Vanagon / T3 / T25 Rear wheel disc brake conversion

[willem maas]

Vanagon / T3 / T25 Rear Wheel Disc Brake Conversion

I decided to install disc brakes at the rear to bring the brakes up to the same standard as that of new vehicles in the same weight category as the T3. Although drum brakes are tried and tested it does have its drawbacks.
Drum brakes operate totally different than disc brakes. The leading shoe is "dragged" into the friction surface of the drum, thus achieving a greater braking force. The other shoe is "trailing", moving against the direction of rotation and is thrown away from the friction surface of the drum and is far less effective. This is why “trailing” shoes has a longer lining than the “leading” shoes.

By design, brake shoes’ efficiency varies from installation until replacement. When new brake shoes are installed, the contact area of the brake lining rubbing against the brake drum does not match the contact area of the drum. This is because the radius of the lining on the new brake shoe is smaller than the radius of the worn drum. (Even if new drums are installed this is still the case). Only towards the end of the brake shoe’s “life” will all of the lining area start rubbing against the drum as its radius increases because of wear. This is a major drawback of brake shoes because they are most “effective” when most of the lining area has worn off for its radius to be the same of the drum. None of this apply to disc brakes. Brake pads have consistent contact area on the brake disc from installation until it needs replacement.

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Most of the parts necessary for the disc brake conversion are readily available to be purchased, new or used. The only hurdle is the bracket where the brake calliper must be attached to. Fortunately, the bearing carrier has sufficient support for attaching a brake calliper bracket to it. Being not OEM, the bracket had to be purpose made. However, it can be purchased on-line in a kit, complete with all the fittings. Unfortunately, the poor exchange rate of ZAR compared to USD and other foreign currencies make these kits very expensive.

There are plenty of forums on the topic of DIY rear wheel disc brake conversions for the VW T3. After research on what other people had done and not willing to purchase the expensive bolt-on kits, I decided to make my own.
After the installation is done a brake service technician who has passed the ASE Series A5 certification exam, must inspect, test, and certify that the braking power complies to the minimum braking power for your vehicle.

Disclaimer: The parts, images, descriptions, and technical comment made are not instructions on how to do a rear wheel disc brake conversion. It is merely a list of parts and steps that I took to do the disc brake conversion. Therefore, the installation and/or making of the adaptor bracket is carried out at user’s own risk.


Parts:

The parts depicted below are the basic parts needed. The bolt lengths depend on the thickness of the steel used for manufacturing the adaptor bracket.
Allen Key bolts and Hexagon bolts used are high tensile 10.9 and 12.9 graded steel. All bolts, nuts, new wheel studs and castle nuts were sand-blasted, and zinc plated as can be seen in the images to follow).

Brake Discs:
VW Sharan 2.8 VR6 Syncro.

Brake calliper & carrier:
VW Golf MK4 1998-2005.

Brake Pads:
VW Golf MK4 Rear disc brake pads.

Handbrake cable & retaining clip:
VW Golf MK2.

The cables from the VW Golf Mk2 / Jetta 88-92 were used. It has the correct attachments on both ends, and the correct length between the caliper and the cable balancer.

M14 x 1.5 x 60mm long Wheel Studs:

Because the face of the brake disc is thicker than that of the drum, the original studs were too short and had to be replaced with longer ones. Bear in mind that wheel nuts must make at least six full rotations before starting to grip for tightening.

Brake fluid hoses:
VW GOLF MK4 adapted to fit.

I am not sure whether the disc brake conversion require a different proportioning valve in the brake fluid circuit. I asked a few brake service specialists about this but could not get a definite answer.

The front brake’s hydraulic pressure is always more than the pressure at the rear. The proportioning valve decreases the pressure sent to the rear brakes because the front brakes do most of the braking. If the proportioning valve is the wrong type or not functioning properly, the rear wheels may lock up when braking hard on wet or gravel surfaces. I couldn’t find any information on-line regarding hydraulic pressure values when drum brakes are replaced with disc brakes. It seems the only solution is to have the brakes tested at a reputable brake service centre which have the necessary hydraulic testing equipment.

I have done a few hard braking stops to see whether the rear wheels lock up or if the bus is veering left or to the right. Although the brake pads still need to wear in, the brakes performed better than expected. Surely, this way of testing is not scientific, but it gives a good indication that the brakes are working until I have them properly tested.

