BobMurphy
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- Joined
- Mar 1, 2010
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Aarrrgh, No . . . Not another Handbrake thread 
.
Well, sort of. I've just carried out a modification that I've been wanting to do for yonks and my non-functioning handbrake is now brilliant
.
We have covered the assembly and setting-up of the handbrakes many times on different threads and websites so there is nothing new here, however I thought I'd show you all what I did
.
The mechanism:
The adjuster is at the bottom of the shoes and spreads them out to give the correct running tolerance with the drum. Despite this, there is always far too much motion at the Bellcrank Lever at the back which ends-up pulled well away from the backplate.
The reason for this is that the Bellcrank pulls a cable that pulls the lower end of a lever that pivots at the top of the leading shoe. The lever bears on a steel bar (the Parking Brake Shoe Strut) that links the two shoes together. The contact is a little over one inch below the pivot point meaning that there is about a 5:1 mechanical advantage on the force applied to the shoe by the cable.
Unfortunately this also means that the lower tip of the lever has to move five times the distance of the shoe.
The 'Strut' is a Compensator, when one shoe contacts the drum the lever keeps moving until the other shoe is also in contact. The same force is thereby applied to each shoe.
Spreading the shoes at their lower end via the adjuster has little effect on the top of the shoes where minimal clearance is required if we don't want excessive lever/Bellcrank movement.
The answer is to increase the length of The Strut to give minimal shoe clearance. This has been done before by someone who welded up the slots in the Strut to spread the shoes further. This can then be adjusted (down) with an Angle Grinder until the minimal clearance is obtained.
I took a slightly different route. . . . . . .
I started by closing the adjuster right up on one side and slackened the O/S handbrake cable (on the '90 Series' the cable adjustment is at the handbrake lever, on the '100 Series' its in the cable that stretches across the rear of the back axle). This meant that the Bellcranks were slack and I wound the adjusters out so that the end of the Bellcrank was as close to the backplate as it could get.
I then pulled one Bellcrank out as far as I could without damaging the springs and noted where it was pointing.
I then removed the rear disk and noted the clearance between the 'Strut' and the shoes.
I pulled the Bellcrank back to where it had been and noted the new clearance between the Strut and the shoe. it had increased by at least 5mm.
As the handbrake hadn't been 'on' at all during this exercise I knew that I could increase the length of the Strut by 5mm whilst keeping running clearance.
The original, standard Strut can be seen spanning the shoes here:
It was all renewed last year and had been washed with Industrial de-greaser for the pictures
.
I then measured the distance between the inner end of the slots in the Struts - 69mm.
I decided to increase the length to 74mm.
I cut the strut in half and set it above a piece of 2mm steel plate at the appropriate distance:
I then clamped the assembly between two welding clamps and held them in a vice:
After welding & grinding down the result looked like this:
A coat of silver 'Smoothrite' later and the original and modified Struts look like this:
Before modifying the second one I fitted the first one to the brake:
Fitting the disk/drum showed that I still had running clearance with everything slackened off.
So the second was also modified.
On re-assembly, I fitted the disks and put a couple of wheel nuts on each to hold them steady in their running position.
I then opened-up the adjuster until I was just getting shoe contact with the drum on each side.
The Bellcranks then brought the handbrake on well within the reach of the adjusting setscrew that holds them off the Backplate. I pulled each on lightly and wound the adjuster in to give a 2mm gap with the backplate.
I then tightened the cable adjuster at the rear differential - it needed far less thread than before.
The rear disks rotated cleanly so I fitted the wheels and took the 100 for a run around the yard . . .
The Result:
"Bloomin' Amazing". Before, the handbrake was just an ornament and wouldn't stop the truck creeping in 'Drive' or 'Reverse' on tickover. Now its solid, the handbrake is on with the lever half-way up its travel and it will hold the truck and a heavy trailer without any problems.
I took it for a spin on the road today and its a huge relief to have it working properly. I highly recommend this 'mod'
.
