72 Corvette Wiper Door Linkage Rebuild

TimP

CCCUK Member
This article is a little large for one post so I have split it into 2 parts. Here's part 1....

Ever since my 72 Corvette arrived I wanted to get the wiper door open and have a look inside the wiper well but the door was absolutely stuck - no amount of pulling, pushing or swearing would make it budge. Weeks of dousing the linkages and bushes in Plus Gas - usually a reliable help - had absolutely no effect. I definitely didn't want to force anything so decided to leave any further investigation until later in the restoration.

Roll the clock forward a year and the front end bodywork and the front and rear suspension are nearly done. In the picture below I have trial fitted the hood to make sure that the body and hood are reasonably well aligned - the gap that previously existed between the front edge of the hood and the bodywork has now gone.

1-Wiper hood test fit.JPG

Although it wasn't on the critical path for getting the car finished I thought that spending some time on the wiper mechanism would be a good antidote to some of the more heavy duty stuff I had been working on for the previous 6 months or so.

The wiper assembly is constructed of a cranked steel rod supported by three bushed aluminium brackets that locate the rod transversely across the body allowing the rod to rotate. The brackets are bolted to the bulkhead: one at each end of the rod and one towards the middle but offset to the passenger side. The two brackets at the ends of the rod locate a 5 bar link arrangement that when activated, move the attached wiper door upwards and outwards keeping the door parallel to the ground. There are two further linkages. One connects to the vacuum actuator that operates the wiper door and a second which when extended, trips a switch to provide an electrical signal when the wiper door has reached its upper limit. For additional support the left and right aluminium brackets are connected to two small steel brackets, one either side, that bolt to the birdcage just below the windscreen.

Back to my car .... the wiper door was still stuck and the only way I was going to get it open was to strip it down in situ by removing the grille, then wiper motor and washer tubes. After this was done the wipers and connecting links could be removed by undoing the 4 bolts connecting each wiper pivot to the bulkhead. The actuator mechanism rod had already rusted through but the actuator and bracket were removed anyway to give more space. The limit switch mechanism was also disconnected and removed.
2-Wiper actuator B4.JPG 3-Wiper limit switch B4.JPG

This gave enough room to get access to the bolts high up under the wiper door that keep the left and brackets in place. Once these bolts and the bulkhead bolts were undone the whole door and related mechanism could be removed as a unit from the car.

On the bench the wiper door was removed from the rest of the mechanism. Fortunately the four shoulder bolts came out quite easily even though only one bolt head was intact enough to put a socket on it - the other three had corroded requiring the remaining stubs to be filed down and removed with a set of Mole grips.

All the linkage rivets at each end of the cranked rod were drilled out so that the individual lever elements could be removed, cleaned, de-rusted and repainted. The plastic bushes in these links had hardened and most of them cracked or split on removal.

4-Wiper 5 bar link in pieces.JPG

Even after all this, the bar would still not rotate in the brackets - it was still seized solid. Thus a jig was made using some joinery brackets from Wickes and a large piece of 3/4" plywood and the wiper door mechanism was mounted on this to mimic the way it is located in the car - the brackets taking the place of the Corvette bulkhead. In the picture below (taken towards the end of the rebuild) you will notice a photocopy of a page from the Factory Assembly Manual which provides really useful guidance on the restoration. I find it useful to copy a page and laminate it so that it can be wiped clean periodically and saves the FAM from getting messed up.

5-Wiper assembly total B4 welding.JPG

A separate jig was constructed so that I could hold the rod still, cut the rod between two fixed points with a cutting disc and then remove and renew the end bracket bushes. I started on the right hand side, refurbished the bracket, replaced the bush, then dressed the two ends of the rod and welded them back together. The left hand side bracket was done in the same way.