Here is my version of how I did the conversion.

Drum and 46mm nut removed.

Fortunately, the bearing carrier has sufficient anchor points for bolting the adaptor bracket to. When braking, only rotational forces are transferred to the adaptor bracket which is bolted to the bearing carrier. Four bolts are adequate to handle normal braking stress. After consultation with brake repair specialists, it was concluded that the backing-plate which held the drum shoes in place and bolted to the bearing carrier were subjected to comparable rotational stress when braking, as is the case with the new adaptor bracket bolted to the same bearing carrier.

Brake shoes, backing-plate and dowel at bottom removed.

All surface rust on the mounting surface for the adaptor bracket on the bearing carrier was removed with a grinder wire brush. Fortunately, South Africa’s roads are not salted during winter. My T3 is a 1996 2.6i model and has minimal rust.

Before I started the process, I compiled a drawing to keep track of the measurements necessary to make the adaptor plate. The dimensions are for reference only and depends on the type of brake disc, type of brake calliper as well as thickness of steel decided on to make the adaptor bracket.

For drilling, a template was glued in place on the steel plate and then punched. Photos taken during the making of the brackets are of the left and right brackets respectively and not necessarily in the order I made them.

Mild steel plate with holes drilled and material removed. The 5mmø (0.197 inch) drilled and tapped holes are for fastening of the splash / dust guard on the face of the bracket with M6 bolts.

8mm (0.315 inch) thick steel would have been strong enough for manufacturing the bracket. 10mm (0.394 inch) thick left-over steel plate from a previous project was used.

A separate piece of steel for bolting the calliper carrier to was used. It was cut from a section of 10mm (0.394 inch) thick angle iron.

A flat-Head Carbide Deburring tool in my drill-press was used to remove material to the correct thickness and shape.

The two sections of steel for the adaptor bracket were secured to a pre-drilled steel plate with bolts and nuts to ensure no warping took place when the two sections were welded together. Although not visible in the photo, shims varying in thickness was used to obtain the correct vertical height difference between the two sections of steel to ensure clearance for the brake disc / calliper carrier.

Final test-fit of the two sections spot-welded together.
It took several adjustments and test-fits of the adaptor bracket to ensure that the brake disc cleared the calliper carrier which is bolted to the lower part of the adaptor bracket. The clearance between the disc and the calliper carrier is about 1.2mm (0.047 inch).

The two sections after being welded together. Afrox Vitemax electrodes were used.

A cut-out in the lower section of the bracket is necessary for the calliper piston housing to clear the bracket.

The finished brackets after heat treatment.
Usually all supporting brackets for brake equipment are manufactured from hardened steel. Although the mild steel used for the brackets are 10mm (0.394 inch) thick, I had them heat treated, nonetheless.

I noticed that the adaptor plates from some of the kits available have a recess which matches the shape of the upper and lower tabs on the bearing carrier. I mentioned this to various brake part specialists to get their opinion. They all agreed that the recess is most likely to prevent the adaptor bracket from rotating if the bolts fail while applying the brakes. If the bolts fail, the next to fail will be the two smaller bolts holding the calliper to the calliper carrier.

If such a recess was necessary to prevent the braking assembly from rotating, the drum brake backing-plate would also have a recess and made from thicker material to accommodate a recess.
The weakest point (if any), on the whole fastening setup are the two 8mm locking bolts which holds the calliper to the carrier. If bolts are to fail for some or other reason, these bolts will most likely fail first, and not the four 10mm bolts holding the adaptor bracket to the bearing carrier.

I have been wrenching on cars for the better part of 40 years. I have never seen a disc brake setup where more than two bolts hold a calliper carrier in place, or where a calliper carrier is fastened to a bracket that has a machined recess.

[In hindsight it is a good idea to completely remove the two tabs from the bearing carrier. With the tabs out of the way, the adaptor bracket can be made so that it can be bolted directly to the bulkier section of the bearing carrier with the 22mm bolts. Such a bracket will require some creative designing, but it will be much more robust and way better secured by the larger bolts. If I experience problems with the current setup, I will make a bracket in this fashion].

The adaptor brackets are mirrored for the left and right callipers respectively. After heat treatment I sand-blasted, zinc-plated and finished them with yellow passivate.