I can tick that one off (just need to do the same on the '95
).
Bob.
.Well, sort of. I've just carried out a modification that I've been wanting to do for yonks and my non-functioning handbrake is now brilliant
.We have covered the assembly and setting-up of the handbrakes many times on different threads and websites so there is nothing new here, however I thought I'd show you all what I did
.The mechanism:
The adjuster is at the bottom of the shoes and spreads them out to give the correct running tolerance with the drum. Despite this, there is always far too much motion at the Bellcrank Lever at the back which ends-up pulled well away from the backplate.
The reason for this is that the Bellcrank pulls a cable that pulls the lower end of a lever that pivots at the top of the leading shoe. The lever bears on a steel bar (the Parking Brake Shoe Strut) that links the two shoes together. The contact is a little over one inch below the pivot point meaning that there is about a 5:1 mechanical advantage on the force applied to the shoe by the cable.
Unfortunately this also means that the lower tip of the lever has to move five times the distance of the shoe.
The 'Strut' is a Compensator, when one shoe contacts the drum the lever keeps moving until the other shoe is also in contact. The same force is thereby applied to each shoe.
Spreading the shoes at their lower end via the adjuster has little effect on the top of the shoes where minimal clearance is required if we don't want excessive lever/Bellcrank movement.
The answer is to increase the length of The Strut to give minimal shoe clearance. This has been done before by someone who welded up the slots in the Strut to spread the shoes further. This can then be adjusted (down) with an Angle Grinder until the minimal clearance is obtained.
I took a slightly different route. . . . . . .
I started by closing the adjuster right up on one side and slackened the O/S handbrake cable (on the '90 Series' the cable adjustment is at the handbrake lever, on the '100 Series' its in the cable that stretches across the rear of the back axle). This meant that the Bellcranks were slack and I wound the adjusters out so that the end of the Bellcrank was as close to the backplate as it could get.
I then pulled one Bellcrank out as far as I could without damaging the springs and noted where it was pointing.
I then removed the rear disk and noted the clearance between the 'Strut' and the shoes.
I pulled the Bellcrank back to where it had been and noted the new clearance between the Strut and the shoe. it had increased by at least 5mm.
As the handbrake hadn't been 'on' at all during this exercise I knew that I could increase the length of the Strut by 5mm whilst keeping running clearance.
The original, standard Strut can be seen spanning the shoes here:
It was all renewed last year and had been washed with Industrial de-greaser for the pictures
.I then measured the distance between the inner end of the slots in the Struts - 69mm.
I decided to increase the length to 74mm.
I cut the strut in half and set it above a piece of 2mm steel plate at the appropriate distance:
I then clamped the assembly between two welding clamps and held them in a vice:
After welding & grinding down the result looked like this:
A coat of silver 'Smoothrite' later and the original and modified Struts look like this:
Before modifying the second one I fitted the first one to the brake:
Fitting the disk/drum showed that I still had running clearance with everything slackened off.
So the second was also modified.
On re-assembly, I fitted the disks and put a couple of wheel nuts on each to hold them steady in their running position.
I then opened-up the adjuster until I was just getting shoe contact with the drum on each side.
The Bellcranks then brought the handbrake on well within the reach of the adjusting setscrew that holds them off the Backplate. I pulled each on lightly and wound the adjuster in to give a 2mm gap with the backplate.
I then tightened the cable adjuster at the rear differential - it needed far less thread than before
.The rear disks rotated cleanly so I fitted the wheels and took the 100 for a run around the yard . . .
The Result:
"Bloomin' Amazing". Before, the handbrake was just an ornament and wouldn't stop the truck creeping in 'Drive' or 'Reverse' on tickover. Now its solid, the handbrake is on with the lever half-way up its travel and it will hold the truck and a heavy trailer without any problems.
I took it for a spin on the road today and its a huge relief to have it working properly. I highly recommend this 'mod'
.I can tick that one off (just need to do the same on the '95
).Bob.
).