6-Wiper jig B4.JPG

However these bushes, brackets and levers are not available individually - although the entire mechanism can be bought as a unit if required. I did some research and found some oil filled flanged bronze bushes and also some nylon bushes that could be used for the three supporting brackets where the rod passes through. I also found some bronze bushes that could replace the smaller linkage bushes but as the plastic stock ones are available I decided to buy these (from Corvette Kingdom) as these would be easier to fit.
7-Wiper bracket bronze bush.JPG
Either the bronze or nylon bushes could have been used - each bush type has its own pros and cons. Bronze: better mechanical fit but poor corrosion characteristics when employed with an aluminium casting that gets wet. These also required some fettling before they would fit correctly (a very small reduction in the outside diameter). Nylon: slightly inferior mechanical fit but otherwise very similar to the original items and corrosion resistant. I decided in the end to use the bronze bushes and just keep an eye on them periodically for any tell-tell signs of a corrosive reaction between the bronze and aluminium. Unfortunately the difficult-to-replace aluminium bracket will corrode in preference to the made-in-thousands bronze bush so it was an important consideration.

8-Wiper 5 bar link trial fit.JPG

The bronze bushes can be bought in small numbers relatively cheaply from UK distributors. The only place I found the nylon bushes of the right size was from a wholesaler in Burnley so I had to buy a hundred..... Fortunately they are very cheap. If anyone wants some let me know!

Both types of bushes can be seen below on the jig. A nylon bush has been installed and is being tested for fit.

9-Wiper drv bracket and bushes.JPG

continued in the next post........
 

Attachments

TimP

CCCUK Member
... carried on from before.

The middle support bracket (next to the actuator lever) also had a new bronze bush fitted at the same time as the left bracket. The actuator lever next to it has a spring mechanism, presumably to provide some element of relief if the actuator movement is greater than the lever mechanisms can tolerate - the spring will take the excess load.
10-Wiper spring mech B4.JPG

This bush, a plastic tube between the cranked rod and the lever, was also completely seized and the only way to remove it was to burn it out with a blow lamp. A new bush was formed out of 8 of the flanged nylon bushes - one complete one at the bracket end, a modified one at the spring end and 6 bushes between them with their flanges carefully removed. Once cleaned up and painted, the lever and spring were replaced on the rod and this mechanism now works as it should.
11-Wiper actuator lever after.JPG 12-Wiper spring mech after.JPG
The rod was welded back together again taking time to make sure that both ends were properly aligned and any damaged paintwork was repaired.

13-Wiper pre weld LHS.JPG 14-Wiper rod after welding.JPG

All the linkages were then reassembled but instead of riveting them together in the conventional way the rivets are still used but instead held in place by star lock washers.
15-Wiper starlock.JPG
This allows them to be installed quite gently with a c-clamp, held securely in place and yet removable if required (not a particularly easy job but a lot easier than drilling out and replacing a rivet). All the plastic bushes were liberally sprayed with white lithium grease, the bronze ones with a wheel bearing grease I had left over from earlier work.

One of the two levers in the actuator lever mechanism had corroded to the point where it could not be refurbished and a replacement was made out of a steel bar bought from Wickes. Fortunately the rusted part had enough metal left to take critical measurements. It is not a particularly difficult shape and a few hours work with a cutting disc, file and drill had this new part completed and ready for painting.
16-Wiper-mid bracket.JPG 18-Wiper Actuator Linkage-small.JPG
There are additional steel brackets that are bolted to the left and right aluminium brackets that provide additional location. These are relatively fragile and have corroded quite extensively in the area where they attach to the birdcage at the lower corner of the windscreen. These will be repaired using fresh steel later in the build process.
19-Wiper bulkhead bracket.JPG
With all bushes replaced and lubricated the mechanism now works well and can be operated with relatively little effort.
20-Wiper-final.JPG
Hopefully this rebuild will prove effective and durable - time will tell. It has been an interesting exercise to do and (if it works reliably) probably has saved me a few hundred pounds along the way compared to buying a complete new mechanism. The star lock washers, 6 bronze and 100 nylon bushes cost just over £50 in total.
This mechanism will now be incorporated into a bench based rig that will include all the vacuum components (headlights and wipers) so that I can test out the whole system and each individual part before putting everything back in the car. This will also allow me to understand how each component functions and will help with any diagnosis required when it (almost inevitably) won't work when re-installed. More of this next year when I hope to submit an article on this for publication in the club magazine.
 
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