The original hub before being cut to size to fit inside the brake disc.

The overall outside diameter for the hubs had to be 144mm (5.67 inch) to fit inside the brake discs. I was contemplating having the hubs machined to the correct size in a lathe to ensure 100% roundness to avoid vibration when it rotates. A machine shop advised me that the original hubs were not balanced anyway because of a cut-out on it the way it came from the factory. A twelve-sided polygon was used as a template to draw an outline on the hubs as a guide for cutting to size.

The hub after being cut and rounded to achieve the required 144mm (5.67 inch) diameter. With material removed, the balance will be better than the original hub with the factory cut-out. The diameter of the hub was reduced by 26mm (1.03 inch).

To correctly align the brake discs on the hubs, I drilled and tapped holes to receive M10 countersunk disc retaining screws. This was necessary because the stud-holes in the new brake discs are somewhat larger in diameter than the studs as measured over the protruding splines. I used my bench vice as a press to remove the old studs. I then sand-blasted the hubs and zinc-plated them as was done with the adaptor brackets.

A thrust-bearing and nut was used to install the new wheel studs.

Hubs with the new wheel studs installed.
Although the wheel studs are not head-stamped as 12.9 tensile strength, a hardness tester file confirmed the tensile strength to be between 39-44 HRC.

The holes in the face of the brake discs for the wheel studs have an inside diameter of almost 17mm (0.669 inch). The outside diameter of the wheel studs (as measured over the splines), are 15mm (0.590 inch). To ensure that the brake discs are centered on the studs/hub, machined steel sleeves were placed over the studs. The sleeves have an outside diameter of 16.9mm (0.665 inch), inside diameter of 15.1mm (0.594 inch) and a height of 8.5mm (0.335 inch).

With the brake disc positioned on the wheel hub, the sleeves over the wheel studs are flush with the face of the brake disc.

1.5mm (0.059 inch) thick stainless-steel sheet was used for the dust / splash guards to be bolted onto the face of the new adaptor bracket. I noticed that most of the kits are supplied without a dust/splash guard. These guards must be installed because the back of the hub with the oil seal in the bearing carrier will be partially exposed to the elements. With the brake drum setup, the back of the oil seal was enclosed inside the drum / backing-plate housing.

M6 stainless steel bolts were used to fasten the dust shields to the adaptor brackets.
4.5mm (0.177 inch) thick spacers and an 84mmø x 5mm thick O-ring were positioned between the dust shield and the adaptor bracket. The spacers and O-ring were inserted to reduce the gap between the dust shield and brake disc to mostly prevent ingress of dirt/dust and/or water. As mentioned earlier, the outer part of the oil seal in the hub is partially exposed to the elements. (See schematic section for position of spacers and O-ring).

Adaptor bracket with dust shield, spacers and O-ring fitted.

Dust shields from a VW Sharan would have saved a lot of time and effort. Shields could not be found on-line or second-hand either. Surplus stainless-steel sheets were used to make them.

Refurbished second-hand brake callipers and carriers.

Schematic section indicating position of alloy rim on brake disc, brake disc on hub, dust shield on spacers and adaptor bracket on the bearing carrier. Dimensions depend on steel thickness, brake disc and brake calliper/carrier used.

Schematic plan indicating the calliper carrier and the adaptor bracket on the bearing carrier.

Schematic elevation indicating dust / splash shield on the adaptor bracket.

Adaptor bracket bolted to the bearing carrier.

Loctite 248 Threadlocker was applied to all bolts.

All bolts and nuts for attaching the calliper carrier to the adaptor bracket and the adaptor bracket to the bearing carrier are 12.9 high tensile strength. They were sand-blasted and zinc-plated.

Top view of adaptor bracket bolted to the bearing carrier.
I did not want to compromise the entegrity of the anchor points on the bearing carrier by drilling and/or cutting thread to accommodate bolts. I used the existing unthreaded hole at the top, dowel pin hole and two threaded holes at the bottom to determine bolt and bolt/nut sizes.

Dust shield bolted to the adaptor bracket.

Hub & castle nut installed.

View of the partially exposed oil seal in the bearing carrier with the hub, dust shield and adaptor bracket installed. (The O-ring and 4.5mm thick spacers are not visible here. They are positioned to the right between the dust shield and adaptor bracket).
With the brake disc installed on the hub there is a 4.7mm (0.185 inch) gap between the back of the brake disc and the front of the dust shield. (See scematic section for reference).

