Fitting a remote brake servo

Adding brake 'servo assistance' to a 65 year old car.

Anyone who drives a Traction Avant will tell you that it can be a bit 'hairy' when having to brake hard as the car only has 'old fashioned' drum brakes with no 'assistance' unlike modern cars which have more efficient disc brakes and servo assistance. Traction Avant Brakes were designed for road conditions in the 1930's!

I personally thought it may not be necessary to try and add some modern brake 'assistance' to my Traction Avant but that changed after a few 'near misses' recently with other road users pulling out in front or braking heavily at the last minute in front of me.......

The simplest way to try and improve braking on a Traction Avant is to add vacuum servo assistance. Basically when you decelerate the engine creates 'suction' in the intake manifold and that is used to draw on a diaphragm which pushes a remote brake slave cylinder whilst you push on the brake pedal which reduces the effort required by the driver when applying the brakes.

However it's important to ensure that the cars braking system is in good condition before attempting to fit a brake servo.

Unfortunately there is no room to fit a modern master cylinder/servo combination in a Traction Avant due to the location of the master cylinder, so a 'remote' installation of a servo is the only alternative. I was advised by a long term Traction owner not to add to much 'assistance' and a servo with a 2:1 ratio was ideal and not to go above 3:1.

I therefore bought a Powertune 'kit' from MGB Hive an MGB specialist in Cambridge. It is a copy of the original 'Delphi' type used on many 1960's cars (the fitting instructions are the same word for word) and is 7" (17.8cm) diameter and has a boost ratio of 1.90:1. It comes complete with a mounting bracket, additional support, brake pipe and vacuum hose. As there is no non return valve for the vacuum line I sourced one from eBay to fit into the intake manifold.

First job is to mount the servo in a suitable place, which on a French car means the right hand side. The downside to that location is that it is near the exhaust manifold so it may require some kind of heat shield though it does just sit at the minimum recommendation of 6" (15.25cm) away from the exhaust manifold once all secured in place.

Once the angle on the mounting bracket was increased it was bolted to the 'jambone' with 7mm bolts (they were left over from another job) up from the passenger foot-well (image 1) then once secure I had to make a distance piece to go under the front additional support which I did using some 20x50mm mild steel tubing I had from a previous project, adding an extra layer of mild steel strip which I had welded in place locally by Wheels and Welds and bolting that through the hull inspection cover (image 2) before fitting that back to the car. Finally the additional support bracket was fastened in place after drilling and tapping the home made support bar M6, then using M6 bolts to secure it.

Servo in situ     spacer block     The servo securely in place

I sourced a new set of manifold gaskets from Renel Auto in France before going to the next stage as the manifold needs to be removed (same process as shown here ) then drilled and tapped 1/8" BSP so the non return valve can be fitted and the vacuum hose attached as shown in image "1" below. The manifold needs to be removed, turned upside down before drilling to ensure that no metal 'swarf' is left in the manifold as that could be sucked into the engine and cause serious damage......

Remember: It's always best practice to replace any gasket with a new one once it's removed, even if it's only a few months old.

Once the manifold was refitted I realised I had a problem.... The servo kit I bought used 3/8th UNF fittings for 3/16" brake line and a Traction Avant uses 6mm / 1/4" brake line so I had to find a way to adapt it.

Non Return Valve situ     3/8 UNF fitting modified     6mm brake pipe fitting

I did try drilling out a 3/8" UNF fitting to 6.5mm and that would go over the 1/4" pipe as per image "2" above, however the flare on the pipe would not enter into the servo without some remedial action (basically grinding the flare down a bit). However drilling out the male 3/16th fitting meant that the area that would squeeze the flared pipe end to seal against a fluid leak was very small in area and could possibly cut the pipe rather than compressing it and with braking systems you really need to have them 100% safe and so resorted to 'Plan B'

I went online and found a 7/16th" UNF to 3/8th" UNF inline brake pipe connector at Car Builder Solutions.

Now the 7/16th female tube nuts are drilled to take 6mm or 1/4" brake pipe as shown in image "3" above, so now it's just a matter of making up a pair of brake pipes to go across the engine bay, plumbing them in and bleeding the system. That job will be done by James at Traction Repairs as I don't have a pipe flaring tool.

To 'Plumb' the servo in means taking the output line from the master cylinder on the left of the car, across to the servo mounted on the right of the car, then brining the 'boosted' fluid back across to the left side of the car.

That's not as easy as it sounds as it meant going down from the top of the 'jambone', back to the bulkhead, then across under the floor, forward again, then back up to the opposite 'jambone' (the small diagram sort of explains it but fails to show the intricacy of the bends required). In the end it was decided to make the pipes in 2 halves and use a coupler in the middle. The coupler I fortunately managed to source locally from Dave at Ashington Autospares from some 'New Old Stock' going back to the 1970's!

The pipe run     Hydraulic Pipework completed     Servo hydraulic pipe route

OK so does it work and was all the effort worthwhile. In a word, YES. Whilst there is no real difference in ordinary driving as gentle pressure on the brakes doesn't give any actual 'boost' so the car still drives like a 'classic', when the brake pedal is pressed 'firmly', stopping power is really improved. A really firm 'dab' of the pedal in an emergency can actually 'lock up' the front wheels on a dry road.

The unit described and fitted was designed for a Mini, MGB etc. which weigh less than a Traction Avant, so to get a more positive brake feel at all levels, you may want to go to a servo with a nearer 3:1 ratio. That's a personal choice.

Overall though, the effect gives one more confidence whilst driving in modern traffic. That confidence got a boost today when a 1960's MG Magnette in front on the way to the same rally as we were had to brake hard to avoid someone who just decided to reverse out onto a main road. The new servo meant that we stopped in plenty of time as well. Without it, well it could have been a very close call.....

Last Update: 2nd July 2017.