Diff housings and brakes FB to HR - differences?

[vmx-mxr]

A spin off from EKjimmy ....

With the two drum to drum diffs (FB and HR) side by side it was a good opportunity to compare them.

Widths are identical

Centre casting appears identical - and GM parts bible confirms it with old FE to EJ #7408407 superseded by #7421813 which according to the manual will fit 48 to HR. #7421813 coincidentally is the part number for EH, HD, HR

Spring saddle spacing is identical although the pressings are vastly different which begs the question - is the HR mounting stronger, stiffer, better?
Backing plate mounting flanges on housing appear identical (meaning HR backing plates should bolt straight on meaning the self adjusting slave cylinders etc should all just bolt in)

I can't see any reason why you couldn't leave the housing and the centre in place and swap the brakes and shove the FB EK axles back in?

I guess what I am getting at is, can the FB EK housing and centre stay put and the HR brake assemblies be substituted along with their smaller slave cylinders?

Seems like it would save some jigging around and you wouldn't have to search for the elusive shock mounts or root around with the bump rubbers ?

While stuffing around we also measured a Torrie banjo housing and it is approx 70mm narrower - if that helps anyone

Comments and ideas please ....

Dave Mac

[Trev]

They have a different bolt pattern for the axles and backing plate to the flange.
Just considering the cost of brake cylinders for a HR ($22 each) and an FB/EK (around $100 or more each), also HR brakes on rear to match the HR front disc, there is 2 reasons to change over , Trev .

[thropzed]

I always use the EH diff housing Dunno why, But there is always one around when I need it.
Cheers Theo Z................................

[jake08]

Just changed mine over yesterday- Measured the width roughly- hr nearly an inch wider?

possibly the drums were loose because I was sure they were the same.

Not the best photos but thought some one might be interested- you can see the different bracket locations for the brake line splitter . I didnt want to use a custom hose or move the bracket so I got about four inches of bundy tube and used a front brake hose. (male/female)

[EKjimmy]

Jake, unless someones sold you a dud, when measuring the diffs go from the insides of the backing plates if they're bolted down tight. Measure from the same places on either diff and try to run your tape measure across the diff in the same way eg. if the tape measure goes from inside of backing plates and runs over the top in line with the seam weld across the width, do the same with the other diff.

[vmx-mxr]

Hi Jake

Now I'm totally confused, lol!

The two housing we have that are supposedly an FB (and I saw the rooted ute it was removed from) and an HR (which definitely IS an HR one) when measured up are exactly the same width between backing plates and the spring saddles are on exactly the same width centre to centre. It gets confusing when what I have looks the same as what you have in your pics except the casing at the back on mine are both the same (later style) and yet everything else including the spring saddles ie the later bigger HR and the smaller FB EK ones are like yours, and yet a look at both EK's here show the bulge yours has for the crown wheel. Stuffed if I know?

I'll try and get pics but was wondering if the supposed FB housing could be an EJ EH one?

Any clues anyone?

Dave Mac

[ben jones]

If the centre shape is the same as the HR but it has sadle plates the same as the FB/EK then it's an EJ/EH housing
The very round smallish with bulge for crownwheel housing is FB/EK or earlier

[jake08]

Jake, unless someones sold you a dud, when measuring the diffs go from the insides of the backing plates if they're bolted down tight. Measure from the same places on either diff and try to run your tape measure across the diff in the same way eg. if the tape measure goes from inside of backing plates and runs over the top in line with the seam weld across the width, do the same with the other diff.

Jimmy you're absolutley right- if i had measured them that way they may be the same, with the difference being due to the drums,but as the whole reason was to use those hr brakes I needed to know my existing wheel rim combo would still be ok- as it happens it wasn't ? Maybe next post I can come up with some answers rather then more questions!

[fbvan]

Jake

So you used the HR diff, brakes etc. and the FB/EK axles fitted? Just finished with an extra inch in width?
Is that right? Why not use the HR axles too?
This model is new for me and I am not sure of the finer details with interchanging parts.

Brian

[jake08]

nope just changed the entire rear- all HR. This was the simplest option for me when upgrading the front end to a HR disk front. - combining disk front with standard EK/FB rear drums can result in rear brake lock up due to the cylinders not being designed for the boosted pressure.
Apparently the cylinders wont bolt into EK backing plates- and HR backing plates won't bolt onto the EK housing-
All i did was reunite the complete HR drum rear with the disk front it came from originally- as not all HRs had the disk front you need to be sure the rear drums( or at least the cylinders) are from a disk front car. As to the difference in width- i believe diff housings and axles are much the same- the difference i registered is either a result of inaccurate measuring or larger drums( havent compared them) in any case its only an issue if you have wider wheels and/or lowered rear.
If you want to do this you need to consider
-rear handbrake cable- still looking into whats required here myself but EK on won't do
-rear uni joint-hr is same part as front and is a u-bolt type- EK rear bolts to diff and has cast wings- these are expensive so good riddance
- bump stops - no real issue here but as you can see in photo Hr has them on the housing while EK are on the body .
- mounting- you can either use EK lower shock mounting plates with ubolts (EK) or the HR clamp/bolt type .

[reddo]

Use the entire HR rear end.
Backing plate stud pattern is square on FB/EK
Different to a HR.
Handbrake cables to suit HR in FB / EK are available on ebay from a bloke in Vic who makes them up.
Use the HR outer cable retainer clips to the body.

Flexible brake hose from body to HR brake block on housing fouls on shocky ( am running air shocks whic=h are fatter than stock shocks). move the block 30mm towards the diff centre.

Been through all this when i done the rear end on the FB panno 12 months ago.

HR housing sits straight on fb springs. same width.
cant use FB axles in HR housing unless you press the bearing off and replace with HR retainer plates which have offset holes ( not square pattern like FB) ... y bother just use the HR axles.

If the donor car or your car had/has a disc brake front end you will need to use the smaller dia wheel cylinders and shoes to suit.. also available from ebay foe $69.oo.
If you are converting the front to disc.....
Remove the restrictor valve from the drum brake master if running a disc front end otherwise the disc pads will clamp on .. and stay on when you apply the brakes

If ya simply wacking a HR drum brake rear out of an all drum donor car .. and your fronts are drums....then ya dont have to worry about any of the above... just whack it in... and change your rear uni to suit the HR yoke.and fit the ebay handbrake cable..
Clear as mud aye

Reddo