Brake disc fitted on the hub.

Brake pads fitted to the calliper carrier.

Calliper bolted to the calliper carrier. The split-pin in the castle-nut was inserted after the nut was torqued with the wheels on the ground.

After installation of the callipers, new brake lines were fitted, and I then bled the complete braking circuit. I also bled the clutch slave cylinder to ensure all old brake fluid was replaced with new fluid. As part of preventative maintenance, I always replace the brake fluid on a yearly basis because of brake fluid’s hygroscopic properties.

Unfortunately, one of the cable retainers broke when I removed the old cable. A new one couldn’t be sourced, so I made a new one. It was made from mild steel and then zinc-plated.

I refreshed the balancer bar by sand blasting and zinc-plating it.
I do not foresee that adjustment for the brake cables will be necessary. As the brake pads wear thinner, the calliper piston protrudes to automatically compensate for wear. The levers to which the brake cables are attached at the callipers, activates at the back of the calliper’s pistons. The lever’s downward movement will stay the same as the calliper’s piston’s position corrects for wear.

When the callipers were refurbished I painted them with Rust-Oleum Calliper Paint to match the alloy rims.

Not clear to see here, but there is about a 4mm (0.157 inch) clearance between the calliper and the 15 inch rim. The bolts for fastening the calliper to the carrier are the only 10.9 high tensile bolts used. These bolts were supplied with the new brake pads.

A better view of the clearance between the calliper and the rim.

Conclusion:

In South-Africa, the T3 / T25 shape VW was still manufactured after being discontinued in other countries.

Final edition of the South African produced T3 with larger side windows, 15-inch wheels, running boards and 5-cylinder 2.6i engine.


VW South Africa eventually equipped the T3 with a 5-cylinder engine carried over from their Audi models. It was also fitted with 15-inch wheels. The last iteration of this 5-cylinder engine installed in the T3’s in South Africa was stroked to 2.6 litre capacity and equipped with a Bosch Motronic fuel-injection system. This combination was good for 100kw (135hp), at the wheels. With this engine upgrade, VWSA upgraded the solid front disc brakes to larger 278mm diameter ventilated discs with single piston callipers. Unfortunately, the rear drum brakes stayed until VWSA discontinued production of the T3’s in 2002. Unladen, the braking power was acceptable. Fully loaded, poor braking power (from the drum brakes), at the rear were scary at times.

The difference in braking with discs at the rear is somewhat better. Most likely, the reason for no drastic braking increase is that the larger ventilated discs at the front already does most of the braking. The brakes are more responsive thou. The parking brake is much more efficient because the brake pads are almost in direct contact with the brake discs when the parking brake is engaged. In contrast, the brake shoes must still “travel” before touching the contact area of the drum.

To further improve the braking power, a larger diameter brake booster can be installed. The VW brake booster can be replaced with a BMW E30 brake booster with minor adjustments.

According to discussions on forums, this conversion is relatively easy to do. However, the brake booster is not available new anymore and used ones in good condition are hard to come by.
Another option is to fit dual piston callipers all round. An increase in calliper piston area increases braking pressure on the brake disc.

Yet another option is to install larger diameter brake discs with larger brake pads to increase the friction area. This option however will require 16-inch rims.

Unfortunately, I didn’t weigh the discs and smaller hubs before installation. On feel, they are lighter than the combined weight of the drums and larger hubs. Although minimal, this weight saving equates to less engine power / torque necessary to initiate and maintain rotational momentum of the wheel / brake disc.

I recommend this rear brake disc conversion. Not only for the T3 but for any vehicle that has drum brakes fitted to the rear. Maintenance wise it is quite simple to replace brake pads.

A special tool is needed though to rotate and press at the same time to push the calliper piston back before installing new pads.

Safe travelling,
W

For those not willing to make the disc brake adaptor plate themself, complete kits are available from various suppliers. Below links are web sites where I read on how to do this conversion and got information from. A big shout-out and credit to them.

