheel:
One of the big hassles in the late 1970's was the drum brake rear ends of the Toyota stock like RT104, T18 and RA Celicas.
The hassle with the 104GT was the disc brake booster and the poor pressure differential resulting in locked up rear end under high rate stops.
I remember both Hilton and Hurray in the 1979 Repco trying to source a rear disc brake assembly for the Liftback 18RG powered Celicas they were running, reason mainly after creek crossings no rear brakes and often running off in corners due to low brake performance.
Hurry solved the problem in time but in hindesite they needed to wait 11 years for the coil spring live rear axle of the Avante Corona RT142 with the 22RE which needed to stop well.

First I removed the axles and diff from a Corona Mark 2 and noticed that when you pull the axles out there is a four bolt backing / bearing plate assembly which has the handbrake cables and the shoes fitted and a hydraulic piston.

BACKING PLATE FRONT AND REAR SHOWING CALIPER MOUNTING AND HANDBRAKE LEVER.

The AVANTE RT142? also has a matching four bolt rear assembly which holds the bearing retaining plate and a thick alloy caliper mounting plate/handbrake assembly.

SO I removed this and measured it against the Corna 104 and the Mark 2 MX 13 Corona rear using the studs from that and it fitted perfectly.

So the questions are:

Are the studs from the Mark 2 sufficient to take the strain of the rear disc brake backing plate?
OR Should I tap the Corona diff housing and use the large (15mm) headed bolts used in the Australian Assembled AVANTE? (I hate non standard metric measurements that are ODD i.e. not 10,12,14.)

The handbrake and fluid lines are a formality that I need to sort out,
such as mounting the brackets for the steel/hose attaching unions and looping the handbrake cable from the Avante into the Corona system.

Do I need to put the Avante pressure relief valve in the rear brake liens? Or no?

QED

PHOTOS.

ROTOR INSIDE and DRUM HANDBRAKE

ROTORS

CALIPERS (Brackets hold/secure steel brake line and provide a flexible line support
These need to be secured somehow on the Corona/Celica axle housing to take the early steel line which normally terminates at the backing plate on the drum brakes.

BACKING PLATE/HANDBRAKE LEVER. This uses a loop attachment and short steel cable..

COMMENTS PLEASE?

**TurboRA28** · 10-10-2006, 01:53 PM

I just used the Corona MKII bolts/nuts to hold the backing plate on.

I used the rubber section of the Advante brake line that goes onto the caliper and re-routed my original steel lines to suit.

Still trying to work out what to do with handbrake cables. I am using RA28 ones with the ends cut off, looped over, and crimped in place. Not working so well.

I removed the valve from the master cylinder that sits on the rear brake line. I used a 4 wheel disc brake bias valve. Seems pretty good but I think the rear brakes could have more bias. Might invest in a adjustable valve one day.

**RT104GT** · 10-10-2006, 02:48 PM

I just used the Corona MKII bolts/nuts to hold the backing plate on
Are you happy with the securing using the 14mm nuts? Did you use the bearing plate from the Avante or the Mark 2 one that has no ring? The AVANTE has a ring extension that matches the bearing diameter

I used the rubber section of the Advante brake line that goes onto the caliper and re-routed my original steel lines to suit.
Did you use the small steel plate held by two 10mm that was bolted to the Avante axle or if not how did you fasten the junction between the rubber and the steel line to the axle housing?

Still trying to work out what to do with handbrake cables. I am using RA28 ones with the ends cut off, looped over, and crimped in place. Not working so well.
How about taking the whole cable all the way back to the handbrake lever or even using the whole assembly unbolted from the car, that way the saddles could loop around the handbrake activation-lever in the backing plate, like they are supposed to?

I removed the valve from the master cylinder that sits on the rear brake line. I used a 4 wheel disc brake bias valve. Seems pretty good but I think the rear brakes could have more bias. Might invest in a adjustable valve one day

Yeah I am concerned about this also, if you lock up at high speed you could come to grief not enough and you cant stop!

**TurboRA28** · 11-10-2006, 10:00 AM

Mine's all a bit povo at the moment .. But...

I didn't have any concerns about the 14mm bolts. But i'm not an engineer either so probably not qualified to answer that. I just went on the basis that is what everyone else has used that has done this conversion and never heard of any failures.

The bearing retainer ring thing... I made my own out of some mild steel tube and they are more like a C shape so they can be slipped on and off without pressing the bearing off.

The plate with 2x bolt holes on the brake lines, its still there just floating in the wind. One day i'll weld a bracket to the diff housing and secure it.

Good idea about the handbrake cables.. Let me know how you go!

I have no problems with the rears locking, I feel like they are actually not getting enough fluid? Never had them lock up before the fronts anyway. Maybe the MA70 bias valve is pretty spot on!

Cheers
Joel

**GA61XX** · 11-10-2006, 12:29 PM

as i have done a few of these drum to disc conversion's here is what i know so far ! The corona RT142 or RT141 disc brake rear will fit straight into the RA40 and RA60, ( plug & play ) use's corona handbrake cables, and for W57 manual i have used the tail shaft from an auto RT141-142,
When i have done TA22,s it is best to get a RA23-28 diff as they have the same wheel bearing & stud's,you will also need the uni' joint for the tailshaft.
So when doing the RA23/28/40/60 disc brake upgrade, you will kneed a RT141-142 dona' diff for parts like bearing retainer plates L. & R., also 2 handbrake cables L. & R.
Bolts used.. 8 new 10mm x 45mm long metric fine High tensile bolts ( these will use the orig' nuts).
So when doing the RA23-28 disc upgrade, you will also have to cut off the old shocker mounts & weld the mounts on from the dona' diff, as the shockers will hit the new calipers if you don't .

also 2 x drivers side handbrake cables ( this is the short one )