Also, a big thank you for the Samba.com for their platform allowing for sharing and learning!

https://gowesty.com/products/rear_disc_kit-vanagon
https://burleymotorsports.net/product/rear-disc-brake-kit-new-generation/
https://www.busdepot.com/dbkit
https://epytec.de/en/brake-system/adapters/14460/v...er-adapter
https://smallcar.com/vanagon-bus-upgrades/driving-...grade-kit/
https://ultimate-engineering.co.uk/reardisckit.html

[MsTaboo]

Welcome to the Samba.
Nicely done first post.
I really like the SA big window buses, especially the new cabin/engine vent on the D pillar. Too bad SA didn't build the Syncro this way.
_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

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[calsurf]

Impressive, nice work.

[jimf909]

[Crankey]

Nice work !
I don't know about anyone else but there are a lot of pictures missing in your post here.
Judging from what is showing up I best they're really cool pictures with a lot of info so maybe you'd want to look into it and upload your images to the samba gallery.

I don't think I have that same caliper. I think the go west kit has calipers from a eurovan but the look bigger from the outside, could be some of your missing pictures.

The only issue I have with the kit on my truck is the parking/emergency brake. It feels weak at 2 clicks and it's hard to pull 2 clicks, you can feel the handbrake lever actually bend to the side when it pull that hard.
Still, with my driveway having roughly a 5° slope the park brake will slide just a little as the vehicle rocks as I get out. There's just no way I'd ever parallel park on a sloped street.
I could be wrong but I think it's the lesser leverage clamping on a smaller diameter section of a disc as well as the lesser gripping area of pads vs shoes.
To me it's just been easier to find a level street to park on than make sense of all the different methods of fixing park brake force. The garage at home is level and parking at work is level so that's 95% of my life right there.

[OlisGarage]

Wow, just WOW! Super nice work. Thank you for also including the diagrams!

Looks amazing.

Finally, some of your pictures aren’t loading for me. Most did though. But wow, such great work.
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1981 VW Vangagon TDI (in progress)
1984 VW Rabbit Convertible (daily)
2003 VW Jetta Wagon TDI (recovering from a hit and run)

[kamzcab86]

Very impressive! And a whole lot more work than I put into the conversion project [I simply bought GoWesty's kit ]. GW's kit does include dust shields. The very first release of their kit, however, did not include the shields and my dad's Westy's rear disc got rock damage as a result. He contacted GW and they sent him dust shields to install.

[Kdj]

That is fantastic fab work using minimal tooling! Thanks for the detailed drawings. For someone with the skills to do this, you have created detailed how too. Again great post

[willem maas]

[willem maas]

[willem maas]

[willem maas]

[willem maas]

[willem maas]

[willem maas]

[Detrar]

What a wicked write up. Thank you for the time you put in to show us what you've done

[SplitBusVanatic]

wonderful post.
thank you for doing this and documenting it so well.
would you ever consider offering these for sale ?

[willem maas]

[willem maas]

[Nitramrebrab72]

Very nice job!!! Extremely professional but is it the right upgrade for all Vanagons ???

I have a T25 Westfalia totally original as regards wheels ,brakes, tyres, that weighs in at over 5000lbs.
Going down the mountain roads in the pyrenees mountains and also at Mont Ventoux which is the longest stretch of extremely steep road in Europe. Used by European car manufacturer BMW Jaguar just to name a few, to test their new cars (especially the brakes) where BMW have broken new pre introduction cars it is tough!!!!
After doing the mountain descent many times I have found the following.

Engine braking is a must at all times!!!
The VW recommended grease in the front bearings can not stand upto the excessive heat and will lead to premature bearing failure on the pre 83 smaller wheel bearings, but not the rear drums as they don't get as hot.

Also found that the front to rear braking balancing is very well designed by VW and any extra rear braking will lead to premature rear brake lock up, very important especially in the snow so will be needed to be accompanied by better front brakes.

The above leads me to believe larger front disc set up seems a lot more crucial than a rear brake upgrade as VW SouthAfrica (on their 5cyl high powered engines) came to the same conclusion that the harder you brake or the steeper the hill the more load is transferred on to the front brakes and removed from the rear.
Putting more heat braking on the front discs but also removing heat from the rear making for cooler rear drums the steeper the hill but obviously due to longer time spent with the foot on the brakes on steeper hills will lead to hotter overall brakes but pro-rata the steeper the hill the cooler the rear drums will be.

Also Redline CV2 extra high temp wheelbearing grease saves my bearings in the mountains.